ICS 93.020  
 
Reference number  
DRS 113: 2020  
© RSB 2020  
  
 RWANDA 
STANDARD  DRS  
113  
 
Second  edition  
2020 -mm-dd 
 
Geotechnical Design  — General 
requirements   
  
DRS 113: 2020  
©RSB 2020  - All rights reserved                  ii 
 In order to match with technological development and to keep continuous progress in industries, 
standards are subject to periodic review. Users shall ascertain that they are in possession of the latest 
edition  
 
 
 
 
 
 
 
 
© RSB yyyy 
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ePortal: www.portal.rsb.gov.rw   DRS 113: 2020  
iii                ©RSB 2020  - All rights reserved  
 Contents  Page 
Foreword  ................................ ................................ ................................ ................................ ...........................  vii 
1 Scope  ................................ ................................ ................................ ................................ ......................  1 
2 Normative references  ................................ ................................ ................................ ............................  2 
3 Terms and definitions  ................................ ................................ ................................ ...........................  2 
4 Symbols, units and Abbreviations  ................................ ................................ ................................ .... 45 
4.1 Symbols  ................................ ................................ ................................ ................................ ................  45 
4.2 Abbreviations  ................................ ................................ ................................ ................................ ....... 10 
4.3 Units  ................................ ................................ ................................ ................................ ..................  1011 
5 Basis of geotechnical design  ................................ ................................ ................................ .............  11 
5.1 Design requirements  ................................ ................................ ................................ ...........................  11 
5.2 Design  situations  ................................ ................................ ................................ ................................ . 14 
5.3 Durability  ................................ ................................ ................................ ................................ ..........  1516 
5.4 Geotechnical design by calculation  ................................ ................................ ................................ .. 16 
5.4.1  General  ................................ ................................ ................................ ................................ .................  16 
5.4.2  Actions  ................................ ................................ ................................ ................................ .............  1718 
5.4.3  Ground properties  ................................ ................................ ................................ ...........................  1920 
5.4.4  Geometrical data  ................................ ................................ ................................ .............................  2021 
5.4.5  Characteristic values  ................................ ................................ ................................ ......................  2021 
5.4.6  Design values  ................................ ................................ ................................ ................................ .. 2223 
5.4.7  Ultimate Limit States  ................................ ................................ ................................ ...........................  24 
5.4.8  Serviceability limit states  ................................ ................................ ................................ ...............  2829 
5.4.9  Limiting values for movements of foundations  ................................ ................................ ...............  29 
5.5 Design by prescriptive measures  ................................ ................................ ................................ ...... 30 
5.6 Load tests and tests on experimental models  ................................ ................................ .............  3031 
5.7 Observational method ................................ ................................ ................................ .....................  3031 
5.8 Geotechnical Design Report  ................................ ................................ ................................ ..........  3132 
6 Geotechnical data  ................................ ................................ ................................ ............................  3233 
6.1 General  ................................ ................................ ................................ ................................ .............  3233 
6.2 Geotechnical investigations  ................................ ................................ ................................ ...............  33 
6.2.1  General  ................................ ................................ ................................ ................................ .................  33 
6.2.2  Preliminary in vestigations  ................................ ................................ ................................ ..............  3334 
6.2.3  Design investigations  ................................ ................................ ................................ .....................  3334 
6.3 Evaluation of geotechnical parameters  ................................ ................................ ........................  3435 
6.3.1  General  ................................ ................................ ................................ ................................ .............  3435 
6.3.2  Characterisation of soil and rock type  ................................ ................................ ..............................  35 
6.3.3  Weight density  ................................ ................................ ................................ ................................ . 3637 
6.3.4  Density index  ................................ ................................ ................................ ................................ ... 3637 
6.3.5  Degree of compaction  ................................ ................................ ................................ .....................  3637 
6.3.6  Shear strength  ................................ ................................ ................................ ................................ . 3637 
6.3.7  Soil stiffness  ................................ ................................ ................................ ................................ .... 3738 
6.3.8  Quality and properties of rocks and rock masses  ................................ ................................ ....... 3738 
6.3.9  Permeability and consolidation parameters of soil and rock  ................................ .........................  40 
6.3.10  Geotechnical parameters from field tests ................................ ................................ .....................  4041 
6.4 Ground Investigation Report  ................................ ................................ ................................ ..........  4344 
6.4.1  Requirements  ................................ ................................ ................................ ................................ ... 4344 
6.4.2  Presentation of geotechnical information  ................................ ................................ ....................  4344 
6.4.3  Evaluation of geotechnical information  ................................ ................................ ............................  45 DRS 113: 2020  
©RSB 2020  - All rights reserved                  iv 
 7 Supervision of construction, monitoring and maintenance  ................................ ..........................  46 
7.1 General  ................................ ................................ ................................ ................................ .................  46 
7.2 Supervision  ................................ ................................ ................................ ................................ .........  47 
7.2.1  Plan of supervision  ................................ ................................ ................................ .............................  47 
7.2.2  Inspection and control  ................................ ................................ ................................ .......................  47 
7.2.3  Assessment of the design  ................................ ................................ ................................ .................  48 
7.3 Checking ground conditions  ................................ ................................ ................................ .........  4849 
7.3.1  Soil and rock  ................................ ................................ ................................ ................................ ... 4849 
7.3.2  Ground -water  ................................ ................................ ................................ ................................ ...... 49 
7.4 Checking construction  ................................ ................................ ................................ .......................  50 
7.5 Moni toring  ................................ ................................ ................................ ................................ ....... 5051 
7.6 Maintenance  ................................ ................................ ................................ ................................ ........  52 
8 Fill, dewatering, ground improvement and reinforcement  ................................ .............................  52 
8.1 General  ................................ ................................ ................................ ................................ .................  52 
8.2 Fundamental requir ements  ................................ ................................ ................................ ................  53 
8.3 Fill construction  ................................ ................................ ................................ ................................ .. 53 
8.3.1  Principles  ................................ ................................ ................................ ................................ .............  53 
8.3.2  Selection of fill material  ................................ ................................ ................................ .................  5354 
8.3.3  Selection of procedures for fill placement and compaction  ................................ ..........................  55 
8.3.4  Checking the fill  ................................ ................................ ................................ ................................ .. 56 
8.4 Dewatering  ................................ ................................ ................................ ................................ ...........  57 
8.5 Ground improvement and reinforcement  ................................ ................................ .........................  58 
9 Spread foundations  ................................ ................................ ................................ ............................  59 
9.1 General  ................................ ................................ ................................ ................................ .................  59 
9.2 Limit states  ................................ ................................ ................................ ................................ ..........  59 
9.3 Actions and design situations  ................................ ................................ ................................ ....... 5960 
9.4 Design and construction considerations  ................................ ................................ .....................  5960 
9.5 Ultimate limit state design  ................................ ................................ ................................ .................  61 
9.5.1  Overall stability  ................................ ................................ ................................ ................................ ... 61 
9.5.2  Bearing resistance  ................................ ................................ ................................ ..............................  61 
9.5.3  Sliding resistance  ................................ ................................ ................................ ...............................  62 
9.5.4  Loads with large eccentricities  ................................ ................................ ................................ .........  63 
9.5.5  Structural failure due to foundation movement  ................................ ................................ ..........  6364 
9.6 Serviceability limit state design  ................................ ................................ ................................ ........  64 
9.6.1  General  ................................ ................................ ................................ ................................ .................  64 
9.6.2  Settlement  ................................ ................................ ................................ ................................ ........  6465 
9.6.3  Heave  ................................ ................................ ................................ ................................ ...................  66 
9.6.4  Vibration analysis  ................................ ................................ ................................ ...............................  66 
9.7 Foundations on rock; additional design considerations ................................ ................................  66 
9.8 Structural design of spread foundations  ................................ ................................ .........................  67 
9.9 Preparation of the subsoil  ................................ ................................ ................................ .................  67 
10 Pile foundations  ................................ ................................ ................................ ..............................  6768 
10.1  General  ................................ ................................ ................................ ................................ .............  6768 
10.2  Limit states  ................................ ................................ ................................ ................................ ..........  68 
10.3  Actions and design situations  ................................ ................................ ................................ ....... 6869 
10.3.1  General  ................................ ................................ ................................ ................................ .............  6869 
10.3.2  Actions due to ground displacement  ................................ ................................ ...............................  69 
10.4  Design methods and design considerations  ................................ ................................ ...............  7071 
10.4.1  Design methods  ................................ ................................ ................................ ..............................  7071 
10.4.2  Desig n considerations  ................................ ................................ ................................ .......................  71 
10.5  Pile load tests  ................................ ................................ ................................ ................................ ...... 72 
10.5.1  General  ................................ ................................ ................................ ................................ .................  72 
10.5.2  Static load tests  ................................ ................................ ................................ ................................ .. 73 
10.5.3  Dynamic load tests  ................................ ................................ ................................ .............................  74 DRS 113: 2020  
v                ©RSB 2020  - All rights reserved  
 10.5.4  Load test report  ................................ ................................ ................................ ...............................  7475 
10.5.5  Axially loaded piles  ................................ ................................ ................................ .............................  75 
10.5.6  Compressive ground resistance  ................................ ................................ ................................ ........  76 
10.5.7  Ground tensile resistance  ................................ ................................ ................................ ..................  82 
10.5.8  Vertical displacements of pile foundations (Serviceability of supported  structure)  ..................  86 
10.6  Transversely loaded piles  ................................ ................................ ................................ ..................  87 
10.6.1 General  ................................ ................................ ................................ ................................ .................  87 
10.6.2  Transverse load resistance from pile load tests  ................................ ................................ ..............  87 
10.6.3  Transverse load resistance from ground test results and pile strength  ................................ ....... 88 
10.6.4  Transverse displacement  ................................ ................................ ................................ ...................  88 
10.7 Structural design of piles  ................................ ................................ ................................ ...................  88 
10.8  Supervision of construction  ................................ ................................ ................................ ...............  89 
11 Anchorages  ................................ ................................ ................................ ................................ ..........  91 
11.1  General  ................................ ................................ ................................ ................................ .................  91 
11.2  Limit states  ................................ ................................ ................................ ................................ ...........  91 
11.3  Design situations and actions  ................................ ................................ ................................ ...........  92 
11.4  Design and construction considerations ................................ ................................ ..........................  92 
11.5  Ultimate limit state design  ................................ ................................ ................................ ..................  93 
11.5.1  Design of the anchorage ................................ ................................ ................................ .....................  93 
11.5.2  Design values of pull -out resistance determined from the results of tests  ................................ .. 93 
11.5.3  Design values of pull -out resistance determined by calculations  ................................ .................  94 
11.5.4  Design value of the structural resistance of the anchorage  ................................ ...........................  94 
11.5.5  Design value of the anchorage load  ................................ ................................ ................................ .. 94 
11.6  Serviceability limit state design  ................................ ................................ ................................ .........  94 
11.7  Suitability tests  ................................ ................................ ................................ ................................ .... 95 
11.8  Acceptance tests  ................................ ................................ ................................ ................................ . 95 
11.9  Supervi sion and monitoring  ................................ ................................ ................................ ...............  95 
12 Retaining structures  ................................ ................................ ................................ ............................  95 
12.1  General  ................................ ................................ ................................ ................................ .................  95 
12.2  Limit states  ................................ ................................ ................................ ................................ ...........  95 
12.3  Actions, ge ometrical data and design situations  ................................ ................................ ............  97 
12.3.1  Actions  ................................ ................................ ................................ ................................ .................  97 
12.3.2  Geometrical data  ................................ ................................ ................................ ................................ . 98 
12.3.3  Design situations  ................................ ................................ ................................ ................................ . 99 
12.4  Design and construction considerations ................................ ................................ ..........................  99 
12.4.1  General  ................................ ................................ ................................ ................................ .................  99 
12.4.2  Drainage systems  ................................ ................................ ................................ ..............................  101 
12.5  Determination of earth pressures  ................................ ................................ ................................ .... 101 
12.5.1  General  ................................ ................................ ................................ ................................ ...............  101 
12.5.2  At rest values of earth pressure  ................................ ................................ ................................ ...... 103 
12.5.3  Limiting values of earth pressure  ................................ ................................ ................................ .... 103 
12.5.4  Intermediate values of earth pressure  ................................ ................................ ............................  104 
12.5.5  Compaction effects  ................................ ................................ ................................ ...........................  104 
12.6  Water pressures  ................................ ................................ ................................ ................................  104 
12.7  Ultimate limit state design  ................................ ................................ ................................ ................  104 
12.7.1  General  ................................ ................................ ................................ ................................ ...............  104 
12.7.2  Foundation failure of gravity walls  ................................ ................................ ................................ .. 105 
12.7.3  Rotational failure of embedded walls  ................................ ................................ ..............................  106 
12.7.4  Vertical failure of embedded walls  ................................ ................................ ................................ .. 107 
12.7.5  Structural design of retaining structures ................................ ................................ ........................  108 
12.7.6  Failure by pull -out of anchorages  ................................ ................................ ................................ .... 109 
12.8  Serviceability limit state design  ................................ ................................ ................................ ....... 109 
12.8.1  General  ................................ ................................ ................................ ................................ ...............  109 
12.8.2  Displacemen ts ................................ ................................ ................................ ................................ ... 110 DRS 113: 2020  
©RSB 2020  - All rights reserved                  vi 
 13 Hydraulic failure  ................................ ................................ ................................ ................................  111 
13.1  General  ................................ ................................ ................................ ................................ ...............  111 
13.2  Failure by uplift  ................................ ................................ ................................ ................................ . 112 
13.3  Failu re by heave  ................................ ................................ ................................ ................................  114 
13.4  Internal erosion  ................................ ................................ ................................ ................................ . 115 
13.5  Failure by piping  ................................ ................................ ................................ ...............................  116 
14 Overall stability  ................................ ................................ ................................ ................................ . 117 
14.1  General  ................................ ................................ ................................ ................................ ...............  117 
14.2  Limit states  ................................ ................................ ................................ ................................ ........  117 
14.3  Actions and design situations  ................................ ................................ ................................ .........  117 
14.4  Design and construction considerations  ................................ ................................ .......................  118 
14.5  Ultimate limit state design  ................................ ................................ ................................ ...............  120 
14.5.1  Stability analysis for slopes  ................................ ................................ ................................ ............  120 
14.5.2  Slopes and cuts in rock masses  ................................ ................................ ................................ ..... 121 
14.5.3  Stability of excavations  ................................ ................................ ................................ ....................  122 
14.6  Serviceability limit state design  ................................ ................................ ................................ ...... 122 
14.7  Monitoring  ................................ ................................ ................................ ................................ .........  123 
15 Embankments  ................................ ................................ ................................ ................................ ... 123 
15.1  General  ................................ ................................ ................................ ................................ ...............  123 
15.2  Limit states  ................................ ................................ ................................ ................................ ........  123 
15.3  Actions and design situations  ................................ ................................ ................................ .........  124 
15.4  Design and construction considerations  ................................ ................................ .......................  125 
15.5  Ultimate limit state design  ................................ ................................ ................................ ...............  126 
15.6  Serviceability limit state design  ................................ ................................ ................................ ...... 127 
15.7  Supervision and monitoring  ................................ ................................ ................................ ............  127 
Annex  A (normative)  Partial and correlation factors for ultimate limit states and recommended 
values  ................................ ................................ ................................ ................................ .................  129 
A.1 Partial factors and correlations factors  ................................ ................................ ..........................  129 
A.2 Partial factors for equilibrium limit state (EQU) verification  ................................ ........................  129 
A.3 Partial factors for structural (STR) and geotechnical (GEO) limit states verification  ...............  130 
A.3.1  Partial factors on actions ( F) or the effects of actions ( E) ................................ ..........................  130 
A.4 Partial factors for soil parameters ( M) ................................ ................................ ...........................  131 
A.5 Partial resistance factors ( R) ................................ ................................ ................................ ..........  131 
A.5.1  Partial resistance factors for spread foundations  ................................ ................................ .........  131 
A.5.2  Partial resistance factors for pile foundations  ................................ ................................ ..............  132 
A.6 Partial factors for uplift limit state (UPL) v erifications  ................................ ................................ . 136 
A.7 Partial factors for hydraulic heave limit state (HYD) verification  ................................ ................  138 
 DRS 113: 2020  
vii                ©RSB 2020  - All rights reserved  
 Foreword   
Rwanda Standard s are prepared  by Technical Committees and approved by R wanda Standards Board (RSB) 
Board  of Directors in  accordance with the procedures of RSB, in compliance with Annex 3 of the WTO/TBT 
agreement on the preparation, adoption and application of standards.  
The main task of technical committees is to prepare national standards.  Final Draft Rwanda S tandards 
adopted by Technical committ ees are ratifie d by me mbers of RSB Board of Director s for publication and 
gazettment as Rwanda Standards.  
WD 113 was prepared by Technical Committee RSB/TC 09, Civil Engineering and Building materials  
In the preparation of this standard, reference was made to the following standard  (s): 
1) EN 1997 -1: Geotechnical design - Part 1: General rules  
The assistance de rived from the above source is hereby acknowledged with thanks.  
This second . edition  cancels and replaces the first . edition (RS  113: 2011of which  have  been te chnically 
revised.  
Committee membership  
The following organizations were represented on the Technical Committee on Civil Engineering and Building 
Materials  (RSB/TC 09) in the preparation of this standard.  
University of Rwanda – College of Science and Technology (UR -CST)  
City of Kigali  
Green Effect Engineering  
Integrated Polytechnic Regional Centre –Kigali (IPRC)  
TECOS Ltd  
NPD  
REAL Contractors Ltd  
Rwanda Housing Authority (RHA)  
Rwanda Transport Development Agency (RTDA)  DRS 113: 2020  
©RSB 2020  - All rights reserved                  viii 
 Gasabo 3D  
BJ Construction Ltd  
Masss Design Group - Rwanda  
Institut d’ Enseignement Supérieur ( INES - Ruhengeri ) 
NPD Ltd  
EAG Industries Ltd  
Institution of Engineers Rwanda  
CIMERWA Ltd  
Rwanda Standards Board (RSB) – Secretariat  
 DRS 113: 2020  
1                ©RSB 2020  - All rights reserved  
 Geotechnical design — General rules  
1 Scope   
1.1 This Draft Rwanda Standards is covers the requirements for strength, stability, serviceability and 
durability  of structures. Other requirements, e.g. concerning thermal or sound insulation, are not considered.  
WD 113 is intended to be applied to the geotechnical aspects of the design of buildings and civil engineering 
works which includes basis of geotechnical de sign, geotechnical data, ground improvement and 
reinforcement, foundations, retaining structures, hydraulic failure and overall stability  
1.2 The provisions of this standard are based on the assumptions given below:  
— data required for design are collecte d, recorded and interpreted appropriately by qualified personnel;  
— structures are designed by appropriately qualified and experienced personnel;  
— adequate continuity and communication exist between the personnel involved in data collection, 
design and co nstruction;  
— adequate supervision and quality control are provided in factories, in plants, and on site;  
— execution is carried out according to the relevant standards and specifications by personnel having the 
appropriate skills and experience;  
— constru ction materials are used as specified in this standard or in the relevant material specifications;  
— the structure will be adequately maintained to ensure its safety and serviceability for the designed 
service life;  
— the structure will be used for the pur pose defined for the design.  
These assumptions need to be considered both by the designer and the client. To prevent uncertainty, 
compliance with them should be documented, e.g. in the geotechnical design report.  
1.3 Distinction between Principles and Appl ication Rules in this standard  
1.3.1   Depending on the character of the individual clauses, distinction is made between Principles and 
Application Rules.  
1.3.2  The Principles comprise:  
— general statements and definitions for which there is no alternative;  
— requirements and analytical models for which no alternative is permitted unless specifically stated.  
1.3.3  In this standard, the Principles are preceded by the letter P.  
1.3.3  The Application Rules are examples of generally recognised rules, which follow the Principles and 
satisfy their requirements.   
©RSB 2020  - All rights reserved                  2 
 1.3.4  The Application rules are identified by a number in brackets where they appear in this standard  
2 Normative references  
The following documents are referred to in the text in such a way that some or all of their content constitutes 
requirements of this document.  For dated references, only the edition cited applies. For undated references, 
the latest edition of the referenced document (including any amendments) applies.  
RS ISO 17892, Geotechnical inves tigation and testing — Laboratory testing of soil  
RS 230 -1/ISO 6934 -1, Steel for the prestressing of concrete — Part 1: General requirements . 
3 Terms and definitions  
For the purposes of this document, the following terms and definitions apply.  
3.1 
geotechni cal action  
action transmitted to the structure by the ground, fill, standing water or ground -water  
3.2 
comparable experience  
documented or other clearly established information related to the ground being considered in design, 
involving the same types of s oil and rock and for which similar geotechnical behaviour is expected, and 
involving similar structures. Information gained locally is considered to be particularly relevant  
3.3  
ground  
soil, rock and fill in place prior to the execution of the constructio n works  
3.4 
structure  
organised combination of connected parts, including fill placed during execution of the construction works, 
designed to carry loads and provide adequate rigidity  
3.5 
derived value  
value of a geotechnical parameter obtained by theory, correlation or empiricism from test results  DRS 113: 2020  
3                ©RSB 2020  - All rights reserved  
 3.6 
stiffness  
material resistance against deformation  
3.7 
resistance  
capacity of a component, or cross -section of a component of a structure to withstand actions without 
mechanical failure e.g. resistance of the ground, bending resistance, buckling resistance, tensile resistance  
3.8 
permanent anchorage  
anchorage with a design life of more than two years  
3.7 
temporary anchorage  
anchorage with a design life of less than two years  
3.8acceptance test  
load test on site  to confirm that each anchorage meets the design requirements  
3.9 
suitability test  
load test on site to confirm that a particular anchor design will be adequate in particular ground conditions  
3.10 
investigation test  
load test to establish the ultimate resistance of an anchor at the grout/ground interface and to determine the 
characteristics of the anchorage in the working load range  
3.11 
anchor bond length  
length of the anchor that is bonded directly to the ground through a grout body   
©RSB 2020  - All rights reserved                  4 
 3.12 
tendon free length  
the length of the tendon between the anchor head and the proximal end of the tendon bond length  
3.13 
tendon bond length  
length of the tendon that is bonded directly to the grout and capable of transmitting the applied tensile load  
3.14 
gravity walls  
walls of stone or plain or reinforced concrete having a base footing with or without a heel, ledge or buttress. 
The weight of the wall itself, sometimes including stabilising masses of soil, rock or backfill, plays a significant 
role in the support of the  retained material. Examples of such walls include concrete gravity walls having 
constant or variable thickness, spread footing reinforced concrete walls and buttress walls.  
3.15 
embedded walls  
relatively thin walls of steel, reinforced concrete or timber,  supported by anchorages, struts and/or passive 
earth pressure. The bending capacity of such walls plays a significant role in the support of the retained 
material while the role of the weight of the wall is insignificant.  
Examples of such walls include ca ntilever steel sheet pile walls, anchored or strutted steel or concrete sheet 
pile walls and diaphragm walls.  
3.16 
composite retaining structures  
walls composed of elements from the above two types of wall. A large variety of such walls exists and 
examples  include double sheet pile wall cofferdams, earth structures reinforced by tendons, geotextiles or 
grouting and structures with multiple rows of ground anchorages or soil nails.  
4 Symbols , units and Abbreviations  
4.1 Symbols  
For the purpose of this standard, the  following symbols apply.  
A'           effective base area  
Ab           base area under pile  
Ac                  total base area under compression  DRS 113: 2020  
5                ©RSB 2020  - All rights reserved  
 As;I                pile shaft surface area in layer i 
ad                  design value of geometrical data  
anom             nominal value of geometrical data  
a           change made to nominal geometrical data for particular design purposes  
b             width of a foundation.  
b'            effective width of a foundation  
Cd           limiting design value of t he effect of an action  
c             cohesion intercept  
c'            cohesion intercept in terms of effective stress  
cu           undrained shear strength  
cu;d         design value of undrained shear strength  
d             embedment depth;  
Ed                 design value of the effect of actions  
Estb;d       design value of the effect of stabilising actions  
Edst;d       design value of the effect of destabilising actions  
Fc;d         design axial compression load on a pile or a group of piles  
Fd           design value of an action  
Fk           characteristic value of an action  
Frep         representative value of an action  
Ft;d                design axial tensile load on a tensile pile or a group of tensile piles  
Ftr;d              design value of the transverse load on a pile or a pile foundation  
Gdst;d           design value of the destabilising permanent actions for uplift verification  
Gstb;d      design value of the stabilising permanent vertical actions for uplift verification  
G´stb;d         design value of the stabilising permanent vertical actions for heave verification  (submerged weight)  
H            horizontal load, or component of total action acting parallel to the foundation Base  
Hd                 design value of H  
h             height of a wall 
h             water level for hydraulic heave   
©RSB 2020  - All rights reserved                  6 
 h'            height of a soil prism for verifying hydraulic heave  
hw;k         characteristic value of the hydrostatic water head at the bottom of a soil prism  
K0           coefficient of earth pressure a t rest  
K0;          coefficient of earth pressure at rest for a retained earth surface inclined at  Horizonta  
k             ratio d/ φcv.d 
l              foundation length;  
l′             effective foundation length  
n             number of e.g. piles or test profiles  
P             load on an anchorage  
Pd                 design value of P 
Pp           proof load in a suitability test of a grouted anchorage  
Qdst;d      design value of the destabilising variable vertical actions for uplift verification  
qb;k         characteristic value of base resistance pressure  
qs;i;k       characteristic value of shaft friction in stratum i 
Ra           anchorage pull -out resistance  
Ra;d              design value of Ra 
Ra;k              characteristic value of Ra 
Rb;cal       pile base resistance, calculated from ground test results, at the ultimate limit state  
Rb;d         design value of the base resistance of a pile  
Rb;k         characteristic value of the base resistance of a pile  
Rc                 compressive resis tance of the ground against a pile, at the ultimate limit state  
Rc;cal       calculated value of Rc  
Rc;d         design value of Rc  
Rc;k         characteristic value of Rc  
Rc;m         measured value of Rc in one or several pile load tests  
Rd           design value of the resistance to an action  
Rp;d         design value of the resisting force caused by earth pressure on the side of a  foundation  
Rs;d         design value of the shaft resistance of a pile  DRS 113: 2020  
7                ©RSB 2020  - All rights reserved  
 Rs;cal       ultimate shaft friction, calculated usi ng ground parameters from test results  
Rs;k             characteristic value of the shaft resistance of a pile  
Rt                 ultimate tensile resistance of an isolated pile  
Rt;d         design value of the tensile resistance of a pile or of a group of  piles, or of the  structural tensile resistance of an anchorage  
Rt;k         characteristic value of the tensile resistance of a pile or a pile group  
Rt;m        measured tensile resistance of an isolated pile in one or several pile load tests  
Rtr                resistance of a pile to transverse loads  
Rtr;d        design resistance of transversally loaded pile  
Sdst;d       design value of the destabilising seepage force in the ground  
Sdst;k          characteristic value of the destabilising seepage force in the ground  
S            settlement  
s0                 immediate settlement  
s1                  settlement caused by consolidation  
s2                  settlement caused by creep (secondary settleme nt) 
Td           design value of total shearing resistance that develops around a block of ground in which a group of tension piles is placed, or on the part of the  structure in  contact with the ground  
u             pore-water pressure  
udst;d    design v alue of destabilising total pore -water pressure  
V            vertical load, or component of the total action acting normal to the foundation  base  
Vd           design value of V 
V'd          design value of the effective vertical action or component of the total action acting normal to the 
foundation base  
Vdst;d           design value of the destabilising vertical action on a structure  
Vdst;k     characteristic value of the destabilising vertical action on a structure  
Xd           design value of a material pr operty  
Xk           characteristic value of a material property  
Z            vertical distance  
α            inclination of a foundation base to the horizontal  
             slope angle of the ground behind a wall (upward positive)   
©RSB 2020  - All rights reserved                  8 
              structure -ground interface friction angle  
d            design value of  
             weight density  
'            effective weight density  
a            partial factor for anchorages  
a;p          partial factor for permanent anchorages  
a;t           partial factor for temporary anchorages  
b            partial factor for the base resistance of a pile  
c'            partial factor for the effective cohesion  
cu           partial factor for the undrained shear strength  
E            partia l factor for the effect of an action  
f                    partial factor for actions, which takes account of the possibility of unfavourable  deviations  of  
the action values from the representative values  
F            partial factor for an action  
G                  partial factor for a permanent action  
G;dst       partial factor for a permanent destabilising action  
G;stb       partial factor for a permanent stabilising action  
m           partial factor for a soil parameter (material property)  
m;I              partial factor for a soil parameter in stratum i 
M           partial factor for a soil parameter (material property), also accounting for model uncertainties  
Q                  partial factor for a variable action  
qu           partial fa ctor for unconfined strength  
R                   partial factor for a resistance  
R;d               partial factor for uncertainty in a resistance model  
R;e               partial factor for earth resistance  
R;h               partial factor for sliding r esistance  
R;v          partial factor for bearing resistance  
s            partial factor for shaft resistance of a pile  DRS 113: 2020  
9                ©RSB 2020  - All rights reserved  
 S;d          partial factor for uncertainties in modelling the effects of actions  
Q;dst        partial factor for a destabilising action causing hydraulic failure  
Q;stb        partial factor for a stabilising action against hydraulic failure  
s;t           partial factor for tensile resistance of a pile  
t                    partial factor for total resistance of a pile  
w            weight density of water  
φ’                  partial factor for the angle of shearing resistance (tan φ ’) 
             partial factor for weight density  
             direction angle of H 
             correlation factor depending on the number of piles tested or of profiles of tests  
a            correlation factor for anchorages  
1; 2       correlation factors to evaluate the results of static pile load tests  
3; 4           correlation factors to derive the pile resistance from ground investigation results, not being  pile load tests  
5; 6          correlation factors to derive the pile resistance from dynamic impact tests  
            factor for converting the characteristic value to the representative value  
stb;d       design value of stabilising total vertical stress  
'h;0         horizontal component of effective earth pressure at rest  
 (z)        stress normal to a wall at depth z 
 (z)         stress tangential to a wall at depth z 
 φ’           angle of shearing resistance in terms of effective stress  
φ cv         critical state angle of shearing resistance  
φ cv;d       design value of φ cv 
φ’d          design value of φ’  
 
 
 
  
©RSB 2020  - All rights reserved                  10 
 4.2 Abbreviati ons 
CFA    Continuous flight auger piles  
OCR     over-consolidation ratio  
4.3 Units  
For geotechnical calculations, the following units or their multiples are recommended:  
—  force                                                         kN 
—  mass                                                          kg 
—  moment                                                     kNm 
—  mass density                                             kg/m3 
—  weight density                                           kN/m3 
—  stress, pressure, strength and stiffness    kPa 
—  coefficient of permeability                         m/s 
—  coefficient of consolidation                       m2/s 
 
 
 
 
 
 
 
 
 
 DRS 113: 2020  
11                ©RSB 2020  - All rights reserved  
 5 Basis of geotechnical design  
5.1 Design requirements  
5.1.1  For each geotechnical des ign situation it shall be verified that no relevant limit state is exceeded.  
5.1.2  When defining the design situations and the limit states, the following factors should be considered:  
a) site conditions with respect to overall stability and ground movements;  
b) nature and size of the structure and its elements, including any special requirements such as the 
design life;  
c) conditions with regard to its surroundings (e.g.: neighbouring structures, traffic,  utilities, vegetation, 
hazardous chemicals);  
d) ground conditio ns; 
e) ground -water conditions;  
f) regional seismicity;  
g) influence of the environment (hydrology, surface water, subsidence, seasonal changes of temperature 
and moisture).  
5.1.3  Limit states can occur either in the ground or in the structure or by combined failure in the structure 
and the ground.  
5.1.4  Limit states should be verified by one or a combination of the following:  
a) use o f calculations as described in 5 .4; 
b) adoption of prescrip tive measures, as described in 5 .5; 
c) experimental models a nd load tests, as  described in 5 .6; 
d) an observa tional method, as described in 5 .7. 
5.1.5 In practice, experience will often show which type of limit state will govern the design and the 
avoidance of other limit states may be verified by a control check.  
5.1.6  Buildings shou ld normally be protected against the penetration of ground -water or the transmission of 
vapour or gases to their interiors.  
5.1.7  If practicable, the design results should be checked against comparable experience.   
©RSB 2020  - All rights reserved                  12 
 5.1.8  In order to establish minimum requir ements for the extent and content of geotechnical investigations, 
calculations and construction control checks, the complexity of each geotechnical design shall be identified 
together with the associated risks. In particular, a distinction shall be made be tween:  
a) light and simple structures and small earthworks for which it is possible to ensure that  the minimum 
requirements will be satisfied by experience and qualitative geotechnical investigations, with negligible 
risk; 
b) other geotechnical structures.  
5.1.9  For structures and earthworks of low geotechnical complexity and risk, such as defined above, 
simplified design procedures may be applied.  
5.1.10  To establish geotechnical design requirements, three Geotechnical Categories, 1, 2 and 3, may be 
introdu ced as per Table 1 below.  
Table 1  — Geotechnical categories of structures  
Category  Description  Risk of geotechnical 
failure  
1 Small and relatively simple 
structures  Negligible  
2 Conventional types of structures and 
foundation with no difficult ground or 
loading conditions  No exceptional risk  
3 All other structures  Abnormal risk  
5.1.11  A preliminary classification of a structure according to Geotechnical Category should normally be 
performed prior to the geotechnical investigations. The category should b e checked and changed, if 
necessary, at each stage of the design and construction process.  
5.1.12  The procedures of higher categories may be used to justify more economic designs, or if the 
designer considers them to be appropriate.  
5.1.13  The various desi gn aspects of a project can require treatment in different Geotechnical Categories. It 
is not required to treat the whole of the project according to the highest of these categories.  
5.1.14  Geotechnical Category 1 should only include small and relatively s imple structures:  
a) for which it is possible to ensure that the fundamental requirements will be satisfied  on the basis of 
experience and qualitative geotechnical investigations;  
b) with negligible risk.  
5.1.15  Geotechnical Category 1 procedures should be used  only where there is negligible risk in terms of 
overall stability or ground movements and in ground conditions, which are known from comparable local 
experience to be sufficiently straightforward. In these cases the procedures may consist of routine metho ds for 
foundation design and construction.  DRS 113: 2020  
13                ©RSB 2020  - All rights reserved  
 5.1.16  Geotechnical Category 1 procedures should be used only if there is no excavation below the water 
table or if comparable local experience indicates that a proposed excavation below the water table will be 
straightforward.  
5.1.17  Geotechnical Category 2 should include conventional types of structure and foundation with no 
exceptional risk or difficult soil or loading conditions  
5.1.18  Designs for structures in Geotechnical Category 2 should normally include qu antitative geotechnical 
data and analysis to ensure that the fundamental requirements are satisfied.  
5.1.19  Routine procedures for field and laboratory testing and for design and execution may be used for 
Geotechnical Category 2 designs.  
NOTE  The following  are examples of conventional structures or parts of structures complying with Geotechnical 
Category 2:  
a) spread foundations;  
b) raft foundations;  
c) pile foundations;  
d) walls and other structures retaining or supporting soil or water;  
e) excavations;  
f) bridge piers and abutments;  
g) embankments and earthworks;  
h) ground anchors and other tie -back systems;  
i) tunnels in hard, non -fractured rock and not subjected to special water tightness or other requirements.  
5.1.20  Geotechnical Category 3 should include structures or parts of s tructures, which fall outside the limits 
of Geotechnical Categories 1 and 2.  
5.1.2  Geotechnical Category 3 should normally include alternative provisions and rules to those in this 
standard.  
NOTE  Geotechnical Category 3 includes the following examples : 
a) very large or unusual structures;  
b) structures involving abnormal risks, or unusual or exceptionally difficult ground or  loading conditions;  
c) structures in highly seismic areas;   
©RSB 2020  - All rights reserved                  14 
 d) structures in areas of probable site instability or persistent ground movements t hat require separate investigation 
or special measures.  
5.2 Design situations  
5.2.1   Both short -term and long -term design situations shall be considered.  
5.2.2 In geotechnical design, the detailed specifications of design situations should include, as appropriate:  
a) the actions, their combinations and load cases;  
b) the general suitability of the ground on which the structure is located with respect to  
c) overall stability and ground movements;  
d) the disposition and classification of the various zones of soil, r ock and elements of  
e) construction, which are involved in any calculation model;  
f) dipping bedding planes;  
g) mine workings, caves or other underground structures;  
h) in the case of structures resting on or near rock:  
i) interbedded hard and soft strata;  
j) faults, joint s and fissures;  
k) possible instability of rock blocks;  
l) solution cavities, such as swallow holes or fissures filled with soft material, and  continuing solution 
processes;  
m) the environment within which the design is set, including the following:  
n) effects of scou r, erosion and excavation, leading to changes in the geometry of the  ground surface;  
o) effects of chemical corrosion;  
p) effects of weathering;  
q) effects of freezing;  
r) effects of long duration droughts;  DRS 113: 2020  
15                ©RSB 2020  - All rights reserved  
 s) variations in ground -water levels, including, e.g. the effect s of dewatering, possible  flooding, failure of 
drainage systems, water exploitation;  
t) the presence of gases emerging from the ground;  
u) other effects of time and environment on the strength and other properties of materials; e.g. the effect 
of holes created by animal activities;  
v) earthquakes;  
w) ground movements caused by subsidence due to mining or other activities;  
x) the sensitivity of the structure to deformations;  
y) the effect of the new structure on existing structures, services and the local environment.  
5.3 Durability  
5.3.1  At the geotechnical design stage, the significance of environmental conditions shall be assessed as 
per RS ISO ISO 14688 -2, and ISO 22475 -1 requirements in relation to durability and to enable provisions to 
be made for the protection or ad equate resistance of the materials.  
5.3.2  In designing for durability of materials used in the ground, the following should be considered:  
a) for concrete:  aggressive agents in the ground -water or in the ground or fill material, such as acids or 
sulfate salts ;  
b) for steel:  
1) chemical attack where foundation elements are buried in ground that is sufficiently  permeable to  
allow the percolation of ground -water and oxygen;  
2) corrosion on the faces of sheet pile walls exposed to free water, particularly in the mean water 
level zone;  and 
3) the pitting type of corrosive attack on steel embedded in fissured or porous concrete, particularly 
for rolled steel where the mill scale, acting as a cathode, promotes electrolytic action with the 
scale -free surface acting as an anod e; 
c) for timber:  fungi and aerobic bac teria in the presence of oxygen ; 
d) for synthetic fabrics:  the ageing effects of UV exposure or ozone degradation or the combined effects of  
temperature and stress, and secondary effects due to chemical degradation.  
5.3.2  Reference should be m ade to durability provisions in construction materials Rwanda standards.   
©RSB 2020  - All rights reserved                  16 
 5.4 Geotechnical design by calculation  
5.4.1  General  
5.3.1.1 Design by calculation shall be in accordance with the fundamental requirements and with the 
particular rules of this standard.  
Design by calculation involve s: 
a) actions, which may be either imposed loads or imposed displacements, e.g. from  
b) ground movements;  
c) properties of soils, rocks and other materials;  
d) geometrical data;  
e) limiting values of deformation s, crack width s, vibrations etc.;  
f) calculation models.  
5.3.1.2 It should be considered that knowledge of the ground conditions depends on the extent and quality of 
the geotechnical investigations. Such knowledge and the control of workmanship are usually more significant  
to fulfilling the fundamental requirements than is precision in the calculation models and partial factors.  
5.3.1.3 The calculation model shall describe the assumed behaviour of the ground for the limit state under 
consideration.  
5.3.1.4 If no reliable ca lculation model is available for a specific limit state, analysis of another limit state 
shall be carried out using factors to ensure that exceeding the specific limit state considered is sufficiently 
improbable. Alternatively, design by prescriptive measu res, experimental models and load tests, or the 
observational method, shall be performed.  
5.3.1.5 The calculation model may consist of any of the following:  
a) an analytical model;  
b) a semi -empirical model;  
c) a numerical model.  
5.3.1.6 Any calculation model shall  be either accurate or err on the side of safety.  
5.3.1.7 A calculation model may include simplifications.  DRS 113: 2020  
17                ©RSB 2020  - All rights reserved  
 5.3.1.8 If needed, a modification of the results from the model may be used to ensure that the design 
calculation is either accurate or errs on the side of safety.  
5.3.1.9 If the modification of the results makes use of a model factor, it should take account of the following:  
a) the range of uncertainty in the results of the method of analysis;  
b) any systematic errors known to be associated with the method  of analysis.  
5.3.1.10   If an empirical relationship is used in the analysis, it shall be clearly established that it is relevant 
for the prevailing ground conditions.  
5.3.1.11 Limit states involving the formation of a mechanism in the ground should be read ily checked using a 
calculation model. For limit states defined by deformation considerations, the deformations should be 
evaluated by calculation as described in 5.4.8, or otherwise assessed.  
NOTE  Many calculation models are based on the assumption of a s ufficiently ductile performance of the 
ground/structure system. A lack of ductility, however, will lead to an ultimate limit state characterized by sudden collapse . 
5.3.1.12  Numerical methods can be appropriate if compatibility of strains or the interactio n between the 
structure and the soil at a limit state are considered.  
5.3.1.13  Compatibility of strains at a limit state should be considered. Detailed analysis, allowing for the 
relative stiffness of structure and ground, may be needed in cases where a co mbined failure of structural 
members and the ground could occur. Examples include raft foundations, laterally loaded piles and flexible 
retaining walls. Particular attention should be paid to strain compatibility for materials that are brittle or that 
have  strain -softening properties.  
5.3.1.14  In some problems, such as excavations supported by anchored or strutted flexible walls, the 
magnitude and distribution of earth pressures, internal structural forces and bending moments depend to a 
great extent on the  stiffness of the structure, the stiffness and strength of the ground and the state of stress in 
the ground.  
5.3.1.125  In these problems of ground -structure interaction, analyses should use stress -strain 
relationships for ground and structural materials an d stress states in the ground that are sufficiently 
representative, for the limit state considered, to give a safe result.  
5.4.2  Actions  
5.3.2.1 The values of geotechnical actions to be used shall be selected, since they are known before a 
calculation is perform ed; they may change during that calculation.  
NOTE  Values of geotechnical actions may change during the course of calculation . In such cases they will be 
introduced as a first estimate to start the calculation with a preliminary, known value.  
5.3.2.2 Any in teraction between the structure and the ground shall be taken into account when determining 
the actions to be adopted in the design.   
©RSB 2020  - All rights reserved                  18 
 5.3.2.3 In geotechnical design, the following should be considered for inclusion as actions:  
a) the weight of soil, rock and w ater; 
b) stresses in the ground;  
c) earth pressures and ground -water pressure ; 
d) free water pressures, including wave pressures;  
e) ground -water pressures;  
f) seepage forces;  
g) dead and imposed loads from structures;  
h) surcharges;  
i) mooring forces;  
j) removal of load or excavation of ground;  
k) traffic loads;  
l) movements caused by mining or other caving or tunnelling activities;  
m) swelling and shrinkage caused by vegetation, climate or moisture changes;  
n) movements due to creeping or sliding or settling ground masses;  
o) movements du e to degradation, dispersion , decomposition, self -compaction and  
p) solution;  
q) movements and accelerations caused by earthquakes, explosions, vibrations and  
r) dynamic loads;  
s) temperature effects, including frost action;  
t) ice loading;  
u) imposed pre -stress in ground  anchors or struts;  
v) downdrag.  DRS 113: 2020  
19                ©RSB 2020  - All rights reserved  
 5.3.2.4 Consideration shall be given to the possibility of variable actions occurring both jointly and 
separately.  
5.3.2.5 The duration of actions shall be considered with reference to time effects in the material properties o f 
the soil, especially the drainage properties and compressibility of fine -grained soils.  
5.3.2.6 Actions, which are applied repeatedly, and actions with variable intensity shall be identified for 
special consideration with regard to, e.g. continuing movem ents, liquefaction of soils, change of ground 
stiffness and strength.  
5.3.2.7 Actions that produce a dynamic response in the structure and the ground shall be identified for 
special consideration.  
5.3.2.8 Actions in which ground - and free -water forces pred ominate shall be identified for special 
consideration with regard to deformations, fissuring, variable permeability and erosion.  
NOTE  Unfavourable (or destabilising) and favourable (or stabilising) permanent actions may in some situations be 
considered as coming from a single source. If they are considered so, a single partial factor may be applied to the sum of 
these actions or to the sum of their effects.  
5.4.3  Ground properties  
5.3.3.1 Properties of soil and rock masses, as quantified for design calculations by geotechnical parameters, 
shall be obtained from test results, either directly or through correlation, theory or empiricism, and from other 
relevant data.  
5.3.3.2 Values obtained from test results and other data shall be interpreted appropriately for the  limit state 
considered.  
5.3.3.3 Account shall be taken of the possible differences between the ground properties and geotechnical 
parameters obtained from test results and those governing the behaviour of the geotechnical structure.  
5.3.3.4 The difference s to which 2.4.3(3) refers can be due to the following factors:  
a) many geotechnical parameters are not true constants but depend on stress level and  
b) mode of deformation;  
c) soil and rock structure (e.g. fissures, laminations, or large particles) that may play a  
d) different role in the test and in the geotechnical structure;  
e) time effects;  
f) the softening effect of percolating water on soil or rock strength;  
g) the softening effect of dynamic actions;   
©RSB 2020  - All rights reserved                  20 
 h) the brittleness or ductility of the soil and rock tested;  
i) the method  of installation of the geotechnical structure;  
j) the influence of workmanship on artificially placed or improved ground;  
k) the effect of construction activities on the properties of the ground.  
5.3.3.5 When establishing values of geotechnical parameters, the following should be considered:  
a) published and well recognised information relevant to the use of each type of test in  the appropriate 
ground conditions;  
b) the value of each geotechnical parameter compared with relevant published data and local and 
general experience;  
c) the variation of the geotechnical parameters that are relevant to the design;  
d) the results of any large scale field trials and measurements from neighbouring  constructions;  
e) any correlations between the results from more than one type of test;  
f) any significant deterioration in ground material properties that may occur during the  lifetime of the 
structure.  
5.3.3.6 Calibration factors shall be applied where necessary to convert laboratory or field test results  into 
values that represent the behavio ur of the soil and rock in the ground, for the actual limit state, or to take 
account of correlations used to obtain derived values from the test results.  
5.4.4  Geometrical data  
The level and slope of the ground surface, water levels, levels of interfaces betwee n strata, excavation levels 
and the dimensions of the geotechnical structure shall be treated as geometrical data.  
5.4.5  Characteristic values  
5.4.5.1  Characteristic values of geotechnical parameters  
5.3.5.1.1  The selection of characteristic values for geotechnical parameters shall be based on results and 
derived values from laboratory and field tests, complemented by well -established experience.  
5.3.5.1.2  The characteristic value of a geotechnical parameter shall be selected as a cautious estimate of the 
value affec ting the occurrence of the limit state.  
5.3.5.1.3  The greater variance of c' compared to that of tan φ' shall be considered when their characteristic 
values are determined.  DRS 113: 2020  
21                ©RSB 2020  - All rights reserved  
 5.3.5.1.4  The selection of characteristic values for geotechnical parameters shall take account of the following:  
a) geological and other background information, such as data from previous projects;  
b) the variability of the measured property values and other relevant information, e.g.  
c) from existing knowledge;  
d) the extent of the field and labo ratory investigation;  
e) the type and number of samples;  
f) the extent of the zone of ground governing the behaviour of the geotechnical structure at the limit 
state being considered;  
g) the ability of the geotechnical structure to transfer loads from weak to stron g zones in the ground.  
5.3.5.1.5  Characteristic values can be lower values, which are less than the most probable values, or upper 
values, which are greater.  
5.3.5.1.6  For each calculation, the most unfavourable combination of lower and upper values of ind ependent 
parameters shall be used.  
5.3.5.1.7  The zone of ground governing the behaviour of a geotechnical structure at a limit state is usually 
much larger than a test sample or the zone of ground affected in an in situ test. Consequently the value of the 
governing parameter is often the mean of a range of values covering a large surface or volume of the ground. 
The characteristic value should be a cautious estimate of this mean value.  
5.3.5.1.8  If the behaviour of the geotechnical structure at the limit st ate considered is governed by the lowest 
or highest value of the ground property, the characteristic value should be a cautious estimate of the lowest or 
highest value occurring in the zone governing the behaviour.  
5.3.5.1.9  When selecting the zone of grou nd governing the behaviour of a geotechnical structure at a limit 
state, it should be considered that this limit state may depend on the behaviour of the supported structure. For 
instance, when considering a bearing resistance ultimate limit state for a bu ilding resting on several footings, 
the governing parameter should be the mean strength over each individual zone of ground under a footing, if 
the building is unable to resist a local failure. If, however, the building is stiff and strong enough, the gove rning 
parameter should be the mean of these mean values over the entire zone or part of the zone of ground under 
the building.  
5.3.5.1.10  If statistical methods are employed in the selection of characteristic values for ground properties, 
such methods shou ld differentiate between local and regional sampling and should allow the use of a priori 
knowledge of comparable ground properties.  
5.3.5.1.11  If statistical methods are used, the characteristic value should be derived such that the 
calculated probability  of a worse value governing the occurrence of the limit state under consideration is not 
greater than 5  %.  
©RSB 2020  - All rights reserved                  22 
 NOTE  In this respect, a cautious estimate of the mean value is a selection of the mean value of the limited set of 
geotechnical parameter values, with a confidence level of 95  %; where local failure is concerned, a cautious estimate of 
the low value is a-5 % fractile.  
5.3.5.1.12  When using standard tables of characteristic values related to soil investigation parameters, the 
characteristic value sha ll be selected as a very cautious value.  
5.4.5.2  Characteristic values of geometrical data  
5.3.5.2.1  Characteristic values of the levels of ground and ground -water or free water shall be measured, 
nominal or estimated upper or lower levels.  
5.3.5.2.2  Characteristi c values of levels of ground and dimensions of geotechnical structures or elements 
should usually be nominal values.  
5.4.6  Design values  
5.4.6.1  Design values of actions  
5.3.6.1.1  The design value of an action ( Fd) shall either be assessed directly or shall be derived from 
representative values using the following equation:  
Fd = F.Frep                                                                                                      (2.1a)  
with 
Frep= ψ.F k                                                                                                         (2.1b)  
5.3.6.1.2  Appropriate values of 
 shall be taken from RS 471 . 
5.3.6.1.3  The partial factor F for persistent and transient situations defined in Annex A shall be used in 
equation (2.1a).  
NOTE 1 The values of the partial factors may be set by the national building regulatory authority  
NOTE 2 The recommended values in Annex A indicate the appropriate level of safety for conventional designs.  
5.3.6.1.4  If design values of geotechnical actions are as sessed directly, the values of the partial factors 
recommended in Annex A should be used as a guide to the required level of safety.  
5.3.6.1.5  When dealing with ground -water pressures for limit states with severe consequences (generally 
ultimate limit stat es), design values shall represent the most unfavourable values that could occur during the 
design lifetime of the structure. For limit states with less severe consequences (generally serviceability limit 
states), design values shall be the most unfavourab le values which could occur in normal circumstances . 
5.3.6.1.6  Design values of ground -water pressures may be derived either by applying partial factors to 
characteristic water pressures or by applying a safety margin to the characteristic water level in accordance 
with 8.4.4(1 ). DRS 113: 2020  
23                ©RSB 2020  - All rights reserved  
 5.3.6.1.7  The following features, which may affect the water pressures should be considered:  
a) the level of the free water surface or the ground -water table;  
b) the favourable or unfavourable effects of drainage, both natural and artificial, taking  
c) account of its future maintenance;  
d) the supply of water by rain, flood, burst water mains or other means;  
e) changes of water pressures due to the growth or removal of veg etation.  
5.3.6.1.8  Consideration should be given to unfavourable water levels that may be caused by  changes in the 
water catchment and reduced drainage due to blockage, freezing or other causes.  
5.3.6.1.9  Unless the adequacy of the drainage system can be d emonstrated and its maintenance ensured, the 
design ground -water table should be taken as the maximum possible level, which may be the ground surface.  
5.4.6.2  Design values of geotechnical parameters  
5.3.6.2.1  Design values of geotechnical parameters ( Xd) shall ei ther be derived from characteristic values 
using the following equation:  
Xd = Xk / M                                                                                                                   (2.2) 
or shall be assessed directly.  
5.3.6.2.2  The partial factor M for persistent and transient situations defined in Annex A shall be used in 
equation (2.2).  
5.3.6.2.3  If design values of geotechnical parameters are assessed directly, the values of the partial factors 
recommended in Annex A should b e used as a guide to the required level of safety.  
5.4.6.3  Design values of geometrical data  
5.3.6.3.1  The partial action and material factors ( F and M) include an allowance for minor variations in 
geometrical data and, in such cases, no further safety margin on  the geometrical data should be required.  
5.3.6.3.2  In cases where deviations in the geometrical data have a significant effect on the reliability of a 
structure, design values of geometrical data ( ad) shall either be assessed directly or be derived from n ominal 
values using the following equation:  
ad = a nom ± a                                                                                                               (2.3)  
for which values of a are given in 9.5.4(2) and 9.3.2.2   
©RSB 2020  - All rights reserved                  24 
 5.4.6.4  Design values of structu ral properties  
5.3.6.4.1  The design strength properties of structural materials and the design resistances of structural 
elements shall be calculated in accordance with relevant standards.  
5.4.7  Ultimate Limit States  
5.4.7.1  General  
5.3.7.1.1   Where relevant, it shall b e verified that the following limit states are not exceeded:  
a) loss of equilibrium of the structure or the ground, considered as a rigid body, in which the strengths of 
structural materials and the ground are insignificant in providing resistance (EQU);  
b) internal failure or excessive deformation of the structure or structural elements, including e.g. footings, 
piles or basement walls, in which the strength of structural materials is significant in providing 
resistance (STR);  
c) failure or excessive deformation of  the ground, in which the strength of soil or rock is significant in 
providing resistance (GEO);  
d) loss of equilibrium of the structure or the ground due to uplift by water pressure (buoyancy) or other 
vertical actions (UPL);  
e) hydraulic heave, internal erosio n and piping in the ground caused by hydraulic  gradients (HYD).  
NOTE  Limit state GEO is often critical to the sizing of structural elements involved in foundations or retaining 
structures and sometimes to the strength of structural elements.  
5.3.7.1.2  The partial factors in persistent and transient situations defined in Annex A shall be used.  
NOTE  The values of the partial factors are given in tables in Annex A.  
5.3.7.1.3  All values of partial factors for actions or the effects of actions in accidental si tuations should 
normally be taken equal to 1,0. All values of partial factors for resistances should then be selected according 
to the particular circumstances of the accidental situation.  
5.3.7.1.4  More severe values than those recommended in Annex A should be used in cases of abnormal risk 
or unusual or exceptionally difficult ground or loading conditions.  
5.3.7.1.5  Less severe values than those recommended in Annex A may be used for temporary structures or 
transient design situations, where the likel y consequences justify it.  
5.3.7.1.6  When calculating the design value of the resistance, ( Rd ), or the design value of the effect of actions, 
(Ed ), model factors, ( R;d ) or (S;d ) respectively, may be introduced to ensure that the results of the design  
calculation model are either accurate or err on the safe side.  DRS 113: 2020  
25                ©RSB 2020  - All rights reserved  
 5.4.7.2  Verification of static equilibrium  
5.3.7.2.1  When considering a limit state of static equilibrium or of overall displacements of the structure or 
ground (EQU), it shall be verified that:  
Edst;d Estb;d + Td                                                                                                   (2.4)  
With Edst;d = E{F Frep ; Xk / M ; ad }dst                                                                  (2.4a)  
And  Estb;d = E{F Frep ; Xk / M ; ad }stb                                                                (2.4b)  
5.3.7.2.3  The partial factors for persistent and transient situations defined in A.2(1)P and A.2(2)P shall be used 
in equation (2.4).  
NOTE 1 Static equilibrium EQU is mainly relevant in structural design. In geotechnical design, EQU verification will be 
limited to rare cases, such as a rigid foundation bearing on rock, and is, in principle, distinct from overall stability or 
buoyancy problems. If any shearing resistance Td is included, it should be of minor importance.  
NOTE 2 The values of the partial factors may be set by the National annex. Tables A.1 and A.2 give the recommended 
values.  
5.4.7.3  Verification  of resistance for structural and ground lim it states in persistent and transient 
situations  
5.4.7.3.1  General  
When considering a limit state of rupture or excessive deformation of a structural element or section of the 
ground (STR and GEO), it shall be verified that:  
Ed Rd                                                                                                                        (2.5) 
5.4.7.4  Design  effects of actions  
5.3.7.4.1  Partial factors on actions may be applied either to the actions themselves ( Frep) or to their effects 
(E): 
Ed = E{F Frep; Xk/M; ad}                                                                                         (2.6a)  
or 
Ed = E E{Frep; Xk/M; ad}.                                                                                            (2.6b)  
5.3.7.4.2  In some design s ituations, the application of partial factors to actions coming from or through the soil 
(such as earth or water pressures) could lead to design values, which are unreasonable or even physically 
impossible. In these situations, the factors may be applied d irectly to the effects of actions derived from 
representative values of the actions.  
5.3.7.4.3  The partial factors defined in A.3.1(1)P and  A.3.2(1)P shall be used in equations (2.6a) and (2.6b).  
NOTE  The values of the partial factors are given in tables A .3 and A.4 in the annex A   
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 5.4.7.5  Design resistances  
5.3.7.5.1  Partial factors may be applied either to ground properties ( X) or resistances ( R) or to both,  as follows:  
Rd = R{F Frep; Xk/M; ad}                                                                                         (2.7a)  
or 
Rd = R{F Frep; Xk; ad}/R                                                                                                                                          (2.7b)  
or 
Rd = R{F Frep; Xk/M; ad}/R                                                                                                                                    (2.7c)  
NOTE  In design procedures where the effects of actions are factored, the partial factor for actions 
F = 1,0. (see also 
B.3(6))  
5.3.7.5.2  The partial factors, defined in A.3.3.1(1)P, A.3.3.2(1)P, A.3.3.4(1)P, A.3.3.5(1)P and  A.3.3.6(1)P shall 
be used in equations (2.7a, b, and c).  
NOTE  The values of the partial factors are given in tables A.5, A.6, A.7, A. 8, A.12, A.13 and A.14.  
5.4.7.6  Design Approaches  
5.4.7.6.1  General  
The manner in which equations (2.6) and (2.7) are applied shall be determined using one of three Design 
Approaches.  
NOTE 1 Further clarification of the Design Approaches is provided in Annex B.  
NOTE 2 The p artial factors in Annex A to be used in equations (2.6) and (2.7) are grouped in sets denoted by A (for 
actions or effects of actions), M (for soil parameters) and R (for resistances). They are selected according to the Design 
Approach used.  
5.4.7.6.1.1  Design Approac h 1 
5.3.7.6.1.1.1  Except for the design of axially loaded piles and anchors, it shall be verified that a limit state of 
rupture or excessive deformation will not occur with either of the following combinations of sets of partial 
factors:  
Combination 1: A1 “+” M1 “+” R1 
Combination 2: A2 “+” M2 “+” R1 
where “+” implies: “to be combined with”.  
NOTE  In Combinations 1 and 2, partial factors are applied to actions and to ground strength parameters.  DRS 113: 2020  
27                ©RSB 2020  - All rights reserved  
 5.3.7.6.1.1.2  For the design of axially loaded piles and anchors, it shall be verified that a limit state of rupture 
or excessive deformation will not occur with either of the following combinations of sets of partial factors:  
Combination 1: A1 “+” M1 “+” R1 
Combination 2: A2 “+” (M1 or M2) “+” R4 
NOTE 1 In Comb ination 1, partial factors are applied to actions and to ground strength parameters. In Combination 2, 
partial factors are applied to actions, to ground resistances and sometimes to ground strength parameters.  
NOTE 2 In Combination 2, set M1 is used for calculating resistances of piles or anchors and set M2 for calculating 
unfavourable actions on piles owing e.g. to negative skin friction or transverse loading.  
5.4.7.6.1.1.3  If it is obvious that one of the two combinations governs the design,  calculations for the other 
combination need not be carried out. However, different combinations may be critical to different aspects of 
the same design.  
5.4.7.6.1.2  Design Approach 2  
5.3.7.6.1.2.1  It shall be verified that a limit state of rupture or excessive deform ation will not occur with the 
following combination of sets of partial factors:  
Combination: A1 “+” M1 “+” R2 
NOTE 1 In this approach, partial factors are applied to actions or to the effects of actions and to ground resistances.  
NOTE 2 If this approach is used for slope and overall stability analyses the resulting effect of the actions on the failure 
surface is multiplied by E and the shear resistance along the failure surface is divided by R:e. 
5.4.7.6.1.3  Design Approach 3  
It shall be verified t hat a limit state of rupture or excessive deformation will not occur with the following 
combination of sets of partial factors:  
Combination: ( A1* or A2†) “+” M2 “+” R3 
*on structural actions  
†on geotechnical actions  
NOTE 1 In this approach, partial factors  are applied to actions or to the effects of actions from the structure and to 
ground strength parameters.  
NOTE 2 For slope and overall stability analyses, actions on the soil (e.g. structural actions, traffic load) are treated as 
geotechnical actions by u sing the set of load factors A2.  
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 5.4.7.7  Verification procedure and partial factors for uplift  
5.3.7.7.1  Verification for uplift (UPL) shall be carried out by checking that the design value of the combination 
of destabilising permanent and variable vertical action s (Vdst;d) is less than or equal to the sum of the design 
value of the stabilising permanent vertical actions ( Gstb;d) and of the design value of any additional resistance 
to uplift ( Rd): 
Vdst,d Gstb;d + Rd                                                                                                          (2.8) 
where  
Vdst,d = G dst;d +Qdst;d 
5.3.7.7.2  Additional resistance to uplift may also be treated as a stabilising permanent vertical action (G stb;d). 
5.3.7.7.3  The partial factors for Gdst;d, Qdst;d, Gstb;d and Rd for persistent and transient situations defined in 
A.4(1)P and A.4(2)P shall be used in equation (2.8).  Tables A.15 and A.16 give the recommended values.  
5.4.7.8  Verification of resistance to failure by heave due to seepage of water in the ground  
5.3.7.8.1  When considering a limit state of failure due to heave by seepage of water in the ground (HYD, see 
13.3), it shall be verified, for every relevant soil column, that the design value of the destabilising total pore 
water pressure ( Vdst;d ) at the b ottom of the column, or the design value of the seepage force ( Sdst;d) in the 
column is less than or equal to the stabilising total vertical stress ( stb;d) at the bottom of the column, or the 
submerged weight ( G´stb;d) of the same column:  
udst;d stb;d                                                                                                          (2.9a)  
Sdst;d G´stb;d                                                                                                           (2.9b)  
5.3.7.8.2  The partial factors for udst;d, stb;d, Sdst;d and G´stb;d for persistent and transient situations 
defined in A.5(1)P shall be used in equations 2.9a and 2.9b.  
5.4.8  Serviceability limit states  
5.43.8.1 Verification for serviceability limit states in the ground or in a structural section, element or 
connection, shall either require that:  
Ed Cd,                                                                                                                                                                                      (2.10)  
or be done through the method given in 2.4.8(4).  
5.3.8.2 Values o f partial factors for serviceability limit states should normally be taken equal to 1,0.  
5.3.8.3 Characteristic values should be changed appropriately if changes of ground properties e.g. by 
ground -water lowering or desiccation, may occur during the life o f the structure.  DRS 113: 2020  
29                ©RSB 2020  - All rights reserved  
 5.3.8.4 It may be verified that a sufficiently low fraction of the ground strength is mobilised to keep 
deformations within the required serviceability limits, provided this simplified approach is restricted to design 
situations where:  
a) a value of the deformation is not required to check the serviceability limit state;  and 
b) established comparable experience exists with similar ground, structures and application method.  
5.3.8.5 A limiting value for a particular deformation is the value at whic h a serviceability limit state, such as 
unacceptable cracking or jamming of doors, is deemed to occur in the supported structure. This limiting value 
shall be agreed during the design of the supported structure.  
5.4.9  Limiting values for movements of foundations  
5.3.9.1 In foundation design, limiting values shall be established for the foundation movements.  
5.3.9.2 Any differential movements of foundations leading to deformation in the supported structure shall be 
limited to ensure that they do not lead to a limi t state in the supported structure.  
5.3.9.3 The selection of design values for limiting movements and deformations shall take account of the 
following:  
a) the confidence with which the acceptable value of the movement can be specified;  
b) the occurrence and rate  of ground movements;  
c) the type of structure;  
d) the type of construction material;  
e) the type of foundation;  
f) the type of ground;  
g) the mode of deformation;  
h) the proposed use of the structure;  
i) the need to ensure that there are no problems with the services entering  the structure.  
5.3.9.4 Calculations of differential settlement shall take account of:  
a) the occurrence and rate of settlements and ground movements;  
b) random and systematic variations in ground properties;   
©RSB 2020  - All rights reserved                  30 
 c) the loading distribution;  
d) the construction method (including the sequence of loading);  
e) the stiffness of the structure during and after construction.  
5.5 Design by prescriptive measures  
In design situations where calculation models are not available or not necessary, exceeding limit states may 
be avoided by th e use of prescriptive measures. These involve conventional and generally conservative rules 
in the design, and attention to specification and control of materials, workmanship, protection and 
maintenance procedures  against frost action and chemical or biological attack, for which direct calculations 
are not generally appropriate.  
5.6 Load tests and tests on experimental models  
5.6.1 When the results of load tests or tests on large or small scale models are used to justify a design , or 
in order to complement  one of the other alternatives mentioned in 2.1(4), the following features shall be 
considered and allowed for:  
a) differences in the ground conditions between the test and the actual construction;  
b) time effects, especially if the duration of the test is much less than the duration of  loading of the 
actual construction;  
c) scale effects, especially if small models are used. The effects of stress levels shall be  considered, 
together with the effects of particle size.  
5.6.1 Tests may be carried out on a sample of t he actual construction or on full scale or smaller scale 
models.  
5.7 Observational method  
5.7.1 When prediction of geotechnical behaviour is difficult, it can be appropriate to apply the approach 
known as "the observational method", in which the design is revi ewed during construction.  
5.7.2 The following requirements shall be met before construction is started:  
a) acceptable limits of behaviour shall be established;  
b) the range of possible behaviour shall be assessed and it shall be shown that there is an acceptable  
probability that the actual behaviour will be w ithin the acceptable limits;  
c) a plan of monitoring shall be devised, which will reveal whether the actual behaviour lies within the 
acceptable limits. The monitoring shall make this clear at a sufficiently ear ly stage, and with 
sufficiently short intervals to allow contingency actions to be undertaken successfully;  DRS 113: 2020  
31                ©RSB 2020  - All rights reserved  
 d) the response time of the instruments and the procedures for analysing the results  shall be sufficiently 
rapid in relation to the possible evolution  of the system;  
e) a plan of contingency actions shall be devised, which may be adopted if the monitoring reveals 
behaviour outside acceptable limits.  
5.7.3 During construction, the monitoring shall be carried out as planned.  
5.7.4 The results of the monitori ng shall be assessed at appropriate stages and the planned contingency 
actions shall be put into operation if the limits of behaviour are exceeded.  
5.7.5 Monitoring equipment shall either be replaced or extended if it fails to supply reliable data of 
appropriate type or in sufficient quantity.  
5.8 Geotechnical Design Report  
5.8.1 The assumptions, data, methods of calculation and results of the verification of safety and 
serviceability shall be recorded in the Geotechnical Design Report.  
5.8.2 The level of detail of the Geotechnical Design Reports will vary greatly, depending on the type of 
design. For simple designs, a single sheet may be sufficient.  
5.8.3 The Geotechnical Design Report should normally include the following items, with cross  reference to 
the Ground Investigation Report (see 6.4) and to other documents, which contain more detail:  
a) a description of the site and surroundings;  
b) a description of the ground conditions;  
c) a description of the proposed construction, including actions;  
d) design values of s oil and rock properties, including justification, as appropriate;  
e) statements on the codes and standards applied;  
f) statements on the suitability of the site with respect to the proposed construction and  
g) the level of acceptable risks;  
h) geotechnical design cal culations and drawings;  
i) foundation design recommendations;  
j) a note of items to be checked during construction or requiring maintenance or monitoring.   
©RSB 2020  - All rights reserved                  32 
 5.8.4 The Geotechnical Design Report shall include a plan of supervision and monitoring, as appropriate. 
Items, which require checking during construction or, which require maintenance after construction shall be 
clearly identified. When the required checks have been carried out during construction, they shall be recorded 
in an addendum to the Report.  
5.8.5 In relation to supervision and monitoring the Geotechnical Design Report should state:  
a) the purpose of each set of observations or measurements;  
b) the parts of the structure, which are to be monitored and the locations at which  observations are to be 
made;  
c) the frequency with which readings are to be taken;  
d) the ways in which the results are to be evaluated;  
e) the range of values within which the results are to be expected;  
f) the period of time for which monitoring is to continue after construction is complete;  
g) the par ties responsible for making measurements and observations, for interpreting the results 
obtained and for maintaining the instruments.  
5.8.6 An extract from the Geotechnical Design Report, containing the supervision, monitoring and 
maintenance requirements for the completed structure, shall be provided to the owner/client.  
6 Geotechnical data  
6.1 General  
6.1.1 Careful collection, recording and interpretation of geotechnical information shall always be made. 
This information shall include geology, geomorphology, seismicity, hydrology and history of the site. 
Indications of the variability of the ground shall be taken into account.  
6.1.2  Geotechnical investigations shall be planned taking into account the construction and performance 
requirements of the proposed st ructure. The scope of geotechnical investigations shall be continuously 
reviewed as new information is obtained during execution of the work.  
6.1.3  Routine field investigations and laboratory testing shall be carried out and reported generally in 
accordanc e with internationally recognised standards and recommendations.  
6.1.4  Deviations from these standards and additional test requirements shall be reported.  DRS 113: 2020  
33                ©RSB 2020  - All rights reserved  
 6.2 Geotechnical investigations  
6.2.1  General  
6.2.2  Geotechnical investigations shall provide sufficient data c oncerning the ground and the ground -water 
conditions at and around the construction site for a proper description of the essential ground properties and a 
reliable assessment of the characteristic values of the ground parameters to be used in design calcul ations.  
6.2.3  For very large or unusual structures, structures involving abnormal risks or unusual or exceptionally 
difficult ground or loading conditions, and structures in highly seismic areas , it is possible that the extent of 
investigations specified i n this standard will not be sufficient to meet the design requirements.  
6.2.4  If the character and extent of the investigations are related to the Geotechnical Category of the 
structure, ground conditions that may influence the choice of Geotechnical Categ ory should be determined as 
early as possible in the investigation.  
6.2.5  The investigation s should include visual inspection s of the site to enable the design assumptions to 
be verified during construction . 
6.2.2  Preliminary investigations  
Preliminary investiga tions shall be carried out:  
a) to assess the general suitability of the site;  
b) to compare alternative sites, if relevant;  
c) to estimate the changes that may be caused by the proposed works;  
d) to plan the design and control investigations, including identification of the extent of  
e) ground, which may have significant influence on the behaviour of the structure;  
f) to identify borrow areas, if relevant.  
6.2.3  Design investigations  
6.2.3.1  Design investigations shall be carried out:  
a. to provide the information required for an ad equate design of the temporary and permanent 
works;  
b. to provide the information required to plan the method of construction;  
c. to identify any difficulties that may arise during construction.   
©RSB 2020  - All rights reserved                  34 
 6.2.3.2  The design investigation shall identify in a reliable way the disposition and properties of all ground 
relevant to or affected by the proposed construction.  
6.2.3.3  The parameters, which affect the ability of the structure to satisfy its performance criteria shall be 
established before the start of the final desi gn. 
6.2.3.4  In order to ensure that the design investigation covers all relevant ground formations, particular 
attention should be paid to the following geological features:  
a) ground profile;  
b) natural or man -made cavities;  
c) degradation of rocks, soils, or fill  materials;  
d) hydrogeological effects;  
e) faults, joints and other discontinuities;  
f) creeping soil and rock masses;  
g) expansible and collapsible soils and rocks;  
h) presence of waste or man -made materials.  
6.2.3.5  The history of the site and its surroundings shall be  taken into account.  
6.2.3.6  The investigation shall be carried out at least through the formations, which are assessed as being 
relevant to the project.  
6.2.3.7  The existing ground -water levels shall be established during the investigation. Any free water  levels 
observed during the investigation shall be recorded.  
6.2.3.8  The extreme water levels of any water source, which might influence the ground -water pressures 
should be established.  
6.2.3.9  The location and capacities of any dewatering or water abstra ction wells in the vicinity of the site 
shall be established.  
6.3 Evaluation of geotechnical parameters  
6.3.1  General  
In the following requirements concerning the evaluation of geotechnical parameters, only the most commonly 
used laboratory and field tests have been  referred to. Other tests may be used provided their suitability has 
been demonstrated through comparable experience.  DRS 113: 2020  
35                ©RSB 2020  - All rights reserved  
 6.3.2  Characterisation of soil and rock type  
6.3.2.1  The character and basic constituents of the soil or rock shall be identified before the res ults of other 
tests are interpreted.  
6.3.2.2  The material shall be examined, identified and described in accordance with a recognized 
nomenclature. A geological evaluation shall be made.  
6.3.2.3  Soils should be classified and soil layers described accordin g to an acknowledged geotechnical soil 
classification and description system.  
6.3.2.4  Rock should be classified in terms of the quality of the solid (stone) material and jointing.  
Stone quality should be described in terms of weathering, particle organisat ion, dominant grain size of 
minerals, and hardness and toughness of the main mineral. Jointing should be characterised in terms of joint 
type, width, spacing and fill quality.  
6.3.2.5  In addition to visual inspection, a number of tests for classification, identification and quantification of 
soils and rocks may be used, such as for soils:  
a. grain size distribution;  
b. weight density;  
c. porosity;  
d. water content;  
e. grain shape;  
f. grain surface roughness;  
g. density index;  
h. Atterberg limits;  
i. swelling;  
j. carbonate content;  
k. organic matter content for rocks:  
l. mineralogy;  
m. petrography;   
©RSB 2020  - All rights reserved                  36 
 n. water content;  
o. weight density;  
p. porosity;  
q. sound velocity;  
r. quick water absorption;  
s. swelling;  
t. slake -durability index;  
u. uniaxial compressive strength.  
6.3.3  Weight  density  
6.3.3.1  The weight density shall be determined with sufficient accuracy to establish design or characteristic 
values of the actions that derive from it.  
6.3.3.2  The weight density should be determined on specimens of soil and rock taken from undisturbed 
samples.  Alternatively, it may be deri ved from well established or documented correlations based on, for 
example, penetration tests.  
6.3.4  Density index  
The density index shall express the degree of compaction of a non -cohesive soil with respect to the loosest 
and densest condition as defined by sta ndard laboratory procedures.  
6.3.5  Degree of compaction  
The degree of compaction of natural ground or fill shall be expressed as the ratio between dry weight density 
and maximum dry weight density obtained from a standard compaction test.  
6.3.6  Shear strength  
6.3.6.1   In assessing the shear strength of soil, the influence of the following features shall be considered:  
a. the stress level imposed on the soil;  
b. anisotropy of strength, especially in clays of low plasticity;  
c. fissures, especially in stiff clays;  
d. strain rate eff ects;  DRS 113: 2020  
37                ©RSB 2020  - All rights reserved  
 e. very large strains where these may occur in a design situation;  
f.  pre-formed slip surfaces;  
g. time effects;  
h. sensitivity of cohesive soil;  
i.  degree of saturation.  
6.3.6.2  When the shear strength assessment is based on test results, the level of confidence  in them  theory 
used to derive shear strength values should be taken into account, as well as the possible disturbance during 
sampling and heterogeneity of samples.  
6.3.6.3  As to time effects, it should be considered that the period for which a soil will b e effectively undrained 
depends on its permeability, the availability of free water and the geometry of the situation.  
6.3.6.4  The values of effective shear strength parameters c' and tan φ' shall be assumed to be constant only 
within the range of stresses  for which they have been evaluated.  
6.3.7  Soil stiffness  
6.3.7.1  In assessing the soil stiffness, the following features shall be considered:  
a. drainage conditions;  
b. level of mean effective stress;  
c. natural or artificial pre -consolidation;  
d. level of imposed shear st rain or induced shear stress, this latter often normalised with respect 
to the shear strength at failure.  
6.3.7.2  Reliable measurements of the stiffness of the ground are often very difficult to obtain from field or 
laboratory tests. In particular, owing t o sample disturbance and other effects, measurements obtained from 
laboratory specimens often underestimate the in -situ stiffness of the soil. Observations of the behaviour of 
previous constructions should therefore be analysed wherever available.  
6.3.8  Quality and properties of rocks and rock masses  
6.3.8.1  General assessment  
6.3.8.1.1  In assessing the quality and properties of rocks and rock masses, a distinction shall be drawn 
between the behaviour of rock material as measured on undisturbed core samples and the behaviour of much 
larger rock masses, which include structural discontinuities such as bedding planes, joints, shear zones and 
solution cavities. Consideration shall be given to the following characteristics of the joints:   
©RSB 2020  - All rights reserved                  38 
 a) spacing;  
b) orientation;  
c) aperture;  
d) persistence (continuity);  
e) tightness;  
f) roughness, including the effects of previous movements on the joints;  
g) filling.  
6.3.8.1.2  In addition, when assessing the properties of rocks and rock masses, the following items shall be 
considered, if relevant:  
a) in situ stresses;  
b) water pressure;  
c) pronounced variations in properties between different layers.  
6.3.8.1.3  Estimates of rock mass properties, such as:  
a) strength and stiffness,  
b) jointing, especially in fractured zones,  
c) water permeability of the joint system,  
d) deformation properties of weathered rock,  
may be obtained by using the concept of rock mass classification described in this standard.  
6.3.8.1.4  The sensitivity of rocks to e.g. climate or stress changes, shall be assessed.  Consideration shall also 
be give n to the influence of chemical degradation on the performance of rock foundations.  
6.3.8.1.5  In assessing the quality of rocks and rock masses, consideration should be given to the following 
features:  
a) some porous soft rocks degrade rapidly to soils of low strength, especially if exposed  to weathering;  
b) some rocks exhibit high solution rates due to ground -water causing channels, caverns  and sinkholes, 
which may develop to the ground surface;  DRS 113: 2020  
39                ©RSB 2020  - All rights reserved  
 c) when unloaded and exposed to the air, certain rocks experience prono unced swelling  
d) due to the absorption of water by clay minerals.  
6.3.8.2  Uniaxial compressive strength and deformability of rock materials  
In assessing the uniaxial compressive strength and deformability of rock materials the influence of the 
following features shall be considered:  
a) the orientation of the axis of loading with respect, for example, to specimen  anisotropy, bedding 
planes, foliation;  
b) method of sampling, storage history and environment;  
c) number of specimens tested;  
d) the geometry of the tested specimens;  
e) water content and degree of saturation at time of test;  
f) test duration and stress rate;  
g) method for determination of the Young's modulus and the axial stress level or levels at which it is 
determined.  
6.3.8.3  Shear strength of joints  
6.3.8.3.1   In assessing the she ar strength of joints of rock materials, the influence of the following features 
shall be considered:  
a) orientation of the joint within the rock test in relation to the assumed direction of actions;  
b) orientation of the shear test;  
c) number of specimens tested;  
d) dimensions of the sheared area;  
e) pore-water pressure conditions;  
f) possibility of progressive failure governing the behaviour of the rock in the ground.  
6.3.8.3.2  Planes of weakness in rock normally coincide with joints or planes of bedding, schistosity or 
cleavage, or with the interface between soil and rock or concrete and rock. Measurements of the shear 
strength on these planes should normally be used for the limit equilibrium analysis of rock masses.   
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 6.3.9  Permeability and consolidation parameters of soil and ro ck 
6.3.9.1  Permeability and consolidation parameters of soil  
6.3.9.1.1  In assessing permeability and consolidation parameters, the following factors shall be considered:  
a) the effects of heterogeneity;  
b) the effects of anisotropy;  
c) the effects of fissures or faults;  
d) the effects of stress changes under the proposed loading.  
6.3.9.1.2  Permeability measurements made on small laboratory samples may not be representative of the in -
situ conditions. Whenever possible, in -situ tests, which measure average properties of a larg e ground volume 
should therefore be preferred. However, consideration should be given to possible changes in the permeability 
with increased effective stress above the in -situ value.  
6.3.9.1.3  Sometimes permeability should be evaluated on the basis of know ledge of the grain size distribution.  
6.3.9.2  Permeability parameters of rock  
6.3.9.2.1  Since the permeability of rock masses depends mainly on the degree of jointing and the existence of 
other discontinuities such as fractures and fissures, it shall be measured b y appropriate in situ tests or 
evaluated from local experience.  
6.3.9.1.2  In situ permeability may be determined by a system of pumping tests combined with flow logging, 
with due consideration of the spatial, hydrogeological flow conditions around the stru cture and the mapping of 
the patterns of joints and other discontinuities.  
6.3.9.1.3  Laboratory permeability tests should only be used to study the effect of discontinuities, for example, 
in terms of variable aperture.  
6.3.10  Geotechnical parameters from field te sts 
6.3.10.1  Cone penetration test  
In assessing values of the cone resistance, the sleeve friction and, possibly, the porewater pressure during 
penetration, the following aspects shall be taken into account:  
a) the detailed design of the cone and friction sleeve. This  may affect the results significantly and 
allowance must therefore be made for the type of cone used;  
b) the results can only be interpreted with confidence when the succession of soil layers  is established; 
in many situations borings will therefore be needed  in conjunction with the penetration tests;  DRS 113: 2020  
41                ©RSB 2020  - All rights reserved  
 c) the effects of ground -water and overburden;  
d) in heterogeneous soils in which widely fluctuating results are recorded, the penetration values shall be 
selected for the zone of soil relevant to the construction;  
e) established correlations with other test results, such as density measurements and  other forms of 
penetration testing.  
6.3.10.2  Standard penetration and dynamic probing test  
In assessing blow counts, the following features shall be considered:  
a) type of test;  
b) detailed description of the test procedure;  
c) ground -water conditions;  
d) the influence of the overburden pressure;  
e) the nature of the ground, particularly if cobbles or coarse gravel are encountered.  
6.3.10.3   Vane test  
6.3.10.3.1  The following shall be considered when assessing  the test results:  
a) details of the test procedure;  
b) whether standardised vane equipment has been used;  
c) whether measurements have been made at several depths to provide a profile of  
d) strength in the succession of soil layers;  
e) skin friction along the rod.  
6.3.10.3.1  Vane tests may be used for the assessment of undrained shear strength, cu ,of cohesive soil.  
NOTE The vane test is a simple and cheap way of checking the trafficability of soft ground for heavy equipment and 
vehicles.  
6.3.10.3.1  To obtain derived values of cu , the measured values should be corrected by a factor based on 
local experience and depending for example, on the liquid limit, plasticity index and effective vertical stress.   
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 6.3.10.4  Weight sounding test  
6.3.10.4.1  In assessing weig ht sounding test results, the following features shall be taken into account:  
a) detailed description of the test procedure;  
b) ground -water conditions;  
c) influence of overburden pressure;  
d) nature of the ground, particularly if cobbles or coarse gravel are encounte red. 
6.3.10.4.2  Weight sounding tests may be used for the assessment of soil layer boundaries and the density 
of non -cohesive soils.  
6.3.10.5  Pressure -meter test  
6.3.10.5.1   In assessing the values of the limit pressure and the pressure  meter modulus, the following  
features shall be taken into account:  
a) the type of equipment;  
b) the procedure used to install the pressure  meter in the ground.  
6.3.10.5.2  Test curves, which exhibit more than a moderate degree of disturbance should not be used.  
Where the limit pressure is n ot reached during the test, a moderate and conservative extrapolation of the 
curve may be used to estimate it. For tests in which only the initial part of the pressure -meter curve is 
determined, general correlations or, preferably, local correlations from the same site may be used 
conservatively to estimate the limit pressure from the pressure -meter modulus.  
6.3.10.6  Dilatometer test  
6.3.10.6.1  In assessing dilatometer values the installation procedure shall be taken into account.  
6.3.10.6.2  The succession of soil layers and especially some basic parameters such as granularity and 
degree of saturation shall be determined prior to the test.  
6.3.10.6.3  If strength parameters are to be evaluated, the penetration resistance should be taken into 
account.  
6.3.10.6.4  The d ilatometer values should be used as an index for determining derived values of the 
stiffness moduli of the soil succession.  DRS 113: 2020  
43                ©RSB 2020  - All rights reserved  
 6.3.10.7  Compacti bility tests  
6.3.10.7.1  In assessing the compactibility of a fill material, the following features shall be taken into 
accou nt: 
a) type of soil or rock;  
b) grain size distribution;  
c) grain shape;  
d) the heterogeneity of the material;  
e) the degree of saturation or water content;  
f) type of plant to be used  
6.3.10.7.2  When using field measurements (e.g. soundings, dynamic compaction tests, plate  load tests, 
settlement records) to control site compaction, the results of field compaction trials should be related to 
standard laboratory compaction test values in order to assess the compactibility of a soil or a rock fill.  
6.4  Ground Investigation Report  
6.4.1  Requirements  
6.4.1.1  The results of a geotechnical investigation shall be compiled in a Ground Investigation  Report, which 
shall form a part of the Geotechnical Design Report described in 5.7. 
6.4.1.2  Refer ence shall be made to RS ISO 17892: for information on the use of laboratory and field tests for 
geotechnical parameters.  
6.4.1.3  The Ground Investigation Report should normally consist of:  
a) a presentation of all available geotechnical information including geological features and relevant 
data;  
b) a geotechnical evaluation of the information, stating the assumptions made in the interpretation of the 
test results.  
The information may be presented as one report or as separate parts.  
6.4.2  Presentation of geotechnical information  
6.4.2.1  The presentation of geotechnical information shall include:  
a) a factual account of all field and laboratory work;   
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 b) documentation of the methods used to carry out the field investigations and the laboratory testing.  The 
documentation shall be based on the test reports  
6.4.2.2  In addition, the factual account should include the following information, as relevant:  
a) names of all consultants and subcontractors;  
b) purpose and scope of the geotechnical investigation;  
c) dates between which field and laboratory work was performed;  
d) field recon naissance of the general area of the project noting particularly:  
e) evidence of ground -water;  
f) behaviour of neighbouring structures;  
g) exposures in quarries and borrow areas;  
h) areas of instability;  
i) difficulties during excavation;  
j) history of the site;  
k) geology of the site, including faulting;  
l) survey data;  
m) information from available aerial photographs;  
n) local experience of the area;  
o) information about the seismicity of the area;  
p) procedures used for sampling and transportation and storage of samples;  
q) types of field equ ipment used;  
r) tabulation of quantities of field and laboratory work, and presentation of field  observations, which were 
made by the supervising field personnel during the  subsurface explorations;  
s) data on fluctuations of any ground -water table with time in t he boreholes during the performance of 
the field work and in piezometers after the completion of the fiel d work;  DRS 113: 2020  
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 t) compilation of boring logs, including photographs of the cores, with descriptions of  subsurface 
formations based on field descriptions and on the results of the laboratory tests;  
u) the occurrence, or the possibility of occurrence, of radon;  
v) data on frost susceptibility of soils;  
w) grouping and presentation of field and labora tory test results in appendices  
6.4.3  Evaluation of geotechnical information  
6.4.3.1  The evaluation of the geotechnical information shall include as appropriate:  
a) a review of the field and laboratory work. Any limitations in the data (e.g. defective, irrelevant, 
insufficient or inaccurate) shall be pointed out and commented upon. Th e sampling and sample 
transportation and storage procedures shall be considere d when interpreting the test results. Any 
particularly adverse test results shall be considered carefully in order to determine if they are 
misleading or represent a real phenome non that must be accounted for in the design;  
b) a review of the derived values of geotechnical parameters;  
c) any proposals for necessary further field and laboratory work, with comments justifying the need for 
this extra work. Such proposals shall be accompani ed by a detailed programme for the extra 
investigations to be carried out with specific reference to the questions that have to be answered.  
6.4.3.1  In addition, the evaluation of the geotechnical data should include the following, if  relevant:  
a) tabulation and graphical presentation of the results of the field and laboratory work in relation to the 
requirements of the project and, if deemed necessary,  
b) histograms illustrating the range of values of the most relevant data and their distribution;  
c) depth of the g round -water table and its seasonal fluctuations;  
d) subsurface profile(s) showing the differentiation of the various formations;  
e) detailed descriptions of all formations including their physical properties and their deformation and 
strength characteristics;  
f) comments on irregularities such as pockets and cavities;  
g) the range and any grouping of derived values of the geotechnical data for each stratum.   
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 7 Supervision of construction, monitoring and maintenance  
7.1 General  
7.1.1  To ensure the safety and quality of a struc ture, the following shall be undertaken, as appropriate:  
a) the construction processes and workmanship shall be supervised;  
b) the performance of the structure shall be monitored during and after construction;  
c) the structure shall be adequately maintained  
7.1.2  Supervision of the construction process, including workmanship, and any monitoring of the 
performance of the structure during and after construction, shall be specified in the Geotechnical Design 
Report.  
7.1.3  Supervision of the construction process, includ ing workmanship, should involve the following, as 
appropriate:  
a) checking the validity of the design assumptions;  
b) identifying the differences between the actual ground conditions and those assumed  
c) in the design;  
d) checking that the construction is carried out  according to the design.  
7.1.4  Observations and measurements of the behaviour of the structure and its surroundings should be 
made, as appropriate:  
a) during construction, to identify any need for remedial measures or alterations to the construction 
sequence, for example;  
b) during and post construction, to evaluate the long -term performance  
7.1.5  Design decisions, which are influenced by the results of the supervision and monitoring shall be 
clearly identified.  
7.1.6  The amount of construction supervisi on and the quantity of field and laboratory testing required to 
control and monitor performance should be planned during the design stage.  
7.1.7   In the case of unexpected events, the methods, extent and frequency of monitoring shall be 
reviewed.  
7.1.8  The level and quality of supervision and monitoring shall be at least equal to those assumed in the 
design and shall be consistent with the values selected for the design parameters and partial factors.  DRS 113: 2020  
47                ©RSB 2020  - All rights reserved  
 7.2 Supervision  
7.2.1  Plan of supervision  
7.2.1.1  The plan include d in the Geotechnical Design Report shall state acceptable limits for the 
results to be obtained by the supervision.  
7.2.1.2  The plan should specify the type, quality and frequency of supervision, which should be 
commensurate with:  
— the degree of uncertai nty in the design assumptions;  
— the complexity of the ground and loading conditions;  
— the potential risk of failure during construction;  
— the feasibility of implementing design modifications or corrective measures during construction.  
7.2.2  Inspection and con trol 
7.2.2.1  The construction work shall be inspected on a continuous basis and the results of the inspection shall 
be recorded.  
7.2.1.2  For Geotechnical Category 1, the supervision programme may be limited to inspection, simple quality 
controls and a qualitative assessment of the performance of the structure.  
7.2.1.3  For Geotechnical Category 2, measurements of ground properties or the behaviour of structures 
should often be required.  
7.2.1.4  For Geotechnical Category 3, additional measurements should be required during each significant 
stage of construction.  
7.2.1.5  Records shall be maintained of the following, as appropriate:  
a) significant ground and ground -water features;  
b) sequence of works;  
c) quality of materials;  
d) deviations from design;  
e) as-built drawings;  
f) results of measurements and of their interpretation;   
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 g) observations of the environmental conditions;  
h) unforeseen events.  
7.2.1.6  Records of temporary works should also be kept. Interruptions to the works, and their condition on 
re-commencement, shou ld be recorded.  
7.2.1.7  The results of the inspection and control shall be made available to the designer before any changes 
are decided.  
7.2.1.8  In general, the design documents and records of what was constructed should be stored for 10 
years, unless agr eed otherwise. More important documents should be stored for the lifetime of the relevant 
structure.  
7.2.3  Assessment of the design  
7.2.3.1  The suitability of the construction procedures and the sequence of operations shall be reviewed in 
the light of the ground  conditions, which are encountered; the predicted behaviour of the structure shall be 
compared with the observed performance. The design shall be assessed on the basis of the results of the 
inspection and supervision.  
7.2.3.2  The assessment of the design s hould include a careful review of the most unfavourable conditions, 
which occur during construction with regard to:  
a) ground conditions;  
b) ground -water conditions;  
c) actions on the structure;  
d) environmental impacts and changes inc luding landslides and rock falls  
7.3 Checking ground conditions  
7.3.1  Soil and rock  
7.3.1  The descriptions and geotechnical properties of the soils and rocks in or on which the structure is 
founded or located shall be checked during construction.  
7.3.2  For Geotechnical Category 1, the descriptions of the soils and rocks should be checked by:  
a) inspecting the site;  
b) determining the types of soil and rock within the zone of influence of the structure;  
c) recording descriptions of the soil and rock exposed in excavations.  DRS 113: 2020  
49                ©RSB 2020  - All rights reserved  
 7.3.3  For Geotechnical Category 2, t he geotechnical properties of the soil or rock in or on which the 
structure is founded or located should also be checked. Additional site investigation may be needed. 
Representative samples should be recovered and tested to determine the index properties, strength and 
deformability.  
7.3.4  For Geotechnical Category 3, additional requirements should include further investigations and 
examination of details of the ground or fill conditions, which may have important consequences for the design.  
7.3.5  Indirect e vidence of the geotechnical properties of the ground (for example, from pile driving records) 
should be recorded and used to assist in interpreting the ground conditions.  
7.3.6  Deviations from the ground type and properties assumed in the design shall be reported without 
delay.  
NOTE Normally these deviations are reported to the designer.  
7.3.7  The principles used in design shall be checked to ensure that they are appropriate for the 
geotechnical features of the ground, which are encountered.  
7.3.2  Ground -water  
7.3.2.1   As appropriate, the ground -water levels, pore -water pressures and ground -water chemistry 
encountered during execution shall be compared with those assumed in the design.  
7.3.2.2  More thorough checks should be performed for sites on which significan t variations of ground type 
and permeability are known or believed to exist.  
7.3.2.3  For Geotechnical Category 1, checks should usually be based on previously documented experience 
in the area or on indirect evidence.  
7.3.4  For Geotechnical Categories 2 an d 3, direct observations should normally be made of the ground -
water conditions if these greatly affect either the method of construction or the performance of the structure.  
7.3.5  Ground -water flow characteristics and the pore -water pressure regime should  be obtained by means 
of piezometers, which preferably should be installed before the start of construction operations. It may 
sometimes be necessary to install piezometers at large distances from the site as part of the monitoring 
system.  
7.3.6  If pore -water pressure changes occur during construction that may affect the performance of the 
structure, pore -water pressures should be monitored until construction is complete or until the pore -water 
pressures have dissipated to safe values.  
7.3.7  For structures below ground -water level, which may be subject to uplift, pore -water  pressures should 
be monitored until the weight of the structure is sufficient to rule out the possibility of uplift.  
7.3.8  Chemical analysis of mobile water should be performed when any p art of the permanent or 
temporary works may be significantly affected by chemical attack.   
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 7.3.9  The effect of construction operations (including processes such as dewatering, grouting and 
tunnelling) on the ground -water regime shall be checked.  
7.3.10  Deviations from the ground -water features assumed in the design shall be reported without delay.  
7.3.11  The principles used in design shall be checked to ensure that they are appropriate for the ground -
water features, which are encountered.  
7.4 Checking constructi on 
7.4.1  Site operations shall be checked for compliance with the method of construction assumed in the 
design and stated in the Geotechnical Design Report. Observed differences between the design assumptions 
and the site operations shall be reported witho ut delay.  
7.4.2  Deviations from the methods of construction assumed in the design and stated in the Geotechnical 
Design Report shall be explicitly and rationally considered and implemented.  
7.4.3  The principles followed in design shall be checked to ensure  that they are appropriate for the 
sequence of construction operations, which are used.  
7.4.4  For Geotechnical Category 1, a formal construction schedule need not normally be included in the 
Geotechnical Design Report.  
NOTE  The sequence of construction ope rations is normally decided by the contractor.  
7.4.5  For Geotechnical Categories 2 and 3, the Geotechnical Design Report may give the sequence of 
construction operations envisaged in the design.  
NOTE  Alternatively, the Geotechnical Design Report can state that the sequence of construction is to be decided by 
the contractor.  
7.5 Monitoring  
7.5.1  Monitoring shall be applied:  
a) to check the validity of predictions of performance made during the design;  
b) to ensure that the structure will continue to perform as required after completion.  
7.5.2  The monitoring programme shall be carried out in accordance with the Geotechnical Design Report 
(see 5.7.3)  
7.5.3  Records of the actual performance of structures should be made in order to collect databases of 
comparable ex perience.  
7.5.4  Monitoring should include measurement of the following:  DRS 113: 2020  
51                ©RSB 2020  - All rights reserved  
 a) deformations of the ground affected by the structure;  
b) values of actions;  
c) values of contact pressure between ground and structure;  
d) pore-water pressures;  
e) forces and displacements (vertic al or horizontal movements, rotations or distortions) in structural 
members.  
7.5.5  Results of measurements should be integrated with qualitative observations including architectural 
appearance.  
7.5.6  The length of any post -construction monitoring period sh ould be altered as a result of observations 
made during construction. For structures that may impact unfavourably on appreciable parts of the 
surrounding physical environment, or for which failure may involve abnormal risks to property or life, 
monitoring should be required for more than ten years after construction is complete, or throughout the life of 
the structure.  
7.5.7  The results obtained from monitoring shall always be evaluated and interpreted and this shall 
normally be done in a quantitative manne r. 
7.5.8  For Geotechnical Category 1, the evaluation of performance may be simple, qualitative and based on 
inspection.  
7.5.9  For Geotechnical Category 2, the evaluation of performance may be based on measurements of 
movements of selected points on the str ucture.  
7.5.10  For Geotechnical Category 3, the evaluation of performance should normally be based on the 
measurement of displacements and analyses, which take account of the sequence of construction operations.  
7.5.11  For structures that may have an adver se effect on ground or ground -water conditions, the possibility 
of leakage or of alterations to the pattern of ground -water flow, especially when fine grained soils are involved, 
shall be taken into account when planning the monitoring programme.  
7.5.12  Examples of this type of structure are:  
a) water retaining structures;  
b) structures intended to control seepage;  
c) tunnels;  
d) large underground structures;  
e) deep basements;   
©RSB 2020  - All rights reserved                  52 
 f) slopes and earth retaining structures;  
g) ground improvements.  
7.6 Maintenance  
7.6.1  The maintenance required to ensure the safety and serviceability of the structure shall be specified.  
NOTE  Normally this is specified to the owner/client.  
7.6.2  The maintenance specifications should provide information on:  
a) critical parts of the structure, which require regular inspection;  
b) works prohibited without a design review of the structure prior to their execution;  
c) frequency of the inspection.  
8 Fill, dewatering, ground improvement and reinforcement  
8.1 General  
8.1.1  The provisions in this Section shall apply where adequ ate ground conditions are achieved by:  
a) placing natural soil, crushed rock, blasted stone or certain waste products;  
b) dewatering;  
c) treating ground;  
d) reinforcing ground.  
NOTE1  Situations where soil or granular material is placed for engineering purposes include : 
a) fills beneath foundations and ground slabs;  
b) backfill to excavations and retaining structures;  
c) general landfill including hydraulic fill, landscape mounds and spoil heaps;  
d) embankments for small dams and infrastructure.  
NOTE 2 Dewatering of ground may be temporary or permanent.  DRS 113: 2020  
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 NOTE 3 Ground, which is treated to improve its properties may be either natural ground or fill. The ground 
improvement may be either temporary or permanent.  
8.1.2  Design procedures for geotechnical works that include the use of fill , dewatering,  improvement and 
reinforceme nt shall be those presented in clause  6 to 12.  
8.2 Fundamental requirements  
8.2.1  Fill and dewatered, improved or reinforced ground shall be capable of sustaining the actions arising 
from its function and from its envir onment.  
8.2.1  These fundamental requirements shall also be satisfied for the ground on which the fill is placed.  
8.3 Fill construction  
8.3.1  Principles  
8.3.1.1  When designing fill constructions it shall be considered that the adequacy of the fill depends on the 
following:  
a) good material handling properties,  
b) adequate engineering properties after compaction.  
8.3.1.2  Transport and placement of the fill should be considered in the design.  
8.3.2  Selection of fill material  
8.3.2.1  The criteria for specifying material as suitable for use as fill shall be based on achieving adequate 
strength, stiffness, durability and permeability after compaction. These criteria shall take account of the 
purpose of the fill and the requirements of any structure to be placed on it.  
8.3.2.2  Suitable fill materials may include most graded natural granular materials and certain waste products 
such as selected colliery waste and pulverised fuel ash. Some manufactured materials, such as light 
aggregate, may also be used in some circumstances. Some cohesiv e materials may be suitable but require 
particular care.  
8.3.2.3  The following aspects shall be taken into account when specifying a fill material:  
a) grading;  
b) resistance to crushing;  
c) compactibility;  
d) permeability;   
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 e) plasticity;  
f) strength of underlying ground;  
g) organic content;  
h) chemical aggression;  
i) pollution effects;  
j) solubility;  
k) susceptibility to volume changes (swelling clays and collapsible materials);  
l) low temperature and frost susceptibility;  
m) resistance to weathering;  
n) effect of excavation, transportation and placement;  
o) possibility of cementation occurring after placement (e.g. blast furnace slags).  
8.3.2.4  If local materials in their natural state are not suitable for use as fill, it can be necessary to adopt one 
of the following procedures:  
a) adjust the water c ontent;  
b) mix with cement, lime or other materials;  
c) crush, sieve or wash;  
d) protect with appropriate material;  
e) use drainage layers.  
8.3.2.5  Frozen, expansive or soluble soils should not normally be used as fill material.  
8.3.2.6  When the selected material cont ains potentially aggressive or polluting chemicals, adequate 
provisions shall be adopted to prevent it from attacking structures or services or polluting the ground -water. 
Such materials shall only be used in large amounts in permanently monitored location s. 
8.3.2.7  In case of doubt, the fill material shall be tested at source to ensure that it is suitable for its intended 
purpose. The type, number and frequency of the tests shall be selected according to the type and 
heterogeneity of the material and the n ature of the project.  
8.3.2.8  In Geotechnical Category 1, inspection of the material may often be sufficient.  DRS 113: 2020  
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 8.3.2.9  Material used for fill with specified severe requirements regarding bearing resistance, settlement and 
stability shall not contain matter such as snow, ice or peat in any significant amount.  
8.3.2.10  In fills with no specified requirements for bearing resistance, settlement or stability, the fill material 
may contain small amounts of snow, ice or peat.  
8.3.3  Selection of procedures for fill placem ent and compaction  
8.3.3.1  Compaction criteria shall be established for each zone or layer of fill, related to its purpose and 
performance requirements.  
8.3.3.2  The procedures for fill placement and compaction shall be specified in such a way that stabilit y of the 
fill is ensured during the entire construction period and the natural subsoil is not adversely affected.  
8.3.3.3  The compaction procedure for fill shall be specified depending on the compaction criteria and on the 
following:  
a) the origin and nature of the material;  
b) the placement method;  
c) the placement water content and its possible variations;  
d) the initial and final thickness of the lift;  
e) the local climatic conditions;  
f) the uniformity of compaction;  
g) the nature of underlying ground.  
8.3.3.4  In order to develop an appropriate procedure for compaction, a trial compaction should be performed 
at the site using the intended material and compaction equipment. This allows the determination of the 
compaction procedure (method of placement, compaction equipment,  layer thickness, number of passes, 
adequate techniques for transportation, amount of water that shall be added) to be followed. A trial 
compaction may also be used to establish the control criteria.  
8.3.3.5  Where there is a possibility of rainfall during t he placement of cohesive fill material, the fill surface 
should at all stages be profiled so as to permit adequate run -off. 
8.3.3.6  At temperatures below freezing, fill may require heating before placement and frost protection of the 
fill surface. The need  of these measures should be evaluated case -by-case, taking into account the quality of 
the fill material and the required degree of compaction.  
8.3.3.7  Backfill placed around foundations and beneath floor slabs shall be compacted such that damaging 
subsid ence does not occur.   
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 8.3.3.8  Fill should be placed on an undisturbed and drained ground surface. Any mixing of the fill with the 
ground should be prevented by using a filter textile or filter layer.  
8.3.3.9  Before placing fill underwater, all soft material  encountered should be removed by dredging or other 
means.  
8.3.4  Checking the fill  
8.3.4.1   Fill shall be inspected or tested to ensure that the material, its placement water content and the 
compaction procedures comply with the specification.  
8.3.4.2  Testing ne ed not be performed for some combinations of materials and compaction procedures if the 
compaction procedure has been proved by a field trial or by comparable experience.  
8.3.4.3  Compaction should be tested by one of the following methods:  
a) measurement of d ry density and, if required by the design, measurement of the water content;  
b) measurement of properties such as, for example, penetration resistance or stiffness. Such 
measurement cannot always determine if satisfactory compaction has been  achieved in cohes ive 
soils 
8.3.4.4  Minimum fill densities determined, for example, by Proctor percentages, should be specified and 
checked on site.  For rock fill or fill containing a large amount of coarse particles, compaction should be 
checked by field methods. The Proct or test is not applicable to these materials.  
8.3.4.5  Site checking may be made by one of the following:  
a) ensuring that compaction has been performed according to the procedure deduced from a field trial or 
from comparable experience;  
b) checking that the sett lement induced by an additional pass of the compaction equipment is equal to or 
less than a specified value;  
c) plate loading tests;  
d) seismic or dynamic methods.  
8.3.4.6  In cases where over -compaction is not acceptable, an upper bound limit for the compaction shall be 
specified.  
8.3.4.7  Over -compaction can cause the following undesirable effects:  
a) the development of slickensides and high soil stiffnesses in slopes;  
b) high earth pressures on buried and earth retaining structures;  DRS 113: 2020  
57                ©RSB 2020  - All rights reserved  
 c) crushing of materials such as soft rocks, slags and volcanic sands used as light weight fills.  
8.4 Dewatering  
8.4.2  Any scheme for removing water from the ground or for lowering the water pressure shall be based on 
the results of a geotechnical or hydrogeological investigation.  
8.4.3  Water may be removed from the ground by gravity drainage, by pumping from sumps, well points or 
bored wells, or by electro -osmosis. The scheme adopted will depend on:  
a) the existing ground and ground -water conditions;  
b) the characteristics of the project: e.g. excavatio n depth and extent of dewatering.  
8.4.4   Part of the dewatering scheme may be a system of recharge wells at some distance from the 
excavation.  
8.4.5  In the dewatering scheme the following conditions should be considered, as appropriate:  
a) in the case of exca vations, the sides of the excavation remain stable at all times under the effect of 
ground -water lowering; also, excessive heaving or rupture of the base, for example due to excessive 
water pressure b eneath a less permeable layer, does not occur;  
b) the schem e does not lead to excessive settlements or damage to nearby structures;  
c) the scheme avoids excessive loss of ground by seepage from the sides or base of the excavation;  
d) except in the case of fairly uniformly graded material, which can establish itself as a  filter material, 
adequate filters are provided around the sumps to ensure that there is no significant transportation of 
soil with the pumped water;  
e) water removed from an excavation is normally discharged far enough from the excavated area;  
f) the dewatering  scheme is so designed, arranged and installed as to maintain the water levels and 
pore-water pressures anticipated in the design without significant fluctuations;  
g) there is adequate margin of pumping capacity and back -up capacity is available in the case o f 
breakdown;  
h) when allowing the ground -water to return to its original level, care is taken to prevent problems such 
as collapse of soils having a sensitive structure, e.g. loose sand;  
i) the scheme does not lead to excessive transport of contaminated water to  the excavation;  
j) the scheme does not lead to excessive extraction in a drinking water catchment area.   
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 8.4.6  The effectiveness of dewatering shall be checked by monitoring the ground -water level, the pore -
water pressures and the ground movements, as necessa ry. Data shall be reviewed and interpreted frequently 
to determine the effects of dewatering on the ground conditions and  on the behaviour of nearby structures.  
8.4.7  If a pumping operation is to continue over a long period of time, the ground -water shall be checked 
for the presence of dissolved salts and gases, which could either result in corrosion of the well screens or 
cause clogging of the screens by the precipitation of salts.  
8.4.8  Systems for long term dewatering shall be designed to prevent cloggin g by bacterial action or other 
causes.  
8.5  Ground improvement and reinforcement  
8.5.1  A geotechnical investigation of the initial ground conditions shall be carried out before any ground 
improvement or reinforcement method is chosen or used.  
8.5.2  The ground improvement method for a particular situation shall be designed taking into account the 
following factors where appropriate:  
a) thickness and properties of the ground or fill material;  
b) magnitude of water pressure in the various strata;  
c) nature, size and positi on of the structure to be supported by the ground;  
d) prevention of damage to adjacent structures or services;  
e) if the ground improvement is temporary or permanent;  
f) in terms of anticipated deformations, the relationship between the ground    
g) improvement method  and the construction sequence;  
h) the effects on the environment including pollution by toxic substances or changes in  
i) ground -water level;  
j) the long -term deterioration of materials.  
8.5.3  The effectiveness of the ground improvement shall be checked against t he acceptance criteria by 
determining the induced changes in the appropriate ground properties.  DRS 113: 2020  
59                ©RSB 2020  - All rights reserved  
 9 Spread foundations  
9.1 General  
The provisions of this Section apply to spread foundations including pads, strips and rafts . Some of the 
provisions may be applied to  deep foundations such as caissons.  
9.2 Limit states  
The following limit states shall be considered and an appropriate list shall be compiled:  
a) loss of overall stability;  
b) bearing resistance failure, punching failure, squeezing;  
c) failure by sliding;  
d) combined fail ure in the ground and in the structure;  
e) structural failure due to foundation movement;  
f) excessive settlements;  
g) excessive heave due to swelling, frost and other causes;  
h) unacceptable vibrations.  
9.3 Actions and design situations  
9.3.1  Design situations shall be selected in accordance with 5 .2. 
9.3.2  The actions listed in 5.4.2 should be considered when selecting the limit states for calculation.  
9.3.3  If structural stiffness is significant, an analysis of the interaction between the str ucture and the ground 
should be performed in order to determine the distribution of actions.  
9.4 Design and construction considerations  
9.4.1  When choosing the depth of a spread foundation the following shall be considered:  
a) reaching an adequate bearing stratum;  
b) the depth above which shrinkage and swelling of clay soils, due to seasonal weather changes, or to 
trees and shrubs, may cause appreciable movements;   
©RSB 2020  - All rights reserved                  60 
 c) the depth above which frost damage may occur;  
d) the level of the water table in the ground and the problems, which may occur if excavation for the 
foundation is required below this level;  
e) possible ground movements and reductions in the strength of the bearing stratum by seepage or 
climatic effects or by construction procedures;  
f) the effects of excavation s on nearby foundations and structures;  
g) anticipated excavations for services close to the foundation;  
h) high or low temperatures transmitted from the building;  
i) the possibility of scour;  
j) the effects of variation of water content due to long periods of drought , and  subsequent periods of 
rain, on the properties of volume -unstable soils in arid climatic areas;  
k) the presence of soluble materials, e.g. limestone, claystone, gypsum, salt rocks;  
9.4.2  Frost damage will not occur if:  
a) the soil is not frost -susceptible;  
b) the foundation level is beneath frost -free depth;  
c) frost is eliminated by insulation where appropriate.  
9.4.3  In addition to fulfilling the performance requirements, the design foundation width shall take account 
of practical considerations such as economic  excavation, setting out tolerances, working space requirements 
and the dimensions of the wall or column supported by the foundation.  
9.4.4  One of the following design methods shall be used for spread foundations:  
a) a direct method, in which separate analyses are carried out for each limit state. When checking 
against an ultimate limit state, the calculation shall model as closely as possible the failure 
mechanism, which is envisaged. When checking against a  serviceability limit state, a settlement 
calculation shall be used;  
b) an indirect method using comparable experience and the results of field or laboratory measurements 
or observations, and chosen in relation to serviceability limit state loads so as to satisfy the 
requirements of all relevant limit s tates;  
c) a prescriptive method in which a presumed bearing resistance is used ( see 5 .5). DRS 113: 2020  
61                ©RSB 2020  - All rights reserved  
 9.4.5  Calculation models for ultimate and serviceability limit state design of spread foundations on soil 
given in 9.5 and 9 .6 respectively should be applied. Presumed b earing pressures for the design of spread 
foundations on rock should be applied according to 9.7. 
9.5 Ultimate limit state design  
9.5.1  Overall stability  
9.5.1  Overall stability, with or without the foundations, shall be checked particularly in the following 
situati ons: 
a) near or on a natural or man -made slope;  
b) near an excavation or a retaining wall;  
c) near a river, a canal, a lake, a reservoir or the sea shore;  
d) near mine workings or buried structures.  
9.5.1  For such situations, it shall be demonstrated using the princip les described in Clause 14 , that a 
stability failure of the ground mass containing the foundation is sufficiently improbable.  
9.5.2  Bearing resistance  
9.5.2.1  General  
9.5.2.1.1  The following inequality shall be satisfied for all ultimate limit states:  
Vd Rd                                                                                                                      (6.1) 
9.5.2.1.2   Rd shall be calculated according to 5 .4. 
9.5.2.1.3  P Vd shall include the weight of the foundation, the weight of any backfill materi al and all earth 
pressures, either favourable or unfavourable. Water pressures not caused by the foundation load shall be 
included as actions.  
9.5.2.2  Analytical method  
9.5.2.2.1   A commonly recognized analytical method should be used.  
9.5.2.2.2   An analytical eva luation of the short -term and long -term values of Rd shall be considered, 
particularly in fine -grained soils.  
9.5.2.2.3   Where the soil or rock mass beneath a foundation presents a definite structural pattern of 
layering or other discontinuities, the assumed rupture mechanism and the selected shear strength and 
deformation parameters shall take into account the structural characteristics of the ground.   
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 9.5.2.2.4   When calculating the design bearing resistance of a foundation on layered deposits, the 
properties of which vary greatly between one another, the design values of the ground parameters shall be 
determined for each layer.  
9.5.2.2.5   Where a strong formation underlies a weak formation, the bearing resistance may be calculated 
using the shear stre ngth parameters of the weak formation. For the reverse situation, punching failure should 
be checked.  
9.5.2.2.6   Analytical methods are often not applicable to the design situations described in 9.5.2.2. 
Numerical procedures should then be applied to determine the most unfavourable failure mechanism.  
9.5.2.2.7   The overall stability calc ulations described in clause 14  may be applied.  
9.5.3  Sliding resistance  
9.5.3.1  Where the loading is not normal to the foundation base, foundations shall be checked against failure 
by sliding on the base.  
9.5.3.1  The following inequality shall be satisfied:  
Hd Rd + Rp;d                                                                                                    (6.2) 
9.5.3.2  Hd shall include the design va lues of any active earth forces imposed on the foundation.  
9.5.3.3  Rd shall be calculated according to 5 .4. 
9.5.3.4  The values of Rd and Rp;d should be related to the scale of movement anticipated under the limit 
state of loading considered. For large movements, the p ossible relevance of post -peak behaviour should be 
considered. The value of Rp;d selected should reflect the anticipated life of the structure.  
9.5.3.5  For foundations bearing within the zone of seasonal movements of clay soils, the possibility that the 
clay could shrink away from the vertical faces of foundations shall be considered.  
9.5.3.6  The possibility that the soil in front of the foundation may be removed by erosion or human activity 
shall be considered.  
9.5.3.7  For drained conditions, the design sh ear resistance, Rd, shall be calculated either by factoring the 
ground properties or the ground resistance as follows;  
Rd = V'd tan d                                                                                             (6.3a)  
or 
Rd = (V’d tan k) / R;h                                                                                    (6.3b)  
NOTE  In design procedures where the effects of actions are factored, the partial factor for the actions ( F) is 1,0 and V’d = 
V’k in equation (6.3b).  DRS 113: 2020  
63                ©RSB 2020  - All rights reserved  
 9.5.3. 8 In determining V' d, account shall be taken of whether Hd and V'd are dependent or independent 
actions.  
9.5.3.9  The design friction angle d may be assumed equal to the design value of the effective critical state 
angle of shearing resistance, φ' cv;d , for cast -in-situ concrete foundations and equal to 2/3 φ'cv;d for smooth 
precast foundations. Any effective cohesion c' should be neglected.  
9.5.3.10   For undrained conditions, the design shearing resistance, Rd, shall be calculated either by 
factoring the g round properties or the ground resistance as follows:  
Rd = Ac cu;d                                                                                                (6.4a)  
or 
Rd = (Ac cu;k) / R;h                                                                                         (6.4b)  
9.5.3.11   If it is possible for water or air to reach the interface between a foundation and an  undrained clay 
subgrade, the following check shall be made:  
Rd  0,4 Vd                                                                                                     (6.5) 
9.5.3.11   Requirement ( 9.5) may only be disregarded if the formation of a gap between the foundation and 
the ground will be prevented by sucti on in areas where there is no positive bearing pressure.  
9.5.4  Loads with large eccentricities  
9.5.4.1  Special precautions shall be taken where the eccentricity of loading exceeds 1/3 of the width of a 
rectangular footing or 0,6 of the radius of a circular footing.  
Such precautions include:  
a) careful review of the design values  of actions in accordance with 5 .4.2; 
b) designing the location of the foundation edge by taking into account the magnitude of construction 
tolerances.  
9.5.4 .2 Unless special care is taken during the works, tolerances up to 0,10 m should be considered.  
9.5.5  Structural failure due to foundation movement  
9.5.5.1  Differential vertical and horizontal foundation displacements shall be considered to ensure that they 
do not lead to an ultimate limit sta te occurring in the supported structure.  
9.5.5.2  A presumed bearin g pressure may be adopted provided displacements will not cause an ultimate 
limit state in the structure.  
9.5.5.3  In ground that may swell, the potential differential heave shall be assessed  and the foundations and 
structure designed to resist or accommodate it.   
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 9.6 Serviceability limit state design  
9.6.1  General  
9.6.1.1  Account shall be taken of displacements caused by actions on the found ation, such as those listed in 
5.4.2 
9.6.1.2  In assessing the m agnitude of foundation displacements, account shall be taken of comparable 
experience, as defined in 3.5 . If necessary, calculations of displacements shall also be carried out.  
9.6.1.3  For soft clays, settlement calculations shall always be carried out.  
9.6.1.4  For spread foundations on stiff and firm clays in Geotechnical Categories 2 and 3, calculations of 
vertical displacement (settlement) should usually be undertaken. Methods that may be used to calculate 
settlements caused by loads on the foundation ar e given in 9.6.2. 
9.6.1.5  The serviceability limit state design loads shall be used when calculating foundation displacements 
for comparison with serviceability criteria.  
9.6.1.6   Calculations of settlements should not be regarded as accurate. They merely provide an 
approximate indication.  
9.6.1.7  Foundation displacements shall be considered both in terms of displacement of the entire foundation 
and differential displacements of parts of the foundation.  
9.6.1.8  The effect of neighbouring foundations and fil ls shall be taken into account when calculating the 
stress increase in the ground and its influence on ground compressibility.  
9.6.1.9  The possible range of relative rotations of the foundation shall be assessed and compared with the 
relevant limiting val ues for movements discussed in 5 .4.9. 
9.6.2  Settlement  
9.6.2.1  Calculations of settlements shall include both immediate and delayed settlement.  
9.6.2.3  The following three components of settlement should be considered for partially or fully saturated 
soils:  
a) s0: immediate settlement; for fully -saturated soil due to shear deformation at constant volume, and for 
partially -saturated soil due to both shear deformation and volume reduction;  
b) s1: settlement caused by consolidation;  
c) s2: settlement caused by creep.  
9.6.2.4  Commonly recognized methods for evaluating settlements should be used.  DRS 113: 2020  
65                ©RSB 2020  - All rights reserved  
 9.6.2.5  Special consideration should be given to soils such as organic soils and soft clays, in which 
settlement may be prolonged almost indefinitely due to creep.  
9.6.2.6  The depth of the compressible soil layer to be considered when calculating settlement should depend 
on the size and shape of the foundation, the variation in soil stiffness with depth and the spacing of foundation 
elements.  
9.6.2.7  This depth may normally be taken as t he depth at which the effective vertical stress due to the 
foundation load is 20 % of the effective overburden stress.  
9.6.2.8  For many cases this depth may also be roughly estimated as 1 to 2 times the foundation width, but 
may be reduced for lightly -loaded, wider foundation rafts.  
NOTE This approach is not valid for very soft soils.  
9.6.2.9  Any possible additional settlement caused by self -weight compaction of the soil shall be assessed.  
9.6.2.10   The following should be considered:  
a) the possible effects o f self -weight, flooding and vibration on fill and collapsible soils;  
b) the effects of stress changes on crushable sands.  
9.6.2.11   Either linear or non -linear models of the ground stiffness shall be adopted, as appropriate.  
9.6.2.12   To ensure the avoidance of a serviceability limit state, assessment of differential settlements and 
relative rotations shall take account of both the distribution of loads and the possible variability of the ground.  
9.6.2.13   Differential settlement calculations that ignore the s tiffness of the structure tend to be over -
predictions. An analysis of ground -structure interaction may be used to justify reduced values of differential 
settlements.  
9.6.2.14    Allowance should be made for differential settlement caused by variability of t he ground unless it 
is prevented by the stiffness of the structure.  
9.6.2.15   For spread foundations on natural ground, it should be taken into account that some differential 
settlement normally occurs even if the calculation predicts uniform settlement on ly. 
9.6.2.16   The tilting of an eccentrically loaded foundation should be estimated by assuming a linear 
bearing pressure distribution and then calculating the settlement at the corner points of the foundation, using 
the vertical stress distribution in the  ground beneath each corner point an d the settlement calculation methods 
described above.  
9.6.2.17   For conventional structures founded on clays, the ratio of the bearing capacity of the ground, at 
its initial undrained shear strength, to the applied servi ceability loading should be calculated (see 5.4.8). If this 
ratio is less than 3, calculations of settlements should always be undertaken. If the ratio is less than 2, the 
calculations should take account of non -linear stiffness effects in the ground.   
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 9.6.3  Heave  
9.6.3.1  The following causes of heave shall be distinguished:  
a) reduction of effective stress;  
b) volume expansion of partly saturated soil;  
c) heave due to constant volume conditions in fully saturated soil, caused by settlement of an adjacent 
structure.  
9.6.3.2  Calculations of heave shall include both immediate and delayed heave.  
9.6.4  Vibration analysis  
9.6.4.1  Foundations for structures subjected to vibrations or to vibrating loads shall be designed to ensure 
that vibrations will not cause excessive settlements . 
9.6.4.2  Precautions should be taken to ensure that resonance will not occur between the frequency of the 
dynamic load and a critical frequency in the foundation -ground system, and to ensure that liquefaction will not 
occur in the ground.  
9.6.4.3  Vibrations caused by earthquakes shall be considered using relevant standards on structural design 
for earthquake resistance.  
9.7 Foundations on rock; additional design considerations  
9.7.1  The design of spread foundations on rock shall take account of the fol lowing features:  
a) — the deformability and strength of the rock mass and the permissible settlement of the     supported 
structure;  
b) the presence of any weak layers, for example solution features or fault zones, beneath the foundation;  
c) the presence of bedding  joints and other discontinuities and their characteristics (for example filling, 
continuity, width, spacing);  
d) the state of weathering, decomposition and fracturing of the rock;  
e) disturbance of the natural state of the rock caused by construction activities , such as, for example, 
underground works or slope excavation, being near to the foundation.  
9.6.4.2  Spread foundations on rock may normally be designed using the method of presumed bearing 
pressures. For strong intact igneous rocks, gneissic rocks, limest ones and sandstones, the presumed bearing 
pressure is limited by the compressive strength of the concrete foundation.  DRS 113: 2020  
67                ©RSB 2020  - All rights reserved  
  9.6.4.3   The settlement of a foundation may be assessed on the basis of comparable experience related 
to rock mass classification.  
9.8 Struct ural design of spread foundations  
9.8.1  Structural failure of a spread foundation shall b e prevented in accordance with 5 .4.6.4.  
9.8.2  The bearing pressure beneath a stiff foundation may be assumed to be distributed linearly.  A more 
detailed analysis of so il-structure interaction may be used to justify a more economic design.  
9.8.3  The distribution of bearing pressure beneath a flexible foundation may be derived by modelling the 
foundation as a beam or raft resting on a deforming continuum or series of spri ngs, with appropriate stiffness 
and strength.  
9.8.4  The serviceability of strip and raft foundations shall be checked assuming serviceability limit state 
loading and a distribution of bearing pressure corresponding to the deformation of the foundation and the 
ground.  
9.8.5  For design situations with concentrated loads acting on a strip or raft foundation, forces and bending 
moments in the foundation may be derived from a subgrade reaction model of the ground, using linear 
elasticity. The moduli of subgrade reaction may be assessed by a settlement analysis with an appropriate 
estimate of the bearing pressure distribution. The moduli may be adjusted so that the computed bearing 
pressures do not exceed values for which linear behaviour may be assumed.  
9.8.6  Total and differential settlements of the structure as a whole should be calculated in accordance with 
9.6.2. For this purpose, subgrade reaction models are often not appropriate.  More precise methods, such as 
finite element computations, should be used when groundstructure interaction has a dominant effect.  
9.9 Preparation of the subsoil  
9.9.1  The subsoil shall be prepared with great care. Roots, obstacles and enclosures of weak soil shall be 
removed without disturbing the ground. Any resulting holes shall be fil led with soil (or other material) to 
replicate the stiffness of the undisturbed ground.  
9.9.2  In soils susceptible to disturbance, such as clay, the sequence of excavation for a spread foundation 
should be specified to minimise disturbance. Usually it is s ufficient to excavate in horizontal slices. In cases 
where heave is to be controlled, excavation should be in alternate trenches, the concrete being cast in each 
trench before excavating intermediate ones.  
10 Pile foundations  
10.1  General  
10.1.1  The provisions of  this s ection apply to end -bearing piles, friction piles, tension piles and transversely 
loaded piles installed by driving, by jacking, and by screwing or boring with or without grouting.  
10.1.2  The provisions of this Section should not be applied directly  to the design of piles that are intended 
as settlement reducers, such as in some piled raft foundations.   
©RSB 2020  - All rights reserved                  68 
 10.2 Limit states  
10.2.1  The following limit states shall be considered and an appropriate list shall be compiled:  
a) loss of overall stability;  
b) bearing resistance failure of the pile foundation;  
c) uplift or insufficient tensile resistance of the pile foundation;  
d) failure in the ground due to transverse loading of the pile foundation;  
e) structural failure of the pile in compression, tension, bending, buckling o r 
f) shear;  
g) combined failure in the ground and in the pile foundation;  
h) combined failure in the ground and in the structure;  
i) excessive settlement;  
j) excessive heave;  
k) excessive lateral movement;  
l) unacceptable vibrations.  
10.3 Actions and design situations  
10.3.1    General  
10.3.1.1   The actions listed in 9.2.4  should be considered when selecting the design situations.  
10.3.1.2   Piles can be loaded axially and/or transversely.  
10.3.1.3   Design situations shal l be derived in accordance with 5.2. 
10.3.1.4   An analysis of the inte raction between structure, pile foundation and ground can be necessary to 
prove that the limit state requirements are met.  DRS 113: 2020  
69                ©RSB 2020  - All rights reserved  
 10.3.2  Actions due to ground displacement  
10.3.2.1   General  
10.3.2.1  .1 Ground in which piles are located may be subject to displacement caused by co nsolidation, 
swelling, adjacent loads, creeping soil, landslides or earthquakes. Consideration shall be given to these 
phenomena as they can affect the piles by causing downdrag (negative skin friction), heave, stretching, 
transverse loading and displaceme nt. 
10.3.2.1  .2 For these situations, the design values of the strength and stiffness of the moving ground should 
usually be upper values.  
10.3.2.1  .3 One of the two following approaches shall be adopted for design:  
a) the ground displacement is treated as an  action. An interaction analysis is then carried out to 
determine the forces, displacements and strains in the pile;  
b) an upper bound to the force, which the ground could transmit to the pile shall be introduced as the 
design action. Evaluation of this force  shall take account of the strength of the soil and the source of 
the load, represented by the weight or compression of the moving soil or the magnitude of disturbing 
actions.  
10.3.2.2  Down  drag (negative skin friction)  
10.3.2.2.1  If ultimate limit state design cal culations are carried out with the downdrag load as an action, its 
value shall be the maximum, which could be generated by the downward movement of the ground relative to 
the pile.  
10.3.2.2.2  Calculation of maximum downdrag loads should take account of the  shear resistance at the 
interface between the soil and the pile shaft and downward movement of the ground due to self -weight 
compression and any surface load around the pile.  
10.3.2.2.3  An upper bound to the downdrag load on a group of piles may be calcul ated from the weight of 
the surcharge causing the movement and taking into account any changes in groundwater pressure due to 
ground -water lowering, consolidation or pile driving.  
10.3.2.2.4  Where settlement of the ground after pile installation is expecte d to be small, an economic 
design may be obtained by treating the settlement of the ground as the action and carrying out an interaction 
analysis.  
10.3.2.2.5  The design value of the settlement of the ground shall be derived taking account of material 
weigh t densities and compressibility in accordance with 5.4.3 . 
10.3.2.2.6  Interaction calculations should take account of the displacement of the pile relative to the 
surrounding moving ground, the shear resistance of the soil along the shaft of the pile, the w eight of the soil 
and the expected surface loads around each pile, which are the cause of the downdrag.  
10.3.2.2.7  Normally, downdrag and transient loading need not be considered simultaneously in load 
combinations.   
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 10.3.2.3  Heave  
In considering the effect of heave , or upward loads, which may be generated along the pile shaft, the 
movement of the ground shall generally be treated as an action.  
NOTE 1 Expansion or heave of the ground can result from unloading, excavation, frost action or driving of adjacent piles. 
It can also be due to an increase of the ground -water content resulting from the removal of trees, cessation of abstraction 
from aquifers, prevention (by new construction) of evaporation and from accidents.  
NOTE 2 Heave may take place during construction, be fore piles are loaded by the structure, and may cause unacceptable 
uplift or structural failure of the piles.  
10.3.2.4  Transverse loading  
10.3.2.4.1  Consideration shall be given to transverse actions originating from ground movements around a 
pile. 
10.3.2.4.2  Consi deration should be given to the following list of design situations, which may result in 
transverse actions on a pile:  
a) different amounts of surcharge on either side of a pile foundation (e.g. in or near an embankment);  
b) different levels of excavation on eit her side of a pile foundation (e.g. in or near a cutting);  
c) a pile foundation constructed in a creeping slope;  
d) inclined piles in settling ground;  
e) piles in a seismic region.  
10.3.2.4.3  Transverse loading should normally be evaluated by considering the intera ction between the 
piles, treated as stiff or flexible beams, and the moving soil mass. When the horizontal deformation of weak 
soil layers is large and the piles are widely spaced, the resulting transverse loading of the piles depends 
mainly on the shear s trength of the weak soil layers.  
10.4 Design methods and design considerations  
10.4.1  Design methods  
10.4.1.1   The design shall be based on one of the following approaches:  
a) the results of static load tests, which have been demonstrated, by means of calculations or otherwise, 
to be consistent with other relevant experience;  
b) empirical or analytical calculation methods whose validity has been demonstrated by static load tests 
in comparable situations;  DRS 113: 2020  
71                ©RSB 2020  - All rights reserved  
 c) the results of dynamic load tests whose validity has been demonstrat ed by static load tests in 
comparable situations;  
d) the observed performance of a comparable pile foundation, provided that this approach is supported 
by the results of site investigation and ground testing.  
10.4.1.2  Design values for parameters used in the  calculations should  be in general accordance with  
clause 6 , but the results of load tests may also be taken into account in selecting parameter values.  
10.4.1.1 3 Static load tests may be carried out on trial piles, installed for test purposes only, befor e the 
design is finalised, or on working piles, which form part of the foundation.  
10.4.2   Design considerations  
10.4.2.1   The behaviour of individual piles and pile groups and the stiffness and strength of the structure 
connecting the piles shall be considered.  
10.4.2.2   In selecting calculation methods and parameter values and in using load test results, the 
duration and variation in time of the loading shall be considered.  
10.4.2.3   Planned future placement or removal of overburden or potential changes in the g roundwater 
regime shall be considered, both in calculations and in the interpretation of load test results.  
10.4.2.4   The choice of type of pile, including the quality of the pile material and the method of installation, 
shall take into account:  
a) the ground  and ground -water conditions on the site, including the presence or possibility of 
obstructions in the ground;  
b) the stresses generated in the pile during installation;  
c) the possibility of preserving and checking the integrity of the pile being installed;  
d) the effect of the method and sequence of pile installation on piles, which have already been installed 
and on adjacent structures or services;  
e) the tolerances within, which the pile can be installed reliably;  
f) the deleterious effects of chemicals in the ground;  
g) the possibility of connecting different ground -water regimes;  
h) the handling and transportation of piles;  
i) the effects of pile construction on neighbouring buildings.   
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 10.4.2.5   In considering the aspects listed above, the following items should receive atten tion: 
a) the spacing of the piles in pile groups;  
b) displacement or vibration of adjacent structures due to pile installation;  
c) the type of hammer or vibrator used;  
d) the dynamic stresses in the pile during driving;  
e) for those types of bored pile where a fluid is used inside the borehole, the need to keep the pressure 
of the fluid at a level to ensure that the borehole will not collapse and that hydraulic failure of the base 
will not occur;  
f) cleaning of the base and sometimes the shaft of the borehole, especially un der bentonite, to remove 
remoulded materials;  
g) local instability of a shaft during concreting, which may cause a soil inclusion within the pile;  
h) ingress of soil or water into the section of a cast -in-situ pile and possible disturbance of wet concrete 
by the  flow of water through it;  
i) the effect of unsaturated sand layers around a pile extracting water from the concrete;  
j) the retarding influence of chemicals in the soil;  
k) soil compaction due to the driving of displacement piles;  
l) soil disturbance due to the borin g of a pile shaft.  
10.5 Pile load tests  
10.5.1  General  
10.5.1.1   Pile load tests shall be carried out in the following situations:  
a) when using a type of pile or installation method for which there is no comparable experience;  
b) when the piles have not been tested under c omparable soil and loading conditions;  
c) when the piles will be subject to loading for which theory and experience do not provide sufficient 
confidence in the design. The pile testing procedure shall then provide loading similar to the 
anticipated loading;  DRS 113: 2020  
73                ©RSB 2020  - All rights reserved  
 d) when observations during the process of installation indicate pile behaviour that deviates strongly and 
unfavourably from the behaviour anticipated on the basis of the site investigation or experience, and 
when additional ground investigations do not clarif y the reasons for this deviation.  
10.5.1.2   Pile load tests may be used to:  
a) assess the suitability of the construction method;  
b) determine the response of a representative pile and the surrounding ground to load,  both in terms of 
settlement and limit load;  
c) to allow judgement of the overall pile foundation.  
10.5.1.3   Where load tests are not practical due to difficulties in modelling the variation in the load (e.g. 
cyclic loading) very cautious design values for the material properties should be used.  
10.5.1.4   If one pile load test is carried out, it shall normally be located where the most adverse ground 
conditions are believed to occur. If this is not possible, an allowance shall be made when deriving the 
characteristic value of the compressive resistance.  
10.5.1.5   If load tests are carried out on two or more test piles, the test locations shall be representative of 
the site of the pile foundation and one of the test piles shall be located where the most adverse ground 
conditions are believed to occur.  
10.5. 1.6  Between the installation of the test pile and the beginning of the load test, adequate time shall be 
allowed to ensure that the required strength of the pile material is achieved and the pore -water pressures 
have regained their initial values.  
10.5.1.7   In some cases it can be necessary to record the pore -water pressures caused by pile installation 
and their subsequent dissipation in order to take a proper decision regarding the start of the load test.  
10.5.2  Static load tests  
10.5.2.1  Loading procedure  
10.5.2. 1.1 The pile load test procedures, particularly with respect to the number of loading steps, the 
duration of these steps and the application of load cycles, shall be such that conclusions can be drawn about 
the deformation behaviour, creep and rebound of a  piled foundation from the measurements on the pile. For 
trial piles, the loading shall be such that conclusions can also be drawn about the ultimate failure load.  
10.5.2. 1.2  Devices for the determination of loads, stresses or strains and displacements sh ould be 
calibrated prior to the test.  
10.5.2. 1.3  The direction of the test load applied to compression or tensile piles should coincide with the 
longitudinal axis of the pile.  
10.5.2. 1.4  Pile load tests for the purpose of designing a tensile pile foundat ion should be carried out to 
failure. Extrapolation of the load -displacement graph for tension tests should not be used.   
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 10.5.2.2  Trial piles  
10.5.2.2.1  The number of trial piles required to verify the design shall depend on the following:  
a) the ground conditions and  their variability across the site;  
b) the Geotechnical Category of the structure , if appropriate;  
c) previous documented evidence of the performance of the same type of pile in similar ground 
conditions;  
d) the total number and types of pile in the foundation desi gn. 
10.5.2.2.2  The ground conditions at the test site shall be investigated thoroughly. The depth of borings or 
field tests shall be sufficient to ascertain the nature of the ground both around and beneath the pile tip. All 
strata likely to contribute sign ificantly to pile behaviour shall be investigated.  
10.5.2.2.3  The method used for the installation of the trial piles shall be fully documented in accordance 
with 10.9. 
10.5.2.3   Working piles  
10.5.2.3.1  It shall be specified that the number of working pile load tests shall be selected on the basis of 
the recorded findings during installation.  
10.5.2.3.2  The test load applied to working piles shall be at least equal to the design load for the 
foundation.  
10.5.3  Dynamic load tests  
10.5.3.1   Dynamic load tests may be used to estimate the compressive resistance provided an adequate 
site investigation has been carried out and the method has been calibrated against static load tests on the 
same type of pile, of similar length and cross -section, and in co mparable soil condition s, (10.6.2.4 to 10 .6.2.6).  
10.5.3.2   If more than one type of dynamic test is used, the results of different types of dynamic test shall 
always be considered in relation to each other.  
10.5.3.3   Dynamic load tests may also be used as an indicator of the co nsistency of the piles and to 
detect weak piles.  
10.5.4  Load test report  
It shall be specified that a factual report shall be written for all load tests. Where appropriate, this report shall 
include:  
a) a description of the site;  DRS 113: 2020  
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 b) the ground conditions with reference  to ground investigations;  
c) the pile type;  
d) description of the pile installation and of any problems encountered during theworks;  
e) a description of the loading and measuring apparatus and the reaction system;  
f) calibration documents for the load cells, the jack s and the gauges;  
g) the installation records of the test piles;  
h) photographic records of the pile and the test site;  
i) test results in numerical form;  
j) —time-displacement plots for each applied load when a step loading procedure is used;  
k) the measured load -displa cement behaviour;  
l) reasons for any departures from the above requirements .  
10.5.5  Axially loaded piles  
10.5.5.1  Limit state design  
10.5.5.1.1   The design shall demonstrate that exceeding the following limit states is sufficiently 
improbable:  
a) ultimate limit states of compr essive or tensile resistance failure of a single pile;  
b) ultimate limit states of compressive or tensile resistance failure of the pile foundation as a whole;  
c) ultimate limit states of collapse or severe damage to a supported structure caused by excessive 
displacement or differential displacements of the pile foundation;  
d) serviceability limit states in the supported structure caused by displacement of the piles.  
10.5.5.1.2   Normally the design should consider the margin of safety with respect to compressive or 
tensile resistance failure, which is the state in which the pile foundation displaces significantly downwards or 
upwards with negligible increase or decrease of resistance (see 10.6.2 and 10.6.3).  
10.5.5.1.3   For piles in compression it is often difficult to define an ultimate limit state from a load 
settlement plot showing a continuous curvature. In these cases, settlement of the pile top equal to 10% of the 
pile base diameter should be adopted as the "failure" criterion.   
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 10.5.5.1.4   For piles that undergo  significant settlements, ultimate limit states may occur in supported 
structures before the resistance of the piles is fully mobilised. In these cases a cautious estimate of the 
possible range of the settlements shall be adopted in design.  
NOTE Settlement  of piles is considered in 10.6.4 
10.5.5.2  Overall stability  
10.5.5.2.1  Failure due to loss of overall stability of foundations involving piles in compression shall be 
considered in accordance with clause 14 . 
10.5.5.2.2  Where there is a possibility of instability, failure surfaces both passing below the piles and 
intersecting the piles should be considered.  
10.5.5.2.3 Failure due to uplift of a block of soil containing piles shal l be checked in accordance with  10.6.3.1 . 
10.5.6   Compressive ground resistance  
10.5.6.1  General  
10.5.6.1.1   To demonstrate that the pile foundation will support the design load with adequate safety 
against compressive failure, the following inequality shall be satisfied for all ultimate limit state load cases and 
load combinations:  
Fc;d   Rc;d                                                                                                                                                                 (7.1) 
10.5.6.1.2  In principle Fc;d should include the weight of the pile itself and Rc;d should include the 
overburden pressure of the soil at the foundation base. However these two items may be disregarded if they 
cancel approximately. They need not cancel if:  
a) downdrag is significant;  
b) the soil is very light,  
c) the pile extends above the surface of the  ground.  
10.5.6.1.3  For piles in groups, two failure mechanisms shall be taken into account:  
a) compressive resistance failure of the piles individually;  
b) compressive resistance failure of the piles and the soil contained between them acting as a block.  
The de sign resistance shall be taken as the lower value caused by these two mechanisms.  
10.5.6.1.4  The compressive resistance of the pile group acting as a block may be calculated by treating the 
block as a single pile of large diameter.  DRS 113: 2020  
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 10.5.6.1.5  The stiffness  and strength of the structure connecting the piles in the group shall be considered 
when deriving the design resistance of the foundation.  
10.5.6.1.6  If the piles support a stiff structure, advantage may be taken of the ability of the structure to 
redistr ibute load between the piles. A limit state will occur only if a significant number of piles fail together; 
therefore a failure mode involving only one pile need not be considered.  
10.5.6.1.7  If the piles support a flexible structure, it should be assumed that the compressive resistance of 
the weakest pile governs the occurrence of a limit state.  
10.5.6.1.8  Special attention should be given to possible failure of edge piles caused by inclined or eccentric 
loads from the supported structure.  
10.5.6.1.9  If the layer in which the piles bear overlies a layer of weak soil, the effect of the weak layer on 
the compressive resistance of the foundation shall be considered.  
10.5.6.1.10  The strength of a zone of ground above and below the pile base shall be taken into account 
when calculating the pile base resistance.  
NOTE This zone may extend several diameters above and below the pile base. Any weak ground in this zone has a 
relatively large influence on the base resistance.  
10.5.6.1.11  Punching failure should be consi dered if weak ground is present at a depth of less than 4 times 
the base diameter below the base of the pile.  
10.5.6.1.12  Where the pile base diameter exceeds the shaft diameter, the possible adverse effect shall be 
considered.  
10.5.6.1.13  For open -ended d riven tube or box -section piles with openings of more than 500 mm in any 
direction, and without special devices inside the pile to induce plugging, the base resistance should be limited 
to the smaller of:  
a) the shearing resistance between the soil plug and the inside face of the pile;  
b) the base resistance derived using the cross -sectional area of the base.  
10.5.6.2  Ultimate compressive resistance from static load tests  
10.5.6.2.1  The manner in which load tests are carried out shall be in accordance with 10.5 and shall  be 
specified in the Geotechnical Design Report.  
10.5.6.2.2  Trial piles to be tested in advance shall be installed in the same manner as the piles that will 
form the foundation and shall be founded in the same stratum.  
10.5.6.2.3  If the diameter of the tri al pile differs from that of the working piles, the possible difference in 
performance of piles of different diameters should be considered in assessing the compressive resistance to 
be adopted.   
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 10.5.6.2.4  In the case of a very large diameter pile, it is o ften impractical to carry out a load test on a full 
size trial pile. Load tests on smaller diameter trial piles may be considered provided that:  
a) the ratio of the trial pile diameter/working pile diameter is not less than 0,5;  
b) the smaller diameter trial pil e is fabricated and installed in the same way as the piles used for the 
foundation;  
c) the trial pile is instrumented in such a manner that the base and shaft resistance can be derived 
separately from the measurements.  
Note: This approach should be used with caution for open -ended driven piles because of the influence of the diameter on 
the mobilisation of the compressive resistance of a soil plug in the pile.  
10.5.6.2.5  In the case of a pile foundation subjected to downdrag, the pile resistance at failure, or  at a 
displacement that equals the criterion for the verification of the ultimate limit state determined from the load 
test results, shall be corrected. The correction shall be achieved by subtracting the measured, or the most 
unfavourable, positive shaft resistance in the compressible stratum  and in the strata above, where negative 
skin friction develops, from the loads measured at the pile head.  
10.5.6.2.6  During the load test of a pile subject to downdrag, positive shaft friction will develop along the 
total length of the pile and should be considered in accordance with 10.3.2.2 . The maximum test load applied 
to the working pile should be in excess of the sum of the design external load plus twice the downdrag force.  
10.5.6.2.7  When deriving the ultimate characteristic compressive resistance Rc;k from values Rc;m 
measured in one or several pile load tests, an allowance shall be made for the variability of the ground and the 
variability of the effect of pile installation.  
10.5.6.2.8  For structures, which do  not exhibit capacity to transfer loads from "weak" piles to "strong" piles, 
as a minimum, the following equation shall be satisfied:  
                                                   7.2 
Where:  
1 and 2 are correlation factors related to the number of piles tested and are applied to the mean ( Rc;m) mean 
and the lowest ( Rc;m )min of Rc;m  respectively.  
NOTE The values of the correlation factors may be set by the National annex. The recommended values are given in 
Table A.9.  
10.5.6.2.9  For structures having sufficient stiffness and strength to transfer loads from "weak" to "strong" 
piles, the values of  1 and 2 may be divided by 1,1, provided that 1 is never less than 1,0.  
10.5.6.2.10  The systematic and random components of the variations in the ground shall be recognised in 
the interpretation of pile load tests.  
DRS 113: 2020  
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 10.5.6.2.11  The records of the installation of the test pile(s) shall be checked and any deviation from the 
normal execution conditions shall be  accounted for.  
10.5.6.2.12  The characteristic compressive resistance of the ground, Rc;k, may be derived from the 
characteristic values of the base resistance, Rb;k, and of the shaft resistance, Rs;k, such that:  
Rc;k = Rb;k + Rs;k                                                                                               (7.3) 
10.5.6.2.13  These components may be derived directly from static load test results, or estimated on the 
basis of ground test results or dynamic load tests.  
10.5.6.2.14  The design resistance, Rc;d, shall be derived from either:  
Rc;d = Rc;k/t                                                                                                                                                                        (7.4) 
or 
Rc;d = Rb;k/b + Rs;k/s                                                                                        (7.5)  
NOTE  The recommended values for persistent and transient situations are given in Tables A.6, A.7 and A.8  
10.5.6.3  Ultimate compressive resistance from ground test results  
10.5.6.3.1  Methods for assessing the compressive resistance of a pile foundation from ground test results 
shall have been established from pile load tests and from comparable experience as defined in 3.5.2.2. 
10.5.6.3.2  A model factor m ay be introduced as described in 5.4.1 to ensure that the predicted 
compressive resistance is sufficiently safe.  
10.5.6.3.3  The design compressive resistance of a pile, Rc;d, shall be derived from:  
Rc;d = Rb;d + Rs;d                                                                                                                                                 (7.6)  
10.5.6.3.4  For each pile, Rb;d and Rs;d  shall be obtained from:  
Rb;d = Rb;k/b and Rs;d = Rs;k/s                                                                      (7.7) 
NOTE The values of the partial factors for persistent and transient situations  are given in tables A.6, A.7 and A.8.  
10.5.6.3.5  The characteristic values Rb;k and Rs;k shall eithe r be determined by:  
      7.8 
Where:  
 
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  3 and 4 are correlation factors that depend on the number of profiles of tests, n, and are applied 
respectively:  
— to the mean values ( Rc;cal )mean = (Rb;cal + Rs;cal)mean = (Rb;cal)mean +  (Rs;cal)mean 
— and to the  lowest values ( Rc;cal )min = ( Rb;cal + Rs;cal)min,  
or by the method given in  10.6.2.3(8).  
NOTE The recommended values of the correlation factors are given in Table A.10.  
10.5.6.3.6  The systematic and random components of the variation in the ground shall be recognised in the 
interpretation of the ground tests and calculated resistances.  
10.5.6.3.7  For structures with sufficient stiffness and strength to transfer loads from “weak” to “strong” piles, 
the factors 3 and 4 may be divided by 1,1, provide d that 3 is never less than 1,0.  
10.5.6.3.8  The characteristic values may be obtained by calculating:  
                                    7.9 
where qb;k and qs;i;k are characteristic values of base resistance and shaft friction in the various strata, obtained 
from values of ground parameters.  
NOTE If this alternative procedure is applied, the values of the partial factors b and s recommended in Annex 
A may need to be corrected by a model factor larger than 1,0.  
10.5.6.3.9  If Design Approach 3 is use d, the characteristic values of ground parameters shall be 
determined according to 5.4.5. Partial factors shall then be applied to these characteristic values to obtain 
design values of the ground parameters for calculating the design values of the pile re sistance.  
10.5.6.3.10  In assessing the validity of a model based on ground test results, the following items should be 
considered:  
a) soil type, including grading, mineralogy, angularity, density, pre -consolidation,  compressibility and 
permeability;  
b) method of  installation of the pile, including method of boring or driving;  
c) length, diameter, material and shape of the shaft and of the base of the pile (e.g. enlarged base);  
d) method of ground testing.  
10.5.6.4  Ultimate compressive resistance from dynamic impact tests  
10.5.6 .4.1 Where a dynamic impact (hammer blow) pile test [measurement of strain and acceleration 
versus time during the impact event ( 10.5.3) is used to assess the resistance of individual compression piles, 
DRS 113: 2020  
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 the validity of the result shall have been demonstrat ed by previous evidence of acceptable performance in 
static load tests on the same pile type of similar length and cross -section and in similar ground conditions.  
10.5.6.4.2  When using a dynamic impact load test, the driving resistance of the pile should b e measured 
directly on the site in question.  
NOTE A load test of this type can also include a process of signal matching to measured stress wave figures. Signal 
matching enables an approximate evaluation of shaft and base resistance of the pile as well as a simulation of its load -
settlement behaviour.  
10.5.6.4.3  The impact energy shall be high enough to allow for an appropriate interpretation of the pile 
capacity at a correspondingly high enough strain level.  
10.5.6.4.4  The design value of the compressive r esistance of the pile, Rc;d shall be derived  
from: Rc;d = Rc;k/t                                                                                                                                                                (7.10)  
with 
                                                                       7.11 
where 5 and 6 are correlation factors related to the number of piles tested, n, and are applied to the mean 
(Rc;m )mean and the lowest ( Rc;m) min value of Rc;m respectively.  
NOTE  The values of the partial factor and correlation factors are given in Table A.11.  
10.5.6.5  Ultimate compressive resistance by applying pile driving formulae  
10.5.6.5.1  Pile driving formulae shall only be used if the stratification of the ground has been determined . 
10.5.6.5.2  If pile driving formulae are used to assess the ultimate compressive resistance of individual piles 
in a foundation, the validity of the formulae shall have been demonstrated by previous experimental evidence 
of acceptable performance in stati c load tests on the same type of pile, of similar length and cross -section, 
and in similar ground conditions.  
10.5.6.5.3  For end -bearing piles driven into non -cohesive soil, the design value of the compressive 
resistance, Rc;d, shall be assessed by the sam e procedure as in 10 .6.2.4.  
10.5.6.5.4  When a pile driving formula is applied to verify the compression resistance of a pile, the pile 
driving test should have been carried out on at least 5 piles distributed at sufficient spacing in the piling area in 
order to check a suitable blow count for the final series of blows.  
10.5.6.5.5  The penetration of the pile point for the final series of blows should be recorded for each pile.  
 
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 10.5.6.6  Ultimate compressive resistance from wave equation analysis  
10.5.6.6.1  Wave equation analysis shall only be used where stratification of the ground has been 
determined by borings and field tests.  
10.5.6.6.2  Where wave equation analysis is used to assess the resistance of individual compression piles, 
the validity of the analysis s hall have been demonstrated by previous evidence of acceptable performance in 
static load tests on the same pile type, of similar length and cross section, and in similar ground conditions.  
10.5.6.6.3  The design value of the compressive resistance, Rc;d, derived from the results of wave equation 
analysis of a number of representative piles, shall be assessed by the same procedure as in 10.6.2.4, using 
values based on local experience.  
NOTE Wave equation analysis is based on a mathematical model of soil, pi le and driving equipment without stress wave 
measurements on site.  
 The method is usually applied to study hammer performance, dynamic soil parameters and stresses in the 
pile during driving. It is also, on the basis of the models,  
possible to determine th e required driving resistance (blow count) that is usually related to the expected 
compressive resistance of the pile.  
10.5.6.7  Re-driving  
10.5.6.7.1  In the design, the number of piles to be re -driven shall be specified. If re -driving gives lower 
results, these sha ll be used as the basis for ultimate compressive resistance assessment. If re -driving gives 
higher results, these may be considered.  
10.5.6.7.1  Re-driving should usually be carried out in silty soils, unless local comparable experience has 
shown it to be u nnecessary.  
NOTE  Re -driving of friction piles in clayey soils normally results in reduced compressive resistance.  
10.5.7  Ground tensile resistance  
10.5.7.1  General  
10.5.7.1  .1 The design of piles in tension shall be consistent with the design rules given in 7.6.2, where 
applicable. Design rules that are specific for foundations involving piles in tension are presented below.  
10.5.7.1  .2 To verify that the foundation will support the design load with adequate safety against a failure in 
tension, the following inequality shall be satisfied for all ultimate limit state load cases and load combinations:  
Ft;d   =Rt;d                                                                                                                                                                                     (7.12)  
10.5.7.1  .3 For tension piles, two failure mechanisms shall be considered:  
a) pull-out of the piles from the ground mass;  DRS 113: 2020  
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 b) uplift of the block of ground containing the piles.  
10.5.7.1  .4 Verification against uplift failure of the blo ck of ground containing the piles (see Figure 7.1), shall 
be carried out in accordance with 5.4.7.4.  
10.5.7.1  .5 For isolated tensile piles or a group of tensile piles, the failure mechanism may be governed by 
the pull -out resistance of a cone of ground, e specially for piles with an enlarged base or rock socket.  
10.5.7.1  .6 When considering the uplift of the block of ground containing the piles the shear resistance Td 
along the sides of the block may be added to the resisting forces shown in figure 7.1.  
10.5.7.1  .7 Normally the block effect will govern the design tensile resistance if the distance between the 
piles is equal to or less than the square root of the product of the pile diameter and the pile penetration into 
the main resisting stratum.  
10.5.7.1  .8 The group effect, which may reduce the effective vertical stresses in the soil and hence the shaft 
resistances of individual piles in the group, shall be considered when assessing the tensile resistance of a 
group of piles.  
10.5.7.1  .9 The severe adverse  effect of cyclic loading and reversals of load on the tensile resistance shall 
be considered.  
10.5.7.1  .10 Comparable experience based on pile load tests should be applied to appraise this effect.  
10.5.7.2   Ultimate tensile resistance from pile load tests  
10.5.7.2.1  Pile load tests to determine the ultimate tensile resistance of an isolated pile, Rt, shall be carried 
out in accordance with 10.5.1, 10.5.2 and 10.5.4, and with regard to 10.6.2.2.  
10.5.7.2.2  The design tensile resistance, Rt;d, shall be derive d from:  
Rt;d = Rt;k/s;t                                                                                                           (7.13)  
NOTE The recommended values for persistent and transient situations are given in Tables A.6, A.7 and A.8.  
 
 
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1 ground surface  
2 ground -water level  
3 side of the ‘block’, where resistance Td develops  
Figure 7.1 — Examples of uplift (UPL) of a group of piles  
10.5.7.2.3  Normally when piles are to be loa ded in tension, it should be specified that more than one pile 
should be tested. In the case of a large number of tension piles, at least 2 % should be tested.  
10.5.7.2.4  The records of the installation of the test pile(s) shall be checked and any deviatio n from the 
normal construction conditions shall be accounted for in the interpretation of the pile load test results.  
10.5.7.2.5  The characteristic value of the pile tensile resistance shall be determined  
                                                                   7.14 
where 1 and 2 are correlation factors related to the number of piles tested, n, and are applied respectively to 
the mean ( Rt;m )mean and the lowest ( Rt;m )min value of the measured tensile resistances.  
NOTE  The recommended values  of the correlation factors are given in Table A.9 . 
DRS 113: 2020  
85                ©RSB 2020  - All rights reserved  
 10.5.7.3  Ultimate tensile resistance from ground test results  
10.5.7.3.1  Methods for assessing the tensile resistance of a pile foundation from ground test results shall 
have been established from pile load tests and from comparable experience as defined in 3.5. 
10.5.7.3.2  A model factor may be introduced as described in 5.4.1 to ensure that the predicted tensile 
resistance is sufficiently safe.  
10.5.7.3.3  The design value of tensile resistance of a pile, Rt;d, sha ll be derived from:  
Rt;d = Rt;k / s;t                                                                                                   (7.15)  
where:  
Rt;k = Rs;k                                                                                                         (7.16)  
NOTE  The recommended values for persistent and transient situations are given in Tables A.6, A.7 and A.8 .  
10.5.7.3.4  The characteristic value Rt;k shall either be determined by:  
                                             (7.17)  
where 3 and 4 are correlation factors that depend on the number of profiles of tests, n, and are applied 
respectively to the mean ( Rs;cal )mean and to the lowest val ue (Rs;cal)min of Rs;cal, or by the method given in 10 
.6.3.3 . 
NOTE values of the correlation factors  are given in table A.10.  
10.5.7.3.5  The systematic and random components of the variation in the ground shall be recognised in the 
interpretation of the  calculated tensile resistance.  
10.5.7.3.6  The characteristic value of tensile resistance may be obtained by calculating:  
                                                                         (7.18)  
Where  
 qs;i;k are characteristic values of shaft friction in the various strata obtained from values of ground properties.  
NOTE   If this alternative procedure is applied, the value of the partial factor s,t recommended from Annex A, may need to 
be corrected by a mode l factor larger than 1,0 . 
 
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 10.5.7.3.7  If Design Approach 3 is used, the characteristic values of ground parameters shall be 
determined according to 5.4.5; partial factors shall then be applied to these characteristic values to obtain 
design values of the gr ound parameters to calculate the design values of the pile resistance.  
10.5.7.3.8  The assessment of the validity of a model based on ground test results should be in accordance 
with 10.6.2.3 . 
10.5.8  Vertical displacements of pile foundations (Serviceability of su pported  structure)  
10.5.8.1  General  
10.5.8.1.1  Vertical displacements under serviceability limit state conditions shall be assessed and checked 
against the requirements given in 5.4.8 and 5.4.9. 
10.5.8.1.2  When calculating the vertical displacements of a pile foun dation, the uncertainties involved in the 
calculation model and in determining the relevant ground properties should be taken into account. Hence it 
should not be overlooked that in most cases calculations will provide only an approximate estimate of the 
displacements of the pile foundation.  
NOTE For piles bearing in medium -to-dense soils and for tension piles, the safety requirements for the ultimate limit state 
design are normally sufficient to prevent a serviceability limit state in the supported structu re. 
10.5.8.2   Pile foundations in compression  
10.5.8.2.1  The occurrence of a serviceability limit state in the supported structure due to pile settlements 
shall be checked, taking into account downdrag, where probable.  
NOTE When the pile toe is placed in a medium -dense or firm layer overlying rock or very hard soil, the partial safety 
factors for ultimate limit state conditions are normally sufficient to satisfy serviceability limit state conditions.  
10.5.8.2.2  Assessment of settlements shall include both the settle ment of individual piles and the 
settlement due to group action.  
10.5.8.2.3  The settlement analysis should include an estimate of the differential settlements that may 
occur.  
10.5.8.2.4  When no load test results are available for an analysis of the interaction of the piled foundation 
with the superstructure, the load -settlement performance of individual piles should be assessed on empirically 
established safe assumptions.  
10.5.8.3  Pile foundations in tension  
10.5.8.3.1  The assessment of upward displacements s hall be in accordance with the principles of  10.6.4.2.  
NOTE Particular attention should be paid to the elongation of the pile material.  
10.5.8.3.2  When very severe criteria are set for the serviceability limit state, a separate check of the 
upward displac ements shall be carried out.  DRS 113: 2020  
87                ©RSB 2020  - All rights reserved  
 10.6 Transversely loaded piles  
10.6.1  General  
10.6.1.1   The design of piles subjected to transverse loading shall be consistent with the design rules 
given in 10.4 and 10.5, where applicable. Design rules specifically for foundations involving piles subjected to 
transverse loading are presented below.  
 10.6.1.2   failure, the following inequality shall be satisfied for all ultimate limit state load cases and load 
combinations:  
Ftr;d    Rtr;d                                                                                                                      (7.19)  
10.6.1.3   One of the following failure mechanisms should be considered:  
a) for short piles, rotation or translation as a rigid body;  
b) for long slender piles, bending failure of the  pile, accompanied by local yielding and displacement of 
the soil near the top of the pile.  
10.6.1.4   The group effect shall be considered when assessing the resistance of transversely loaded piles.  
10.6.1.5   It should be considered that a transverse load applied to a group of piles may result in a 
combination of compression, tension and transverse forces in the individual piles.  
10.6.2  Transverse load resistance from pile load tests  
10.6.2.1   Transverse pile load tests shall be carried out in accordance with 10.5.2. 
10.6.2.2   Contrary to the load test procedure described in 7.5, tests on transversely loaded piles need not 
normally be continued to a state of failure. The magnitude and line of action of the test load should simulate 
the design loading of the pile.  
10.6.2.3   An allowance shall be made for the variability of the ground, particularly over the top few metres 
of the pile, when choosing the number of piles for testing and when deriving the design transverse resistance 
from load test results.  
10.6.2.4   Reco rds of the installation of the test pile(s) should be checked, and any deviation from the 
normal construction conditions should be accounted for in the interpretation of the pile load test results. For 
pile groups, the effects of interaction and head fixit y should be accounted for when deriving the transverse 
resistance from the results of load tests on individual test piles.   
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 10.6.3  Transverse load resistance from ground test results and pile strength  
10.6.3.1  Parameters  
10.6.3.1  .1 The transverse resistance of a pile or pile group shall be calculated using a compatible set of 
structural effects of actions, ground reactions and displacements.  
10.6.3.1  .2 pile in the ground, in accordance with 10.8. 
10.6.3.1  .3 The calculation of the transverse resistance of a long slender pile may be carried out using the 
theory of a beam loaded at the top and supported by a deformable medium characterized by a horizontal 
modulus of subgrade reaction.  
10.6.3.1  .4 The degree of freedom of rotation of the piles at the connection with the stru cture shall be taken 
into account when assessing the foundation’s transverse resistance.  
10.6.4  Transverse displacement  
10.6.4.1   The assessment of the transverse displacement of a pile foundation shall take into account:  
a) the stiffness of the ground and its varia tion with strain level;  
b) the flexural stiffness of the individual piles;  
c) the moment fixity of the piles at the connection with the structure;  
d) the group effect;  
e) the effect of load reversals or of cyclic loading.  
10.6.4.2   A general analysis of the displaceme nt of a pile foundation should be based on expected 
degrees of kinematic freedom of movement.  
10.7 Structural design of piles  
10.7.1  Piles shall be verified against structural failure in accordance with 5.4.6.4.  
10.7.2  The structure of piles shall be designed to accommodate all the situations to which the piles will be 
subjected. These include:  
a) the circumstances of their use e.g. corrosion conditions;  
b) the circumstances of their installation e.g. adverse ground conditions such as boulders, steeply 
inclined bedro ck surfaces;  
c) other factors influencing driveability, including quality of joints;  DRS 113: 2020  
89                ©RSB 2020  - All rights reserved  
 d) for precast piles, the circumstances of their transportation to site and installation.  
10.7.3  During structural design, construction tolerances as specified for the type of p ile, the action 
components and the performance of the foundation shall be taken into account.  
10.7.4  Slender piles passing through water or thick deposits of very weak soil shall be checked against 
buckling.  
10.7.5  Normally a check for buckling is not requ ired when the piles are contained by soils with a 
representative, undrained shear strength, cu, that exceeds 10 kPa.  
10.8 Supervision of construction  
10.8.1  A pile installation plan shall form the basis for the piling works.  
10.8.2  The plan should give the foll owing design information:  
a) the pile type;  
b) the location and inclination of each pile, including tolerances on position;  
c) pile cross -section;  
d) for cast -in-situ piles, data about the reinforcement;  
e) pile length;  
f) pile number;  
g) required pile load carrying capacity;  
h) pile toe level (with respect to a fixed datum within or near the site), or the required  
i) penetration resistance;  
j) installation sequence;  
k) known obstructions;  
l) any other constraints on piling activities.  
10.8.3  It shall be specified that the installation of al l piles is monitored and records are made as the piles are 
installed.  
10.8.4  The record for each pile should include aspects of construction, such as the following:   
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 a) pile number;  
b) installation equipment;  
c) pile cross -section and length;  
d) date and time of instal lation (including interruptions to the installation process);  
e) concrete mix, volume of concrete used and method of placing for cast -in-situ piles;  
f) weight density, pH, Marsh viscosity and fines content of bentonite slurry (when used);  
g) for continuous flight a uger piles or other injection piles, volumes and pumping pressures of the grout 
or concrete, internal and external diameters, pitch of screw and penetration per revolution;  
h) for displacement piles, the values of driving resistance measurements such as weigh t and drop or 
power rating of hammer, blow frequency and number of blows for at least the last 0,25 m penetration;  
i) the power take -off of vibrators (where used);  
j) the torque applied to the drilling motor (where used);  
k) for bored piles, the strata encountered in the borings and the condition of the base if the performance 
of the pile toe is critical;  
l) obstructions encountered during piling;  
m) deviations of position and direction and as -built elevations.  
10.8.5  Records should be kept for at least a period of five years after completion of the works. As  built 
records should be compiled after completion of the piling and kept with the construction documents.  
10.8.6  If site observations or inspection of records reveal uncertainties about the quality of installed piles , 
investigations shall be carried out to determine their condition and if remedial measures are necessary. These 
investigations shall include either performing a static pile load or integrity test, installing a new pile or, in the 
case of a displacement pi le, re -driving the pile, in combination with ground tests adjoining the suspect pile.  
 10.8.7  Tests shall be used to examine the integrity of piles for which the quality is sensitive to the installation 
procedures if the procedures cannot be monitored in a  reliable way.  
10.8.8  Dynamic low strain integrity tests may be used for a global evaluation of piles that might have severe 
defects or that may have caused a serious loss of strength in the soil during construction. Defects such as 
insufficient quality of  concrete and thickness of concrete cover, both of which can affect the long term 
performance of a pile, often cannot be found by dynamic  tests and other tests, such as sonic tests, vibration 
tests or coring, may be needed in supervising the execution.  DRS 113: 2020  
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 11 Anchorages  
11.1 General  
11.1.1   This clause  applies to the design of temporary and permanent anchorages used:  
a) to support a retaining structure;  
b) to provide the stability of slopes, cuts or tunnels;  
c) to resist uplift forces on structures;  by transmitting a tensile fo rce to a load bearing formation of soil or 
rock.  
d) pre-stressed anchorages consisting of an anchor head, a tendon free length and a tendon bond 
length bonded to the ground by grout;  
e) non pre -stressed anchorages consisting of an anchor head, a tendon free leng th and a restraint such 
as a fixed anchor length bonded to the ground by grout, a deadman anchorage, a screw anchor or a 
rock bolt.  
11.1.2  The application of design requirements given in this clause is limited  to soil nails.  
11.1.3  Clause  10  shall apply to the design of anchorages comprising tension piles.  
11.2  Limit states  
The following limit states shall be considered for anchorages, both individually and in combination:  
a) structural failure of the tendon or anchor head, caused by the applied stresses;  
b) distor tion or corrosion of the anchor head;  
c) for grouted anchors, failure at the interface between the body of grout and the ground;  
d) for grouted anchors, failure of the bond between the steel tendon and the grout;  
e) for deadman anchorages, failure by insufficient r esistance of the deadman;  
f) loss of anchorage force by excessive displacements of the anchor head or by creep and relaxation;  
g) failure or excessive deformation of parts of the structure due to the applied anchorage force;  
h) loss of overall stability of the reta ined ground and the retaining structure;  
i) interaction of groups of anchorages with the ground and adjoining structures.   
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 11.3 Design situations and actions  
11.3.1  When selecting the design situations, consideration shall be given to:  
a) all circumstances during the construction of the structure;  
b) all anticipated circumstances during the design life of the structure;  
c) all pertinent limit states of the list compiled in 8.2, and their combinations;  
d) the anticipated level of the ground -water and water pressures in confined aquifers;  
e) the consequences of the failure of any anchorage;  
f) the possibility that the forces applied to the anchorage during pre -stressing  (anchorage load) may 
exceed the forces required for the design of the structure.  
11.3.2  The anchorage load, P, shall be treated as an unfavourable action for the anchorage design.  
11.4 Design and construction considerations  
11.4.1  The design of the anchorage and the specification for its execution shall take into account any 
adverse effects of tensile stresses transmitted to ground beyond the vicinity of the anchorage.  
11.4.2  The zone of ground into which tensile forces are to be transferred shall be included in site 
investigations.  
11.4.3  For pre -stressed anchorages, the anchor head shall allow the tendon or rod to be stresse d, proof -
loaded and locked -off and, if required by the design, released, de -stressed and re -stressed.  
11.4.4  For all types of anchorage, the anchor head shall be designed to tolerate angular deviations of the 
anchor force, and to be able to accommodate def ormations, which may occur during the design life of the 
structure.  
11.4.5  Where different materials are combined in an anchorage, their design strengths shall be assessed 
with due account of the compatibility of their deformation performance.  
11.4.6  Since  the effect of anchorage systems depends on their tendon free lengths, the following 
requirements shall be fulfilled:  
a) the anchor force shall act in ground that is sufficiently distant from the retained  volume of ground that 
the stability of this volume is  not adversely affected;  
b) the anchor force shall act in ground that is sufficiently distant from existing foundations to avoid any 
adverse effects on them;  DRS 113: 2020  
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 c) measures shall be taken to avoid adverse interactions between the tendon bond  lengths of 
anchorages t hat pass close to each other;  
11.4.7  Adverse interactions between the tendon bond lengths of anchorages should be avoided, if possible, 
by keeping a space not less than 1,5 m between them.  
11.4.8  Only anchorage systems shall be used that have been tested b y investigation tests or for which 
successful comparable experience is documented in terms of both performance and durability.  
11.4.9  The direction of the tendon shall normally be such as to provide self -stressing with deformations due 
to potential failure  mechanisms. In case this is not feasible, adverse effects shall be taken into account in the 
design.  
11.4.10  For grouted anchorages and screw anchorages, the characteristic value of the pull -out resistance, 
Ra;k, shall be determined on the basis of suitab ility tests according to 8.7 or comparable experience. The 
design resistance shall be checked by acceptance tests after execution.  
11.4.11  The performance of the tendon free length of pre -stressed ground anchorages shall be checked in 
accordance with RS 23 0-1/ISO 6934 -1 
11.4.12  A sufficient lock -off force shall be used to ensure that the anchorage resistance under serviceability 
limit state conditions will be mobilised with tolerable head displacements.  
11.4.13  Corrosion protection of anchorages having a st eel tendon shall be designed taking into account the 
aggressiveness of the ground environment.  
11.4. 14 Suitable means, such as the use of a protective sheath or the provision of sacrificial steel, should be 
specified if necessary to protect steel tendons against corrosion.  
11.5 Ultimate limit state design  
11.5.1  Design of the anchorage  
11.5.1.1   The design value, Ra;d , of the pull -out resistance, Ra, of an anchorage shall fulfil the limit 
condition:  
Pd   Ra;d                                                                                                               (8.1) 
11.5.1.2  Design values of pull -out resistance may be determined from the results of tests on anchorages, or 
by calculations.  
11.5.2   Design values of pull -out resistance determined from the results of tes ts 
11.5.2.1   The design value of the pull -out resistance shall be derived from the characteristic value using 
the equation:  
Ra;d = Ra;k/a                                                                                               (8.2)  
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 NOTE The partial factor, a, takes into account unfavourable deviations of the pull -out resistance of the anchorage.  
11.5.2.2   The partial factors a defined in A.3.3.4(1) shall be used in equation (8.2).  
NOTE   The value of the partial factor for persiste nt and transient situations are given in Table A.12.  
11.5.2.3   The characteristic value should be related to the suitability test results by applying a correlation 
factor a. 
NOTE  11.5.2(3) refers to those types of anchorage that are not individually chec ked by acceptance tests.  
11.5.3  Design values of pull -out resistance determined by calculations  
The design value of pull -out resistance shall be assessed according to the principles in 5.4.7 and 5.4.8, where 
appropriate.  
11.5.4  Design value of the structural resistance of the anchorage  
11.5.4.1   The structural design of the anchorage shall satisfy the following inequality:  
Ra;d   Rt;d                                                                                                        (8.3) 
11.5.4.2   The material resis tance of the anchorages, Rt;d, shall be calculated according  to relevant 
standards for design of bridges.  
11.5.4.3   If anchors are submitted to suitability tests, Rt;d shall take account of the proof load.  
11.5.5  Design value of the anchorage load  
The design val ue of the anchorage load, Pd, shall be derived from the design of the retained structure as the 
maximum value of  
a) the ultimate limit state force applied by the retained structure, and if relevant  
b) the serviceability limit state force applied by the retained structure.  
11.6 Serviceability limit state design  
11.6.1   For the verification of a serviceability limit state in the supported structure, shall be regarded as a 
spring.  
11.6.2  For pre -stressed anchorages (e.g. grouted anchorages), the spring shall be regarded as an elastic, 
pre-stressed spring.  
11.6.3  The most adverse combination of the minimum or maximum anchorage stiffness and minimum or 
maximum pre -stress should be selected when analysing the design situation indicated in 11.6. DRS 113: 2020  
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 11.6.4  A model factor should b e applied to the SLS force to ensure that the resistance of the anchorage is 
sufficiently safe.  
11.6.5  When considering a non -pre-stressed anchorage as a (non -pre-stressed) spring, its stiffness should 
be selected to achieve compatibility between calculate d displacements of the retained structure and the 
displacement and elongation of the anchorage.  
11.6.6  Account should be taken of the effects of any deformations imposed on adjacent foundations by the 
anchorage pre -stress force.  
11.7 Suitability tests  
11.7.1  Suitability tests shall be specified for grouted anchorages, screw anchorages and rock bolts.  
11.7.2  At least three suitability tests should be performed for each distinct condition of ground and structure 
to determine the characteristic resistance of the a nchor.  
11.8 Acceptance tests  
11.8.1  It shall be specified in the design that all grouted anchorages shall be subjected to acceptance tests 
prior to lock -off and before they become operational.  
11.8.1  The procedure for acceptance tests shall follow the rules giv en in BS EN 1537:1999 for grouted 
anchorages.  
11.8.1  Where groups of anchorages are crossing with tendon bond lengths at spacings of less than 1,5 m, 
random control tests should be made after completion of the lock -off action.  
11.9 Supervision and monitoring  
Supervision and monitoring shall follow the rules given in clause 4 of this standard where appropriate.  
12 Retaining structures  
12.1 General  
The provisions of this clause  shall apply to structures, which retain ground comprising soil, rock or backfill and 
water. Mat erial is retained if it is kept at a slope steeper than it would eventually adopt if no structure were 
present. Retaining structures include all types of wall and support systems in which structural elements have 
forces imposed by the retained material . 
12.2 Limit states  
12.2.1   A list shall be compiled of limit states to be considered. As a minimum the following limit states shall 
be considered for all types of retaining structure:   
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 a) loss of overall stability;  
b) failure of a structural element such as a wall, anc horage, wale or strut or failure of the connection 
between such elements;  
c) combined failure in the ground and in the structural element;  
d) failure by hydraulic heave and piping;  
e) movement of the retaining structure, which may cause collapse or affect the appearance or efficient 
use of the structure or nearby structures or services, which rely on it;  
f) unacceptable leakage through or beneath the wall;  
g) unacceptable transport of soil particles through or beneath the wall;  
h) unacceptable change in the ground -water  regime.  
12.2.2  In addition, the following limit states shall be considered for gravity walls and for composite retaining 
structures:  
a) bearing resistance failure of the soil below the base;  
b) failure by sliding at the base;  
c) failure by toppling; and for embedd ed walls:  
d) failure by rotation or translation of the wall or parts thereof;  
e) failure by lack of vertical equilibrium.  
12.2.3  For all types of retaining structure, combinations of the above mentioned limit states shall be taken 
into account, if relevant.  
12.2.4 Design of gravity walls often requires solution of the same types of problem encountered in the 
design of spread foundations and embankments and slopes. When considering the limit states, the principles 
of clause  9 should therefore be applied, as approp riate. Special care should be taken to account for bearing 
resistance failure of the ground below the base of the wall under loads with large eccentricities and 
inclinations (see 9.5.4).  DRS 113: 2020  
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 12.3 Actions, geometrical data and design situations  
12.3.1  Actions  
12.3.1.1  Basic actions  
The actions listed in 5.4.2(4) should be considered.  
12.3.1.2  Weight of backfill material  
Design values for the weight density of backfill material shall be estimated from knowledge of available 
material. The Geotechnical Design Report shall specify the checks, wh ich shall be made during the 
construction process to verify that the actual field values are no worse than those used in the design.  
12.3.1.3  Surcharges  
Determination of design values for surcharges shall take account of the presence, on or near the surface of 
the retained ground, of, for example, nearby buildings, parked or moving vehicles or cranes, stored material, 
goods and containers.  
12.3.1.4  Weight of water  
Design values for the weight density of water shall reflect whether the water is fresh, saline or charged with 
chemicals or contaminants to an extent that the normal value needs amendment.  
 
12.3.1.5   Wave and ice forces  
12.3.1.5  .1 Design values for forces imposed by reflected waves shall be selected on the basis of national  
data for the climatic and hydraulic conditions at the site.  
12.3.1.5  .2 When selecting design values for static forces imposed by a sheet of ice, the following shall be 
taken into account:  
a) the initial temperature of the ice before warming begins;  
b) the rate  at which the temperature increases;  
c) the thickness of the ice sheet.  
12.3.1.6  Seepage forces  
Seepage forces due to different ground -water levels behind and in front of a retaining structure shall be 
considered as they may change the earth pressure behind the wall a nd reduce the earth resistance in front of 
the wall.   
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 12.3.1.7  Collision forces  
12.3.1.7.1  The determination of design values for collision impact forces, caused by, for example, waves, 
ice floes or traffic, may take account of the energy absorbed by the colliding m ass and by the retaining 
system, e.g. by fenders and/or guide structures.  
12.3.1.7  .2 For lateral impacts on retaining walls, the increased stiffness exhibited by the retained ground 
should be considered.  
12.3.1.7  .3 The risk of the occurrence of liquefact ion due to lateral impact on embedded walls should be 
investigated.  
12.3.1.7  .4 The impact load of an ice floe colliding with a retaining structure shall be calculated on the basis 
of the compressive strength of the ice and the thickness of the ice floe. T he salinity and homogeneity of the 
ice shall be considered in calculating the compressive strength.  
12.3.1.8  Temperature effects  
12.3.1.8  .1 The design of retaining structures shall take into account the temporal and spatial effects of 
abnormal temperature changes.  
12.3.1.8  .2 These effects should be considered particularly when determining the loads in struts and props.  
12.3.1.8  .3 The Structural Fire Design Parts of the material should be consulted when dealing with the 
effects of fire.  
12.3.1.8  .4 Special precaut ions, such as selection of suitable backfill material, drainage or insulation, shall 
be taken to prevent ice lenses forming in the ground behind retaining structures.  
12.3.2  Geometrical data  
12.3.2.1  Basic data  
Design values for geometrical data shall be derived in accord ance with the principles stated in 5.4.6.3.  
12.3.2.2  Ground surfaces  
12.3.2.2  .1 Design values for the geometry of the retained material shall take account of the variation in the 
actual field values. The design values shall also take account of anticipated excavation or possible scour in 
front of the retaining structure.  
12.3.2.2  .2 In ultimate limit state calculations in which the stability of a retaining wall depends on the ground 
resistance in front of the structure, the level of the resisting soil should  be lowered below the nominally 
expected level by an amount a. The value of a should be selected taking into account the degree of site 
control over the level of the surface. With a normal degree of control, the following should be applied:  
a) for a cantilever wall, a should equal 10 % of the wall height above excavation level, limited to a 
maximum of 0,5 m;  DRS 113: 2020  
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 b) for a supported wall, a should equal 10 % of the distance between the lowest support and the 
excavation level, limited to a maximum of 0, 5 m. 
12.3.2.2  .3 Smaller values of a, including 0, may be used when the surface level is specified to be 
controlled reliably throughout the appropriate execution period.  
12.3.2.2  .4 Larger values of a should be used where the surface level is particularl y uncertain.  
12.3.2.3  Water levels  
12.3.2.3.1  The selection of design or characteristic values for the positions of free water and phreatic 
surfaces shall be made on the basis of data for the hydraulic and hydrogeological conditions at the site.  
12.3.2.3.2  Account shall be taken of the effects of variation in permeability on the ground -water regime.  
12.3.2.3.3  The possibility shall be considered of adverse water pressures due to the presence of perched 
or artesian water tables.  
12.3.3  Design situations  
12.3.3.1   The follow ing items shall be considered:  
a) variations in soil properties, water levels and pore -water pressures in space;  
b) anticipated variations in soil properties, water levels and pore -water pressures in time;  
c) variation in actions and in the ways they are combined;  
d) excavation, scour or erosion in front of the retaining structure;  
e) the effects of compaction of the backfilling behind the retaining structure;  
f) the effects of anticipated future structures and surcharge loadings or unloadings on or close to the 
retained mat erial;  
g) anticipated ground movements due, for example, to subsidence or frost action.  
12.3.2.3.2  For waterfront structures, ice and wave forces need not be applied simultaneously at the same 
point.  
12.4 Design and construction considerations  
12.4.1  General  
12.4.1.1   Both ultimate and serviceability limit states shall be considered using the procedures described 
in 5.4.7 and 5 .4.8.  
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 12.4.1.2   It shall be demonstrated that vertical equilibrium can be achieved for the assumed pressure 
distributions and actions on the wall.  
12.4.1.3   The verification of vertical equilibrium may be achieved by reducing the wall friction parameters.  
12.4.1.4   As far as possible, retaining walls should be designed in such a way that there are visible signs 
of the approach of an ultimate limit s tate. The design should guard against the occurrence of brittle failure, e.g. 
sudden collapse without conspicuous preliminary deformations.  
12.4.1.5   For many earth retaining structures, a critical limit state should be considered to occur if the wall 
has displaced enough to cause damage to nearby structures or services. Although collapse of the wall may 
not be imminent, the degree of damage may considerably exceed a serviceability limit state in the supported 
structure.  
12.4.1.6   The design methods and par tial factor values recommended by this standard are usually 
sufficient to prevent the occurrence of ultimate limit states in nearby structures, provided that the soils involved 
are of at least medium density or firm consistency and that adequate constructi on methods and sequences 
are adopted. Special care should be taken, however, with some highly over -consolidated clay deposits in 
which large at rest horizontal stresses may induce substantial movements in a wide area around excavations.  
12.4.1.7   The compl exity of the interaction between the ground and the retaining structure sometimes 
makes it difficult to design a retaining structure in detail before the actual execution begins. In this case use of 
the observational method for the design ( see 5.9) should be considered.  
12.4.1.8   The design of retaining structures shall take account of the following items, where appropriate:  
a) the effects of constructing the wall, including:  
b) the provision of temporary support to the sides of excavations;  
c) the changes of in sit u stresses and resulting ground movements caused both by the wall excavation 
and its construction;  
d) disturbance of the ground due to driving or boring operations;  
e) provision of access for construction;  
f) the required degree of water tightness of the finished w all; 
g) the practicability of constructing the wall to reach a stratum of low permeability, so forming a water 
cut-off. The resulting equilibrium ground -water flow problem shall be assessed;  
h) the practicability of forming ground anchorages in adjacent ground;  
i) the practicability of excavating between any propping of retaining walls;  
j) the ability of the wall to carry vertical load;  DRS 113: 2020  
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 k) the ductility of structural components;  
l) access for maintenance of the wall and any associated drainage measures;  
m) the appearance and du rability of the wall and any anchorages;  
n) for sheet piling, the need for a section stiff enough to be driven to the design penetration without loss 
of interlock;  
o) the stability of borings or slurry trench panels while they are open;  
p) for fill, the nature of m aterials available and the means used to compact them adjacent to the wall, in 
accordance with 9.3. 
12.4.2  Drainage systems  
12.4.2.1   If the safety and serviceability of the designed structure depend on the successful performance 
of a drainage system, the consequences of its failure shall be considered, having regard for both safety and 
cost of repair. One of the following conditions (or a combination of them) shall apply:  
a) a maintenance programme for the drainage system shall be specified and the design sha ll allow 
access for this purpose;  
b) it shall be demonstrated both by comparable experience and by assessment of any water discharge, 
that the drainage system will operate adequately without maintenance.  
12.4.2.2   The quantities, pressures and eventual chemic al content of any water discharge should be taken 
into account.  
12.5 Determination of earth pressures  
12.5.1  General  
12.5.1.1   Determination of earth pressures shall take account of the acceptable mode and amount of any 
movement and strain, which may occur at the limit state under consideration.  
12.5.1.2   In the following context the words "earth pressure" should also be used for the total earth 
pressure from soft and weathered rocks and should include the pressure of ground -water.  
12.5.1.3   Calculations of the mag nitudes of earth pressures and directions of forces resulting from them 
shall take account of:  
a) the surcharge on and slope of the ground surface;  
b) the inclination of the wall to the vertical;   
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 c) the water tables and the seepage forces in the ground;  
d) the amount and direction of the movement of the wall relative to the ground;  
e) the horizontal as well as vertical equilibrium for the entire retaining structure;  
f) the shear strength and weight density of the ground;  
g) the rigidity of the wall and the supporting system;  
h) the wall roughness.  
12.5.1.5   The amount of mobilised wall friction and adhesion should be considered as a function   
 of: 
a) the strength parameters of the ground;  
b) the friction properties of the wall -ground interface;  
c) the direction and amount of movement of th e wall relative to the ground;  
d) the ability of the wall to support any vertical forces resulting from wall friction and adhesion.  
12.5.1.5   The amount of shear stress, which can be mobilised at the wall -ground interface should be 
determined by the wall -ground interface parameter  
12.5.1.6   A concrete wall or steel sheet pile wall supporting sand or gravel may be assumed to have a 
design wall ground interface parameter  
     
 k  should not exceed 2/3 for precast concrete or steel sheet piling.  
12.5.1.7   For concrete cast against soil, a value of k = 1,0 may be assumed.  
12.5.1.8   For a steel sheet pile in clay under undrained conditions immediately after driving, no adhesive 
or frictional resistance should be assumed. Increases in these values may take place o ver a period of time.  
12.5.1.9   The magnitudes of earth pressures and directions of resultant forces shall be calculated 
according to the selected design approach (see 5.4.7.3), and the limit state being considered.  
12.5.1.10  The value of an earth pressure  at an ultimate limit state is generally different from its value at a 
serviceability limit state. These two values are determined from two fundamentally different calculations. 
Consequently, when expressed as an action, earth pressure cannot have a single  characteristic value.  
 
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 12.5.1.11  In the case of structures retaining rock masses, calculations of the ground pressures shall take 
account of the effects of discontinuities, with particular attention to their orientation, spacing, aperture, 
roughness and the mechanical characteristics of any joint filling material.  
12.5.1.12  Account shall be taken of any swelling potential of the ground when calculating the pressures on 
the retaining structure.  
12.5.2  At rest values of earth pressure  
12.5.2.1   When no movement of  the wall relative to the ground takes place, the earth pressure shall be 
calculated from the at rest state of stress. The determination of the at rest state shall take account of the 
stress history of the ground.  
12.5.2.2   For normally consolidated soil,  at rest conditions should normally be assumed in the ground 
behind a retaining structure if the movement of the structure is less than  
12.5.2.3   For a horizontal ground surface, the at rest  earth pressure coefficient, K0, should be determined 
from:  
                                                                  (9.1) 
The formula should not be used for very high values of OCR.  
12.5.2.4   If the ground slopes upwards from the wall at an angl e  φ to the horizontal, the horizontal 
component of the effective earth pressure  
  may be related to the effective overburden pressure q' by the ratio K o where  
  Ko = K o . (sin )                                                                                             (9.2) 
The direction of the resulting force should then be assumed to be parallel to the ground surface.  
12.5.3  Limiting values of earth pressure  
12.5.3.1   Limiting values of earth  pressures shall be determined taking account of the relative movement 
of the soil and the wall at failure and the corresponding shape of the failure surface.  
12.5.3.2   Limiting values of earth pressure assuming straight failure surfaces can significantly deviate from 
the values assuming curved failure surfaces for high angles of internal friction and wall ground interface 
parameters  and so lead to unsafe results.  
  
12.5.3.3   In cases  where struts, anchorages or similar elements impose restraints on movem ent of the 
retaining structure, it should be considered that the limiting active and passive values of earth pressure, and 
their distributions, may not be the most adverse ones.  
 
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 12.5.4  Intermediate values of earth pressure  
12.5.4.1   Intermediate values of earth p ressure occur if the wall movements are insufficient to mobilise the 
limiting values. The determination of the intermediate values of earth pressure shall take account of the 
amount of wall movement and its direction relative to the ground.  
12.5.4.2   The i ntermediate values of earth pressures may be calculated using, for example, various 
empirical rules, spring constant methods or finite element methods.  
12.5.5  Compaction effects  
12.5.5.1   The determination of earth pressures acting behind the wall shall take acco unt of the additional 
pressures generated by any placing of backfill and the procedures adopted for its compaction.  
NOTE  Measurements indicate that the additional pressures depend on the applied compactive energy, the 
thickness of the compacted layers and  the travel pattern of the compaction plant. Horizontal pressure normal 
to the wall in a layer may reduce when the next layer is placed and compacted. When backfilling is complete, 
the additional pressure normally acts only on the upper part of the wall.  
12.5.5.2   Appropriate compaction procedures shall be specified with the aim of avoiding excessive 
additional earth pressures, which may lead to unacceptable movements.  
12.6 Water pressures  
12.6.1   Determination of characteristic and design water pressures shall take account of water levels both 
above and in the ground.  
12.6.2  When checking the ultimate and serviceability limit states, water pressures shall be accounted for in 
the combinations of ac tions in accordance with 5.4.5.3 and 5.4.6.1, considering the possible risks indicated in 
12.4.1(5).  
12.6.3  For structures retaining earth of medium or low permeability (silts and clays), water pressures shall 
be assumed to act behind the wall. Unless a reliabl e drainage system is installed (see 10.4.2), or infiltration is 
prevented, the values of water pressures shall correspond to a water table at the surface of the retained 
material.  
12.6.4  Where sudden changes in a free water level may occur, both the  non-steady condition occurring 
immediately after the change and the steady condition shall be examined.  
12.6.5  Where no special drainage or flow prevention measures are taken, the possible effects of water -filled 
tension or shrinkage cracks shall be consi dered.  
12.7 Ultimate limit state design  
12.7.1  General  
12.7.1.1   The design of retaining structures shall be checked at the ultimate limit state for the design 
situations appropriate to that state, as specified in 12.3.3, using the design actions or action effects and  
design resistances.  DRS 113: 2020  
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 12.7.1.2   All relevant limit modes shall be considered. These will include, as a minimum, limit modes of 
the types illustrated in figures 12.1 to 9 / 12.6 for the most commonly used retaining structures.  
12.7.1.3   Calculations for ultim ate limit states shall establish that equilibrium can be achieved using the 
design actions or effects of actions and the design strengths or resistances, as specified in clause 5.4. 
Compatibility of deformations shall be considered in assessing design stre ngths or resistances.  
12.7.1.4   Upper or lower design values, whichever are more adverse, shall be used for the strength or 
resistance of the ground.  
12.7.1.5   Calculation methods may be used, which redistribute earth pressure in accordance with the 
relati ve displacements and stiffnesses of ground and structural elements.  
12.7.1.6   For fine grained soils, both short - and long -term behaviour shall be considered.  
12.7.1.7   For walls subject to differential water pressures, safety against failure due to hydrau lic heave 
and piping shall be checked.  
 Overall stability  
12.7.2.1   The principles in clause 14  shall be used as appropriate to demonstrate that an overall stability 
failure will not occur and that the corresponding deformations are sufficiently small.  
12.7.2.2   As a minimum, limit modes of the types illustrated in figure 9.1 should be considered, taking 
progressive failure and liquefaction into account as relevant.  
12.7.2  Foundation failure of gravity walls  
12.7.3.1   The principles of Section 6 shall be used as a ppropriate to demonstrate that a foundation failure 
is sufficiently remote and that deformations will be acceptable. Both bearing resistance and sliding shall be 
considered.  
12.7.3.2   As a minimum, limit modes of the types illustrated in Figure 9.2 should be considered.  
  
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Figure 9.1 — Examples of limit modes for overall stability of retaining structures.  
 
 
Figure 9.2 — Examples of limit modes for foundation failures of gravity walls  
12.7.3  Rotational failure of embedded walls  
12.7.4.1   It shall be demonstrated by equilibrium calculations that embedded walls have sufficient 
penetr ation into the ground to prevent rotational failure.  
 
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Figure 9.3 — Examples of limit modes for rotational failures of embedded walls  
12.7.4.2   As a minimum, limit modes of the types illustrated in Figure 9.3 should be considered.  
12.7.4.3   The design magnitude and direction of shear stress between the soil and the wall shall be 
consistent with the relative vertical displacement, which would occur in the design situation.  
12.7.4  Vertical fail ure of embedded walls  
12.7.5.1   It shall be demonstrated that vertical equilibrium can be achieved using the design soil strengths 
or resistances and design vertical forces on the wall.  
12.7.5.2   As a minimum, the limit mode of the type illustrated in Figu re 9.4 should be considered.  
12.7.5.3   Where downward movement of the wall is considered, upper design values shall be used in the 
calculation of prestressing forces, such as those from ground anchorages, which have a vertical downward 
component.  
12.7.5.4   The design magnitude and direction of shear stress between the soil and the wall shall be 
consistent with the check for vertical and rotational equilibrium.  
12.7.5.5   If the wall acts as the foundation for a structure, vertical equilibrium shall be checke d using the 
principles of clause 6. 
 
 
 
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Figure 9.4 — Example of a limit mode for vertical failure of embedded walls  
12.7.5  Structural design of retaining structures  
12.7.6.1   Retaining structures, including their supporting structural elements such as anchorages and 
props, shall be verified against structural failure in accordance with 5.4  
12.7. 6.2  As a minimum, limit modes of the types illustrated in Figure 9.5 should be co nsidered.  
 
 
 
 
 
 
 
Figure 9.5 — Examples of limit modes for structural failure of retaining structures  
 
12.7.6.3    For each ultimate limit state, it shall be demonstrated that the required strengths can be 
mobilised, with compatible deformations in the ground and the structure.  
12.7.6.4   In structural elements, reduction in strength with deformation due to effects suc h as cracking of 
unreinforced sections, large rotations at plastic hinges or local buckling of steel sections should be 
considered.  
DRS 113: 2020  
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 12.7.6   Failure by pull -out of anchorages  
12.7.7.1   It shall be demonstrated that equilibrium can be achieved without pull -out fail ure of ground 
anchorages . 
 
Figure 9.6 — Examples of limit modes for failure by pull -out of anchors.  
12.7.7.1   Anchors shall b e designed in accordance with clause  8. 
12.7.7.2   As a minimum, limit modes of the types illustrated in Figure 9.6 (a, b) should b e considered.  
12.7.7.3   For deadman anchors, the failure mode illustrated in Figure 9.6 (c) should also be considered.  
12.8 Serviceability limit state design  
12.8.1   General  
12.8.1.1   The design of retaining structures shall be checked at the serviceability limit state using the 
appropriate design situations as specified in 12.3.3. 
12.8.1.2   Design values of earth pressures for the serviceability limit state shall be derived using 
chara cteristic values of all soil parameters.  
12.8.1.3   Permanent surcharge loads behind the retaining wall shall be derived using their characteristic 
values.  
12.8.1.4   The assessment of design values of earth pressures should take account of the initial stres s, 
stiffness and strength of the ground and the stiffness of the structural elements.  
 
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 12.8.1.5   The design values of earth pressures should be derived taking account of the allowable 
deformation of the structure at its serviceability limit state. These pre ssures may not necessarily be limiting 
values.  
12.8.2  Displacements  
12.8.2.1   Limiting values for the allowable displacements of walls and the ground adjacent to them shall 
be established in accordance with 5.4.8, taking into account the tolerance to displacement s of supported 
structures and services.  
12.8.2.2   A cautious estimate of the distortion and displacement of retaining walls, and the effects on 
supported structures and services, shall always be made on the basis of comparable experience. This 
estimate sha ll include the effects of construction of the wall. The design may be justified by checking that the 
estimated displacements do not exceed the limiting values.  
12.8.2.3   If the initial cautious estimate of displacement exceeds the limiting values, the design shall be 
justified by a more detailed investigation including displacement calculations.  
12.8.2.4   It shall be considered to what extent variable actions, such as vibrations caused by traffic loads 
behind the retaining wall, contribute to the wall d isplacement.  
12.8.2.5   A more detailed investigation, including displacement calculations, shall be undertaken in the 
following situations:  
a) where nearby structures and services are unusually sensitive to displacement;  
b) where comparable experience is not wel l established.  
12.8.2.6   Displacement calculations should also be considered in the following cases:  
a) where the wall retains more than 6 m of cohesive soil of low plasticity,  
b) where the wall retains more than 3 m of soils of high plasticity;  
c) where the wall i s supported by soft clay within its height or beneath its base.  
12.8.2.7   Displacement calculations shall take account of the stiffness of the ground and structural 
elements and the sequence of construction.  
12.8.2.8   The behaviour of materials assumed in displacement calculations should be calibrated by 
comparable experience with the same calculation model. If linear behaviour is assumed, the stiffnesses 
adopted for the ground and structural materials should be appropriate for the degree of deformation 
computed. Alternatively, complete stress -strain models of the materials  may be adopted.  
12.8.2.9   The effect of vibrations on displacements shal l be considered with regard to 9.6.4. DRS 113: 2020  
111                ©RSB 2020  - All rights reserved  
 13 Hydraulic  failure  
13.1 General  
13.1.1  The provisions of this Section apply to four  modes of ground failure induced by pore -water pressure 
or pore -water seepage, which shall be checked, as relevant:  
a) failure by uplift (buoyancy);  
b) failure by heave;  
c) failure by internal erosion;  
d) failure by piping.  
NOTE1   Buoyancy occurs when pore -water pres sure under a structure or a low permeability ground layer becomes larger 
than the mean overburden pressure (due to the structure and/or the overlying ground layer).  
NOTE 2   Failure by heave occurs when upwards seepage forces act against the weight of the soil, reducing the vertical 
effective stress to zero. Soil particles are then lifted away by the vertical water flow and failure occurs (boiling).  
NOTE 3   Failure by internal erosion is produced by the transport of soil particles within a soil stratum, at  the interface of 
soil strata, or at the interface between the soil and a structure. This may finally result in regressive erosion, leading to 
collapse of the soil structure.  
NOTE 4   Failure by piping is a particular form of failure, for example of a rese rvoir, by internal erosion, where erosion 
begins at the surface, then regresses until a pipe -shaped discharge tunnel is formed in the soil mass or between the soil 
and a foundation or at the interface between cohesive and non -cohesive soil strata. Failure occurs as soon as the 
upstream end of the eroded tunnel reaches the bottom of the reservoir.  
NOTE 5  The conditions for hydraulic failure of the ground can be expressed in terms of total stress and pore -water 
pressure or in terms of effective stresses and hydraulic gradient. Total stress analysis is applied to failure by uplift. For 
failure by heave, both total and effective stresses are applied. Conditions are put on hydraulic gradients in order to contro l 
internal erosion and piping.  
13.1.2  In situations where the pore -water pressure is hydrostatic (negligible hydraulic gradient) it is not 
required to check other than failure by uplift.  
13.1.3  The determination of hydraulic gradients, pore -water pressures or seepage forces shall take account 
of: 
a) the variat ion of soil permeability in time and space;  
b) variations in water levels and pore -water pressure in time;  
c) any modification of the boundary conditions (e.g. downstream excavation).   
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 13.1.4  It should be considered that the relevant soil stratification may be di fferent for different failure 
mechanisms.  
13.1.5  When hydraulic heave, piping or internal erosion are significant dangers to the integrity of a 
geotechnical structure, measures shall be taken to decrease the hydraulic gradient.  
13.1.6  The measures most commonly adopted to reduce erosion or to avoid hydraulic failure are:  
a) lengthening the seepage path by screens or shoulders;  
b) modifications of the project in order to resist the pressures or gradients;  
c) seepage control;  
d) protective filters;  
e) avoidance of disper sive clays without adequate filters;  
f) slope revetments;  
g) inverted filters;  
h) relief wells;  
i) reduction of hydraulic gradient.  
13.2 Failure by uplift  
13.2.1  The stability of a structure or of a low permeability ground layer against uplift shall be checked by 
comparing  the permanent stabilising actions (for example, weight and side friction) to the permanent and 
variable destabilising actions from water and, possibly, other sources.  
Examples of situations where uplift stability shall be checked are given in Figure 7.1 a nd Figure 10.1.  
13.2.2  The design shall be checked against failure by uplift using inequality (2.8) of 5.4.7.4. In this 
inequality, the design value of the vertical component of the stabilising permanent actions ( Gstb;d ) is, for 
example, the weight of the  structure and of ground layers, the design resistance ( Rd) is the sum of, for 
example, any friction forces, ( Td), and any anchor forces, ( P). Resistance to uplift by friction or anchor forces 
may also be treated as a stabilising permanent vertical action (Gstb;d). The design value of the vertical 
component of the destabilising permanent and variable actions, ( Vdst;d ), is the sum of the water pressures 
applied under the structure (permanent and variable parts) and any other upwards forces.  
13.2.3  In simple  cases, the check of equation (2.8) in terms of forces may be replaced by a check in terms 
of total stresses and pore -water pressures.  DRS 113: 2020  
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a) Uplift of a buried hollow structure      b) Uplift of a lightweight embankment during flood          
1 (ground) -water table                             1) (ground) -water table                               
2 water tight surface                                2) Water tight surfac e 
                                                                3) Lightwe ight embankment material  
                                                
            
c) Uplift of the bottom of an excavation                                            d) Execution of a slab below water level  
4 former ground surface          1 (ground) -water table  
 5 sand              2 water t ight surface  
6 clay              5 sand  
7 gravel              6 sand  
8 injected sand  
 
                                                                        
                                                                        
 
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                                                               e) Structure anchored to resist uplift  
    1 (ground) -water table       5 sand  
    9 anchorage  
Figure 10.1 — Examples of situations where uplift might be critical  
13.3 Failure by heave  
13.3.1  The stability of soil against heave shall be checked by verifying either equation (2.9a) or equation 
(2.9b) for every relevant soil column. Equation (2.9a) expresses the condition for stability in terms of pore -
water pressures and total stresses. Equation (2.9b) expresses the same condition in terms of seepage forces 
and submerged weights. An example of situations  where h eave shall be checked is given in Figure 10.2  
13.3.2  The determination of the characteristic value of the pore -water pressure shall take into account all 
possible unfavourable conditions, such as:  
a) thin layers of soil of low permeability;  
b) spatial effects su ch as narrow, circular or rectangular excavations below water level.  
NOTE 1   Where the soil has a significant cohesive shear resistance, the mode of failure changes from failure by heave to 
failure by uplift. The stability is then checked by using the pro visions of 10.2 where additional resisting forces may be 
added to the weight.  
NOTE 2   Stability against heave will not necessarily prevent internal erosion, which should be checked independently, 
when relevant.  
 DRS 113: 2020  
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1 excavation level (left); water table (right)    3 sand  
2 water       
Figure 10.2 — Example of situation where heave might be critical  
 
13.3.3  The measures most commonly adopted to resist failure by heave are:  
a) decreasing the water pressure below the soil mass subjected to heave;  
b) increasing the resisting weight.  
13.4   Internal erosion  
13.4.1  Filter criteria shall be used to limit the danger of material transport by internal erosion.  
 13.4.2  Where an ultimate limit state due to internal erosion can occur, measures such as filter protection 
shall be applied at the free surface of the ground.  
13.4.3 Filter protection should generally be provided by use of natural non -cohesive soil that fulfils adequate 
design criteria for filter ma terials. In some cases, more than one filter layer may be necessary to ensure that 
the particle size distribution changes in a stepwise fashion to obtain sufficient protection both for the soil and 
the filter layers.  
13.4.4 Alternatively, artificial filter  sheets such as geotextiles may be used provided it can be established 
that they sufficiently prevent transport of fines.  
 
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 13.4.5 If the filter criteria are not satisfied, it shall be verified that the critical hydraulic gradient is well below 
the design va lue of the gradient at which soil particles begin to move.  
13.4.6 The critical hydraulic gradient for internal erosion shall be established taking into consideration at 
least the following aspects:  
a) direction of flow;  
b) grain size distribution and shape of grains;  
c) stratification of the soil.  
13.5 Failure by piping  
13.5.1  Where prevailing hydraulic and soil conditions can lead to the occurrence of piping (see figure 10.3), 
and where piping endangers the stability or serviceability of the hydraulic structure, presc riptive measures 
shall be taken to prevent the onset of the piping process, either by the application of filters or by taking 
structural measures to control or to block the ground -water flow.  
 
1 free water table       2 piezometric level in the permeable s ubsoil  
3 low permeability soil      4 permeable subsoil  
5 possible well; starting point for pipe   6 possible pipe  
Figure 10.3 — Example of conditions that may cause piping  
NOTE Suitable structural measures are:  
— application of berms on the land side of a retaining embankment, thus displacing the possible starting point of piping 
farther away from the structure and decreasing the hydraulic gradient at  this point;  
— application of impermeable screens below the base of the hydraulic structure by which the  g roundwater flow is either 
blocked or the seepage path is increased, thereby decreasing the  hydraulic gradient to a safe value.  
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 13.5.2  During periods of extremely unfavourable hydraulic conditions such as floods, areas susceptible to 
piping shall be inspec ted regularly so that necessary mitigating measures can be taken without delay. 
Materials for such measures shall be stored in the vicinity.  
13.5.3  Failure by piping shall be prevented by providing sufficient resistance against internal soil erosion in 
the areas where water outflow may occur.  
13.5.4  Such failure can be prevented by providing:  
a) sufficient safety against failure by heave where the ground surface is horizontal;  
b) sufficient stability of the surface layers in sloping ground (local slope stability) . 
13.5.5  local slope stability, account shall be taken of the fact that joints or interfaces between the structure 
and the ground can become preferred seepage paths.  
14 Overall stability  
14.1  General  
14.1.1  The provisions in this Section shall apply to the overal l stability of and movements in the ground, 
whether natural or fill, around foundations, retaining structures, natural slopes, embankments or excavations.  
14.1.2  Account should be taken of overall stability clauses, related to specific structures, in clause  6 to 10 
and 12.  
14.2 Limit states  
14.2.1  All possible limit states for the particular ground shall be considered in order to fulfil the fundamental 
requirements of stability, limited deformations, durability and limitations in movements of nearby structu res or 
services.  
14.2.2  Some possible limit states are listed below:  
a) loss of overall stability of the ground and associated structures;  
b) excessive movements in the ground due to shear deformations, settlement, vibration or heave;  
c) damage or loss of serviceab ility in neighbouring structures, roads or services due to movements in the 
ground.  
14.3 Actions and design situations  
14.3.1  The list in 5.4.2 should be taken into account when selecting the actions for calculation of limit states.  
  
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 14.3.2  The effects of the f ollowing circumstances shall be taken into account, as appropriate:  
a) construction processes;  
b) new slopes or structures on or near the particular site;  
c) previous or continuing ground movements from different sources;  
d) vibrations;  
e) climatic variations, including temperature change (freezing and thawing), drought and heavy rain;  
f) vegetation or its removal;  
g) human or animal activities;  
h) variations in water content or pore -water pressure;  
i) wave action.  
14.3.3  In ultimate limit states, design free water and ground -water l evels, or their combination, shall be 
selected from available hydrological data and in situ observations to give the most unfavourable conditions 
that could occur in the design situation being considered. The possibility of failure of drains, filters or se als 
shall be considered.  
14.3.4  The possibility of emptying a canal or water reservoir for maintenance, or due to dam failure, should 
also be considered. For serviceability limit states, less severe, more typical water level or pore -water pressure 
may be u sed. 
14.3.5  For slopes along waterfronts, the most unfavourable hydraulic conditions are normally steady 
seepage for the highest possible ground -water level and rapid draw -down of the free water level.  
14.3.6  In deriving design distributions of pore -water pressure, account shall be taken of the possible range 
of permeability anisotropy and variability of the ground.  
14.4 Design and construction considerations  
14.4.1  The overall stability of a site and movements of natural or made ground shall be checked taking into 
account comparable experience, according to 3.5 . 
14.4.2  The overall stability and movement of ground supporting existing buildings, new structures, slopes or 
excavations shall be considered.  
14.4.3  In cases where the stability of the ground cannot be clearly verified prior to design, additional 
investigations, monitoring and analysis should be specified according to the provisions of 14.7. 
14.4.4  Typical str uctures for which an analysis of overall stability should be performed are:  DRS 113: 2020  
119                ©RSB 2020  - All rights reserved  
 a) ground retaining structures;  
b) excavations, slopes or embankments;  
c) foundations on sloping ground, natural slopes or embankments;  
d) foundations near an excavation, cut or buried structu res, or shore.  
NOTE Stability problems or creep movements occur primarily in cohesive soils with a sloping ground surface. However, 
instability can also occur in non -cohesive soils and fissured rocks in slopes where the inclination, which may be 
determined  by erosion, is close to the angle of shearing resistance. Increased  movements are often observed at elevated 
pore-water pressures or close to the ground surface during freezing and thawing cycles.  
14.4.4  If the stability of a site cannot readily be verified or the movements are found to be not acceptable for 
the site's intended use, the site shall be judged to be unsuitable without stabilising measures.  
14.4.5  The design shall ensure that all construction activities in and on the site can be planned and 
executed such that the occurrence of an ultimate or serviceability limit state is sufficiently improbable.  
14.4.6  Slope surfaces exposed to potential erosion shall be protected if required, to ensure that the safety 
level is retained.  
14.4.7  Slopes sho uld be sealed, planted or protected artificially. For slopes with berms, a drainage system 
within the berm should be considered.  
14.4.8  Construction processes shall be taken into account as far as they might affect the overall stability or 
the magnitude of  movement.  
14.4.9  Potentially unstable slopes may be stabilised by:  
a) a concrete cover with or without anchorage;  
b) an abutment of gabions, either of steel net or geotextile cages;  
c) ground nailing;  
d) vegetation;  
e) a drainage system;  
f) a combination of the above.  
14.4.10 The design should follow the general principles of  clause 11 and 12 .  
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 14.5 Ultimate limit state design  
14.5.1  Stability analysis for slopes  
14.5.1 .1 The overall stability of slopes including existing, affected or planned structures shall be verified in 
ultimate limit states (GEO and STR) with design values of actions, resistances and strengths, where the 
partial factors defined in A.3.1(1)P, A.3.2(1)P and A.3.3.6(1)P shall be used.  
NOTE  The values of the partial factors may be set by the National annex. The recom mended values for 
persistent and transient situations are given in Tables A.3, A.4 and A.14.  
14.5. 1.2 In analysing the overall stability of the ground, of soil or rock, all relevant modes of failure shall be 
taken into account.  
14.5. 1.3 When choosing a cal culation method, the following should be considered:  
a) soil layering;  
b) occurrence and inclination of discontinuities;  
c) seepage and pore -water pressure distribution;  
d) short - and long -term stability;  
e) creep deformations due to shear;  
f) type of failure (circular or n on-circular surface; toppling; flow);  
g) use of numerical methods.  
14.5. 1.4 The mass of soil or rock bounded by the failure surface should normally be treated as a rigid body or 
as several rigid bodies moving simultaneously. Failure surfaces or interfaces bet ween rigid bodies may have a 
variety of shapes including planar, circular and more complicated shapes. Alternatively, stability may be 
checked by limit analysis or using the finite element method.  
14.5. 1.5 Where ground or embankment material is relatively homogeneous and isotropic, circular failure 
surfaces should normally be assumed.  
14.5. 1.6 For slopes in layered soils with considerable variations of shear strength, special attention should be 
paid to the layers with lower shear strength. This may require  analysis of noncircular failure surfaces.  
14.5. 1.7 In jointed materials, including hard rock and layered or fissured soils, the shape of the failure surface 
can partly or fully be governed by discontinuities. In this case analysis of three  dimensional wed ges should 
normally be made.  
14.5. 1.8 Existing failed slopes, which can potentially be reactivated should be analysed, considering circular, 
as well as non -circular failure surfaces. Partial factors normally used for overall stability analyses then need 
not be appropriate.  DRS 113: 2020  
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 14.5. 1.9 If the failure surface cannot be assumed to be two -dimensional, the use of threedimensional failure 
surfaces should be considered.  
14.5. 1.10 A slope analysis should verify the overall moment and vertical stability of the slidingm ass. If 
horizontal equilibrium is not checked, inter -slice forces should be assumed to be horizontal.  
14.5. 1.11 In cases where a combined failure of structural members and the ground could occur, ground -
structure interaction shall be considered by allowing  for the difference in their relative stiffnesses. Such cases 
include failure surfaces intersecting structural members such as piles and flexible walls.  
NOTE  In analysing natural slopes, it is generally an advantage to make a first calculation using charac teristic values, 
to get an idea of the global factor of safety, before starting a design. Experiences with comparable cases including 
investigation procedures should be applied.  
14.5. 1.12 Since a distinction between favourable and unfavourable gravity load s is not possible in 
assessing the most adverse slip surface, any uncertainty about weight density of the ground should be 
considered by applying upper and lower characteristic values of it.  
14.5. 1.13 The design shall show that the deformation of the groun d under design actions due to creep or 
regional settlements will not cause unacceptable damage to structures or infrastructure sited on, in or near the 
particular ground.  
14.5.2   Slopes and cuts in rock masses  
14.5.2 .1  The stability of slopes and cuts in rock ma sses shall be checked against translational and 
rotational modes of failure involving isolated rock blocks or large portions of the rock mass, and also against 
rock falls. Particular attention shall be given to the pressure caused by blocked seepage water in joints and 
fissures.  
14.5.2.2   Stability analyses shall be based on reliable knowledge of the pattern of discontinuities 
intersecting the rock mass and of the shear strength of the intact rock and of the discontinuities.  
14.5.2.3   Account should be take n of the fact that failure of slopes and cuts in hard rock masses, with a 
well defined pattern of discontinuities, will generally involve:  
a) sliding of blocks or rock wedges;  
b) toppling of blocks or slabs;  
c) a combination of toppling and sliding;  depending on the orientation of the slope face in relation to that 
of the discontinuities.  
14.5.2.4    rocks and cemented soils may develop along circular or almost circular slip surfaces passing 
through portions of intact rock.  
14.5.2.5   Sliding of isolated blocks and wedges should usually be prevented by reducing the inclination of 
the slope by providing berms, and installing anchors, bolts and internal drainage.   
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 14.5.2.6   cutting slopes, sliding should be prevented by selecting the direction and orientation of the slo pe 
face so that movements of isolated blocks are kinematically impossible.  
14.5.2.7  To prevent toppling failures, anchoring or bolting and internal drainage should normally be applied.  
14.5.2.8   and environmental or polluting agents on the shear strength o f discontinuities and on the 
strength of the intact rock should be taken into account.  
14.5.2.9   In highly fractured rock masses in steep slopes and slopes susceptible to toppling, spalling, 
ravelling and slumping, the possibility of rock falls should alwa ys be analysed.  
14.5.2.10  In cases where reliable provisions to prevent rock falls are not feasible, rock falls should be 
allowed to occur with the provision of nets, barriers or other suitable provision to trap the falling rock.  
14.5.2.11  The design of pr ovisions to trap rock blocks and debris falling down a rock slope should be 
based on a thorough investigation of the possible trajectories of the falling material.  
14.5.3  Stability of excavations  
14.5.3.1  The overall stability of the ground close to an excavation , including excavation spoil and existing 
structures, roads and services shall be checked (see Section / clause  9). 
14.5.3.2  The stability of the bottom of an excavation shall be checked in relation to the design pore -water 
pressure in the ground. For the a nalysis of hydraulic failure (see Section / clause 10). 
14.5.3.3  Heave of the bottom of deep excavations due to unloading shall be considered.  
14.6 Serviceability limit state design  
14.6.1  The design shall show that the deformation of the ground will not cause a  serviceability limit state in 
structures and infrastructure on or near the particular ground.  
14.6.2  Subsidence of the ground due to the following causes should be considered:  
a) change in ground -water conditions and corresponding pore -water pressures;  
b) long-term creep under drained conditions;  
c) volume loss of deep soluble strata;  
d) mining or similar works such as gas extraction.  
14.6.3  Since the analytical and numerical methods available at present do not usually provide reliable 
predictions of the deformation of a natural slope, the occurrence of serviceability limit states should be 
avoided by one of the following:  
a) limiting the mobilised shear strength;  DRS 113: 2020  
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 b) observing the movements and specifying actions to reduce or stop them, if necessary.  
14.7 Monitoring  
14.7.1  The ground shall be monitored using appropriate equipment if:  
a) it is not possible to prove by calculation or by prescriptive measures that the occurrence of the limit 
states given in 14.2 is sufficiently unlikely;  
b) the assumptions made in the calculations are no t based on reliable data.  
14.7.2  Monitoring should be planned to provide knowledge of:  
a) ground -water levels or pore -water pressures in the ground, so that effective stress analyses can be 
carried out or checked;  
b) lateral and vertical ground movements, in ord er to predict further deformations;  
c) the depth and shape of the moving surface in a developed slide, in order to derive the ground strength 
parameters for the design of remedial works;  
d) rates of movement, in order to give warning of impending danger; in such  cases a remote digital 
readout for the instruments or a remote alarm system may be  appropriate.  
15 Embankments  
15.1 General  
15.1.1  The provisions of this Section shall apply to embankments for small dams and for infrastructure.  
15.1.2  For placement and compactio n of fill the provisions in Section 5 should be applied.  
15.2 Limit states  
15.2.1  A list shall be compiled of limit states to be checked in the design of the embankment.  
15.2.2  The following limit states should be checked:  
a) loss of overall site stability;  
b) failur e in the embankment slope or crest;  
c) failure caused by internal erosion;  
d) failure caused by surface erosion or scour;   
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 e) deformations in the embankment leading to loss of serviceability, e.g. excessive settlements or 
cracks;  
f) settlements and creep displacements leading to damages or loss of serviceability in nearby structures 
or utilities;  
g) excessive deformations in transition zones, e.g. the access embankment of a bridge abutment;  
h) loss of serviceability of traffic areas by climatic influences such as freezing and  thawing or extreme 
drying;  
i) creep in slopes during the freezing and thawing period;  
j) degradation of base course material due to high traffic loads;  
k) deformations caused by hydraulic actions;  
l) changes of environmental conditions such as pollution of surface or  ground -water, noise or vibrations.  
15.3 Actions and design situations  
15.3.1  In selecting the actions for the calculation of limit states, the list in  5.4.2 should be considered.  
15.3.2  When deriving the actions that embankments impose on adjacent structures o r any reinforced parts 
of the ground, the differences in the stiffnesses should be considered.  
15.3.3  Design situations shall be selected in accordance with 5.2. 
15.3.4  In addition, the following special design situations shall be taken into account, if re levant:  
a) the effects of the construction process, such as excavations close to the embankment fill and 
vibrations caused by blasting, pile driving or heavy equipment;  
b) the effects of structures planned to be constructed on or close to the embankment;  
c) the ero sion effects of overtopping, ice, waves and rain on the slopes and crest;  
d) temperature effects such as shrinkage.  
15.3.5  The design free water level on the downstream embankment slope and the design ground -water 
level, or their combination, shall be based o n available hydrological data to give the most unfavourable 
conditions that could occur in the design situation considered. The possibility of failure of drains, filters or 
seals shall be considered.  
15.3.6  For shore embankments, the most unfavourable hydr aulic conditions should be considered.  These 
are normally steady seepage for the highest possible ground -water level and rapid draw -down of the free 
water level.  DRS 113: 2020  
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 15.3.7  In deriving design distributions of pore -water pressure, account shall be taken of the possible range 
of anisotropy and heterogeneity of the soil.  
15.3.8  When designing the embankment with respect to settlement, the effective stress decrease in the 
ground, due to submergence of the dry crust or the fill, shall be taken into account.  
15.4 Design a nd construction considerations  
15.4.1  Embankments shall be designed taking into account experience with embankments on similar 
ground and made of similar fill material.  
15.4.2  When assessing the foundation level for an embankment, the following shall be co nsidered, when 
applicable:  
a) reaching an adequate bearing stratum, or applying stabilising measures where this is not practicable;  
b) providing sufficient protection against adverse climatic effects on the bearing capacity of the ground;  
c) the ground -water level with respect to the drainage of the embankment;  
d) avoiding adverse effects on adjacent structures and utilities;  
e) reaching layers with adequately low permeability.  
15.4.3  Design of embankments should ensure that:  
a) the bearing capacity of the subsoil is satisfactory;  
b) the drainage of the various fill layers is satisfactory;  
c) the permeability of the fill material in dams is as low as required;  
d) filters or geosynthetics are specified where necessary to fulfil filter criteria;  
e) the fill material is specified acc ording to the criteria in 10.3.2. 
15.4.4  For embankments on ground with low strength and high compressibility, the construction process 
shall be specified so as to ensure that the bearing capacity is not exceeded and that excessive settlements or 
movements  do not occur during construction ( see 8.3.3. 
15.4.5  When an embankment on compressible ground is raised in layers, piezometer measurements should 
be specified to ensure that pore -water pressures have dissipated to acceptably low values before the next fil l 
layer is placed.  
15.4.6  For embankments retaining water at different levels, the foundation level shall be chosen with 
respect to the permeability of the ground or measures shall be taken to make the structure watertight.   
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 15.4.7  If ground improvement is specified, the volume of ground to be improved should be designed with 
sufficient areal extent to avoid harmful deformations.  
15.4.8  When determining the weight of the embankment f rom the weight density of fill care should be taken 
to include fill particle s of size > 20 mm to 60 mm in the density tests.  They are often not included but can have 
a considerable effect on the weight density.  
15.4.9  Embankment slope surfaces exposed to erosion shall be protected. If berms are designed, a 
drainage facility shall be specified for the berm.  
15.4.10  The slopes should be sealed during embankment construction and planted thereafter, where 
appropriate.  
15.4.11  For embankments carrying traffic, icing on the surface of the pavement should be avoided . The 
thermal capacity of a pavement on an insulation layer or a lightweight fill may be high enough to avoid this.  
15.4.12  Frost penetration on the crest of an earth dam should be restricted to an appropriate level.  
15.4.13  Design of the embankment slope should consider that cr eep movements may occur in slopes during 
freezing and thawing irrespective of the slope stability under dry conditions. This is especially important in 
transition zones, e.g. at bridge abutments.  
15.5 Ultimate limit state design  
15.5.1  In analysing the stabilit y of part or all of an embankment, all possible failure modes shall be 
considered, as stated in clause 14 . 
15.5.2  analysis should be done phase by phase and provisions specified accordingly in the Geotechnical 
Design Report.  
15.5.3  Where lightweight fill m aterials such as expanded polystyrene, expanded clay or foamed concrete 
are used, the possibility of buoyancy effects shall be considered (  clause 13 ). 
15.5.4  Any analysis of embankments containing different fill materials shall adopt strength values that have 
been determined at compatible strains in the materials.  
15.5.5  Where roads or watercourses cross an embankment, special attention should be paid to the spatial 
interaction of the various structural elements.  
15.5.6  When analysing the stability of impr oved ground, the effect of the improving process, e.g. the 
disturbance of soft sensitive clay, should be considered. As the effect of the improvement is time -dependent, it 
should not be taken into account until a steady state has been reached.  
15.5.7  To av oid ultimate limit states caused by surface erosion, internal erosion or hydraulic pressure, the 
provisions in clause  10 and 11 shall be fulfilled.  DRS 113: 2020  
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 15.6 Serviceability limit state design  
15.6.1  The design shall show that the deformation of the embankment will not cause a serviceability limit 
state in the embankment or in structures, roads or services sited on, in or near the embankment.  
15.6.2  The settlement of an embankment on compressible ground should be calculated using the principles 
of 9.6.1. Special atte ntion should be paid to the time dependency of the settlements due to both consolidation 
and secondary effects.  
15.6.3  The possibility of deformations due to changes in the ground -water conditions should be taken into 
account.  
15.6.4  In cases where the def ormations are difficult to predict, the methods of pre -loading or trial 
embankments should be considered, especially in cases where serviceability limit states shall be prevented.  
15.7 Supervision and monitoring  
15.7.1  Supervision and monitoring of embankments shall follow the provisions in clause  4. 
15.7.2  Monitoring should be applied to embankments in one or more of the following situations:  
a) when using the observational method ( see 5.7); 
b) where the stability of an embankment acting as a dam to a large degree de pends on the pore -water 
pressure distribution in and beneath the embankment;  
c) where records of pollution effects of fill or traffic are required;  
d) where control of adverse effects on structures or utilities is required;  
e) where surface erosion is a considerabl e risk.  
15.7.3  In cases where a supervision and monitoring programme is required, the designer shall present it in 
the Geot echnical Design Report (see 5.7) . It shall be specified that the monitoring records are to be evaluated 
and acted upon as necessary.  
15.7.4  A monitoring programme for an embankment should contain the following records:  
a) pore-water pressure measurements in and beneath the embankment;  
b) settlement measurements for the whole or parts of the embankment and influenced structures;  
c) measurements o f horizontal displacements;  
d) checks on strength parameters of fill material during construction;   
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 e) chemical analyses before, during and after construction, if pollution control is required;  
f) observations of erosion protection;  
g) checks on permeability of fill ma terial and of foundation soil during construction;  
h) depth of frost penetration in the crest of an embankment.  
15.7.5  The construction of embankments on soft soil with low permeability should be monitored and 
controlled by means of pore -water pressure measur ements in the soft layers and settlement measurements of 
the fill.  DRS 113: 2020  
129                ©RSB 2020  - All rights reserved  
 Annex  A 
(normative)  
 
Partial and correlation factors for ultimate limit states and recommended 
values  
A.1 Partial factors and correlations factors  
A.1.1  The partial factors  for ultimate limit states in persistent and transient design situations, and the 
correlation factors  for pile foundations in all design situations, shall be those mentioned in this annex.  
A.2 Partial factors for equilibrium limit state (EQU) verification  
A.2.1 For the verification of equilibrium limit sate (EQU) the following partial factors on actions F shall be 
applied:  
— G;dst on destabilising unfavourable permanent actions;  
— G;stb on stabilising favourable permanent actions;  
— Q;dst on destabilising  unfavourable variable actions;  
— Q;stb on stabilising favourable variable actions.  
Table A.1 − Partial factors on actions ( F) 
Action  Symbol  Value  
Permanent 
Unfavorablea 
Favourable b G;dst 
G; stb 1.1,  
0.9 
Variable   
Unfavorablea 
Favourable b Q;dst 
Q; stb 1.5  
0 
        a         Destabilising  
        b         Stabilising  
 
A.2.2  For the verification of equilibrium limit state (EQU) the following partial factors on soil 
parameters M shall be applied, when including minor shearing resistances:  
— φ’ on the tangent of the angle of shearing resistance;   
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 — c’ on effective cohesion;  
— cu on undrained shear strength;  
— qu on unconfined strength;  
— r  on weight density.  
Table A.2 − Partial factors for soil parameters ( M) 
Soil parameter  Symbol  Value  
Angle of shearing resistance a  φ’ 1.25 
Effective cohesion   c’ 1.25 
Undrained shear strength  cu 1.4 
unconfined strength  qu 1.4 
Weight density  r 1 
               a   This factor is applied to tan  φ 
 
A.3 Partial factors for structural (STR) and geotechnical (GEO) limit states 
verification  
A.3.1  Partial factors on actions ( F) or the effects of actions ( E) 
A.3.1.1   For the verification of structural (STR) and geotechnical (GEO) limit states set A1 or set A2 of the 
following partial factors on actions ( F) or the effects of actions ( E) shall be applied:  
— G on permanent unfavourable or favourable actions;  
— Q on variable unfavourable or favourable actions.  
Table A.3 − Partial factors on actions ( F) or the effects of actions ( E) 
Action  Symbol  Set 
A1 A2 
Permanent  unfavourable  
G 1.35 1 
Favourable  1 1 
Variable  Unfavourable  
Q 1.5 1.3 
Favourable  0 0 DRS 113: 2020  
131                ©RSB 2020  - All rights reserved  
  
A.4 Partial factors for soil parameters ( M) 
For the verification of structural (STR) and geotechnical (GEO) limit states set M1 or set M2 of the following 
partial factors on soil parameters( M) shall be applied:  
— φ’ on the tangent of the angle of shearing resistance;  
—c’ on effective cohesion;  
— cu on undrained shear strength;  
— qu on unconfined strength;  
—  on weight density.  
Table A.4 − Partial factors for soil parameters( M) 
Soil parameter  Symbol  Set 
M1 M2 
Angle of shearing resistance a  φ’ 1,0 1,25 
Effective cohesion  c’ 1,0 1,25 
Undrained shear strength  cu 1,0 1,4 
unconfined strength  qu 1,0 1,4 
Weight density  y 1,0 1,0 
                  a  This factor is applied to tan φ 
 
A.5 Partial  resistance factors ( R) 
A.5.1  Partial resistance  factors for spread foundations  
A.5.1.1  For spread foundations and verifications of structural (STR) and geotechnical (GEO) limit states, set 
R1, R2 or R3 of the following partial factors on resistance ( R) shall be applied:  
— R;v on bearing resistance;  
— R;h on sliding resistance.  
NOTE The values to be ascribed to R;v, and R;h  for the three sets R1, R2 and R3 are given in Table A.5.   
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 Table A.5 − Partial resistance factors ( R) for spread foundations  - Resistance Symbol Set  
 
A.5.2  Partial resistance factors for pile foundations  
For pile foundations and verifications of structural (STR) and geotechnical (GEO) limit states, set R1, R2, R3 
or R4 of the fol lowing partial factors on resistance ( R) shall be applied :  
— b on base resistance;  
— s on shaft resistance for piles in compression;  
— t on total/combined resistance for piles in compression;  
— s;t on shaft resistance for piles in tension.  
Table A.6 − Partial resistance factors ( R) for driven piles  - Resistance Symbol Set  
 
 
 
DRS 113: 2020  
133                ©RSB 2020  - All rights reserved  
 Table A.7 − Partial resistance factors ( R) for bored piles  - Resistance Symbol  Set 
 
Table A.8 − Partial resistance factors ( R) for continuous flight auger (CFA) piles Resistance Symbol 
Set 
 
A.5.2.1  Correlation factors for pile foundations  
For verifications of structural (STR) and geotechnical (GEO) limit states, the following correlation factors  
shall be applied to derive the characteristic resistance of axially loaded piles:  
— 1 on the mean values of the measured resistances in static load tests;  
— 2 on the minimum value of the measured resistances in static load tests;  
— 3 on the mean values of the calculated resistances from ground test results;  
— 4 on the minimum value of the calculated resistances from ground test  results;  
— 5 on the mean values of the measured resistances in dynamic load tests;  
— 6 on the minimum val ue of the measured resistances in dynamic load tests.  
 
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Table A.9 − Correlation factors  to derive characteristic values from static pile load tests ( n - number 
of tested piles)  
 
Table A.10 − Correlation factors  to derive characteristic values from grou nd  test results ( n - the 
number of profiles of tests)  
 
Table A.11 − Correlation factors  to derive characteristic values from dynamic impact tests a, b, c, d, e, (n 
- number of tested piles)  
 
DRS 113: 2020  
135                ©RSB 2020  - All rights reserved  
 A.5.2.2  Partial resistance factors for pre -stressed anchorages  
For pre -stressed anchorages and verifications of structural (STR) and geotechnical (GEO) limit states, set R1, 
R2, R3 or R4 of the following partial factors on resistance (R) shall be applied:  
— a;t on temporary anchorages;  
— a;p on permanent anchorages.  
Table A.12 − Partial resistance factors ( R) for pre -stressed anchorages  - Resistance Symbol Set  
 
A.5.2.3  Partial resistance factors ( R) for retaining structures  
For retaining structure and verifications of structural (STR) and geotechnical (GEO) limit states, set R1, R2 or 
R3 of the following partial factors on resistance ( R) shall be applied :  
— R;v on bearing capacity;  
— R;h on sliding resistance;  
— R;e on earth resistance.  
NOTE  The recommended values for the three sets R1, R2 and R3 are given in  Table A.13 . 
 
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 Table A.13 − Partial resistance factors ( R) for retaining structures  - Resistance Symbol Set  
 
A.5.2.4  Partial resistance factors ( R) for slopes and over all stability  
For slopes and overall stability and verifications of structural (STR) and geotechnical (GEO) limit states a 
partial factor on ground resistance ( R;e) shall be applied.  
NOTE The recommended value for the three sets R1, R2 and R3 is given in Table A.14.  
Table A.14 - Partial resistance factors ( R) for slopes and overall stability  - Resistance Symbol Set  
 
A.6 Partial factors for uplift limit state (UPL) verifications  
A.6.1  For the verification of uplift limit state (UPL) the following partial fact ors on actions ( F) shall be 
applied:  
— G;dst on destabilising unfavourable permanent actions;  
— G;stb on stabilising favourable permanent actions;  
— Q;dst on destabilising  unfavourable variable actions.  
NOTE The recommended values are given in Table A.15.  
DRS 113: 2020  
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 Table A.15 − Partial factors on actions ( F) - Action Symbol Value  
 
 
 
A.6.2  For the verification of uplift limit state (UPL) the following partial factors shall be applied when 
including resistances:  
— φ  on the tangent of the angle of shearing res istance;  
—  c’ on effective cohesion;  
—  cu on undrained shear strength;  
— s;t on tensile pile resistance;  
— a on anchorage resistance.  
NOTE. The recommended values are given in Table A.16.  
 
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 Table A.16 − Partial factors for soil parameters and resistances  - Soil parameter Symbol Value  
 
A.7 Partial factors for hydraulic heave limit state (HYD) verification  
For the verification of hydraulic heave limit state (HYD) the following partial factors on actions ( F) shall be 
applied:  
— G;dst on destabilisi ng unfavourable permanent actions;  
— G;stb on stabilising favourable permanent actions;  
— Q;dst on destabilising unfavourable variable actions.  
NOTE The recommended values are given in Table A.17.  
DRS 113: 2020  
139                ©RSB 2020  - All rights reserved  
 Table A.17 − Partial factors on actions ( F) - Action Sym bol Value  
 
 
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 Bibliography  
[1]  BS EN 1991 -4 Eurocode 1 Actions on structures - Part 4 Actions in silos and tanks  
[2] BS EN 1992 Eurocode 2 Design of concrete structures  
[3] BS EN 1993 Eurocode 3 Design of steel structures  
[4] BS EN 1994 Eurocode 4 Design of composite steel  and concrete structures  
[5] BS EN 1995 Eurocode 5 Design of timber structures  
[6] BS EN 1996 Eurocode 6 Design of masonry structures  
[7] BS EN 1998 Eurocode 8 Design of structures for earth quake resistance  
[8] BS EN 1536:1999 Execution of special geotechnical work: Bore d piles  
 
 DRS 113: 2020  
 
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