COMBI-GYRO WALL SYSTEM- High Modulus Steel Combined Wall Ver. Tube / Hat Wall Vol.1 Design

Table of Contents
Chapter 1

Introduction ············································································································· 1

Chapter2

Wall Configuration ···································································································· 1

Chapter3

Wall Properties ········································································································· 2
3-1 Combined Elastic Section Modulus ···································································· 2
3-2 Combined Moment of Inertia ············································································· 2
3-3 Denomination of the Combi-Gyro Wall System ·················································· 2
3-4 Properties of Combi-Gyro Wall ··········································································· 3

Chapter4

Retaining Wall Design ······························································································· 4
4-1 General ··············································································································· 4
4-2 Embedded Depth of Combi-Gyro Wall ······························································· 5
4-3 Passive Mobilisation Mechanism ······································································· 8
4-4 Durability ·········································································································· 14

Chapter5

Design Case Study ·································································································· 17
5-1 Introduction ····································································································· 17
5-2 List of Design Standards and References ·························································· 18
5-3 Ground Conditions ··························································································· 19
5-4 Design Approach ······························································································ 21
5-5 Design Assumptions ························································································· 23
5-6 Assumed Construction Sequence ····································································· 26
5-7 Results ·············································································································· 27
5-8 Summary ·········································································································· 32

Chapter 1

Introduction

The purpose of this document is to provide model practice guidelines for the design of the
Combi-Gyro Wall to be installed by using the Press-in Piling Method.
The press-in piling method is commonly used worldwide because of its very quiet operation, ultra
low vibration, and flexibility of sizes to suit different wall properties and subsoil conditions.
The main attributes of the Combi-Gyro Wall are efficiency of physical wall properties andreusability. The Combi-Gyro Wall comprises steel tubular piles as the primary elements and steel
sheet piles as the secondary elements. The efficiencies of physical wall properties can be optimisedin view of the flexibility of pile size and the spacing of tubular piles for the ground conditions andthe form of the loading.

Chapter 2

Wall Configuration

Combi-Gyro Wall System is a combined wall with great bending stiffness, which incorporates thefollowing elements and acts as a "built-up beam structure".
1. Steel Tubular Piles: Primary elements (High modulus main structural elements)
Tubular piles resist lateral load when used as a retaining wall or cofferdam, and verticalloads when used as bearing piles.
2. Steel Sheet Piles: Intermediate elements (Soil-retaining and load-transferring elements)
Sheet piles transfer soil and hydrostatic pressure to the tubular piles.

TUBE/HAT WALL SYSTEMS
Hat Sheet Piles(Intermediate Elements)

Welding
Connection
PlatesTubular Piles(Primary Elements)

Figure 1. Wall Configuration

1

Chapter 3

Wall Properties

The primary piles of the Combi-Gyro Wall System are installed to a depth necessary to achieve therequired passive toe resistance while steel sheet piles can be supplied in shorter lengths to act
simply as a barrier for the soil or groundwater. These shorter sheets result in an overall reductionin piles required as well as less installation time.
After primary piles and intermediate piles are installed, they are jointed together with welding
connections to achieve effective horizontal load transfer.
The combination of the primary piles and intermediate piles acts as "a built-up beam structure"and combined wall profiles can be calculated as follows:-

3-1 Combined Elastic Section Modulus
Zsys = Zstp + Zssp
Zsys ： Elastic Section Modulus of System
Zstp ： Elastic Section Modulus of Steel Tubular Piles
Zssp ： Elastic Section Modulus of Steel Sheet Piles

3-2 Combined Moment of Inertia
Isys = Istp + Issp
Isys ： Moment of Inertia of System
Istp ： Moment of Inertia of Steel Tubular Piles
Issp ： Moment of Inertia of Steel Sheet Piles

3-3 Denomination of the Combi-Gyro Wall System
D1000 -

OutsideDiameter ofTubular Piles

18 / 25H

Thickness ofTubular Piles

2

Type of Hat
Sheet Piles3-4 Properties of Combi-Gyro Wall
3-4-1 Tube/Hat Wall
Steel Tubular Piles

Hat Sheet Piles
Momentof Inertia
I (cm4)

Momentof Inertia
I(cm4/m)Mass
per m2of wall(kg/m2)

SectionModulusZ(cm3/m)Momentof Inertia
I(cm4/m)System Total
Mass
per m2of wall(kg/m2)

SectionModulusZ(cm3/m)Momentof Inertia
I(cm4/m)Mass
per m2of wall(kg/m2)Type of System

OutsideDiameter(mm)

Wallthickness(mm)

InsideDiameter(mm)

Spacing(mm)

SectionModulus
Z (cm3)

SectionModulusZ(cm3/m)

D800-10/10H

800

10

780

1800

4841

2690

193647107582

108.2

902

10500

96.0

3592

118082204.2

D800-10/25H

800

10

780

1800

4841

2690

193647107582

108.2

1610

24400

126.0

4300

131982234.2

D800-10/45H

800

10

780

1800

4841

2690

193647107582

108.2

2450

45000

163.0

5140

152582271.2

D800-10/50H

800

10

780

1800

4841

2690

193647107582

108.2

2760

51100

186.0

5450

158682294.2

D800-12/10H

800

12

776

1800

5766

3203

230632128129

129.6

902

10500

96.0

4105

138629225.6

D800-12/25H

800

12

776

1800

5766

3203

230632128129

129.6

1610

24400

126.0

4813

152529255.6

D800-12/45H

800

12

776

1800

5766

3203

230632128129

129.6

2450

45000

163.0

5653

173129292.6

D800-12/50H

800

12

776

1800

5766

3203

230632128129

129.6

2760

51100

186.0

5963

179229315.6

D800-14/10H

800

14

772

1800

6676

3709

267050148361

150.8

902

10500

96.0

4611

158861246.8

D800-14/25H

800

14

772

1800

6676

3709

267050148361

150.8

1610

24400

126.0

5319

172761276.8

D800-14/45H

800

14

772

1800

6676

3709

267050148361

150.8

2450

45000

163.0

6159

193361313.8

D800-14/50H

800

14

772

1800

6676

3709

267050148361

150.8

2760

51100

186.0

6469

199461336.8

D800-16/10H

800

16

768

1800

7573

4207

302907168282

171.9

902

10500

96.0

5109

178782267.9

D800-16/25H

800

16

768

1800

7573

4207

302907168282

171.9

1610

24400

126.0

5817

192682297.9

D800-16/45H

800

16

768

1800

7573

4207

302907168282

171.9

2450

45000

163.0

6657

213282334.9

D800-16/50H

800

16

768

1800

7573

4207

302907168282

171.9

2760

51100

186.0

6967

219382357.9

D900-12/10H

900

12

876

1800

7334

4074

330034

183352

146.0

902

10500

96.0

4976

193852242.0

D900-12/25H

900

12

876

1800

7334

4074

330034

183352

146.0

1610

24400

126.0

5684

207752272.0

D900-12/45H

900

12

876

1800

7334

4074

330034

183352

146.0

2450

45000

163.0

6524

228352309.0

D900-12/50H

900

12

876

1800

7334

4074

330034

183352

146.0

2760

51100

186.0

6834

234452332.0

D900-14/10H

900

14

872

1800

8499

4722

382470212483

169.9

902

10500

96.0

5624

222983265.9

D900-14/25H

900

14

872

1800

8499

4722

382470212483

169.9

1610

24400

126.0

6332

236883295.9

D900-14/45H

900

14

872

1800

8499

4722

382470212483

169.9

2450

45000

163.0

7172

257483332.9

D900-14/50H

900

14

872

1800

8499

4722

382470212483

169.9

2760

51100

186.0

7482

263583355.9

D900-16/10H

900

16

868

1800

9649

5360

434189241216

193.8

902

10500

96.0

6262

251716289.8

D900-16/25H

900

16

868

1800

9649

5360

434189241216

193.8

1610

24400

126.0

6970

265616319.8

D900-16/45H

900

16

868

1800

9649

5360

434189241216

193.8

2450

45000

163.0

7810

286216356.8

D900-16/50H

900

16

868

1800

9649

5360

434189241216

193.8

2760

51100

186.0

8120

292316379.8

D900-18/10H

900

18

864

1800

10782

5990

485198269554

217.5

902

10500

96.0

6892

280054313.5

D900-18/25H

900

18

864

1800

10782

5990

485198269554

217.5

1610

24400

126.0

7600

293954343.5

D900-18/45H

900

18

864

1800

10782

5990

485198269554

217.5

2450

45000

163.0

8440

314554380.5

D900-18/50H

900

18

864

1800

10782

5990

485198269554

217.5

2760

51100

186.0

8750

320654403.5

D1000-12/10H

1000

12

976

1800

9091

5050

454544252525

162.4

902

10500

96.0

5952

263025258.4

D1000-12/25H

1000

12

976

1800

9091

5050

454544252525

162.4

1610

24400

126.0

6660

276925288.4

D1000-12/45H

1000

12

976

1800

9091

5050

454544252525

162.4

2450

45000

163.0

7500

297525325.4

D1000-12/50H

1000

12

976

1800

9091

5050

454544252525

162.4

2760

51100

186.0

7810

303625348.4

D1000-14/10H

1000

14

972

1800

10542

5857

527116292842

189.1

902

10500

96.0

6759

303342285.1

D1000-14/25H

1000

14

972

1800

10542

5857

527116292842

189.1

1610

24400

126.0

7467

317242315.1

D1000-14/45H

1000

14

972

1800

10542

5857

527116292842

189.1

2450

45000

163.0

8307

337842352.1

D1000-14/50H

1000

14

972

1800

10542

5857

527116292842

189.1

2760

51100

186.0

8617

343942375.1

D1000-16/10H

1000

16

968

1800

11976

6653

598797

332665

215.7

902

10500

96.0

7555

343165311.7

D1000-16/25H

1000

16

968

1800

11976

6653

598797

332665

215.7

1610

24400

126.0

8263

357065341.7

D1000-16/45H

1000

16

968

1800

11976

6653

598797

332665

215.7

2450

45000

163.0

9103

377665378.7

D1000-16/50H

1000

16

968

1800

11976

6653

598797

332665

215.7

2760

51100

186.0

9413

383765401.7

D1000-18/10H

1000

18

964

1800

13392

7440

669596371998

242.2

902

10500

96.0

8342

382498338.2

D1000-18/25H

1000

18

964

1800

13392

7440

669596371998

242.2

1610

24400

126.0

9050

396398368.2

D1000-18/45H

1000

18

964

1800

13392

7440

669596371998

242.2

2450

45000

163.0

9890

416998405.2

D1000-18/50H

1000

18

964

1800

13392

7440

669596371998

242.2

2760

51100

186.0

10200

423098428.2

D1000-20/10H

1000

20

960

1800

14790

8217

739518410844

268.5

902

10500

96.0

9119

421344364.5

D1000-20/25H

1000

20

960

1800

14790

8217

739518410844

268.5

1610

24400

126.0

9827

435244394.5

D1000-20/45H

1000

20

960

1800

14790

8217

739518410844

268.5

2450

45000

163.0

10667

455844431.5

D1000-20/50H

1000

20

960

1800

14790

8217

739518410844

268.5

2760

51100

186.0

10977

461944454.5

D1000-22/10H

1000

22

956

1800

16171

8984

808572449207

294.8

902

10500

96.0

9886

459707390.8

D1000-22/25H

1000

22

956

1800

16171

8984

808572449207

294.8

1610

24400

126.0

10594

473607420.8

D1000-22/45H

1000

22

956

1800

16171

8984

808572449207

294.8

2450

45000

163.0

11434

494207457.8

D1000-22/50H

1000

22

956

1800

16171

8984

808572449207

294.8

2760

51100

186.0

11744

500307480.8

Table1. Tube /Hat Wall Properties3

Chapter 4

Retaining Wall Design

4-1 General
The orientation of the Combi-Gyro Wall is determined depending on the purpose of the wall. For
normal retaining wall purpose, tubular piles are located at the passive side as described in"Orientation Pattern A" below.
In the case of Orientation Pattern A, the depth of the sheet pile wall can be minimised as the sheet
piles lean against the tubular piles. The depth is determined by taking into consideration the risk ofboiling, heaving and slip circle failure.
Orientation Pattern B is opposite to Orientation Pattern A, i.e. sheet piles are at passive side as
described below. Combi-Gyro Wall in Orientation Pattern B can be selected when a smoother wall
surface is required. Also, as the tubular piles are not exposed, structural degradation due tocorrosion can be minimised.
4-1-1 Orientation Pattern A : Tubular Piles at Passive Side

Welding Connection Plates

Figure 2. Orientation Pattern A

4-1-2 Orientation Pattern B : Sheet Piles at Passive Side

Welding Connection Plates

Figure 3. Orientation Pattern B4

4-2 Embedded Depth of Combi-Gyro Wall
Tubular Piles(Primary Elements)

Dpri

Dint

Sheet Piles(Intermediate Elements)

Figure 4. Orientation Pattern A

Sheet Piles(Intermediate Elements)

Dpri

Dint

Tubular Piles(Primary Elements)

Figure 5. Orientation Pattern B

5

4-2-1 Embedded Depth of Tubular Piles Dpri
Tubular piles, as the primary elements of a combined wall, act as the retaining elements against
the earth and water pressures whilst the secondary elements (intermediate sheet piles) only fill
the gap between the primary elements and transmit the loads resulting from earth and waterpressures to the primary elements. Thus, the design of the combined wall can be undertaken as acontinuous retaining wall.
Limit equilibrium methods are commonly used to assess the required embedded depth of tubularpiles. The methods use an approach based on soil and groundwater parameters that tend towards
worst credible values and assume that the full strength of the ground is mobilised uniformly
around the wall so that the wall is at the point of collapse.
Design parameters could govern the embedded depth of the tubular piles are:
•
•
•
•
•
•
•

stratigraphy;
soil unit weight;
soil strength (cu, c', φ');groundwater levels;
surcharge loads;
retained height; andpropped or cantilevered.

64-2-2 Embedded Depth of Sheet Piles Dint
Orientation Pattern A
In theory the intermediate sheet piles are only required from pile head level to the depth where
the net earth pressure becomes zero (see the schematic earth pressure diagram shown in Figure 6).
In practice the design embedded depth Dint is extended below the zero earth pressure level by one
to two metres for safety reasons. Besides, careful consideration should be given to avoid
underflow in the case of high differential water pressure, or where there is a danger of scour.
Orientation Pattern B
The first step is to neglect the presence of the primary tubular piles and to assume all the earth
and water pressures to be resisted by the intermediate sheet piles, thus, the design embedded
depth Dint is equal to Dpri.
Secondary, performance of the complex wall structure system needs to be assessed by thesoil/structure interaction analysis using the finite element (FE) method. By modelling the wall
elements explicitly, e.g. tubular pile, sheet pile and connection plate, structural forces in eachelement and the serviceability, i.e. wall deflection, can be quantified. Based on outcome of the FE
analysis together with assessment of underflow and etc., Dint can be determined.
In addition the driveability and bending capacity of the sheet piles should also be checked.

Net earth pressure

Zero earth pressure level
Active earth pressure
Passive earth pressure

Figure6. Schematic earth pressure diagram7

4-3 Passive Mobilisation Mechanism
Active soil pressure

Effective Passive AreanD
n: Passive Mobilisation Factor

Figure 7. Schematic effective area for passive soil pressure

When the tubular pile is loaded laterally, distribution of the soil stresses can be simulated based on
the Theory of Elasticity using the Boussinesq equation that considers a point load on the surface ofa semi-infinite, homogeneous, isotropic, weightless, elastic half-space. The concept of the pressurebulb prepared from the Boussinesq's equation by Bowles [1996] , as shown in Figure 8, is useful tovisualise the pressure developed in the effective passive area.
Though there is no simple relationship between the characteristics of the effective passive area(nD) and soil conditions as any relationship is dependent on the tubular pile size/spacing and on
the nature and sequence of the strata, "nD" at a certain distance (H) in low strength cohesive soil isgenerally greater than that in dense cohesion less soil.
Bowles, J.E. [1996] Foundation analysis and design - 5th edition, McGraw-Hill, Singapore.

18

Tubular pile diameter, D

Tubular pile contact pressure, q0

Figure 8. Pressure bulbs formed on the passive side of a tubular pile, showing the intensityof pressure q/q0,based on the Boussinesq equation (after Bowles [1996])

The effective passive area (nD) at the distance H and the angle θ can be obtained from theschematic relationship shown in Figure 8 for a given intensity of the pressure, q/q0.
Earth pressure distributions acting on the Combi-Gyro Wall is rather complex as presented in
Figures 9 and 10 for the orientation patterns A and B, respectively.
At the depths above formation level the earth pressure only acts at the back of the wall without
any reaction force acting in front of the wall. Hence, all the lateral pressure is transferred to thewall below the formation level.
At the depths between the formation level and sheet pile toe level the resultant force of the lateralpressure transferred from the above formation level and the active earth pressure at these depths
is resisted by the passive earth pressure.
Finally, at the depths below the sheet pile toe level the active earth pressure is applied to tubularpiles only. The lateral force transferred from the wall above the sheet pile toe level also acts on thepiles. These forces are resisted by the passive pressure developed in the effective passive zone.

94-3-1 Orientation Pattern A

Tubular Piles(Primary Elements)

Dpri

Dint

Sheet Piles(Intermediate Elements)

Figure 9(a). Combi-Gyro Wall - Section (Pattern A)

Active Soil Pressure

Figure 9(b). Earth pressure diagram - Plan in section A-A (Pattern A, above formation level)

10Active Soil Pressure

Passive Soil Pressure
Figure 9(c). Earth pressure diagram - Plan in section B-B (Pattern A, above SSP toe level)

Active Soil Pressure

Effective Passive AreanD
n: Passive Mobilisation Factor

Figure 9(d). Earth pressure diagram - Plan in section C-C (Pattern A, below SSP toe level)114-3-2 Orientation Pattern B

Sheet Piles(Intermediate Elements)

Dpri

Dint

Tubular Piles(Primary Elements)

Figure 10(a). Combi-Gyro Wall - Section (Pattern B)

Active Soil Pressure

Figure 10(b). Earth pressure diagram - Plan in section D-D (Pattern B, above formation level)

12

Active Soil Pressure

Passive Soil Pressure
Figure 10(c). Earth pressure diagram - Plan in section E-E (Pattern B, above SSP toe level)

Active Soil Pressure

Effective Passive AreanD
n: Passive Mobilisation Factor

Figure 10(d). Earth pressure diagram - Plan in section F-F (Pattern B, below SSP toe level)134-4 Durability
The effective life of unpainted or otherwise unprotected Combi-Gyro Wall, depends upon the
combined effects of imposed stresses and corrosion.
Performance is clearly optimised where low corrosion rates exist at primary elements (tubularpiles) side and/ or positions of high imposed stresses.
Eurocode 3: part 5 consider the end of the effective life of steel sheet piles to occur when any partof the pile reaches the maximum permissible working stress as a result of loss of section due tocorrosion.
The opposite faces of a Combi-Gyro Wall may be exposed to different combinations ofenvironments. The following tables indicate the mean loss of thickness due to corrosion for theseenvironments in temperate climates over a given life span.
4-4-1 Loss of thickness (mm) per face due to corrosion of steel tubular and sheet piles in soils,
with or without groundwater
Environments

5 years

25years

50years

75years

100years

125years

Undisturbed natural soils(sand, silt, clay, schist…)

0.00

0.30

0.60

0.90

1.20

1.50

Polluted natural soils andindustrial sites

0.15

0.75

1.50

2.25

3.00

3.75

Aggressive natural soils(swamp, marsh, peat…)

0.20

1.00

1.75

2.50

3.25

4.00

0.18

0.70

1.20

1.70

2.20

2.70

0.50

2.00

3.25

4.50

5.75

7.00

Non-compacted andnon-aggressive fills(clay, schist, sand, silt…)
Non-compacted andaggressive fills (ashes, slag…)

Table 2. Corrosion Rates in Soil, with or without groundwater

Note1; Corrosion rates in compacted fills are lower than those in non-compacted ones. In
compacted fills the figures in the table should be divided by two.
Note2; The values given for 5 years and 25 years are based on measurements, whereas the othervalues are extrapolated.

14

4-4-2 Loss of thickness (mm) per face due to corrosion of steel tubular and sheet piles
in fresh water or seawater
Environments

5 years

25years

50years

75years

100years

125yearsCommon fresh water (river, shipcanal…) in the zone of highattack(water line)

0.15

0.55

0.90

1.15

1.40

1.65

Very polluted fresh water (sewage,
industrial effluent…) in the zone ofhigh attack (water line)

0.30

1.30

2.30

3.30

4.30

5.30

Sea water in temperate climate in
the zone of high attack (low waterand splash zones)

0.55

1.90

3.75

5.60

7.50

Protection
systemrequired

3.50

4.40

Sea water in temperate climate in
0.25
0.90
1.75
2.60
the zone of permanent immersion
or in the intertidal zone
Table 3. Corrosion Rates in Fresh Water or in Sea Water

Note1; The highest corrosion rate is usually found in the splash zone or at the low water level intidal waters. However, in most cases, the highest bending stresses occur in the permanent
immersion zone.
Note2; The values given for 5 years and 25 years are based on measurements, whereas the othervalues are extrapolated.
Note3; The values in this table for corrosion loss in the low water zone apply to situations where
the effects of Accelerated Low Water Corrosion (ALWC) are not a design requirement.
ALWC is a particularly aggressive form of corrosion associated with bacterial activity at low
water level in marine conditions. Attack is random both within and between locations andtypically at or just above the lowest astronomical tide (LAT) level. Due to the high rate ofsteel loss when ALWC occurs, the life expectancy of a pile will be short and it isrecommended that a protection system is used to control the situation rather thanreliance on sacrificial steel. Suitable options may be painting or cementitious coating but it
is also recommended that consideration is given to installation of a cathodic protection
system either immediately or at a later date if necessary. Whilst this phenomenon might
not affect every location, if ignored, this rapid form of attack can result in costly repair andmaintenance works at an unexpectedly early stage in the life of a structure.

15a) Vertical zoning ofsea water aggressivity
A
C
E
G
MHW

b) Corrosion rate
distribution at side
exposed to sea water

Zone of high attack (splash zone);
Zone of high attack (Low water zone);Buried zone (Water side);Buried zone (Soil side)
Mean high water;c) Typical bending
moment distribution

B
D
F

Intertidal zone;
Permanent immersion zone;
Anchor;

MLW

Mean low water

Figure 11. Corrosion Rate Distribution

4-4-3 Combi-Gyro Wall orientation for waterfront structures
Where Combi-Gyro Wall is constructed as a permanent waterfront structure, especially in marine
environments, the wall orientation is a critical issue to optimise performance and effective life of
the Combi-Gyro Wall.
As the primary elements (tubular piles) resist a majority portion of the bending moment, they arenormally located at soil side so that the corrosion rate on the primary elements is minimised.
In the case of Combi-Gyro Wall, the primary elements can entirely be protected from highcorrosion aggressiveness by the continuous intermediate elements (sheet piles).

Water Side(High Corrosion Aggressivity)

Soil Side(Low Corrosion Aggressivity)

Figure 12. Wall Orientation for Waterfront Structure

16Chapter 5

Design Case Study

5-1 Introduction
These calculations detail the design of a cantilevered Combi-Gyro Wall (Tube/Hat, Pattern A)
forming 5.5m-deep excavation as a temporary retaining structure with a design life of five years,
located at a typical site in central London. The wall comprises steel tubular piles of 900mm
external diameter (with the wall thickness of 16mm) aligned at 1.8m centres and continuous Hat
25H steel sheet piles at the back of the tubular piles.
The Geosolve WALLAP software has been used to analyse the retaining wall in accordance with BS
EN 1997-1 (2004), based on factoring of surcharge loadings, soil strength parameters and an
additional overdig allowance. The code is based on the use of limit equilibrium methods and uses
an approach based on soil and groundwater parameters that tend towards worst credible values todevelop an adequate margin of safety. The wall’s cross section has also been verified against
structural failure, using unfactored soil strength, factored surcharge loadings and an additional
overdig allowance. These ultimate limit state analyses were followed by a serviceability limit state
analysis, using unfactored soil strength and action, to determine the predicted wall deflection,
based on WALLAP.
In order to estimate ground movements adjacent to the retaining walls soil/structure interaction
analyses have also been carried out using a two-dimensional finite element software package"Plaxis". The Plaxis analysis also enabled to calculate wall deflections and structural forces ofindividual members from the Combi-Gyro Wall separately, i.e. primary steel tubular piles andintermediate steel sheet piles.
Once the design of the Combi-Gyro Wall (Tube/Hat, Pattern A) was completed, a cantilevered
Secant Piled Wall that could have the similar serviceability to the Combi-Gyro Wall was determinedthrough a series of sensitivity analyses based on the WALLAP software.
Results of the designs for the cantilevered Combi-Gyro Wall (Tube/Hat, Pattern A) and Secant Piled
Wall will be presented and compared in this report.

175-2 List of Design Standards and References
•
•
•
•
•
•
•
•
•
•

•
•
•
•

Bond, A. and Harris, A. [2008] Decoding Eurocode 7, Taylor and Francis, London.
British Standards Institution [2004] Eurocode 2: Design of concrete structures, Part 1-1:
General rules and rules for buildings, BS EN 1992-1-1.
British Standards Institution [2005] Eurocode 3: Design of steel structures, Part 1-1: Generalrules and rules for buildings, BS EN 1993-1-1.
British Standards Institution [2007] Eurocode 3: Design of steel structures, Part 5: Piling, BS
EN 1993-5.
British Standards Institution [2004] Eurocode 7: Geotechnical design, Part 1: General rules,
BS EN 1997-1.
British Standards Institution [1999] Execution of special geotechnical work – Sheet piled, BS
EN 12063.
CIRIA C580 [2003]: Embedded retaining walls - guidance for economic design.
Eid, M. M., Ahmed, A.A.A., Hefny, A.M. and El-Attar, A.N. [2015] Tunnelling effect on theadjacent pile footings, Journal of American Science.
Borin, D. [2007] WALLAP User's Guide, Ver. 5, Geosolve.
Hight, D.W., McMillan, F., Powell, J.J.M., Jardine, R.J. and Allenou, C.P. [2003] Somecharacteristics of London Clay. Proc. Conf. Characterisation and Engineering, National
University Singapore, Balkema, Vol. 2, pp. 851-907.
Jardine, R.J., Symes, M.J. and Burland, J.B. [1984] The measurement of soil stiffness in thetriaxial apparatus, Geotechnique, Vol.34, No.3, pp.323-340.
Peck, R.B., Hanson, W.E. and Thornburn, T.H. [1974] Foundation Engineering, Wiley, NewYork.
Plaxis b.v. [2015] Plaxis 2D 2015 - Material Model Manual.
Stroud, M.A. [1989] The standard penetration test – its application and interpretation, ICE
Conf. on Penetration Testing in the UK, Birmingham, Thomas Telford, London.

18

5-3 Ground Conditions
5-3-1 Ground Model
Typical ground conditions seen in central London have been adopted for the analyses with thefollowing geological formations:a) Made Ground
The Made Ground generally comprises clayey to gravelly sand or soft to firm sandy
gravelly clay with varying amounts of rubble, concrete and brick. The material has been
assumed as a medium dense granular soil.
b) Terrace Gravel
The Terrace Gravel is generally described as medium dense, angular to sub-rounded,sandy, fine to coarse gravel of flint.
c) London ClayThe London Clay was deposited in a deep marine environment and is relatively
homogeneous in lithology in comparison to the underlying Lambeth Group. The material
is typically described as stiff closely fissured silty clay with K0 values ranging from 1.5 to
2.5 due to its heavily overconsolidated nature. The thickness of the formation in central
London ranges from 20m to 60m..
The following stratigraphy has been established for the retaining wall analysis.

Made Ground:+10.0m AOD to+5.0m AOD

Terrace Gravel:+5.0m AOD

0.0m AOD

London Clay:

0.0m AOD toto-20.0m AOD

5-3-2 Geotechnical Design Parameters
The geotechnical design parameters for each of the formation have been derived, based on
general knowledge and HGC’s experience in working on the London geology.
A summary of the geotechnical parameters used for the retaining wall analysis is presented inTable 4.

19

Thickness (m)Unit weight (kN/m³)

Angle of Shearing
resistance φ’ peak (Deg.)

Effective cohesion (kN/m²)

Undrained shear strength(kN/m²)

Drained Stiffness E’(MN/m²)

Undrained Stiffness Eu(MN/m²)

Drained Poisson’ s ratio, ν

Undrained Poisson’ s
ratio vu

K0

Coefficient of
permeability. K (m/s)

Dilatancy angle for drained
analysis, ψ(Deg.)

18

30

0

-

15

-

0.30

-

0.50

10-5

0

River Terrace
Deposits

5.0

5.0

19

35

0

-

50

-

0.30

-

0.43

10-5

5

London Clay

0.0

40.0

20

20

10

100
+ 7z

80 +
5.6z

100
+ 7z

0.20

0.49

1.50

10-10

12.5

(top of strata mAOD)

5.0

Elevation

10.0

StrataMade
GroundTable 4. Summary of geotechnical parameters for the retaining wall analysis

Notes on design geotechnical parameters
1) Values of the unit weight, Poisson’s ratio and permeability are based on generalknowledge and HGC's experience in working on London geology.
2) For cohesive soils the Poisson’s ratio of νu = 0.49 assigned since νu = 0.50 would results
in an infinite value of bulk modulus in Plaxis analysis (after Plaxis b.v. [2015]).
3) For granular soils the angle of shearing resistance φ’peak derived from correlation withtypical SPT-N values (after Peck et al. [1974]).
4) For granular soils the stiffness E’ derived from correlation with typical SPT-N values
using E’/N = 1.0 for Made Ground and E’/N = 2.0 for Terrace Gravel (after Stroud[1989]).
5) Values of K0 for granular soils derived from the relationship K0 = 1 – sin φ’peak.
6) For granular soils the angle of dilatancy ψ derived from the relationship ψ = φ - 30°(after Plaxis b.v. [2015])
7) London Clay Formation assumed to be "Divisions B/C".
8) For London Clay c’ and φ’peak based on published data and HGC's experience in working
on London geology.
9) For London Clay cu, where z is the depth below top of London Clay stratum, based on
published data and HGC's experience in working on London geology.
10) For London Clay the undrained stiffness Eu derived from correlation using Eu = 1000cu(after Jardine et al. [1984]).
11) For London Clay the drained stiffness E' derived using the relationship E' = Eu (1+ν') /(1+νu).
12) Permeability and the value of K0 for London Clay chosen based on published data (afterHight et al. [2003]).
13) London Clay ψ for drained analysis chosen based on published data and ψ = 0 adopted
for undrained analysis.

20

5-3-3 Design Groundwater Levels
Typical groundwater regime in central London consists of a perched water table within the Terrace
Gravel (the upper aquifer) and a deep water table in the lower aquifer above Chalk, e.g. within the
London Clay, Lambeth Group and Thanet Sand.
The groundwater table for the design life of next five years has been assumed at +3.0m AOD.
During an extreme flooding event the groundwater table at the site might rise to above groundlevel. In such events the structural integrity of the proposed temporary retaining wall might becompromised.
In order to address the risk of the extreme flooding events an observational method approach isenvisaged by means of a number of stand pipe piezometers for the entire duration of theconstruction works. Thus, the following design groundwater levels have been used for the designof the retaining walls as presented in Table 5.

Design case

Active side [mAOD]

Passive side [mAOD]

Worst credible (ULS)

5.0

3.0

Moderately conservative (SLS)

4.0

3.0

Table 5. Design groundwater levels for the retaining wall analysis

Shall the water table on the active side rise higher than the moderately conservative design level(4.0m AOD), dewatering measure shall be considered. Those might include allowing seepage in the
excavation and evacuation of groundwater using sumps, groundwater lowering using relieve wellor similar.

5-4 Design Approach
5-4-1 Retaining Wall Analysis
The Geosolve WALLAP software (ver. 6.05) has been used to analyse the retaining walls inaccordance with Design Approach 1 in BS EN 1997-1 (2004) which requires the following analyses:•••

A serviceability limit state (SLS) analysis using unfactored soil strength and action.
An ultimate limit state (ULS) Combination 1 analysis using unfactored soil strength, factored
surcharge loadings and an additional overdig allowance.
An ultimate limit state (ULS) Combination 2 analysis using factored surcharge loadings,
factored soil properties and an additional overdig allowance.

In order to estimate ground movements adjacent to the retaining walls soil/structure interaction
analyses have also been carried out using a 2D FE software package, Plaxis 2D (ver. 2015.01). The
behaviour of soils and structures during various construction stages and post-construction has
been investigated using a “plain strain” deformation analysis mode, based on unfactored“undrained” and “drained” soil parameters.
The Plaxis analysis also enables to calculate wall deflections and structural forces of individual
members from the Combi-Gyro Wall separately, i.e. primary steel tubular piles and intermediatesteel sheet piles.
21

5-4-2 Partial Factors
The design uses safety factors obtained from BS EN 1997-1, summarised in Table 6. These factors
are applied to both the actions as well as the material properties.
Combination 1

Combination 2

Set

Set

Design Approach 1
A1
Permanent
Actions
Variable

Material
Properties

M1

R1

A2

Unfavourable

γG

1.35

1

Favourable

γG;fav

1

1

Unfavourable

γQ

1.5

1.3

Favourable

γQ;fav

0

0

M2

R1

Reference in
BS EN
1997-1:2004

Table A.3

Angle of shearing

γφ'

1

1.25

Effective cohesion

γc'

1

1.25

Undrained shear strength

γcu

1

1.4

Unconfined strength

γqu

1

1.4

Weight density

γγ

1

1

Table A.4

Table 6. Summary of partial factors used for design of retaining walls (after BS EN 1997-1 [2004])

The partial factor on variable unfavourable actions in DA1 Combinations 1 is 1.5. However,adopting this approach generates unrealistic and onerous load effects in the piles. According toretaining wall design detailed in Bond & Harris [2008] (Section 12.5.1 page 420), variable actions
should be factored by 1.1 in the analysis (derived from 1.5 divided by 1.35) to give realistic load
effects and then a factor of 1.35 should be applied to the induced load effects in order to obtain
design values. As the factor on the load effects is also applied to effects derived from thepermanent surcharge, it is necessary to reduce the factor on permanent actions to 1.0 (1.35/1.35).
This approach has been adopted here and is consistent with the guidance in the Eurocodes where
factors may be applied to actions or effects.

225-5 Design Assumptions
5-5-1 Pile Installation Technique
1) Tubular Piles
Tubular piles are to be installed by the Gyropress Method that utilises rotary jack-in system with
cutting bits attached on pile toe. It is assumed that ground disturbance is limited to the wall-soil
interface and the properties of soil around the tubular piles are unchanged.
2) Steel Sheet Piles
Steel sheet piles are to be installed by the Press-in Method. It is assumed that pre-augering may be
carried out in the active earth pressure side of sheet pile in-pan areas only.
5-5-2 Formation Level
The formation level is at 4.5m AOD, i.e. 5.5m below the pile head/ground surface level.
The depth of unplanned excavation for ULS calculations has been taken as 0.5m as recommended
by BS EN 1997-1.
5-5-3 Surcharge Load
The geotechnical design of the retaining wall included a 10 kN/m² surcharge load on the active side.
This surcharge has been applied at 0.5m from the centre line of the retaining wall.
5-5-4 Serviceability
The allowable horizontal deflection of the cantilevered retaining walls has been taken as 26mm.
It should be noted that installation tolerances of the plan position and vertically of the steel sheet
piles need to be added to the calculated deflection in accordance to BS EN 12063:1999 (see Table
7).

Type of wall

Situation during execution

Plan position of pile top (mm)Verticality2) measured
over the top 1m%
All directions

Sheet pile4)

On land over water

Primary elementof combined wall

≤ 751)≤ 13)≤ 1001)≤ 1.53)

Depending on soil conditions and on length, shape, size andnumber of secondary elements, these values should beestablished in each case in order to ensure that de-clutching is not
likely occur

1) Perpendicular to the wall.
2) Where the design requires piles to be driven at an inclination, the tolerances specified in the table are withrespect to that direction.
3) May amount to 2% in difficult soils, provided that no strict criteria regarding for example watertightness are
specified and de-clutching is not considered to become a problem after excavation.
4) Excluding straight web piles.
NOTE : The tolerances regarding the position and the verticality may be additive.
Table 7. Tolerances of plan position and vertically of the steel sheet piles after installation(after BS EN 12063:1999)23

5-5-5 Pile Section Properties
The pile section properties comprise the elastic modulus of steel or concrete, E, and the pile's
second moment of area, I (moment of inertia), of the section.
1) Combi-Gyro Wall (Tube/Hat, Pattern A)
The Combi-Gyro Wall (Tube/Hat, Pattern A) analysed in this design exercise is comprised of steel
tubular piles of 900mm external diameter at 1.8m centres with the wall thickness of 16mm and"Hat" type steel sheet piles 25H. The theoretical centre lines of the tubular piles and the sheet
piles are spaced 475mm apart in the 2D FE model.
From the wall properties table, provided by Giken, values of the moment of inertia for each wall
member were determined as follows:
Isys = Istp + Issp
= 241,216 + 24,400 = 265,616 [cm⁴/m]
where, Isys: moment of inertia of Combi-Gyro Wall system
Istp: moment of inertia of steel tubular piles
Issp: moment of inertia of steel sheet piles
The moment of inertia of the wall system Isys was assigned from the pile head level to the steel
sheet piles' toe level, where it was reduced to Istp for the rest of the steel tubular piles.
The steel grade and elastic modulus of the steel piles have been assumed to be S 390 GP and 210
GPa, respectively.
2) Secant Piled Wall (hard/firm)
A series of sensitivity analyses has been undertaken to determine an arrangement of thecantilevered secant pile wall that had a similar serviceability performance to the Combi-Gyro Wall
(D900-16 with Hat 25H) in terms of the maximum wall top deflection (i.e. ≈ 26mm).
Based on the sensitivity analyses, 900mm diameter bored piles (hard/firm) with a male-to-malespacing of 1250mm (275mm overlap of male and female piles, as shown in Figure 13) have beenchosen for the retaining wall analysis. The concrete grades have been assumed to be mix strengthof C30/37 N/mm² and C8/10 N/mm² for the male (hard) and female (firm) piles, respectively.
FEMALE PILE

900mm dia.
AREA 0.6362m2

MALE PILE

MALE PILE

AREA
0.3904m2

Figure 13. Arrangement of Secant Piled Wall

24

For calculation of the moment of inertia of the secant piled wall it has been assumed that malepiles will act as the primary retaining elements whilst female piles only fill the gap between themale piles and transmit the loads resulting from earth and water pressures to the male piles. Thus,
the moment of inertia per metre is determined as:
Ispw = Imale / d= π r⁴ / 4 / d = π (0.90/2)⁴ / 4 / 1.2 = 2,576,499 [cm⁴/m]
where, Ispw : moment of inertia of secant piled wall
Imale : moment of inertia of male pilesr : male pile radiusd : male pile spacing (centre to centre)
The elastic modulus of the concrete piles has been taken as 19.6 GPa in accordance with guidancein the WALLAP User's Guide, which is 70% of short-term uncracked concrete modulus value (28GPa).
5-5-6 Wall Friction Angle and Adhesion Factor
Based on BS EN 1997-1, the wall friction angle "δ" and adhesion factor "α" between the soil andthe wall has been assumed as presented in Table 8.
Wall friction angle, δWall adhesion factor, αSteel piles

Concrete piles

Granular soil

⅔ φ'peakφ'peakN/A

Cohesive soil

½ φ'peakφ'peakignoredTable 8. Wall friction and adhesion factors used for the retaining wall analysis (after BS EN 1997-1)

5-5-7 Design LifeThe design is required to take into account all foreseeable events that would adversely affect thestability of the retaining structure. Since the purpose of the retaining walls is for temporary works,
the design life of five years has been adopted and, thus, a check on durability of the steel members
has not been undertaken.

255-6 Assumed Construction Sequence
Sequencing of construction activities will be crucial to ensure that failures do not occur during
construction. Careful consideration will also need to be given to measures required to achieve
ground movement control behind the retaining walls. The following sequence is envisaged for thedesign option provided.
1)
2)
3)
4)

Install a retaining wall (Combi-Gyro Wall or Secant Piled Wall).
Apply surcharge load (UDL 10 kN/m²) on the active side of the wall.
Excavate on the passive side to 4.5m AOD.
Apply water pressure (worst credible case for ULS or moderately conservative case for
SLS).
5) Change geotechnical properties of London Clay from "undrained" to "drained"
conditions to represent the long-term soil conditions (five years after installation of thewall).

26

5-7 Results
5-7-1 Combi-Gyro Wall (Tube/Hat, Pattern A)
1) Summary of Results
Results of WALLAP runs and design summary of retaining wall calculations for the Combi-Gyro Wall
(Tube/Hat, Pattern A) with the toe level of the steel tubular piles at -5.0m AOD are provided inAppendix A. The bending moments and shear forces obtained from the WALLAP analyses are
summarised in Table 9.
Designbending
momentDesignshear
force

Max. wall
top
movement[kNm/m][kN/m]

[mm]

1.35

352

111

26

4.50

1.35

356

112

-

-2.40

1.00

563

143

-

Wall
stability

Calculated max.
bending moment[FoS][kNm/m]Elev.
[mAOD][kN/m]Elev.
[mAOD]

1.64

261

2.30

82

4.50

ULS - Comb.1

-

264

2.30

83

ULS - Comb.2

1.09

563

0.80

143

Analysis case
(EC7)

SLS

Calculated max.
shear force

Loadfactor(EC7)Table 11. Summary of results from WALLAP analysis on the Combi-Gyro Wall (Tube/Hat, Pattern A)2) Wall Stability
BS EN 1997-1 (2004) requires embedded walls to be designed with sufficient embedment lengththat satisfies vertical, horizontal and moment equilibrium, i.e. a factor of safety above unity is
sufficient. Based on the Design Approach 1 - ULS Combination 2 analysis, using factored surcharge
loadings, factored soil properties and an additional overdig allowance, the stability of the
Combi-Gyro Wall has been determined as a minimum factor of safety = 1.09 as presented in Table
9.
3) Structural Forces (WALLAP)
The wall’s cross section must be verified against structural failure. Based on the Design Approach 1- ULS Combination 1 analysis (WALLAP), using unfactored soil strength, factored surcharge loadings
and an additional overdig allowance, the design bending moment and design shear force havebeen determined as 356 kNm/m and 112 kN/m, respectively, as presented in Table 9.
The minimum required section modulus for the wall can be calculated as follows:
Sreq = Md / fy
= 356·10³ / 390 = 914 [cm³/m]
where, Sreq : the minimum required section modulus
Md : design bending moment
fy : yield stress of the steel pile = 390 N/mm²

27

From the wall properties table 3-4-1 Tube/Hat Wall, values of the section modulus for the wall
system, steel tubular pile and steel sheet pile are given below.
•••

Section modulus of the Combi-Gyro Wall system:
Section modulus of the steel tubular pile:
Section modulus of the steel sheet pile:

Ssys = 6970 [cm³/m] (> 914, OK)
Sstp = 5360 [cm³/m] (> 914, OK)
Sssp = 1610 [cm³/m] (> 914, OK)

It is clear that the structural integrity of the Combi-Gyro Wall has been verified in all three cases.
4) Structural Forces (PLAXIS)
The Plaxis analysis allows to calculate structural forces of individual members from the Combi-Gyro
Wall separately, i.e. steel tubular piles and steel sheet piles, based on unfactored soil strength andaction.
Output plots from the Plaxis 2D FE analysis at the final stage, i.e. five years after installation of thewall are provided in Appendix B as summarised in Table 10.
Figure ref.

Plaxis Output Plots

Figure B.1
Figure B.2
Figure B.3
Figure B.4
Figure B.5
Figure B.6
Figure B.7
Figure B.8
Figure B.9
Figure B.10
Figure B.11
Figure B.12
Figure B.13

Connectivity plot
Deformed mesh │u│Total vertical displacements uy
Total horizontal displacements ux
Vector of total displacements │u│
Total shear strain γsDistribution of plastic points
Profile of horizontal wall displacements for CHS D900-16
Profile of wall bending moment for CHS D900-16
Profile of wall shear force for CHS D900-16
Profile of horizontal wall displacements for Hat SSP 25H
Profile of wall bending moment for Hat SSP 25H
Profile of wall shear force for Hat SSP 25H

Table 10. Summary of output plots from Plaxis 2D FE analysis forCombi-Gyro Wall (Tube/Hat, Pattern A)
provided in Appendix B

By comparing the profiles of wall bending moments for the steel tubular pile (Figure B.9) and thesteel sheet pile (Figure B.12), it can be seen that, while the steel tubular pile is carrying the larger
magnitude of bending moment (-189.9 kNm/m), the steel sheet pile's contribution to resist thebending moment is relatively small (-17.68 kNm/m). This significant difference in the resistance tothe bending moment justifies the design assumption made for the role of the intermediate sheet
piles, being a member to transmit the earth and water pressure to the primary tubular piles.
The sum of the bending moments from two wall members calculated by the Plaxis analysis (189.9+ 17.7 ≈ 208 kNm/m) is less than that calculated by the WALLAP SLS analysis (261 kNm/m) as
presented in Table 7.1. It should be noted that the magnitude of the bending moment can be
reduced if further 2D FE analyses are carried out using stress- and strain-dependant hardening soil
constitutive models with small strain stiffness.
285) Intermediate Sheet Piles Toe Level
According to the results from the ULS - Combination 1 analysis, as reported in"Tube-Hat_D900-16-25H_Toe-5mOD_Fmn+4_5mOD_LT_ULS1.rtf" provided in Appendix A, the netpressure becomes zero at an approximate elevation of 4.3m AOD at Stage No. 5. The embedded
depth of the intermediate sheet pile is theoretically required down to this elevation. However, due
to the fact that a water bearing stratum of Terrace Gravel is present further 4.3m below this level,
the design toe level of the sheet piles has been chosen at -1.0m AOD, i.e. 1m into London Clay.
6) Serviceability
The calculated maximum wall top deflection by the WALLAP SLS analysis was recorded as 26mm at
the long-term case as presented in Table 9. Based on the Plaxis 2D FE analysis under the sameloading conditions, the wall movement was predicted to be 25mm as shown in Figure B.8(Appendix B).
It should be noted that the magnitude of the wall displacements is highly influenced by soil
stiffness values assigned to the FE model. Hence, if further 2D FE analyses are carried out using
stress- and strain-dependant hardening soil constitutive models with small strain stiffness, the wall
top deflection can be reduced.
The predicted ground settlement, based on the Plaxis output plots presented in Figures B.2 to B.5(Appendix B), is 21mm at immediately behind the steel sheet piles, reducing almost linearly to
5mm at 5m away from the steel sheet piles.
Figures B.6 and B.7 show the development of the active wedge from the surface point at 5m awayfrom the wall down to the formation level.
5-7-2 Secant Piled Wall
1) Summary of Results
Results of WALLAP runs and design summary of retaining wall calculations for the Secant Piled Wallwith the toe level of the male piles at -5.0m AOD are provided in Appendix C. The bending
moments and shear forces obtained from the WALLAP analyses are summarised in Table 11.
Designbending
momentDesignshear
force

Max. wall
top
movement[kNm/m][kN/m]

[mm]

1.35

331

107

26

4.00

1.35

414

122

-

3.50

1.00

509

131

-

Wall
stability

Calculated max.
bending moment[FoS][kNm/m]Elev.
[mAOD][kN/m]Elev.
[mAOD]

1.72

245

2.30

79

4.50

ULS - Comb.1

-

307

2.30

90

ULS - Comb.2

1.14

509

0.80

131

Analysis case
(EC7)

SLS

Calculated max.
shear force

Loadfactor(EC7)Table 11. Summary of results from WALLAP analysis on the Secant Piled Wall

2) Wall Stability
BS EN 1997-1 (2004) requires embedded walls to be designed with sufficient embedment lengththat satisfies vertical, horizontal and moment equilibrium, i.e. a factor of safety above unity is
sufficient. Based on the Design Approach 1 - ULS Combination 2 analysis, using factored29

surcharge loadings, factored soil properties and an additional overdig allowance, the stability of
the Secant Piled Wall has been determined as a minimum factor of safety = 1.14 as presented inTable 11.
3) Structural Forces (WALLAP)
The wall’s cross section must be verified against structural failure. Based on the Design Approach 1- ULS Combination 1 analysis (WALLAP), using unfactored soil strength, factored surcharge loadings
and an additional overdig allowance, the design bending moment and design shear force havebeen determined as 414 kNm/m and 122 kN/m, respectively, as presented in Table 11. These
values are greater than those values for the Combi-Gyro Wall.
The reinforcement steel to resist bending moments and shear forces induced in the secant "male"piles is determined in accordance with BS EN 1992-1-1 and given below.
• Main steel: (8 x B25) x 15m deep
• Shear steel: 600mm OD B12 hoop at 300mm centres
4) Structural Forces (PLAXIS)
The Plaxis analysis also provides calculation of structural forces for the Secant Piled Wall, based on
unfactored soil strength and action.
Output plots from the Plaxis 2D FE analysis at the final stage, i.e. five years after installation of thewall are provided in Appendix D as summarised in Table 12.

30

Figure ref.

Plaxis Output Plots

Figure D.1
Figure D.2
Figure D.3
Figure D.4
Figure D.5
Figure D.6
Figure D.7
Figure D.8
Figure D.9
Figure D.10

Connectivity plot
Deformed mesh │u│Total vertical displacements uy
Total horizontal displacements ux
Vector of total displacements │u│
Total shear strain γsDistribution of plastic points
Profile of horizontal wall displacements for secant piles
Profile of wall bending moment for secant piles
Profile of wall shear force for secant piles

Table 12. Summary of output plots from Plaxis 2D FE analysis for Secant Piled Wall provided in Appendix D

The bending moment calculated by the Plaxis analysis (222.8 kNm/m, shown in Figure D.9) isslightly less than that calculated based on the WALLAP SLS analysis (245 kNm/m) as presented inTable 11.
5) Female Piles Toe Level
According to the results from the ULS - Combination 1 analysis, as reported in"SPW_Dia900mm_1250mmCC_Toe-5mOD_Fmn+4_5mOD_LT_ULS1.rtf" provided in Appendix C,
the net pressure becomes zero at an approximate elevation of 3.8m AOD at Stage No. 5. The
embedded depth of the female pile is theoretically required down to this elevation. However, due
to the fact that a water bearing stratum of Terrace Gravel is present further 3.8m below this level,similarly to the design of the intermediate sheet piles for the Combi-Gyro Wall, the design toe levelof the female piles has been chosen at -1.0m AOD, i.e. 1m into London Clay.
6) Serviceability
The calculated maximum wall top deflection by the WALLAP SLS analysis was recorded as 26mm at
the long-term case as presented in Table 11. Based on the Plaxis 2D FE analysis under the sameloading conditions, the wall movement was predicted to be 28mm as shown in Figure D.8(Appendix D).
As described in Section 5-7-1 6), the use of advanced soil constitutive models in the FE analyses
could reduce the wall top deflection.
The predicted ground settlement, based on the Plaxis output plots presented in Figures D.2 to D.5(Appendix D), is 23mm at immediately back of the secant piles, reducing almost linearly to 5mm at
5m away from the secant piles.
Figures D.6 and D.7 show a similar trend of development of the active wedge behind the secant
piles but exhibit less plastic points, compared to those calculated for the Combi-Gyro Wall.

31

5-8 Summary
The designs of the Combi-Gyro Wall and the Secant Piled Wall are compared in Table 13.

Wall typePilematerial

Steel
Combi-Gyro
Wall

S 390 GP
Steel
S 390 GP

SecantPiled Wall

Pile section

D900-16
Hat 25H

Concrete

900mm dia.

C 30/37(male)

Concrete

900mm dia.

C 8/10(female)Pile
lengthPilespacing

[m]

[m]

15.0

1.8

11.0

Pile reinforcementWallstability(ULS-C2)

Designbending
moment(ULS-C1)Designshear
force(ULS-C1)

Max. wall
top
movement
(SLS)

[FoS]

[kNm/m][kN/m]

[mm]

1.09

356

112

26

1.14

414

122

26

-

0.9

(8 x B25) x 15m

15.0

11.0

1.25

600mm OD B12
hoop at 300mm
c/c

1.25

-

Table 13. Summary of results for Combi-Gyro Wall and Secant Piled Wall from WALLAP analysis

32

APPENDICESAPPENDIX A

Design of Combi-Gyro Wall (Tube/Hat, Pattern A) based on WALLAP

APPENDIX B

Plaxis 2D FE Analysis of Combi-Gyro Wall (Tube/Hat, Pattern A)

APPENDIX C

Design of Secant Piled Wall based on WALLAP

APPENDIX D

Plaxis 2D FE Analysis of Secant Piled Wall

APPENDIX A
Design of Combi-Gyro Wall based on WALLAP
A-1. Design Summary of Combi-Giro Wall System (Tube-Hat D900-16_25H Pattern A)
A-2. WALLAP run ID: Tube-Hat_D900-16-25H_Toe-5mOD_Fmn+4_5mOD LT SLS
A-3. WALLAP run ID: Tube-Hat_D900-16-25H_Toe-5mOD_Fmn+4_5mOD LT ULS1
A-4. WALLAP run ID: Tube-Hat_D900-16-25H_Toe-5mOD_Fmn+4_5mOD LT ULS2

APPENDIX B
Plaxis 2D FE Analysis of Combi-Gyro Wall
Figure B.1

Connectivity plot

Figure B.2

Deformed mesh │u│

Figure B.3

Total vertical displacements uy

Figure B.4

Total horizontal displacements ux

Figure B.5

Vector of total displacements │u│

Figure B.6

Total shear strain γs

Figure B.7

Distribution of plastic points

Figure B.8

Profile of horizontal wall displacements for CHS D900-16

Figure B.9

Profile of wall bending moment for CHS D900-16

Figure B.10

Profile of wall shear force for CHS D900-16

Figure B.11

Profile of horizontal wall displacements for Hat SSP 25H

Figure B.12

Profile of wall bending moment for Hat SSP 25H

Figure B.13

Profile of wall shear force for Hat SSP 25H

APPENDIX C
Design of Secant Piled Wall based on WALLAP
C-1. Design Summary of SPW (Dia.900mm_1250mmCC).docx
C-2. WALLAP run ID: SPW_Dia900mm_1250mmCC_Toe-5mOD_Fmn+4_5mOD_LT_SLS
C-3. WALLAP run ID: SPW_Dia900mm_1250mmCC_Toe-5mOD_Fmn+4_5mOD_LT_ULS1
C-4. WALLAP run ID: SPW_Dia900mm_1250mmCC_Toe-5mOD_Fmn+4_5mOD_LT_ULS2

APPENDIX D
Plaxis 2D FE Analysis of Secant Piled Wall
Figure D.1

Connectivity plot

Figure D.2

Deformed mesh │u│

Figure D.3

Total vertical displacements uy

Figure D.4

Total horizontal displacements ux

Figure D.5

Vector of total displacements │u│

Figure D.6

Total shear strain γs

Figure D.7

Distribution of plastic points

Figure D.8
Figure D.9
Figure D.10

Profile of horizontal wall displacements for secant piles(Hard/Firm 900mm dia.@ 1250mm centres)
Profile of wall bending moment for secant piles(Hard/Firm 900mm dia.@ 1250mm centres)
Profile of wall shear force for secant piles(Hard/Firm 900mm dia.@ 1250mm centres)Care has been taken to ensure that the contents of this publication are accurate at the time of printing, but GIKEN LTD. and its subsidiaries do not accept
responsibility for error or for information which is found to be misleading. Suggested applications in this technical publication are for information purpose only
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