Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

Retaining Wall Deflection Control in Relation to Augering Area
Tsunenobu NOZAKIGeneral Manager, International Construction Design & Planning Department, Giken Ltd., Tokyo, Japan
Email: nozaki@giken.com

ABSTRACT
When retaining walls are designed, design parameters of undisturbed soil are normally used. In reality, if the retaining
wall is comprised of piles, they are often installed assisted by ancillary equipment, such as water jetting or augering, toreduce installation resistance. To what extent the impact of these ancillary methods has on the soil, and the effect of theretaining wall design is not known.
This report features impacts of driving assistance of pile installation on retaining wall design. A project in Le Mans,
France was used as a case study to observe if the design of a retaining wall is still satisfied, despite a local ground
disturbance by augering.
Key words: Press-in Method, Retaining Wall, Chalk

1. Outline of the project

2. Structural type and piling method

1.1. Place
Le Mans is located on the River Sarthe, in the north

2.1. Site condition
The site is located close to the SNCF (the Frenchwest of France. Traditionally the capital of the province ofnational rail operator) tracks in Le Mans as shown in Fig.

Maine, it is also now the capital of the Sarthe Department

1. The tracks include the TGV (France’s intercity

and the seat of the Roman Catholic diocese of Le Mans.

high-speed rail service) and therefore, there was a

Le Mans is a part of the Pays de la Loire region.

stringent vibration transmission restriction during theThe city has been famous for the Le Mons 24 Hour
sports car endurance race since 1923.

construction. Also, there were residential and commercial
properties adjacent to the site, so construction noise was

The Gare du Mans is the main railway station of Le

restricted.

Mans. It takes 1 hour to reach Paris from Le Mans by
TGV high speed train. There are also TGV connections
to Lille, Marseille, Nantes, Rennes and Brest. Gare duMans is also a hub for regional trains. Le Mans
inaugurated a new light rail system on 17 November
2007.
1.2. Background and objectives of the project
The site is in the square in front of Le Mans train

Sitestation and was previously used as a street level car park.
As a part of the station renovation project, the car park
was rebuilt as a single level underground car park.
Fig. 1- 507 -Site Location Map

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

2.2. Ground condition
The basic soil makeup is alluvial deposits from theRiver Sarthe, which flows through the city of Le Mans.
The alluvial deposits are comprised of mainly coarse
soils as shown in Fig. 2.

Fig. 2

Typical Borehole Log
Fig. 3

Sequence of Pressuremeter Test

“Pressuremeter tests” most commonly used in France,
were carried out to investigate soil characteristics. Fig. 21) Rotary percussion drilling using a STAF System,shows the test results Pl (Pressure Limit) and Em

which includes a STAF tool and a slotted tube,(Pressuremeter Modulus) that were obtained. The outline

confirming to the STDTM specifications (Slottedof the Pressuremeter Test is described in Fig. 3 below.

Tube technique with inside Disintegrating Tooland Mud circulation) for Menard Pressuremeter
testing. Slurry spills out into a sediment tank inwhich the borehole logging can be performed.
2) Extracting the STAF tool and its string of rods
without remoulding the borehole walls.
3) The borehole remained lined. The slotted tube isready to accept the Pressuremeter probe andclean slurry is ready to be circulated.
4) Using the locking device for the probe, the driller
places the Pressuremeter probe into the slotted
tube which is already in position. The probe islocated exactly at the centre level of the steel- 508 -

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

strips which form the slotted tube. Pressuremeterthe volume of the borehole cavity has fully returned to its

testing can then start. The coaxial or twin lines

original position, and is given the coordinates, v0, p0. The

are protected from any squeezing or pinching bypseudo-elastic phase, the straight-line portion of thethe string of STAF tubes.

curve between points A and B, is named so because of its5) The Pressuremeter tests are carried out, starting

resemblance to the elastic behavior of steel or concrete.

from the deepest location. The STAF string ofPoint B is the point at which creep pressure has been

pipes is pulled up to the level of the next test

reached, and is given the coordinates, vf, pf. The plastic

position using a specially designed pullingphase begins at point B and extends to point C, which isdevice. Pressuremeter readings can be recorded

asymptotic to the limit pressure. Point C, which is given

using the GEOSPAD data logger which is fitted

the coordinates vL, Pl, is defined as the point where theto the Pressuremeter Control Unit, according topressure remains constant, despite increasing volume.

EN ISO 22476-4 Standard.

The limit pressure is defined as the pressure required6)

to expand the measuring cell by an amount vo beyond theInterpretations of Test Results
The typical test results of the Pressuremeter are

volume required to inflate the pressuremeter (Vc) and topush the borehole wall back to its original position (vo).
This definition of limit pressure is analogous to defining

shown in Fig. 4.

failure in a triaxial test at a given value of axial strain, forexample 10% to 15%. The Value of Vc depends on thesize of the borehole, as shown in Table 1. The injectedvolume at the limit pressure (vL) is thus:
vL = vo + Vc + vo = 2vo + Vc

(1)

where:
vo = volume required to inflate pressuremeter andpush soil to its original position; andVc = initial volume of measuring cell (see Table 1).
Table 1.

Values of Vc according to pressuremeter probe type(from Gambin and Rousseau, 1988)

Probe

Fig. 4

Example Pressuremeter Test Results(from Baguelin, 1978)

Diameter of Borehole(mm)Vc (cm3)

EX34535

AX44535

BX60535

NX

76790

There are three phases of the deformation curve: (1)the re-establishing phase, from the origin to point A; (2)If the volumetric increase at the end of the test is lessthe pseudo-elastic phase, from point A to point B; and (3)than twice the cavity volume, extrapolation must be used

the plastic phase, from point B to point C.

to determine Pl. Fig. 5 demonstrates this extrapolation

After the borehole is drilled and the augers areprocedure.

withdrawn, the borehole walls relax, thus reducing thecavity volume. As the pressuremeter probe is initiallyinflated, the walls of the borehole are pushed back totheir original position. Point A marks the point at which- 509 -Proceedings of the First International Conference on Press-in Engineering 2018, Kochi(3), and typical ranges of values for soil types are shownin Table 2.
EPMT = 2(1 + νs) V
Where:△p△p(3)△v△v

νs = Poisson’s ratio
V= cavity volume during thepseudo-elastic phase= Vc + vm;
Vo= initial or at-rest volume of themeasuring cell (see Table 1 fortypical values);
vm=themeanvolumeofthe

pseudo-elastic phase= (νf + νo)/2; and3(MPa)(cm )Fig. 5△p/△v= slope of theseudo-elastic phase

Pressure vs. Log Volume Plot for Extrapolation ofLimit Pressure at NCSU Research Site (from Wilson, 1988)

The “net limit pressure,” Pl*, is used in foundation
design, and is calculated using equation (2).
Pl* = Pl – Pho

Table 2.

Range of EPMT and Pl for several soil types (fromGambin and Rousseau, 1988)(2)

Where: Pl = limit pressure; andPho = initial total horizontal pressurein the ground= [(γ-u)z] K0 +u
Although Pho should equal the pressure corresponding tovo (i.e. value corresponding to po), it is difficult toaccurately determine po from the test data due todisturbance of the borehole walls and a lack of points atthe beginning of the test.
The correlations between the pressure meter test andThe pressuremeter can be used in foundation designs for

CPT were evaluated by Baguelin et al. in 1978. In theall types of soils, including residual soils. The settlement

evaluations, the pressure limit Pl and cone resistance qcof foundations can be estimated using a deformationof CPT were correlated in different soil types, asmodulus, EPMT, which can be derived from thedescribed in Table 3 below.

pseudo-elastic phase (or straight-line portion) of the load
deformation diagram. EPMT is a function of Poisson’sratio, the slope of the straight line, and the cavity volume
in the pseudo-elastic range, so it is conventional to use
the mean volume, vm, of the cavity during this phase. The
deformation modulus, EPMT, can be found using equation- 510 -

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

Table 3.

concrete alongside of the temporary sheet pile walls. To

qc/Pl for different soil types accordingallow rapid installation of these basement walls, a bulk

to Baguelin, 1978

qc/Pl

excavation was carried out. In order to achieve the bulk

Very soft to soft clays

close to 1 or 2.5 to 3.5

excavation, the steel sheet piling was used as cantileverFirm to very stiff clay

2.5 to 3.5

walls and anchored walls. The retained height of theVery stiff to hard clay

3 to 4

cantilever sheet pile walls ranged from 3.6m to 5.0m, andVery loose to loose sand and

1 to 1.5 and 3 to 4

the retained height of the anchored sheet pile walls

Soil Description

ranged from 3.3m to 4.9m. Typical cross sections of thecompressive silt
Compact silt

3 to 5

Sand and gravel

5 to 12basement are shown in Fig. 6, Fig. 7 and Fig. 8 below.

The sandy gravel and fine sand layers underlying thefill are generally dense to very dense. The Pl of the sandand gravel layers ranges from 4.13MPa up to 8.14MPa
generally. In the clay and fine sand layer, the Pl exceeds
7.0MPa locally (as shown in Fig. 2). These values arecorrelated to cone resistance qc of 20MPa to 98MPa withthe correlation factors from 5 to 12 described in Table 1,
and the soil is categorized as “dense” to “very dense” (asshown in Table 4 and Table 5 below).
Table 4. Density of Fine Sand (qc/SPTN= 0.4-0.5)

Cone Resistance

SPT NDensity＜24-5

very loose

2-4

4-10

loose

4-12

8-30

medium dense

12-20

24-50

dense

＞20

40-50

very denseqc (MPa)

Fig. 6

Typical Cross Section - 1(Cantilever SSP Wall and RC Cantilever Wall)

Table 5. Density of Sandy Gravel (qc/SPTN= 1.1-1.8)

Cone Resistance

SPT NDensity＜5＜5very loose

5-10

3-9loose

10-30

6-28

medium dense

30-50

17-45

dense

＞50＞45very denseqc (MPa)2.3. Structural typeThe steel sheet piling was used as temporary
retaining walls to construct a single level basement carpark. The basement walls were constructed of reinforced- 511 -Fig. 7

Typical Cross Section - 2(Anchored SSP Wall and RC Basement)Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

Fig. 8

Typical Cross Section - 3(Cantilever SSP Wall and RC Basement)

According to the French railway regulations, theFig. 9

allowable deflection of retaining walls alongside

Retained Height H and Distance between Pile
Line and Railway Track D

railways is calculated by taking into account a. thevelocity of trains, b. the retained height and c. theAs shown in Fig. 10, the distance between thedistance between the railway track (as shown in Table 6

proposed pile line and the existing TGV track was moreand Fig. 9 below).

than 6.0m, which gives the allowable horizontal
deflection of the retaining walls of 100mm as shown inTable 6.

Table 6. 600mm wide U sheet piles, PU12/ PU18 with

Allowable Horizontal Deflection of Retaining Walls

lengths from 8m to 13m were used to satisfy the design

alongside Railways (V＜80km/h)

AllowableDeflection(mm)H≤2m2m ＜ H ≤3m3m ＜ H ≤4m4m ＜ H≤
5mrequirement.

D (m)D≤33＜D≤450

4＜D≤55＜D≤6100

4670100

4161100

345278100

Fig. 10 Pile Line along the TGV Track- 512 -Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

2.4. Piling method
In order to install sheet piles into dense to very

3.2. Productivity
The piling work was carried out from July 24th todense sandy gravel and sandy layers, the Press-in with

September 28th in 2006 by utilizing two SCU600M Silent

simultaneous augering method (Fig. 11) was utilized.

Pilers fitted with Pile Augers. A total of 608, 600mm wide

The in-pan of each sheet pile is attached to the side of theU sheet piles were installed, covering 3,826m2 of the wall

auger casing. The sheet pile and the auger casing are thenarea. The average production rate was approximately

grasped by the chuck of the Silent Piler and installed into

69.6m2 of the wall area per day, which is equivalent tothe ground simultaneously.

116m of the total pile driving length.
3.3. Encountered difficulties
At the design stage, the ground disturbance by theaugering was a concern because the impact of the ground
disturbance on the lateral deflection of the retaining wall
was unknown. In order to minimize the ground
disturbance, 540mm diameter auger heads were used (asshown in Fig. 13). Also, in order to predict probablelateral deflection of the retaining walls, test piling withlateral load testing was carried out. With satisfactory
results, the Press-in with simultaneous augering method
was specified in the tender document.

Fig. 11 Piling Work in Progress

3. Press-in piling3.1. Layout
The pile layout is described in Fig. 12.

Fig. 13

Orientation of Augering Area

4. Additional data
After each pile installation, the area disturbed byaugering was backfilled with augering spoils. Post pile
installation, the lateral deflection of the retaining wall
was continuously monitored through to the projectcompletion. Despite the augering, the actual deflection at
the top of the retaining wall remained within the design
deflection allowance of 38.3mm as shown in Table 7,
Fig 14 and Fig. 15.

Rail Tracks
Fig. 12 Plan View Layout- 513 -Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

Monitoring

LateralMonitoring

Lateral

5. Design consideration
This report reveals that the augering method wasPoint

Deflection

Point

Deflection

effectively used to overcome difficult ground conditions.

(mm)

At the same time, the retaining wall design requirement

Table 7.

Lateral Deflection of Retaining Walls

(mm)
P120

P1331

wasmet,despitetheground

disturbanceasaP211P1423

consequence of the augering. It is thought that theP3

11P1522

following aspects may have contributed to achieving theP410P1622

design requirement.

P59P1717P64P1814

When a retaining wall is loaded laterally,

1) Soil arch effect

P718P19

9

distribution of the soil stress can be simulated based

P84P20

5on the Theory of Elasticity using the Boussinesq

P96P215equation that considers a point load on the surface

P10

10P222P1121P23

6P1238ofasemi-infinite,

homogeneous,isotropic,weightless, elastic half-space. The concept of thesoil arch effect prepared from the Boussinesq's
equation by Bowles [1996], (as shown in Fig. 16).

Pile width, D

Pile contact pressure, q0

Fig. 14

Monitoring Points Location

Design Deflection Allowance 38.3mm
ActualDeflection

Fig. 16

Pressure distribution formed on the passive

side of a pile, showing the intensity of pressure q/q0,
Fig. 15

based on the Boussinesq equation (after Bowles, 1996)

Lateral Deflection of Retaining Walls- 514 -

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

On the project, the auger mostly disturbed thevoid, but are filled with augering spoils. As such,in-pan side of each pile leaving very little disturbed

the augered areas are sufficiently confined and thearea at the out-pan side as shown in Fig. 17.

backfill should transfer the active earth pressure to
the surrounding undisturbed soil to some extent. It
is thought that this “confined effect” contributed toa lateral deflection, which is smaller than the design
deflection. However, this effect is not covered inthis report, and the following aspects should beobserved if checking this issue at another point intime.
a)Measuring density or stiffness of backfillb) Measuring shear strength of backfillc)
Fig. 17

Measuring compressibility of backfilld) Measuring stress on pile surface on passive

Effective passive areaside
The diameter of the auger was selected so thate)

both shoulders of each sheet pile snugly met with

Measuring stress on surface of undisturbed
soil on passive side

the undisturbed soil. The lateral load acting on thef)

sheet pile wall is radially transferred to the soil at

Measuring lateral deflection of retainingwall

the passive side, through the arching action of theg) Making speculation on linking above

soil. The tendency of the arching action whichaspects.

depends on soil characteristics is described as“passive mobilization factor”. The effective passive
area is shown as follows: -6. Concluding remarks
When augering is required to install retaining walls,
it is prudent to give retaining wall design careful

Effective passive area = nW

consideration to this aspect, especially if the retaining

n: Passive mobilisation factor

wall is a cantilevered wall. This is because the impact on

W: Undisturbed area on pile surface

the soil parameters by augering is not scientificallyascertained and it is difficult to evaluate characteristics ofIn general, a passive mobilisation factor of 2-3 isused depending on soil conditions.

the disturbed soil. Therefore, augering may cause

There is no

unexpected large horizontal deflections of retaining walls

simple relationship between the characteristics ofif an overoptimistic retaining wall design is used. On thethe effective passive area (nW) and soil conditions,other hand, if over pessimistic retaining wall design isbecause any relationship is dependent on the pileused, unnecessary remedial works, such as grouting or

size and on the nature and sequence of the strata.

the like, may be required to stabilize the retaining wall.

"nW" at a certain distance (H) in low strength

This willcohesive soil is generally greater than that in dense,economical.

less cohesive soil.

make retaining

wall construction lessUnless retaining walls are installed with a complete
underreamed auger (larger auger diameter than the pile2) Confined effect of disturbed soilwidth), there are some undisturbed areas on the retaining

After pile installation, the auger is extracted andwall surface, which have decent horizontal passive

the augering spoils are backfilled. In general, thestrength for the retaining wall. Based on this, thestrength of the backfill is ignored for retaining wall

retaining wall can be designed with a reasonable passive

design, due to its uncertainty as a result ofmobilization factor, which determines the effective

disturbance. However, the augered areas are not left

passive area. With this approach, retaining walls can be- 515 -Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

designedrathereconomically,avoiding

overestimated/underestimated design.

ReferencesBaguelin. 1978. Correlation between PMT and CPT after
dynamic compaction in reclaimed calcareous sand.
Bowles, J.E. 1996. Foundation analysis and design - 5thedition. McGraw-Hill, Singapore.
Wilson. 1988. NCSU Research Site.
Gambin and Rousseau. 1988. Range of EPMT and Pl forseveral soil types.

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