Diaphragmwall test

Full scale test on environmental impact of diaphragm wall trench
installation in Amsterdam
J.C.W.M. de Wit i) , H.J. Lengkeek ii)

ABSTRACT
This year the construction of the deep underground stations for the new Amsterdam metro line will start. As a
part of the stations’ design a full scale test on the installation of diaphragm wall trenches has been carried out
to investigate the impact on the environment. This paper discusses test program, test results, the interpretation
of the test results and the 3D FE modelling that was used for prediction and validation purposes.
Keywords: deep excavations, underground stations, diaphragm walls, FE modelling, full scale test

1 INTRODUCTION
The excavation of the building pit and the construc-
The new North/South Line metro in Amsterdam will tion of the permanent body can be analysed with a
connect the northern and southern suburbs with the 2D FE-model, in which the full building sequence
city centre (de Wit, 1998). The underground stations, with time schedule is processed (figure 1). The ex-
20-25 m wide and 200-260 m long, will be con- cavation of the diaphragm wall trench however, is
structed at very busy locations and close to historical far more complicated because of the 3 dimensional
buildings. The excavation will be carried out to a behaviour. Therefore it was decided to carry out a
depth of over 30 m in soft soil conditions with high research project on the diaphragm walls’ excavation.
ground water levels. The project consists of the following parts:
− prediction of the impact with a three dimensional
finite element model (3D FE-model);
− full-scale test program at the Mondriaan Tower
construction site in Amsterdam near the Amstel
river;
− interpretation test results;
− validation of the 3D FE-model based on the test
results that have become available.
The first two parts of the test were described exten-
sively in an earlier paper (de Wit et al, 1999) and
will only be summarised here. The interpretation of
the test results and the validation of the 3D FEM-
model are discussed in this paper.

2 DIAPHRAGM WALL INSTALLATION
Figure 1. Typical cross section of underground station. Diaphragm wall installation is carried out incre-
mentally by the construction of individual panels to
The underground stations will be constructed in a some planned sequence. The panels’ dimensions can
building pit of 40 m long braced diaphragm walls. vary considerably depending on the design and the
The historical environment requires a careful ap- local circumstances. The construction of a dia-
proach of all construction processes needed to build phragm panel is carried out from surface level by
the underground station: means of a mechanical device such as a bucket grab
− excavation of the diaphragm wall trench; (figure 2) or hydro fraise.
− excavation of the building pit; A progressive excavation of a trench in the
− construction of permanent body. ground is allowed in such a way that stabilising fluid
i) grade engineer deep underground stations, Design Office North/South Line Amsterdam, ROYAL HASKONING Rotterdam,
Division Transport and Infrastructure, Civil engineering structures and geotechnics , The Netherlands
ii) geotechnical engineer deep underground stations, Design Office North/South Line Amsterdam, Witteveen + Bos Deventer, The
Netherlands
J.C.W.M. de Wit, H.J. Lengkeek. Full scale test on environmental impact of diaphragm wall trench installation in Amsterdam, . Proc. Int. Sym. on Geotechnical
Aspects of Underground Construction in Soft Ground, Toulouse, 2002, France. -1-

(bentonite) is introduced simultaneously as the Table 1. Stratification and soil properties.
trenching operation proceeds. Once the excavation is Layer Z [m NAP] γsat [kN/m3] qc [MPa]
completed the reinforcement cage is inserted into the Fill (sand) 2.0 20.0 10
Holocene Clay -1.0 14.3 0.5
bentonite-filled trench. Furthermore the trench will
Peat (“holland” peat) -3.5 10.3 0.5
be filled with concrete by way of tremie pipes, Clay -7.0 15.2 1.0
thereby displacing the bentonite from the bottom up. Peat (“basis”peat) -11.0 11.7 1.5
During excavation the stability of the trench is Pleistocene Sand -13.5 20.0 20
satisfied by means of a combination of support pres- (1st sand layer)
sure of the bentonite slurry and 3D stress distribution Clay (Eem clay) -17.0 18,5 2.0
in the surrounding ground, referred to as arching. Sand -28.0 19,0 20
Clay -42.0 18,5 2.0

3.2 Diaphragm wall and test location
The test program was carried out at a construction
site for the future 100 m high Mondriaan Tower
(figure 3). Underneath the office building a 2 storey
underground parking is constructed. Diaphragm
walls(length 35 m) are applied as building pit wall
and will act as structural wall to the underground
parking in the final stage. Some of the panels, with a
length of 55 m, will also serve as foundation ele-
ment.

Figure 2. Excavation with a bucket grab.

3 FULL SCALE TEST

The objects of the full-scale test program at the
Mondriaan Tower construction site is to monitor:
− vertical and horizontal deformations of the
ground adjacent to the excavated trench;
− settlement of loaded piles;
− impact on bearing capacity of piles,
due to sequential installation (excavation and con-
creting) of adjoining diaphragm wall panels.

3.1 Stratification and geotechnical parameters
The surface level is at NAP + 2.0 m (ordnance date).
The stratification and geotechnical parameters are Figure 3. Impression of the Mondriaan Tower.
listed in Table 1.
In general the ground conditions are representa- Figure 4 shows (approximately ¼ of the building
tive of a non-uniform stratum with made ground, pit) the diaphragm walls at the test location includ-
Holocene soft clay and peat layers overlaying Pleis- ing the sequence of excavation.
tocene medium dense sand layers and overconsoli- The panel no’s 2 and 3 were excavated in one
dated clay layers. The ground conditions at the test course. The panel no’s 1, 4 and 5 were excavated in
site are comparable to those at the locations of the 2 or 3 courses as a consequence of different widths
future stations of the North/South line. The ground- or shapes.
water level is NAP -0.4 m, the piezometric level of
the deeper aquifers is NAP -3.0 m.


Figure 4. Layout of panel and instrumentation.
Figure 5. Impression of test site, the total station in back-
ground.
3.3 Instrumentation and tests
It was decided to focus more on monitoring of de- 3.4 Test piles
formations of the ground rather than on monitoring In the test field 3 steel piles with a diameter of 110
of changes in stresses. Vertical ground deformations mm, representative for typical historical timber piles
were monitored by: in Amsterdam, were driven into the first sand layer.
− 48 precise levelling points at surface level were During excavation the settlements of the piles were
placed in a regular grid; monitored. The pile settlements are to be compared
− underneath 11 precise levelling points electronic with the vertical ground deformation monitored at
extensometers were installed to monitor vertical the nearest reference point at surface level and the
ground deformations on deeper levels (NAP –8m, nearest extensometer at pile toe level.
-15, -31 and –51). On each pile, installed at a distance of about 0.7
These deformations and also the pile settlements times the panel width to the trench, bearing capacity
(par.3.4) were monitored continuously with a total tests were carried out before and after the excavation
station (figure 5). During the period of excavation of of the diaphragm walls (figure 6).
the panels 1 to 5, which lasted about 3 weeks, each
of these instruments was monitored at least once in
every 20 minutes.
To monitor horizontal deformations 14 tubes for
inclinometers were installed, that were monitored by
hand on pre specified moments related to the exca-
vation and concreting of the panels.
In two panels 3 piezometers were installed at dif-
ferent depths. This was realised by attaching pie-
zometers to the reinforcement cages. The instru-
ments allowed to monitor the changes in pressure of
the bentonite and concrete in time. The wet concrete
pressure is hydrostatic only to a certain depth be-
neath the concrete surface, the so-called “critical
depth” ( Lings et al. 1994). The critical depth is
mainly influenced by the type and temperature of the
concrete mix and by the pouring rate of the concrete. Figure 6. Pile testing.
In this way the lateral pressure of the wet concrete,
which appeared to be an important parameter in the
FE-model, could be determined. 4 TEST RESULTS
To investigate if relief of original stresses within
the stratum has occurred CPT’s (Cone Pressiometer The measurements were carried during the period of
Test) were carried out before and after the installa- 21-09-1998 until 08-02-1999. The diaphragm walls
tion of diaphragm walls. installation at the test field took place from 10-11-
1998 until 03-12-1998. Both the diaphragm wall in-
stallation and test program were carried out satis-

factory. Based on the raw data only it was concluded obvious and temporary errors and was performed
that: by the monitoring experts of Soldata.
1. No significant environmental impact occurred: − The test interpretation is primary focussed on the
- minor vertical ground deformations on surface rectangular shaped panels since these are mostly
level and on deeper levels; applied in the stations’ design. This is achieved
- minor horizontal ground deformations during by using a limited data set in which the immedi-
excavation of the trench; ate impact of the irregular panel shapes was
- substantial horizontal ground deformations in omitted for the benefit of the FE validations. This
soft top layers, however impact on piles was was possible since these panels were installed
not observed; first.
- minor horizontal ground deformations in − Correction of the vertical deformations on deep
bearing sand layers and deep clay layers. levels with the effect of the horizontal deformed
2. Pile bearing capacity was not affected; wire of the extensometer. This will be explained
3. An influence of the depth of a panel on the test later.
results was not monitored, which was already
noted at the predictions;
4. The influence of the width of a panel was limited, 4.2 Surface settlements
which was not confirmed by the predictions. Pos- The targets on surface level show a minor settlement
sibly the sequence of installation played a role. during excavation of the trench, whereas the area
This will be illustrated later; that is influenced is limited. At a distance of 1.2 m to
5. Environmental impact at panels with an irregular the trench (1st grid line) settlements of max. 4 mm
shape was limited but significant larger than at due to excavation were monitored. When the con-
rectangular panels. creting of the panel was almost completed an instant
heave of max. 4 mm at the 1st grid line was ob-
V ertical deform atio n [m m ] H orizo ntal de fo rm atio n [m m ] served at surface level (figure 8). This instant heave
0 0 can be explained by undrained deformation of the
soft clay layers in between the sand layers. The lat-
eral concrete pressure pushed the Holocene layers
aside. Because of undrained behaviour the soils were
-10 -10 not compressed but horizontally displaced. This is
confirmed by the inclinometer measurements.

Vertical surface deformation at several distances
-20 -20
[m] during D-wall installation
0 2 4 6 8 10
4

-30 -30 2
Vertical deformation [mm]

4
0
1
-2 5 2
-40 -40
-20 -10 0 10 20
3
-4
Figure 7. Shaded plot of maximum measured vertical and hori-
zontal deformations. -6

-8
4.1 Interpretation of the test results
-10
After the test program the results were evaluated and
initial during exc. after exc.
interpreted. First of all this resulted in an increase of
after concr. final D-wall
understanding of the effects of diaphragm wall in-
stallation and secondly it made the test results acces- Figure 8. Settlements on surface level.
sible to back analyses to validate the FE model.
For that purpose adjustments of the raw data set
were carried out: 4.3 Horizontal ground deformations
− Data cleaning, which means that obvious spikes, During excavation the horizontal ground deforma-
temporary external influences or temporary bad tions were less than 10 mm. Due to concreting minor
functioning were corrected. This only concerns

horizontal ground deformations were measured in
Total horizontal (inclinometer) displacements
the bearing sand and deep clay layers. Just before the [mm] at distances to D-wall
completion of the concreting an instant large hori-
-200 -150 -100 -50 0 50
zontal deformation away form the trench was meas-
0
ured in the top soft clay layers (figure 9). The maxi-
mum horizontal ground deformation occurred at
NAP-6 m to NAP-9 m. For a single panel this was -5
approx. 100 mm away from the trench (at a distance
of 1.2 m to the trench); for the combined effect of -10
several panels this was approx.150 mm.

Depth [m]
-15

Horizontal displacements (inclinometer) in
time [mm] -20

-150 -100 -50 0 50
0 -25
Reference date: 26-11-1998 7:07
-5
30-11-1998 8:58 -30

-10 1.25 m 2.45 m 4.0 m 5.6 m 7.2 m

Depth [m]
-15 Figure 10. Measured total horizontal deformations wide panel
01-12-1998 14:21
at several distances from trench.
-20

-25 4.4 Subsurface settlements
On deeper levels (15 to 30 m below surface level)
-30
the extensometer results show maximum settlements
-35 that are within the same range as on surface level,
however heave due to the concreting effect was not
26-11-1998 12:13 27-11-1998 7:02 observed. In general the vertical downward ground
30-11-1998 8:58 01-12-1998 14:21 deformations due to excavation do not exceed 2 mm.
Figure 9. Measured horizontal deformations in time at 1.2 m However, most extensometers, especially the ones
from trench. close to the trench, indicated a instant settlement (to
about 4 mm at the 1st grid line) at the end of the con-
Figure 10 shows the measured maximum hori- creting phase. At first it was not clear what could
zontal ground deformations perpendicular to the have caused this movement. However an explana-
trench with an increasing distance to the trench. The tion could be found in relation with the inclinometer
deformations differ from the vertical deformations in results. As was explained before the concreting of
magnitude and extent. Although the horizontal the panel caused substantial horizontal ground de-
ground deformations decrease with the distance to formations of over 10 cm in the soft top layers. As-
the trench, still some 30 mm was monitored at 8 m suming that the extensometer rod has developed a
distance as a combined effect of several panels. similar horizontal deformation, this means that the
rod has to extend, resulting in the registration of a
settlement that in fact has not occurred. When cor-
recting the raw data the settlements develop more
equally which can be considered as a confirmation of
the correction. In figure 11 the corrected and non
corrected settlement lines perpendicular to the trench
immediate after concreting are presented. Finally it
was decided to use both settlement lines bounding an
area in which the actual deformations will occur.


Total vertical displacements (extensometer)
[mm] at NAP-15 m excl./incl. correction for
In the test program, on three levels in the trench
horizontal displacement
0.0 2.0 4.0 6.0 8.0 10.0
piezometers were installed (attached to reinforce-
4.0
ment cage) allowing for monitoring the development
of the lateral pressure during concreting and the be-
ginning of the hardening process (figure 12). The
Vertica displacement [mm]

2.0
test results allowed for a determination of the critical
0.0 depth. However the critical depth appeared to be
varying over the depth of the trench and depending
-2.0 on the pouring rate (in meters height per hour). The
higher pouring rate in the deep part of the trench re-
-4.0 sulted in a larger critical depth.
In table 2 the results are presented. For the pres-
-6.0 sure envelope still a bilinear diagram can be ob-
tained. However the lower part of the diagram
-8.0 doesn’t relate to the bentonite slurry density but to a
excl.correction V11/08 03:12 higher density with a value between bentonite and
incl.correction V11/08 03:12
D-wall concrete.
fit excl.correction
fit incl.correction
Table 2. Results of piezometer measurements in the trench.
Figure 11. Extensometer results (corrected and non corrected). Measurement: At the top At the base Unit
Gradient bentonite slurry 12.0 12.0 kN/m
Gradient wet/hardened con- 23.0 19.0 kN/m
4.5 Pressure tests in trench crete
Critical depth 6 >15 m
From the FE predictions it was learned that the lat- Pouring rate 7 >15 m/hr
eral wet concrete pressure in trench surface has a
significant effect on the horizontal deformations of
the soft top ground layers. From literature (Lings et
al. 1994) it is learned that up to a certain depth, the 4.6 Test piles
so called critical depth, the lateral pressure increases
hydrostatic, based on the wet concrete density. Un-
4.6.1 Pile settlements
derneath this level the increase of lateral is related to
The settlements of the test piles provide information
the bentonite slurry density. This bilinear relation is
whether there is a change of bearing capacity due to
caused by the dissipation of water out of the concrete
the installation of diaphragm wall panels. Pile set-
and the beginning of the hardening process. From
tlements larger than the vertical ground deformations
literature critical depths of 5 to 15 m are known.
at the same location could be an indication of loss of
Piezometer measurement during D-wall pile bearing capacity.
installation [kPa] However, the pile settlements are in the same
0 200 400 600 magnitude as the subsoil settlements. Test piles no.1
5.0 and 3 (about 2.4 m from narrow panel) settled 3 mm
to 6 mm; pile no.2 at (about 5.6 m from wide panel)
0.0 hardly settled (less than 1 mm). Because the pile
-5.0 settlements and the vertical ground deformations at
Depth [m..NAP]

4 the same level correspond very well it is concluded
-10.0 that the bearing capacity is not reduced.
-15.0 3 It appeared from the raw data set that the irregular
panels (Z and corner shape), which are close to the
-20.0 2 piles no. 1 and 3, had a significant influence on the
1 settlements of these piles. For example, the total set-
-25.0
tlements of pile no.1 were primary caused by the in-
-30.0 stallation of the irregular Z-shaped panel and not by
the nearest rectangular panel. For pile no.3 no set-
11:00 12:30
tlements were measured due to the installation of the
14:10 15:30
adjacent wide panel 4, which had a three day bento-
bilinear concrete fit bentonite
nite slurry stage (weekend panel).
Figure 12. Piezometer measurements in the trench.

4.6.2 Horizontal deformations
Attention was paid to the effect of the large hori-
<- Friction ratio (Rf) [%]
zontal deformations in the top soft soil layers as a re-
20 15 10 5 0
sult of concreting the panel. It was investigated if
these deformations could affect the piles. Therefore 0
an upper bound approach was adopted in which the
deformations were considered as induced deforma-
-5
tions to the piles. It then was learned that these de-
formations are not affective, if the stiffness of the

Depth [m..NAP]
-10
piles is limited. A limited stiffness means that the
pile can follow these deformations easily. This is
-15
surely the case with 100-120 mm diameter timber
piles. Concrete piles are more sensible to this phe-
nomenon since their stiffness is usually substantial -20
larger. However, concrete piles are hardly applied
along the metros´ alignment, but it was decided to -25
investigate these locations in more detail.
-30
4.6.3 Bearing capacity tests 0 10 20 30 40
To detect a possible loss of pile bearing capacity the Cone resistance qc [MPa] ->
piles were tested before and after the installation of qc before qc after Rf before Rf after
the diaphragm wall. In advance calculations were
carried out, using CPT’s, to determine the bearing Figure 13. CPT test results before and after diaphragm wall in-
capacity based on the Dutch codes and also an upper stallation.
bound value of the bearing capacity. In the Dutch
Code calculations only the bearing sand layers are 4.7 Cone pressiometer test
taken into account. The upper bound value included
all layers. The pile tests that were carried out before Assessment of the effect of diaphragm wall installa-
the installation of the diaphragm wall indicated a tion on changes in stresses and bearing capacity is
bearing capacity comparable to the Dutch Code made by means of cone pressiometer tests (CPT),
bearing capacity. However, the pile tests that were which were performed before and after the dia-
carried out afterwards indicated a substantial in- phragm wall installation in vicinity of and further
creased bearing capacity approaching the calculated away from of the trench. A change of the cone re-
upper bound value sistance is an indication for a change in the bearing
Apparently the soft layers paid a contribution as capacity of the piles. Figure 13 shows that there is no
well. Possibly caused by the increased effective change in cone resistance in the bearing sand layers
stresses due to the wet concrete pressure, which was and that there is a slight increase of cone resistance
indicated in the CPT’s that were carried out afte r- and friction resistance in the top soft layers. This
wards. The fact that the loading steps in the tests af- could even be an indication for an increase of the
terwards took significantly more time was an indica- pile bearing capacity, which was confirmed by the
tion that the soft soil layers played a role and pile load tests (chapter 4.6.3).
absorbed load. Eventually it was concluded that
there was no loss of pile bearing capacity due to the 4.8 Influence panel width and panel shape
installation of diaphragm walls.
As was stated before the panel width hardly influ-
Table 3. Data pile tests and working load. enced the test result, which was not expected. How-
Pile tests Pile 1 Pile 2 Pile 3 ever this may be explained by the fact that in the test
[kN] [kN] [kN] field the wide panel was installed in between two al-
Prediction by CPT 245-380 175 –300 175-300 ready installed panels. The presence of those two
(min. max) adjacent panels has probably a stiffening effect re-
Ultimate load capacity, 220 185 150 sulting in a reduced impact by the wide panel. Com-
test before paring the horizontal deformations of two adjacent
Ultimate load capacity, 360 280 270
panels 3 (only adjacent panel 2 present) and 4 (adja-
test after
cent panel 3 and 5 present) indicates that there is a
Working load, 150 120 100
significant influence caused by the presence of adja-
during excavation
cent panels and the sequence of installation (fig. 14).
The FE analyses confirms this effect (chapter 5).

5.2 Simulation of installation
Maximum measured Y-displacement, scaled 10 times [m]
The installation of the diaphragm wall is usually
0.0 -5.0 -10.0 -15.0 -20.0
carried out in a relative short period of time. There-
displacement, scaled 10 times
0.0
Maximum measured X-

fore undrained behaviour of the clay and peat layers
-1.0
small panel 3 large panel 3 and drained behaviour of the sand layers is assumed.
-2.0 The installation involves the excavation under beto-
[m]

-3.0 nite slurry support, followed by pouring and subse-
quent hardening of concrete. The construction of the
-4.0
diaphragm wall is modelled using the following
-5.0 stages:
-6.0 1. Excavate a single trench by removing the soil
panel 5a panel 1c panel 2 panel 3 panel 4 elements and simultaneously, applying the bento-
nite pressure on the faces of the trench.
INC02 INC04 INC08 INC08
INC09 INC14 fit panel 3 fit panel 4

2. Fill the trench with concrete by increasing the lat-
Figure 14. Top view of measured horizontal displacements.
eral pressure. The lateral pressure of wet concrete
can be described by the bilinear relation :
At the irregular panel shapes (corner or Z shaped)
the maximum settlements that have been monitored
σh = γc * z z < hcrit
are about double the impact of a rectangular panel.
σh = γc * hcrit + γb * (z – hcrit) z > hcrit
This is true for surface settlements, settlements on
deeper levels and pile settlements. This can be ex-
3. To model the hardening of the concrete, the ele-
plained by the fact that arching in the sub ground ments in the trench are switched on, and the stiff-
will not develop that easy. However the impact is ness and volumetric parameters are changed to
still limited it was decided not to allow irregular those of concrete.
panel shapes close to historical buildings in the un- 4. Construct the adjacent panels, one at the time,
derground stations’ design . using the same procedure, simulating the installa-
tion of a wall.
In case of a constant pouring rate, γ1=γconcrete can be
5 NUMERICAL MODELLING OF DIAPHRAGM adopted above the critical depth and γ2=γbentonite be-
WALL INSTALLATION low the critical depth. However, the test program
showed a different bilinear load distribution in stage
Numerical modelling of the diaphragm wall installa- 2 with a imposed load below the critical depth that is
tion was performed by means of finite element related to a higher density than bentonite slurry,
analyses. The main goal was to develop a validated which means γc>γ2>γb. However, the calculation re-
3D FE-model that can be used to predict the soil de- sults appeared not to be too sensitive to the actual
formations and environmental impact during the in- value of γ2 if γc>γ2>γbγc>γ2>γb , since the soil layers
stallation of the diaphragm walls for the under- below the critical depth are bearing sand layers and
ground stations for North/South line. stiff clay layers.
Using a 3D FE model predictions were performed
before the test program was carried out. Afterwards
the FE model was validated based on the test results 5.3 3D FE predictions
that had become available. An axial symmetric A main objective of the predictions is to gain under-
model was used as a verification of the 3D analyses. standing of the mechanisms that occur during the in-
The calibration was carried out by using the offi- stallation of a diaphragm wall panel. That is also the
cial North/South Line geotechnical parameter set, reason why a relatively simple FE model was
changing the soil parameters within a certain range. adopted, where:
− limited number of ground layers is used;
5.1 FE - model − the relatively simple Mohr Coulomb based soil
model is applied;
For the 3D FE-analyses the 3D version of PLAXIS − the soil properties are taken as the mean values as
has been used. The mesh is build of 3D-wedge- determined at the soil investigation program of
elements with 15 nodes and 6 Gauss-points. For cal- the North/South Line.
culations of one panel a mesh with approximately However this resulted in a somehow simplified
5,000 nodes has been used. Only a quarter of the model, it appeared to be one where the mechanisms
panel is modelled, which means that there are two that occur during installation of diaphragm walls
planes of symmetry (see figure 15). could be detected in a better way and it allowed for

parametric studies. Summarising the next calcula-
tions have been carried out: 300

horizontal effective stress [kPa]
K0-situation
1. calculations of a single panel in homogeneous
ground as a comparison to a model presented in a fase I (bentonite)

conference paper. The results were similar to the 200 stage II (wet concrete)
results that were presented in the paper.
2. calculations of a single panel in the Amsterdam
100
soil, which means a heterogeneous soil profile
3. calculations considering succeeding panels.
Figure 15 illustrates some typical results of the pre- 0
dictions. 0 1 2 3 4 5 6
distance to centre of panel [m]

figure 16. effective horizontal stresses in excavation and con-
creting stage close to trench in horizontal plane.

Prediction of horizontal deformations, stage 1
[mm] (variation of geometry)
0 -10 -20 -30 -40
0

-10

-20
Depth [m NAP]
-30

-40 B

2,05m
-50
L

-60
Figure 15. FE prediction, shaded plot of total displacements.
-70

From the results of these FE predictions the next -80
conclusions could be drawn : b=6,2 l=30 b=2,7 l=30 b=2,7 l=50
1. 3D stress distribution is clearly observed during
both excavation and concreting (figure 16) Figure 17. Illustration vertical arching in heterogeneous
2. during the excavation of the trench small settle- ground.
ments and horizontal deformations in the direc-
tion of the trench occur.
5.4 3D FE validations
3. during concreting heave and horizontal deforma-
tions away form the trench occur as a result of the
hydrostatic wet concrete pressures. 5.4.1 General
4. there is a limited influence of the depth of the It is important to mention that the aim of the valida-
trench. This can be explained by the heterogene- tion was not a perfect fit of the test results, but rather
ous soil profile where vertical arching between a safe upper bound approach that can be used in the
the stiff sand layers reduce the effect of the trench stations’ design. Since the deformations that have
depth ( figure 17); been measured are very small inaccuracies in the
5. there is a significant influence of the width of the system could play a role. Based on the results of the
trench; this was not observed during the test pro- predictions, the test program and the interpretations
gram and became subject of further research at the FE model was already corrected in advance (step
the FE validations. 1):
− More ground layers were introduced.
− Use of advanced non linear soil models that is
necessary to obtain a proper validation (Gourve-
nec et al 1999). The constitutive model that was
selected is the Hardening-Soil model. In the
Hardening Soil model the limiting states of stress

are described by means of the friction angle, φ, Horizontal displacements, stage 2 [mm]
the cohesion, c, and the dilatancy angle, ϕ. The 0 20 40 60 80 100 120
soil stiffness is described much more accurately
by using three different input stiffness’: the tri- 0
axial loading stiffness, E50, the triaxial unloading
stiffness, Eur, and the oedometer loading stiffness,
Eoed. In contrast to the Mohr-Coulomb model, the -10

Depth [m NAP]
Hardening-Soil model also accounts for stress-
dependency of stiffness moduli. This means that
all stiffness’ increase with pressure (figure 18). -20 2,05m

− Higher strength and stiffness for the especially the
deeper soil layers, since the FE predictions did re-
sult in substantial larger deformations than were -30
measured.
The second step was a more fine tuning calibration
which eventually resulted in the so called best fit of -40
the test results(BF). Besides that the soil parameter Test result Best Fit (BF) North/Southline par.set (NZ)
set which has been developed for the North/South
Line was introduced in the validation process (NZ). Figure 19. Horizontal displacements after diaphragm wall in-
However to get results which are comparable to the stallation at 1.2 m distance from trench: 3D FE analyses.
test results, upper bound values from the
North/South Line parameter set for strength and Figure 20 shows the maximum vertical deforma-
stiffness had to be applied for the first sand layers tions of the 1st sand layer at the level NAP-15 m.
and deeper layers. The best fit parameter set con- Again the FE results are comparable to the test re-
tained even higher values for these properties. How- sults. These vertical displacement are especially
ever the upper bound North/South Line approach re- relevant because the sand layer is in most cases the
sults in a safe upper bound of the test results. foundation layer of the timber piles.

hardening
Horizontal distance from panel [m]
shear locus
0 5 10 15 20
4.0
Vertical displacements [mm]

cap with 2.0
compression
hardening 0.0

-2.0

-4.0
ca. -15m

-6.0

Figure 18. PLAXIS Hardening soil model. Soil model
Figure 5: Plaxis Hardening -8.0
Extensometer (no corr.) Extensometer (correction)
5.4.2 Calculation results for a single panel D-wall Best-Fit (BF)
Figure 19 shows the maximum horizontal displace- North/Southline par.set (NZ) Prediction (MC-model)
ments at the centre of the panel, at approximately 2
m from the trench. The maximum displacement oc- Figure 20. Vertical displacements after diaphragm wall instal-
curs in the Holocene top-layers. The calculations lation at NAP-15 m: 3D FE analyses.
with NZ parameters and in particular the BF pa-
rameters are in good agreement with the test-results. 5.4.3 Influence of panel size and installation se-
quence
At the test site 5 panels were monitored with differ-
ent length, width and shape. Like the FE predictions
also the validations showed an increase of impact
when the width of a panel increases. However, this
was not found at the test program where also a wide

panel was part of the test field. The reason for this to be a very powerful tool, since it can be applied
apparent discrepancy probably was the installation very easily and parametric studies can be carried out
sequence of the panels. The adjacent narrow panels in a very short period of time. Despite of the differ-
(width 2.7 m) were installed before the wide panel in ences of a circular and rectangular trench, the 2D
a relatively undisturbed subsoil whereas the wide axial symmetric model gives a reasonable impres-
panel (length is 6.4 m) was installed in between two sion of mechanisms, the stress distribution and the
former installed panels. Those adjacent panels extent of deformations, which can be very useful de-
causes a reduction of the displacements because of: veloping the 3D model.
− load transfer to the adjacent stiff concrete panels;
− hardening of the soil due to the installation of the
adjacent panels the soil is overconsolidated. 6 FINAL CONCLUSIONS
To confirm this explanation the described situation
is simulated with the 3D FE model. Figure 21 shows First of all it is important to conclude that the full
the horizontal displacements of single panels with a scale test did come up to its expectations. The goals
width of 3.2 m (narrow) and 6.4 m (wide). The hori- that were defined in advanced were all more or less
zontal displacement after stage 2 of the single wide satisfied :
panel is about two times the displacement of the nar- − the installation of a diaphragm wall has a minor
row panel. In the same figure also the results are environmental impact and no affect on the bear-
shown of a wide panel in between two former in- ing capacity of the piles;
stalled panels “b=6.2m enclosed (NZ)”. It can be − panels with a irregular shape, like corner panels
concluded that the horizontal deformations are sig- or a Z shaped panel resulting in a substantial
nificantly smaller than for a single wide panel, which higher impact. It is recommended not to apply
meets the explanation made above. these panels when the distance to adjacent build-
ings is small
Calculated horizontal displacements 2 [mm] − modelling the excavation and concreting of a dia-
0 50 100 150 200
phragm wall is reliable using the 3D Finite Ele-
ment Method including advanced non linear con-
stitutive soil models.
0
− The application of the upper bound North/South
Line set for soil properties results in a safe upper
-10 bound of the test results and can be used in the
Depth [m NAP]

underground stations’ design.

-20
REFERENCES
2,05m

-30 Gourvenec, S.M. & W. Powrie (1999). Three-dimensional fi-
nite-element analysis of diaphragm wall installation. Geo-
technique 49, No. 6, 801-823.
-40
Lings, M.L. & C.W.W. Ng & D.F.T. Nash (1994). The lateral
pressure of wet concrete in diaphragm wall panels cast un-
b=3,2m (NZ) b=6,2m (NZ) b=6,2m enclosed (NZ) der bentonite. Proc. Instn. Civ. Engrs Geotech. Engng 107,
July, 163-172.
Figure 21. Horizontal displacements of single panel (narrow Cowland, J.W. & Thorley, C.B.B. 1984, Ground and building
and wide) and enclosed wide panel: 3D FE analyses. settlement associated with adjacent slurry trench excava-
tion, Proceedings third conference on ground movements
and structures, p. 723-728.
5.5 Axial symmetric model Lings, M.L. & Ng, C.W.W. & Nash, D.F.T. (1994), The lateral
pressure of wet concrete in diaphragm wall panels cast un-
In combination with the 3D FE model a 2D FE axial der bentonite, Proc. Instn. Civ. Engrs. Geotech. Engng, 163-
symmetric model was used to test the 3D model and 172.
to investigate all kinds of features like the behaviour Ng, C.W.W & Lings, M.L. & Simpson, B. & Nash, D.F.T.
of the (soft) top layers. The 2D axial symmetric (1995). An approximate analysis of he three-dimensional ef-
analyses confirms the conclusions of minor dis- fects of diaphragm wall installation, Geotechnique 45, No 3,
497-507.
placements during excavation (stage 1). It also Ng, C.W.W. & Yan, R.W.M.(1998). Prediction of Ground De-
shows that the soft clay layers were pushed aside formations during a diaphragm wall panel construcion, 13 e
when the concrete load is applied (stage 2). How- Southeast Asian Geotechncal Conference, Taiwan.
ever, the results of the 2D axial symmetric model Ng, C.W.W. & Yan, R.W.M. (1998b), Stress Transfer and De-
can not be used for validation purposes it appeared formation Mechanisms around a Diaphragm wall panel,


Journal of geotechnical and geoenvironmental engineering.
Vol. 124, No. 7, July 1998.
Wit, de J.C.W.M. (1998). Design of underground stations on
the North/South line. Proc. of the World Tunnel Congres,
Sao Paulo.
Wit, de J.C.W.M. & J.C.S Roelands & M. de Kant (1999). Full
scale test on environmental impact of diphragm wall trench
excavation in Amsterdam. Proc. Int. Sym. on Geotechnical
Aspects of Underground Construction in Soft Ground, To-
kyo, Japan, 723-730.
Wit, de J.C.W.M. & Lengkeek (2002), H.J.Full scale test on
environmental impact of diphragm wall trench excavation in
Amsterdam – the final results. Proc. Int. Sym. on Geotech-
nical Aspects of Underground Construction in Soft Ground,
Toulouse, France.


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