Full scale test on environmental impact of ... - Royal Haskoning

<strong>Full</strong> <strong>scale</strong> <strong>test</strong> 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 <strong>scale</strong> <strong>test</strong> on the installation of diaphragm wall trenches has been carried out
to investigate the impact on the environment. This paper discusses <strong>test</strong> program, <strong>test</strong> results, the interpretation
of the <strong>test</strong> results and the 3D FE modelling that was used for prediction and validation purposes.
Keywords: deep excavations, underground stations, diaphragm walls, FE modelling, full <strong>scale</strong> <strong>test</strong>
1 INTRODUCTION
The new North/South Line metro in Amsterdam will
connect the northern and southern suburbs with the
city centre (de Wit, 1998). The underground stations,
20-25 m wide and 200-260 m long, will be constructed
at very busy locations and close to historical
buildings. The excavation will be carried out to a
depth of over 30 m in soft soil conditions with high
ground water levels.
The excavation of the building pit and the construction
of the permanent body can be analysed with a
2D FE-model, in which the full building sequence
with time schedule is processed (figure 1). The excavation
of the diaphragm wall trench however, is
far more complicated because of the 3 dimensional
behaviour. Therefore it was decided to carry out a
research project on the diaphragm walls’ excavation.
The project consists of the following parts:
− prediction of the impact with a three dimensional
finite element model (3D FE-model);
− full-<strong>scale</strong> <strong>test</strong> program at the Mondriaan Tower
construction site in Amsterdam near the Amstel
river;
− interpretation <strong>test</strong> results;
− validation of the 3D FE-model based on the <strong>test</strong>
results that have become available.
The first two parts of the <strong>test</strong> were described extensively
in an earlier paper (de Wit et al, 1999) and
will only be summarised here. The interpretation of
the <strong>test</strong> results and the validation of the 3D FEMmodel
are discussed in this paper.
Figure 1. Typical cross section of underground station.
The underground stations will be constructed in a
building pit of 40 m long braced diaphragm walls.
The historical environment requires a careful approach
of all construction processes needed to build
the underground station:
− excavation of the diaphragm wall trench;
− excavation of the building pit;
− construction of permanent body.
2 DIAPHRAGM WALL INSTALLATION
Diaphragm wall installation is carried out incrementally
by the construction of individual panels to
some planned sequence. The panels’ dimensions can
vary considerably depending on the design and the
local circumstances. The construction of a diaphragm
panel is carried out from surface level by
means of a mechanical device such as a bucket grab
(figure 2) or hydro fraise.
A progressive excavation of a trench in the
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. <strong>Full</strong> <strong>scale</strong> <strong>test</strong> 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
trenching operation proceeds. Once the excavation is
completed the reinforcement cage is inserted into the
bentonite-filled trench. Furthermore the trench will
be filled with concrete by way of tremie pipes,
thereby displacing the bentonite from the bottom up.
During excavation the stability of the trench is
satisfied by means of a combination of support pressure
of the bentonite slurry and 3D stress distribution
in the surrounding ground, referred to as arching.
Table 1. Stratification and soil properties.
Layer Z [m NAP] γ sat [kN/m 3 ] q c [MPa]
Fill (sand) 2.0 20.0 10
Holocene Clay -1.0 14.3 0.5
Peat (“holland” peat) -3.5 10.3 0.5
Clay -7.0 15.2 1.0
Peat (“basis”peat) -11.0 11.7 1.5
Pleistocene Sand
-13.5 20.0 20
(1 st sand layer)
Clay (Eem clay) -17.0 18,5 2.0
Sand -28.0 19,0 20
Clay -42.0 18,5 2.0
3.2 Diaphragm wall and <strong>test</strong> location
The <strong>test</strong> 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 element.
Figure 2. Excavation with a bucket grab.
3 FULL SCALE TEST
The objects of the full-<strong>scale</strong> <strong>test</strong> 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 concreting)
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
listed in Table 1.
In general the ground conditions are representative
of a non-uniform stratum with made ground,
Holocene soft clay and peat layers overlaying Pleistocene
medium dense sand layers and overconsolidated
clay layers. The ground conditions at the <strong>test</strong>
site are comparable to those at the locations of the
future stations of the North/South line. The groundwater
level is NAP -0.4 m, the piezometric level of
the deeper aquifers is NAP -3.0 m.
Figure 3. Impression of the Mondriaan Tower.
Figure 4 shows (approximately ¼ of the building
pit) the diaphragm walls at the <strong>test</strong> location including
the sequence of excavation.
The panel no’s 2 and 3 were excavated in one
course. The panel no’s 1, 4 and 5 were excavated in
2 or 3 courses as a consequence of different widths
or shapes.
J.C.W.M. de Wit, H.J. Lengkeek. <strong>Full</strong> <strong>scale</strong> <strong>test</strong> 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. -2-

Figure 4. Layout of panel and instrumentation.
3.3 Instrumentation and <strong>test</strong>s
It was decided to focus more on monitoring of deformations
of the ground rather than on monitoring
of changes in stresses. Vertical ground deformations
were monitored by:
− 48 precise levelling points at surface level were
placed in a regular grid;
− underneath 11 precise levelling points electronic
extensometers were installed to monitor vertical
ground deformations on deeper levels (NAP –8m,
-15, -31 and –51).
These deformations and also the pile settlements
(par.3.4) were monitored continuously with a total
station (figure 5). During the period of excavation of
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 excavation
and concreting of the panels.
In two panels 3 piezometers were installed at different
depths. This was realised by attaching piezometers
to the reinforcement cages. The instruments
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 beneath
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.
In this way the lateral pressure of the wet concrete,
which appeared to be an important parameter in the
FE-model, could be determined.
To investigate if relief of original stresses within
the stratum has occurred CPT’s (Cone Pressiometer
Test) were carried out before and after the installation
of diaphragm walls.
Figure 5. Impression of <strong>test</strong> site, the total station in background.
3.4 Test piles
In the <strong>test</strong> field 3 steel piles with a diameter of 110
mm, representative for typical historical timber piles
in Amsterdam, were driven into the first sand layer.
During excavation the settlements of the piles were
monitored. The pile settlements are to be compared
with the vertical ground deformation monitored at
the nearest reference point at surface level and the
nearest extensometer at pile toe level.
On each pile, installed at a distance of about 0.7
times the panel width to the trench, bearing capacity
<strong>test</strong>s were carried out before and after the excavation
of the diaphragm walls (figure 6).
Figure 6. Pile <strong>test</strong>ing.
4 TEST RESULTS
The measurements were carried during the period of
21-09-1998 until 08-02-1999. The diaphragm walls
installation at the <strong>test</strong> field took place from 10-11-
1998 until 03-12-1998. Both the diaphragm wall installation
and <strong>test</strong> program were carried out satis-
J.C.W.M. de Wit, H.J. Lengkeek. <strong>Full</strong> <strong>scale</strong> <strong>test</strong> 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. -3-

factory. Based on the raw data only it was concluded
that:
1. No significant environmental impact occurred:
- minor vertical ground deformations on surface
level and on deeper levels;
- minor horizontal ground deformations during
excavation of the trench;
- substantial horizontal ground deformations in
soft top layers, however impact on piles was
not observed;
- minor horizontal ground deformations in
bearing sand layers and deep clay layers.
2. Pile bearing capacity was not affected;
3. An influence of the depth of a panel on the <strong>test</strong>
results was not monitored, which was already
noted at the predictions;
4. The influence of the width of a panel was limited,
which was not confirmed by the predictions. Possibly
the sequence of installation played a role.
This will be illustrated later;
5. Environmental impact at panels with an irregular
shape was limited but significant larger than at
rectangular panels.
0
-10
Vertical deformation [mm]
Horizontal deformation [mm]
0
-10
obvious and temporary errors and was performed
by the monitoring experts of Soldata.
− The <strong>test</strong> interpretation is primary focussed on the
rectangular shaped panels since these are mostly
applied in the stations’ design. This is achieved
by using a limited data set in which the immediate
impact of the irregular panel shapes was
omitted for the benefit of the FE validations. This
was possible since these panels were installed
first.
− Correction of the vertical deformations on deep
levels with the effect of the horizontal deformed
wire of the extensometer. This will be explained
later.
4.2 Surface settlements
The targets on surface level show a minor settlement
during excavation of the trench, whereas the area
that is influenced is limited. At a distance of 1.2 m to
the trench (1 st grid line) settlements of max. 4 mm
due to excavation were monitored. When the concreting
of the panel was almost completed an instant
heave of max. 4 mm at the 1st grid line was observed
at surface level (figure 8). This instant heave
can be explained by undrained deformation of the
soft clay layers in between the sand layers. The lateral
concrete pressure pushed the Holocene layers
aside. Because of undrained behaviour the soils were
not compressed but horizontally displaced. This is
confirmed by the inclinometer measurements.
-20
-20
Vertical surface deformation at several distances
[m] during D-wall installation
0 2 4 6 8 10
4
-30
-40
-40
-20 -10 0 10 20
Figure 7. Shaded plot of maximum measured vertical and horizontal
deformations.
4.1 Interpretation of the <strong>test</strong> results
After the <strong>test</strong> program the results were evaluated and
interpreted. First of all this resulted in an increase of
understanding of the effects of diaphragm wall installation
and secondly it made the <strong>test</strong> results accessible
to back analyses to validate the FE model.
For that purpose adjustments of the raw data set
were carried out:
− Data cleaning, which means that obvious spikes,
temporary external influences or temporary bad
functioning were corrected. This only concerns
-30
J.C.W.M. de Wit, H.J. Lengkeek. <strong>Full</strong> <strong>scale</strong> <strong>test</strong> 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. -4-
Vertical deformation [mm]
2
0
-2
-4
-6
-8
-10
initial during exc. after exc.
after concr. final D-wall
Figure 8. Settlements on surface level.
5
4.3 Horizontal ground deformations
4
3
During excavation the horizontal ground deformations
were less than 10 mm. Due to concreting minor
2
1

horizontal ground deformations were measured in
the bearing sand and deep clay layers. Just before the
completion of the concreting an instant large horizontal
deformation away form the trench was measured
in the top soft clay layers (figure 9). The maximum
horizontal ground deformation occurred at
NAP-6 m to NAP-9 m. For a single panel this was
approx. 100 mm away from the trench (at a distance
of 1.2 m to the trench); for the combined effect of
several panels this was approx.150 mm.
Horizontal displacements (inclinometer) in
time [mm]
-150 -100 -50 0 50
0
Reference date:
01-12-1998 14:21
26-11-1998 7:07
-5
30-11-1998 8:58
26-11-1998 12:13 27-11-1998 7:02
30-11-1998 8:58 01-12-1998 14:21
-10
-15
-20
-25
-30
-35
Figure 9. Measured horizontal deformations in time at 1.2 m
from trench.
Figure 10 shows the measured maximum horizontal
ground deformations perpendicular to the
trench with an increasing distance to the trench. The
deformations differ from the vertical deformations in
magnitude and extent. Although the horizontal
ground deformations decrease with the distance to
the trench, still some 30 mm was monitored at 8 m
distance as a combined effect of several panels.
Depth [m]
Total horizontal (inclinometer) displacements
[mm] at distances to D-wall
-200 -150 -100 -50 0 50
0
-5
-10
-15
-20
-25
-30
1.25 m 2.45 m 4.0 m 5.6 m 7.2 m
Figure 10. Measured total horizontal deformations wide panel
at several distances from trench.
4.4 Subsurface settlements
On deeper levels (15 to 30 m below surface level)
the extensometer results show maximum settlements
that are within the same range as on surface level,
however heave due to the concreting effect was not
observed. In general the vertical downward ground
deformations due to excavation do not exceed 2 mm.
However, most extensometers, especially the ones
close to the trench, indicated a instant settlement (to
about 4 mm at the 1 st grid line) at the end of the concreting
phase. At first it was not clear what could
have caused this movement. However an explanation
could be found in relation with the inclinometer
results. As was explained before the concreting of
the panel caused substantial horizontal ground deformations
of over 10 cm in the soft top layers. Assuming
that the extensometer rod has developed a
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 correcting
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.
Depth [m]
J.C.W.M. de Wit, H.J. Lengkeek. <strong>Full</strong> <strong>scale</strong> <strong>test</strong> 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. -5-

Vertica displacement [mm]
4.0
2.0
0.0
-2.0
-4.0
-6.0
-8.0
Total vertical displacements (extensometer)
[mm] at NAP-15 m excl./incl. correction for
horizontal displacement
0.0 2.0 4.0 6.0 8.0 10.0
excl.correction V11/08 03:12
incl.correction V11/08 03:12
D-wall
fit excl.correction
fit incl.correction
Figure 11. Extensometer results (corrected and non corrected).
4.5 Pressure <strong>test</strong>s in trench
From the FE predictions it was learned that the lateral
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
so called critical depth, the lateral pressure increases
hydrostatic, based on the wet concrete density. Underneath
this level the increase of lateral is related to
the bentonite slurry density. This bilinear relation is
caused by the dissipation of water out of the concrete
and the beginning of the hardening process. From
literature critical depths of 5 to 15 m are known.
Depth [m..NAP]
0 200 400 600
5.0
0.0
-5.0
-10.0
-15.0
-20.0
-25.0
-30.0
Piezometer measurement during D-wall
installation [kPa]
4
3
1
2
11:00 12:30
14:10 15:30
bilinear concrete fit bentonite
Figure 12. Piezometer measurements in the trench.
In the <strong>test</strong> program, on three levels in the trench
piezometers were installed (attached to reinforcement
cage) allowing for monitoring the development
of the lateral pressure during concreting and the beginning
of the hardening process (figure 12). The
<strong>test</strong> results allowed for a determination of the critical
depth. However the critical depth appeared to be
varying over the depth of the trench and depending
on the pouring rate (in meters height per hour). The
higher pouring rate in the deep part of the trench resulted
in a larger critical depth.
In table 2 the results are presented. For the pressure
envelope still a bilinear diagram can be obtained.
However the lower part of the diagram
doesn’t relate to the bentonite slurry density but to a
higher density with a value between bentonite and
concrete.
Table 2. Results of piezometer measurements in the trench.
Measurement: At the top At the base Unit
Gradient bentonite slurry 12.0 12.0 kN/m
Gradient wet/hardened concrete
23.0 19.0 kN/m
Critical depth 6 >15 m
Pouring rate 7 >15 m/hr
4.6 Test piles
4.6.1 Pile settlements
The settlements of the <strong>test</strong> piles provide information
whether there is a change of bearing capacity due to
the installation of diaphragm wall panels. Pile settlements
larger than the vertical ground deformations
at the same location could be an indication of loss of
pile bearing capacity.
However, the pile settlements are in the same
magnitude as the subsoil settlements. Test piles no.1
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)
hardly settled (less than 1 mm). Because the pile
settlements and the vertical ground deformations at
the same level correspond very well it is concluded
that the bearing capacity is not reduced.
It appeared from the raw data set that the irregular
panels (Z and corner shape), which are close to the
piles no. 1 and 3, had a significant influence on the
settlements of these piles. For example, the total settlements
of pile no.1 were primary caused by the installation
of the irregular Z-shaped panel and not by
the nearest rectangular panel. For pile no.3 no settlements
were measured due to the installation of the
adjacent wide panel 4, which had a three day bentonite
slurry stage (weekend panel).
J.C.W.M. de Wit, H.J. Lengkeek. <strong>Full</strong> <strong>scale</strong> <strong>test</strong> 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. -6-

4.6.2 Horizontal deformations
Attention was paid to the effect of the large horizontal
deformations in the top soft soil layers as a result
of concreting the panel. It was investigated if
these deformations could affect the piles. Therefore
an upper bound approach was adopted in which the
deformations were considered as induced deformations
to the piles. It then was learned that these deformations
are not affective, if the stiffness of the
piles is limited. A limited stiffness means that the
pile can follow these deformations easily. This is
surely the case with 100-120 mm diameter timber
piles. Concrete piles are more sensible to this phenomenon
since their stiffness is usually substantial
larger. However, concrete piles are hardly applied
along the metros´ alignment, but it was decided to
investigate these locations in more detail.
4.6.3 Bearing capacity <strong>test</strong>s
To detect a possible loss of pile bearing capacity the
piles were <strong>test</strong>ed before and after the installation of
the diaphragm wall. In advance calculations were
carried out, using CPT’s, to determine the bearing
capacity based on the Dutch codes and also an upper
bound value of the bearing capacity. In the Dutch
Code calculations only the bearing sand layers are
taken into account. The upper bound value included
all layers. The pile <strong>test</strong>s that were carried out before
the installation of the diaphragm wall indicated a
bearing capacity comparable to the Dutch Code
bearing capacity. However, the pile <strong>test</strong>s that were
carried out afterwards indicated a substantial increased
bearing capacity approaching the calculated
upper bound value
Apparently the soft layers paid a contribution as
well. Possibly caused by the increased effective
stresses due to the wet concrete pressure, which was
indicated in the CPT’s that were carried out afte r-
wards. The fact that the loading steps in the <strong>test</strong>s afterwards
took significantly more time was an indication
that the soft soil layers played a role and
absorbed load. Eventually it was concluded that
there was no loss of pile bearing capacity due to the
installation of diaphragm walls.
Table 3. Data pile <strong>test</strong>s and working load.
Pile <strong>test</strong>s Pile 1
[kN]
Pile 2
[kN]
Pile 3
[kN]
Prediction by CPT 245-380 175 –300 175-300
(min. max)
Ultimate load capacity, 220 185 150
<strong>test</strong> before
Ultimate load capacity, 360 280 270
<strong>test</strong> after
Working load,
during excavation
150 120 100
Depth [m..NAP]
0
-5
-10
-15
-20
-25
20
15
qc before qc after Rf before Rf after
Figure 13. CPT <strong>test</strong> results before and after diaphragm wall installation.
4.7 Cone pressiometer <strong>test</strong>
Assessment of the effect of diaphragm wall installation
on changes in stresses and bearing capacity is
made by means of cone pressiometer <strong>test</strong>s (CPT),
which were performed before and after the diaphragm
wall installation in vicinity of and further
away from of the trench. A change of the cone resistance
is an indication for a change in the bearing
capacity of the piles. Figure 13 shows that there is no
change in cone resistance in the bearing sand layers
and that there is a slight increase of cone resistance
and friction resistance in the top soft layers. This
could even be an indication for an increase of the
pile bearing capacity, which was confirmed by the
pile load <strong>test</strong>s (chapter 4.6.3).
4.8 Influence panel width and panel shape
As was stated before the panel width hardly influenced
the <strong>test</strong> result, which was not expected. However
this may be explained by the fact that in the <strong>test</strong>
field the wide panel was installed in between two already
installed panels. The presence of those two
adjacent panels has probably a stiffening effect resulting
in a reduced impact by the wide panel. Comparing
the horizontal deformations of two adjacent
panels 3 (only adjacent panel 2 present) and 4 (adjacent
panel 3 and 5 present) indicates that there is a
significant influence caused by the presence of adjacent
panels and the sequence of installation (fig. 14).
The FE analyses confirms this effect (chapter 5).
5
0
J.C.W.M. de Wit, H.J. Lengkeek. <strong>Full</strong> <strong>scale</strong> <strong>test</strong> 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. -7-

Maximum measured X-
displacement, <strong>scale</strong>d 10 times
[m]
0.0
0.0
-1.0
-2.0
-3.0
-4.0
-5.0
-6.0
Maximum measured Y-displacement, <strong>scale</strong>d 10 times [m]
-5.0
-10.0
-15.0
small panel 3 large panel 3
-20.0
panel 5a panel 1c panel 2 panel 3 panel 4
INC02 INC04 INC08 INC08
INC09 INC14 fit panel 3 fit panel 4
Figure 14. Top view of measured horizontal displacements.
At the irregular panel shapes (corner or Z shaped)
the maximum settlements that have been monitored
are about double the impact of a rectangular panel.
This is true for surface settlements, settlements on
deeper levels and pile settlements. This can be explained
by the fact that arching in the sub ground
will not develop that easy. However the impact is
still limited it was decided not to allow irregular
panel shapes close to historical buildings in the underground
stations’ design .
5 NUMERICAL MODELLING OF DIAPHRAGM
WALL INSTALLATION
Numerical modelling of the diaphragm wall installation
was performed by means of finite element
analyses. The main goal was to develop a validated
3D FE-model that can be used to predict the soil deformations
and environmental impact during the installation
of the diaphragm walls for the underground
stations for North/South line.
Using a 3D FE model predictions were performed
before the <strong>test</strong> program was carried out. Afterwards
the FE model was validated based on the <strong>test</strong> results
that had become available. An axial symmetric
model was used as a verification of the 3D analyses.
The calibration was carried out by using the official
North/South Line geotechnical parameter set,
changing the soil parameters within a certain range.
5.1 FE - model
For the 3D FE-analyses the 3D version of PLAXIS
has been used. The mesh is build of 3D-wedgeelements
with 15 nodes and 6 Gauss-points. For calculations
of one panel a mesh with approximately
5,000 nodes has been used. Only a quarter of the
panel is modelled, which means that there are two
planes of symmetry (see figure 15).
5.2 Simulation of installation
The installation of the diaphragm wall is usually
carried out in a relative short period of time. Therefore
undrained behaviour of the clay and peat layers
and drained behaviour of the sand layers is assumed.
The installation involves the excavation under betonite
slurry support, followed by pouring and subsequent
hardening of concrete. The construction of the
diaphragm wall is modelled using the following
stages:
1. Excavate a single trench by removing the soil
elements and simultaneously, applying the bentonite
pressure on the faces of the trench.
2. Fill the trench with concrete by increasing the lateral
pressure. The lateral pressure of wet concrete
can be described by the bilinear relation :
σ h = γ c * z
σ h = γ c * h crit + γ b * (z – h crit )
z < h crit
z > h crit
3. To model the hardening of the concrete, the elements
in the trench are switched on, and the stiffness
and volumetric parameters are changed to
those of concrete.
4. Construct the adjacent panels, one at the time,
using the same procedure, simulating the installation
of a wall.
In case of a constant pouring rate, γ 1 =γ concrete can be
adopted above the critical depth and γ 2 =γ bentonite below
the critical depth. However, the <strong>test</strong> program
showed a different bilinear load distribution in stage
2 with a imposed load below the critical depth that is
related to a higher density than bentonite slurry,
which means γ c >γ 2 >γ b . However, the calculation results
appeared not to be too sensitive to the actual
value of γ 2 if γ c >γ 2 >γ b γ c >γ 2 >γ b , since the soil layers
below the critical depth are bearing sand layers and
stiff clay layers.
5.3 3D FE predictions
A main objective of the predictions is to gain understanding
of the mechanisms that occur during the installation
of a diaphragm wall panel. That is also the
reason why a relatively simple FE model was
adopted, where:
− limited number of ground layers is used;
− the relatively simple Mohr Coulomb based soil
model is applied;
− the soil properties are taken as the mean values as
determined at the soil investigation program of
the North/South Line.
However this resulted in a somehow simplified
model, it appeared to be one where the mechanisms
that occur during installation of diaphragm walls
could be detected in a better way and it allowed for
J.C.W.M. de Wit, H.J. Lengkeek. <strong>Full</strong> <strong>scale</strong> <strong>test</strong> 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. -8-

parametric studies. Summarising the next calculations
have been carried out:
1. calculations of a single panel in homogeneous
ground as a comparison to a model presented in a
conference paper. The results were similar to the
results that were presented in the paper.
2. calculations of a single panel in the Amsterdam
soil, which means a heterogeneous soil profile
3. calculations considering succeeding panels.
Figure 15 illustrates some typical results of the predictions.
horizontal effective stress [kPa]
300
K0-situation
fase I (bentonite)
200
stage II (wet concrete)
100
0
0 1 2 3 4 5 6
distance to centre of panel [m]
figure 16. effective horizontal stresses in excavation and concreting
stage close to trench in horizontal plane.
0
0
Prediction of horizontal deformations, stage 1
[mm] (variation of geometry)
-10
-20
-30
-40
-10
Figure 15. FE prediction, shaded plot of total displacements.
From the results of these FE predictions the next
conclusions could be drawn :
1. 3D stress distribution is clearly observed during
both excavation and concreting (figure 16)
2. during the excavation of the trench small settlements
and horizontal deformations in the direction
of the trench occur.
3. during concreting heave and horizontal deformations
away form the trench occur as a result of the
hydrostatic wet concrete pressures.
4. there is a limited influence of the depth of the
trench. This can be explained by the heterogeneous
soil profile where vertical arching between
the stiff sand layers reduce the effect of the trench
depth ( figure 17);
5. there is a significant influence of the width of the
trench; this was not observed during the <strong>test</strong> program
and became subject of further research at
the FE validations.
Depth [m NAP]
-20
-30
-40
-50
-60
-70
-80
b=6,2 l=30 b=2,7 l=30 b=2,7 l=50
Figure 17. Illustration vertical arching in heterogeneous
ground.
5.4 3D FE validations
5.4.1 General
It is important to mention that the aim of the validation
was not a perfect fit of the <strong>test</strong> results, but rather
a safe upper bound approach that can be used in the
stations’ design. Since the deformations that have
been measured are very small inaccuracies in the
system could play a role. Based on the results of the
predictions, the <strong>test</strong> program and the interpretations
the FE model was already corrected in advance (step
1):
− More ground layers were introduced.
− Use of advanced non linear soil models that is
necessary to obtain a proper validation (Gourvenec
et al 1999). The constitutive model that was
selected is the Hardening-Soil model. In the
Hardening Soil model the limiting states of stress
L
B
2,05m
J.C.W.M. de Wit, H.J. Lengkeek. <strong>Full</strong> <strong>scale</strong> <strong>test</strong> 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. -9-

are described by means of the friction angle, φ,
the cohesion, c, and the dilatancy angle, ϕ. The
soil stiffness is described much more accurately
by using three different input stiffness’: the triaxial
loading stiffness, E 50 , the triaxial unloading
stiffness, E ur , and the oedometer loading stiffness,
E oed . In contrast to the Mohr-Coulomb model, the
Hardening-Soil model also accounts for stressdependency
of stiffness moduli. This means that
all stiffness’ increase with pressure (figure 18).
− Higher strength and stiffness for the especially the
deeper soil layers, since the FE predictions did result
in substantial larger deformations than were
measured.
The second step was a more fine tuning calibration
which eventually resulted in the so called best fit of
the <strong>test</strong> results(BF). Besides that the soil parameter
set which has been developed for the North/South
Line was introduced in the validation process (NZ).
However to get results which are comparable to the
<strong>test</strong> results, upper bound values from the
North/South Line parameter set for strength and
stiffness had to be applied for the first sand layers
and deeper layers. The best fit parameter set contained
even higher values for these properties. However
the upper bound North/South Line approach results
in a safe upper bound of the <strong>test</strong> results.
Depth [m NAP]
0
-10
-20
-30
-40
Horizontal displacements, stage 2 [mm]
0 20 40 60 80 100 120
Test result Best Fit (BF) North/Southline par.set (NZ)
Figure 19. Horizontal displacements after diaphragm wall installation
at 1.2 m distance from trench: 3D FE analyses.
Figure 20 shows the maximum vertical deformations
of the 1 st sand layer at the level NAP-15 m.
Again the FE results are comparable to the <strong>test</strong> results.
These vertical displacement are especially
relevant because the sand layer is in most cases the
foundation layer of the timber piles.
2,05m
hardening
shear locus
4.0
Horizontal distance from panel [m]
0 5 10 15 20
cap with
compression
hardening
Figure Figure 18. PLAXIS 5: Hardening Plaxis Hardening soil model. Soil model
Vertical displacements [mm]
2.0
0.0
-2.0
-4.0
-6.0
-8.0
ca. -15m
5.4.2 Calculation results for a single panel
Figure 19 shows the maximum horizontal displacements
at the centre of the panel, at approximately 2
m from the trench. The maximum displacement occurs
in the Holocene top-layers. The calculations
with NZ parameters and in particular the BF parameters
are in good agreement with the <strong>test</strong>-results.
Extensometer (no corr.)
D-wall
North/Southline par.set (NZ)
Extensometer (correction)
Best-Fit (BF)
Prediction (MC-model)
Figure 20. Vertical displacements after diaphragm wall installation
at NAP-15 m: 3D FE analyses.
5.4.3 Influence of panel size and installation sequence
At the <strong>test</strong> site 5 panels were monitored with different
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 <strong>test</strong> program where also a wide
J.C.W.M. de Wit, H.J. Lengkeek. <strong>Full</strong> <strong>scale</strong> <strong>test</strong> 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. -10-

panel was part of the <strong>test</strong> field. The reason for this
apparent discrepancy probably was the installation
sequence of the panels. The adjacent narrow panels
(width 2.7 m) were installed before the wide panel in
a relatively undisturbed subsoil whereas the wide
panel (length is 6.4 m) was installed in between two
former installed panels. Those adjacent panels
causes a reduction of the displacements because of:
− load transfer to the adjacent stiff concrete panels;
− hardening of the soil due to the installation of the
adjacent panels the soil is overconsolidated.
To confirm this explanation the described situation
is simulated with the 3D FE model. Figure 21 shows
the horizontal displacements of single panels with a
width of 3.2 m (narrow) and 6.4 m (wide). The horizontal
displacement after stage 2 of the single wide
panel is about two times the displacement of the narrow
panel. In the same figure also the results are
shown of a wide panel in between two former installed
panels “b=6.2m enclosed (NZ)”. It can be
concluded that the horizontal deformations are significantly
smaller than for a single wide panel, which
meets the explanation made above.
Depth [m NAP]
0
-10
-20
-30
-40
Calculated horizontal displacements 2 [mm]
0 50 100 150 200
b=3,2m (NZ) b=6,2m (NZ) b=6,2m enclosed (NZ)
Figure 21. Horizontal displacements of single panel (narrow
and wide) and enclosed wide panel: 3D FE analyses.
5.5 Axial symmetric model
In combination with the 3D FE model a 2D FE axial
symmetric model was used to <strong>test</strong> the 3D model and
to investigate all kinds of features like the behaviour
of the (soft) top layers. The 2D axial symmetric
analyses confirms the conclusions of minor displacements
during excavation (stage 1). It also
shows that the soft clay layers were pushed aside
when the concrete load is applied (stage 2). However,
the results of the 2D axial symmetric model
can not be used for validation purposes it appeared
2,05m
to be a very powerful tool, since it can be applied
very easily and parametric studies can be carried out
in a very short period of time. Despite of the differences
of a circular and rectangular trench, the 2D
axial symmetric model gives a reasonable impression
of mechanisms, the stress distribution and the
extent of deformations, which can be very useful developing
the 3D model.
6 FINAL CONCLUSIONS
First of all it is important to conclude that the full
<strong>scale</strong> <strong>test</strong> did come up to its expectations. The goals
that were defined in advanced were all more or less
satisfied :
− the installation of a diaphragm wall has a minor
environmental impact and no affect on the bearing
capacity of the piles;
− panels with a irregular shape, like corner panels
or a Z shaped panel resulting in a substantial
higher impact. It is recommended not to apply
these panels when the distance to adjacent buildings
is small
− modelling the excavation and concreting of a diaphragm
wall is reliable using the 3D Finite Element
Method including advanced non linear constitutive
soil models.
− The application of the upper bound North/South
Line set for soil properties results in a safe upper
bound of the <strong>test</strong> results and can be used in the
underground stations’ design.
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Cowland, J.W. & Thorley, C.B.B. 1984, Ground and building
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