Actes du colloque - Volume 2 - page 504

1380
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
a finite element code was used by applying a visco-plastic soil
model on the dump body.
The time-dependent deformation is mainly governed by 2
parameters namely the reference time t
0
and a creep parameter
defined as C
B
or C
K
respectively. The magnitude of both
parameters was determined using the geodetic measurements at
the stations 4900 m, 5900 m and 6600 m where the dumping
process was completed several years ago. A favourable outcome
between the measurements and the results of the simple model
can be found using C
K
= 0.1 % and setting t
0
at the end of the
dumping process. The stress dependent deformation (stiffness)
was evaluated using the data of cone penetration tests reaching
depths of 72 m below the surface of the dump.
0.0
0.2
0.4
0,6
0.8
1.0
1.2
4000
5000
6000
7000
8000
9000
10000
11000
Station [m]
Deformation [m]
C
K
= 0.05 % for 0 m to 45 m and C
K
= 0.10 %
for 45 m down to the base of the landfill
C
K
= 0.10 % independent from the depth,
deformations up to 2030
Start of observation
1.1.2017
C
K
= 0.05 % for 0 m to 90 m and C
K
= 0.10 %
for 90 m down to the base of the landfill
Start of observation
1.7.2017
Start of observation
31.12.2017
South
North
Figure 8. Prediction of the deformation along the planned A 44 for
different depths treated by soil compaction methods and the effect of an
extended time period after dumping before observing deformations
The continuous lines in the diagram show the predicted
settlements of the dump surface considering C
K
= 0.1 %.
Calculations were undertaken until the year 2030 using 11 cross
sections between station 4900 m and 10500 m. The cross
sections were idealized according to a one-dimensional column
of soil layers dumped during different periods in time.
For the given case that the soils within the dump do not
differ regarding to parameter C
K,
the calculated deformation is
mainly dependent on the depth of the dump and time when
dumping is completed or is intended to be completed.
According to the used logarithmic creep model the deformations
plotted in figure 8, an increase along the route occurs mainly
between 8000 m and 10500 m. In the case where the dumping
process has already been completed since 2 or more years from
the start of observation back to the past, the chosen time when
the observation starts has a minor impact on the deformations
since settlement rates are already small.
From stations 8000 m to 10500 m the period between the
end of the dumping and the start of observation has a strong
influence on the calculated deformations that will occur by the
year 2030. Even in a period of 6 months between the end of the
dumping and the start of observation reduces the calculated
settlements significantly. This is of special interest because the
planned construction progress of the A 44 is put on hold until
the superstructure sensitive to deformations is constructed.
In the simulations the effect of different measures of soil
improvement (mainly compaction methods) were examined.
The dashed and dash-doted lines in figure 8 show the
deformation until the year 2030 for compaction methods
reaching a depth of 45 m and 90 m respectively. It is assumed
that the compaction of the different soil layers will lead to a
lower creep parameter of C
K
= 0.05 % (see chapter 3.2). The
calculation show a 45 m deep treatment of the dump still leads
to a comparably high deformation reaching a maximum of
0.95 m. Even a 90 m deep soil improvement will lead to a
calculated deformation of 0.85 m.
The results of the simulations show that providing enough
time between completing the dumping process and the
construction of parts sensitive to settlement is far more efficient
than soil improvement or treating deep soil layers in the dump.
On waiting at least a 6 month period before the construction of
the A 44 autobahn, a major quantity of settlements will already
have been developed. By the used models settlements of 0.4 m
and 0.3 m are to be expected in between mid 2017 and end 2017
respectively until the year 2030. This magnitude will be covered
by the so-called precautionary gradient providing sufficient
drainage of water by the planned crossfall of the roadway and
the embankment of the motorway (Köther and Reeh 2011).
5
SUMMARY
The paper presents the most important project-specific
conditions including the dumping process and the properties of
the dumped soils along the future A 44 routing. Furthermore,
geodetic measurements have shown to give a good overview on
the time-dependent deformation of the Garzweiler dump. By
use of one-dimensional compression tests the deformation
characteristics of the dump body, consisting mainly of poorly-
graded sand were examined. During the test series main
influencing parameters such as initial density and loading rate
were examined.
Using a simple model for the description of the time-
dependent deformation of the dump and its soils the
effectiveness of soil compaction methods is discussed and
evaluated. The parameters governing the stress- and time-
dependent deformations were calibrated by means of field data
from the geodetic measurements and cone penetration testing.
The simulation results cover the period from the end of the
dumping process to the year 2030. Different periods from the
end of dumping until the observation of the beginning of surface
deformation were considered. It is evident that the period
between the end of dumping and the beginning of construction
of parts of the motorway sensitive to settlement, has a large
impact and can therefore impair the serviceability. By far less
impact was predicted in the case that even deep soil layers of
the dump would be compacted.
In general it can be concluded that the concept of dumping
predominantly coarse-grained soils within the planned route of
the A 44 motorway, is suitable for limiting time-dependent
settlements. The simulation results and geodetic measurements
have shown that by allowing the proposed period of at least 6
months between the end of the dumping process and the start of
the construction work the settlements of structures or pavements
sensitive to deformations are reduced significantly.
6
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