Deformation Properties Analysis of Widen High Embankment on Soft Ground

Physical and Numerical Simulation of Geotechnical Engineering
13th Issue, Dec. 2013
Deformation Properties Analysis of Widen High
Embankment on Soft Ground
YANG Chengzhong, HE Guoxian, TAO Xiaomin
Engineering Research Center of Railway Environmental Vibration and Noise, Ministry of Education, East China Jiaotong
University, Nanchang 330013, Jiangxi, P.R.China
[email protected]
ABSTRACT: When the high embankment are widen on the soft ground, its inner strain and deformation
will be more complicated. Considering the Hejiaping link line widen project in Shanghai-Chengdu
Expressway West, applying the Sigma/M model of special software GeoStudio established a twodimension finite element model, applying the equivalent line elasticity theory simulated the deformation
properties of the widen project of the high embankment on soft ground. It shows that with the increases of
elasticity modulus of soft soil embankment and the new embankment, the greatest settlement of
embankment reduces distinctly. If the elasticity modulus of soft soil embankment is greater than 20Mpa
and its ratio of the new and old embankment is bigger than 1, the impact is not distinct. Laying the geogrid
on the new embankment can reduce the lateral deformation of the embankment as well as the settlement
difference between the old and new embankments.
KEYWORDS: Soft ground, High embankment, Widen project, Settlement, Elasticity modulus, Geogrid
1 INTRODUCTION
In recent years, some early built mountain west road can
not meet the needs of the traffic, more and more low grade
highway are faced widen upgrade, and wadding in express
highway construction compared with building has obvious
advantage [1]. It is inevitably that express highway will go
through some soft soil area. To wide high embankment on
soft soil foundation is not a simple engineering. The
stability must be verified and settlement must be
calculated. The settlement calculation is more
complicated. Aiming at soft construction sub grade on
soft soil, Edward W.BRAND (1970) analyzed on the
failure mode of low embankment on soft soil foundation[2],
V. M. Lyatkher (1980) studied the failure characteristics
of embankment slope under dynamic loads by experiments
[3]
, M. N. Pink (1993) analyzed the stability of the
embankment slope with finite element method [4], Sun Wei
(2004) analyzed the deformation properties of widened
express highway engineering [5], Guo Yuzai (2008)
analyzed the stability of widened old high embankment in
the whole process with different calculation methods [6],
MO Baijin (2009) analyzed the uncoordinated
deformation characteristics of widened mountainous area
highway embankment with numerical analysis method and
discussed the destruction models [7], Zhao Chunshen
(2009), Zhang Gaochao (2010) introduced the
construction technology to widened high embankment on
soft soil foundation [8-9]. But the research on the
deformation properties of widened high embankment on
soft soil foundation is relatively less.
In this paper, the professional software Geostudio
Sigma/M module will be used to analyzed the stress and
deformation characteristics of the widened high
embankment on soft soil foundation of Shanghai-Chengdu
© ST. PLUM-BLOSSOM PRESS PTY LTD
expressway west and provides some references for the
widened high embankment on soft soil foundation.
2 PROJECT PROFILE
Shanghai-Chengdu expressway west is an important
part of national planning and constructing express
highway network “7918” Shanghai to Chengdu, lies in the
Hubei west highland of Yunnan-Guizhou plateau
northeast with steep mountain slopes, terrain ups and
downs frequent. Various adverse geological conditions
such as landslides, dangerous rock, Underground River are
very common along the highway. Deep cut slope and high
embankment is very common in route design.
Hejiapinging connections section K2+690…+900 were
upgraded by widened old embankment on soft soil
foundation. In order to understand the internal force and
deformation of the embankment, the typical crosssectional was selected to study and analyze.
3 CALCULATING MODEL AND MATERIAL
PARAMETERS
Simplifying the embankment as follows: Old
embankment top surface width is 5m, the broadened width
is 8m, the embankment height is 35m, the new and old
embankment bottom width is 60m (30m+30m=60m), the
soft ground layer thickness is 6m with 70m width.
According to the material test results, the calculation
parameters of the model lie in Table 1.
The Sigma/M module of Geo Studio provides eight
models. Select the equivalent linear elastic constitutive
model that is regard compacted embankment as
elastomeric; assume under the dead weight the
consolidation deformation of old embankment and soft
Deformation Properties Analysis of Widen High Embankment on Soft Ground
DOI:10.5503/J.PNSGE.2013.13.008
soil foundation have been completed. Therefore, in the
calculation only considers the weight of new fill
embankment, divided the calculation area into finite
element mesh partition, used eight-node quadrilateral
finite element to calculate. The boundary conditions follow
as: the displacements of embankment bottom at two
directions are constrained, the horizontal displacement on
the right is constrained, and the horizontal displacement of
the soft soil embankment on the left is constrained.
Calculating models follows as Figure 1.
Table 1 Calculation parameters
Structural parts
Density
/ kg/m3
Elastic modulus
/Mpa
Poisson ratio
C
/kPa
Internal friction angle
/º
New embankment
2.0×103
20
0.35
10
35
Old embankment
2.4×103
60
0.3
20
30
Soft soil foundation
1.8×103
6
0.38
8
8
The vertical stress moiré chart shows in Figure 3. It
reduces gradually and the maximum is 0.3Mpa.
Figure 1 The analysis model
Figure 3 The vertical stress moiréchart/KPa
4 DEFORMATION PROPERTIES ANALYSIS
4.1.2 Deformation
4.1 First model (not laying geogrid) First model (not
laying geogrid)
Only considered in the new embankment under the dead
weight, the overall horizontal deformation moiré chart
shows in Figure 4.
4.1.1 Stress
Only considered in the new embankment under the dead
weight, the overall horizontal stress moiréchart shows in
Figure 2.
Figure 4 The horizontal deformation moiréchart/m
As can be seen from Figure 4: due to the load of
broaden embankment and the soft soil layer under the
embankment, part of the foundation soil was squeezed out
to the lateral side at the junction center of new
embankment slope bottom and soft soil foundation. The
maximum horizontal displacement is 0.089m, lies in the
underside of new embankment slope feet. The horizontal
displacement of new embankment is larger. The old
embankment also occurred small lateral deformation under
the new embankment squeezing, which basically can be
ignored. The vertical deformation moiré chart shows in
Figure 5.
Figure 2 The horizontal stress moiréchart/Kpa
The maximum tensile stress of the embankment top is
0.22MPa which occurs at the junction of old embankment
and new embankment. It reduces in turn, and is zero in
about 15m. Pressure stress becomes larger gradually. The
maximum pressure stress is 0.16Mpa which occurs at the
top junction of old embankment and new embankment.
35
Physical and Numerical Simulation of Geotechnical Engineering
13th Issue, Dec. 2013
embankment, maintain the elastic modulus of old
embankment 60Mpa and soft soil 20Mpa, as shown in
Figure 7, the change of the maximum of the settlement is
small and in a small area.
Therefore, by increasing the elastic modulus of soft soil
to reduce the maximum settlement is more effective than
by increasing elastic modulus of new embankment.
0.28
the settlement maximum/m
The maximum of vertical settlement is 0.26m, which
occurs on the slope of widened embankment and is about
15m under new embankment top. Foundation settlement
reduces gradually from here center to around by arc. The
settlement rate changes rapidly when the depth close to the
foot. It reaches to the maximum at the foot of the slope,
and then changes smaller until the settlement becomes
zero. The difference settlement can be seen very clearly at
the top of the new embankment and old embankment.
0.24
0.22
0.20
0.18
0.16
0.14
0.12
0.10
0.08
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
the modulus ratio
Figure 7 The relationship between the maximum
settlement and the modulus ratio of new embankment
and old embankment
0.30
the settlement maximum/m
old 60,soft5
old 60,soft 20
0.26
Figure 5 The vertical deformation moiréchart/m
0.28
0.26
0.24
4.2 Second model (Laying geogrid)
0.22
Geogrid design dimensions are consistent with field
construction design. Setting structural bar element
(reinforced structural element) in the same geometric
location in the model to simulate geogrid. The modulus of
geogrid is 200MPa, the density is 2.3×103kg/m3,
Poisson’s ratio is 0.25. The calculation model is shown in
Figure 8.
0.20
0.18
0.16
0.14
6
11
16
21
26
the modulus of soft soil foundation/MPa
Figure 6 The relationship between the maximum
settlement and the modulus of soft soil foundation
new embankment
geogrid
4.1.3 The settlement
Maintain the old embankment and new embankment
modulus 60Mpa and 20Mpa, change the elastic modulus
of soft soil layers, compare the different of the largest
settlement of soft soil foundation at different elastic
modulus. The maximum of settlement shows in Figure 6.
As can be seen: The greater the elastic modulus of soft soil
foundation, the smaller the settlement maximum becomes.
When the elastic modulus of soft soil reaches to 20Mpa,
the maximum of the settlement clearly slows down and the
changing slope gets to zero.
Change the elastic modulus of new embankment,
maintain the old embankment modulus 60Mpa and soft
soil modulus 6Mpa, we can draw new and old
embankment the relationship between the elastic modulus
ratio of new settlement and old settlement and the largest
settlement can be shown in Figure 7. From Figure 7, we
can see that by changing the elastic modulus of new
embankment, the maximum of the settlement becomes
small. By changing the elastic modulus of new
old embankment
soft soil foundation
Figure 8 Model 2
4.2.1 Stress
Only considered in the new embankment under the dead
weight, the overall horizontal stress moiréchart shows in
Figure 9 and the overall vertical stress moiré chart 10.
From Figure 9, we can see that: the maximum horizontal
stress of the embankment top is 0.16 Mpa, which
decreases 27.3% compared with that of not laying geogrid.
36
Deformation Properties Analysis of Widen High Embankment on Soft Ground
DOI:10.5503/J.PNSGE.2013.13.008
(1) The location of the maximum horizontal
displacement of widened high embankment on soft soil
foundation is the junction of the slope feet outside of
widened embankment and soft soil, The widened
embankment slope has the to the trend sliding to outside.
Protection measures should be taken to new embankment.
The location of the largest settlement of embankment is
about 15m from the top of the embankment. As here the
center, along the horizontal direction and the depth
direction, foundation settlement decrease gradually. It
changes great close to the junction of new embankment
and soft layers and becomes smaller quickly near slope
feet. Differential settlement occurs at embankment surface
top. And it is obvious between old embankments.
(2) The variation of the elastic modulus of soft soil
influence on the embankment settlement and differential
settlement at the top greater. The maximum of the
embankment settlement and differential settlement
decrease with the increasing of soft soil elastic modulus.
When the elastic modulus of soft soil to a certain value
(20Mpa), the influence will not be obvious. By Increasing
the modulus of soft soil foundation to reduce maximum
settlement and differential settlement is more effective
than by increasing that of new embankment. Therefore,
the strength of soft ground can be enhanced by rubble
method, and compaction embankment fully (not overcompaction) reduces the embankment settlement and
differential settlement.
(3) Laying Geogrid in new embankment can be
significantly reduced horizontal stress and lateral
deformation, which can effectively prevent new
embankment slope sliding. Additional geogrid has little
effect on the overall vertical stress. But it can significantly
reduce the overall vertical subgrade deformation and
differences settlement between the old embankment and
new embankment.
Figure 9 The horizontal stress moiréchart/Kpa
Figure 10 and Figure 3 by comparison shows that the
vertical stress of the whole embankment changes little and
the effect is not obvious.
Figure 10 The vertical stress moiréchart/Kpa
4.2.2 Deformation
Only considered in the new embankment under the dead
weight, the overall horizontal deformation chart and
vertical deformation show in Figure 11 and Figure 12.
From Figure 11, we can see that: the maximum
horizontal deformation of the embankment top is 0.054m,
which decreases 40% compared with that 0.089m of not
laying geogrid. That is the horizontal deformation
decreases great after laying geogrid. From Figure 12, we
can see that: the maximum of the embankment
displacement is 0.20m, which decreases 25% compared
with that 0.26m of not laying geogrid. The vertical
settlement between new embankment and old embankment
decreases obviously. But differences settlement is still
obvious
REFERENCES
[1].
[2].
Figure 11 The horizontal deformation moiréchart/m
[3].
[4].
[5].
[6].
Figure 12 The vertical deformation moiréchart/m
5 CONCLUSION
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