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Numerical Simulation of Reinforced Soil Slope in Subgrade Widening of
Expressway
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2020 6th International Conference on Energy Science and Chemical Engineering
IOP Conf. Series: Earth and Environmental Science 565 (2020) 012105
IOP Publishing
doi:10.1088/1755-1315/565/1/012105
1
Numerical Simulation of Reinforced Soil Slope in Subgrade
Widening of Expressway
Song-jie Gao1*, Bin Tang1, Jing Zhang1, Gang Zhao1
1Zhong Dian Jian Ji Jiao Expressway investment Development Co. Ltd, Shijiazhuang,
Hebei, 050000, China.
*Corresponding author’s e-mail: 13513276383@139.com
Abstract: The finite difference element software FLAC3D was used to simulate the
reconstruction and expansion project of Xinle-Yuanshi expressway. The model of reinforced
soil slope widening subgrade was established. Based on the comparison of the simulation data
of the sections with different heights and structural forms, the structural behavior of reinforced
soil structure in subgrade widening project was analyzed. The law of structural deformation
and construction control technology were summarized.
1. Introduction
With the increase of the traffic flow of the expressway, some of the original expressways need to be
reconstructed and expanded. The expansion construction in the area with poor geological conditions
puts forward higher requirements for the widening structure[1-2]. How to ensure the overall stability
of the widened subgrade structure, reduce the differential settlement between the old and the new
subgrade joint, and prevent the occurrence of pavement longitudinal cracking has become the focus of
research[3]. Reinforced soil slope is widely used in subgrade widening engineering for its advantages
of reducing land occupation, good seismic resistance, strong adaptability of foundation conditions and
cost saving[4].
The anchoring mechanism of anchoring bar and the function mechanism of geogrids in the joining
between the new and the existing subgrade are analyzed by Wang[5]. Through the 3D finite element
analysis, Qian[6] studied the mechanical performance and influence of geosynthetic-reinforced and
pile-supported (GRPS) embankment in the soft soil subgrade widening project. Ling[7] studied the
performance and treatment method of low liquid limit silty clay widening subgrade through laboratory
test and numerical simulation. Combined with the experimental section of Fangzheng-Harbin section
of Tongjiang Sanya expressway, Yang[8] analyzed the stability of unilateral widening embankment in
the process of step excavation of old road slope and construction of new embankment. Sivathasan[9]
introduced the geotechnical engineering challenges encountered in the widening project of
Expressway and the methods to solve these challenges. In order to know the effect of freeze-thaw
action and soil compression on the post-construction deformation of widening high embankment in
seasonal frozen regions, Shan[10] combined with the survey of Fangzheng-Harbin section of Tongsan
highway.
In this paper, based on the reconstruction and expansion project of Xinle-Yuanshi expressway,
FLAC3D software is used to carry out three-dimensional numerical simulation to analyze the structural
state of widened structure in the construction process and after completion.
2020 6th International Conference on Energy Science and Chemical Engineering
IOP Conf. Series: Earth and Environmental Science 565 (2020) 012105
IOP Publishing
doi:10.1088/1755-1315/565/1/012105
2
2. Project overview and numerical model
2.1. Project overview
Xinle-Yuanshi expressway has been open to traffic for 25 years. The original subgrade is 27 m wide
and 4 m-4.4 m high. After widening, the subgrade wide is 34.5 m , the subgrade high is 4.8 m~6.4 m ,
and the slope rate is 1:0.75. The foundation soil is composed of silt and medium sand from bottom to
top, with thickness of 10 m and 5 m, respectively. The foundation of the newly widened part is treated
with geocell, and the treatment depth is 0.6m. The connection between the new and the original
subgrade shall be excavated by benching. The step high is 0.8m and the step wide is 1.2m. The
original subgrade filler is sandy soil, and the reinforced soil slope is filled with gravelly soil. The
return package structure is used in reinforced soil slope. The reinforcement is TGDG-65 one-way
tensile plastic geogrid with the vertical spacing of 0.4m.
2.2. Numerical model
The Mohr-Coulomb model is adopted for foundation soil and subgrade filler. The elastic model is
adopted for geogrid. Material parameters are shown in table 1-2.
Table 1 Soil material parameters.
Material Bensity
(kN·m-3)
Bulk
modulus
(MPa)
Shear
modulus
(MPa)
Poisson's
ratio
Cohesion
(kPa)
Internal
friction angle
(°)
Medium sand of
foundation 18.2 30 13.8 0.3 0 36
Silt of foundation 19.5 43.3 14.4 0.35 6 37
Original subgrade
filler 18.7 25 18 0.28 10 35
Natural grading
subgrade filler 19 25 18.6 0.28 20 32
Reinforced soil
subgrade filler 20.8 16.7 18.1 0.2 29.5 33.1
Table 2 reinforced material parameters.
Model HDPE TGDG 65
Tensile modulus(kN·m-1) 825
Poisson's ratio 0.2
Thickness(mm) 1.0
Cohesion of coupling spring(kPa) 4.9
Friction angle of coupling spring (°) 5.7
Stiffness per unit area of coupling spring(kPa) 1300
The depth of the foundation is 15 m and the width is 30 m. Two sections with subgrade height of
4.8 m and 5.6 m are selected. Half of the subgrade model is established for simulation analysis, as
shown in Figure 1.
2020 6th International Conference on Energy Science and Chemical Engineering
IOP Conf. Series: Earth and Environmental Science 565 (2020) 012105
IOP Publishing
doi:10.1088/1755-1315/565/1/012105
3
(a) h=4.8 m (b) h=5.6 m
Figure 1. Calculation model of
r
einforced soil slope subgrade.
3. Simulation results of reinforced soil slope subgrade
3.1. Vertical displacement
The vertical displacement distribution after the filling of reinforced soil slope subgrade structure is
shown in Figure 2. It can be seen from the figure that the vertical displacements of two kinds of
reinforced soil slopes increase with the increase of subgrade height. The maximum vertical
displacement in Figure 2 (a) and Figure 2 (b) are 14.8 mm and 18.5 mm, respectively. Compared with
the original subgrade, due to the small degree of compaction at the reinforced slope, a large vertical
displacement occurs within a certain range of the reinforced slope. The gravity center of the new
subgrade lies between the new subgrade shoulder and the original subgrade shoulder, where the
displacement is large. During the design and construction process, the excavation depth of the original
subgrade slope shall be controlled, and the compaction quality of the connection between the new
subgrade and the original subgrade shall be ensured.
(a) h=4.8 m (b) h=5.6 m
Figure 2. Vertical displacement distribution of subgrade.
The change of foundation surface settlement with filling height is shown in Figure 3. It can be seen
from the figure that the foundation surface settlement increases with the increase of filling height.
When the subgrade with 4.8m-high is filled, its surface settlement is 14.2mm. When the subgrade with
5.6m-high is filled, its surface settlement is 17.4mm. With the increase of overburden, the foundation
is gradually consolidated and the settlement rate of the foundation is gradually reduced.
2020 6th International Conference on Energy Science and Chemical Engineering
IOP Conf. Series: Earth and Environmental Science 565 (2020) 012105
IOP Publishing
doi:10.1088/1755-1315/565/1/012105
4
Figure 3. Change of foundation surface
settlement with filling heigh
t
.
Figure 4. Horizontal displacement curve of
slope.
3.2. Horizontal displacement
The horizontal displacement curve of slope is shown in Figure 4. The horizontal displacement
distribution of subgrade is shown in Figure 5.
(a) h=4.8 m (b) h=5.6 m
Figure 5. Horizontal displacement distribution of subgrade.
After the construction of reinforced soil slope subgrade, the horizontal displacement is small. The
horizontal displacement increases first and then decreases along the slope from bottom to top. The
horizontal displacement of the reinforced soil slope is negative, that is to say, the displacement of the
slope toward the center of the subgrade is generated. The horizontal displacement of the section with
subgrade height of 5.6m is large, and the maximum displacement is -2.2mm. The horizontal
displacement of the original subgrade is larger than that of the new one. The maximum horizontal
displacement at the original subgrade shoulder is 3.4mm.
3.3. Structural stability analysis
The safety factors of the two sections are calculated by strength reduction method. The safety
coefficients of the two sections are 2.56 and 2.39, respectively, with high overall stability. This kind of
structural form and reinforcement arrangement method are suitable for the roadbed widening structure.
2020 6th International Conference on Energy Science and Chemical Engineering
IOP Conf. Series: Earth and Environmental Science 565 (2020) 012105
IOP Publishing
doi:10.1088/1755-1315/565/1/012105
5
(a) h=4.8 m (b) h=5.6 m
Figure 6. Shear strain increment of reinforced soil slope.
The shear strain increment of reinforced soil slope is shown in Figure 6. The maximum shear strain
of the two kinds of section is basically distributed in circular arc from the original subgrade shoulder
to the new subgrade toe, and the maximum shear strain point appears at the toe of the slope. Because
there is no reinforced material in the original subgrade, compared with the reinforced part, the shear
strength is lower, so the shear strain is larger. In the process of design and construction, the shear
strain can be reduced by increasing the treatment depth of the foundation and the strength of the
reinforcement at the junction of the subgrade.
4. Conclusion
According to the simulation results, the structural state after the completion of subgrade construction
is analyzed, including the vertical displacement, horizontal displacement and safety stability of the
structure. Some conclusions are drawn.
(ⅰ)For the reinforced soil slope structure, the displacement of the new subgrade changes little, and
the horizontal displacement of the subgrade slope surface to the inner side of the subgrade is produced.
(ⅱ)The settlement of the foundation surface in the widened part increases with the increase of the
filling height, and the growth rate decreases when the filling height reaches 3.5m.
(ⅲ)The maximum increment of shear strain of reinforced soil slope occurs at the toe of original
subgrade.
(ⅳ)The reinforced soil structure becomes a composite structure due to the grid, and the deformation
is more uniform. The safety factor of reinforced slope is high.
Acknowledgments
The study is supported by Hebei Province Natural Science Foundation [Grant No. E2018210097]. All
supports are very gratefully acknowledged.
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2020 6th International Conference on Energy Science and Chemical Engineering
IOP Conf. Series: Earth and Environmental Science 565 (2020) 012105
IOP Publishing
doi:10.1088/1755-1315/565/1/012105
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