Xue Yang
Xinjiang Ruilufeng Engineering Technology Co., Ltd
Abstract: In order to study the influence of different design parameters on the deformation characteristics of highway widening subgrade, a numerical model of widening subgrade was established by finite element software, and the influence of different widening methods, subgrade height, subgrade width and subgrade elastic modulus on the deformation characteristics of old and new subgrade was compared and analyzed. The results show that the double-sided widening method has a good effect on controlling the horizontal deformation and settlement difference between the old and new subgrades, and the increase in the height and width of the subgrade increases the horizontal deformation and uneven settlement of the old and new subgrades, but the increase of the elastic modulus of the subgrade can effectively control the horizontal deformation and uneven settlement of the old and new subgrades.
Keywords: highway widening of the roadbed; design parameters; horizontal deformation; Sedimentation;
About author:XUE Yang (1985—), male, from Peixian, Jiangsu, engineer.;
introduction
With the rapid development of social economy, the road traffic flow and traffic load continue to increase, resulting in the early construction of roads can no longer meet the traffic demand. Therefore, in order to improve the road capacity, the mainland began to carry out large-scale highway subgrade widening projects. Liu Zhanrui et al. [1] established an analysis model of old roadbed by finite element numerical analysis and field investigation, and discussed the influence of different replacement depths of old subgrade on the stress and difference between old and new subgrade. Chen Chao [2] studied the influence of different subgrade fill parameters on the mechanical behavior of vertical displacement, horizontal displacement, vertical stress and shear stress of expressway by establishing a mechanical calculation model under different subgrade fill parameters in the widening section. Zhang Tan et al. [3] used finite element software to establish a numerical model of three widening methods of four-level highway: unilateral widening, double-side widening, excavation and reconstruction, and combined with the measured settlement data on site, the uneven settlement characteristics of the subgrade under different widening methods were analyzed. Wei Gaoming [4] took a highway subgrade widening project as an example, and used numerical simulation to analyze the subgrade deformation, foundation deformation and pavement cross slope change law under different subgrade widening widths. Most of the existing studies focus on the influence of single parameters on the deformation of the widening subgrade, and there is a lack of systematic research on the influence of different design parameters on the deformation of the widening subgrade.
1 Project overview
A high-grade highway in a city, with a total length of 7.62 km, the original road width is 12.5 m, the lane design is two-way four lanes, the maximum driving speed is 70 km/h, the safety level is highway I., the roadbed height is 6 m, the slope ratio is 1:1.5, and it has been operated for 10 a. Due to the increasing traffic volume, the original design lane number can no longer meet the operational demand, so it is planned to widen the original two-way roadbed to improve the operational capacity of the line. After widening, the width of the roadbed was increased from 12.5 m to 24.5 m, the lane was increased to eight lanes in both directions, the height of the roadbed and the ratio of slope remained unchanged, and the widening method was to widen the roadbed simultaneously on both sides, and the width of one side was 6 m. The old and new roadbed are spliced with steps, and the splicing is reinforced by the ramming method, and the width of the steps is 2 m. The new subgrade was filled in 4 layers, each with a fill height of 1.5 m. According to the original geological survey results, the foundation soil layer mainly includes 2 m thick hard shell layer, 10 m thick sub-clay layer and 12 m thick silty clay layer. The section of the widened subgrade is shown in Figure 1.
Figure 1 Widening the roadbed/m Download the original image
2 Build a model
Using the finite element software ABAQUS to establish a numerical model for widening the subgrade, the proposed subgrade is an impervious elastic material, the four-node plane strain unit is used for simulation, the proposed foundation is a permeable plastic material, and the plane strain void water pressure element is used to simulate, and the calculation model contains a total of 637 units and 732 nodes, and the finite element model is shown in Figure 2.
Figure 2 Finite element model Download the original figure
Considering the complexity of the influencing factors of broadening the subgrade, the material of each layer is considered to be homogeneous, continuous and completely bonded during the calculation. Assume that the embankment is considered as a plane strain problem, and the consolidation problem of foundation soil is considered; It is assumed that both the roadbed and the foundation are ideal elastoplastics; It is assumed that the contact between the splicing of the old and new roadbed is continuous, and there is no slippage and falling off; The mole-coulomb elastoplastic model was used for the soil constitutive relationship. Consider that the load is 20 kPa equivalent to the average distribution load. In order to ensure the accuracy of the calculation results, horizontal and vertical displacement constraints are used for the bottom of the model, horizontal displacement constraints are used on both sides, the groundwater table is located at the surface, the top is the permeable boundary, and the rest are impervious boundaries. The soil calculation parameters in the model are shown in Table 1.
Table 1 Soil calculation parameters Download the original figure
3 Results and analysis
3.1 Broadening Methods
In order to compare the influence of different widening methods on the deformation characteristics of the broadening subgrade, a calculation model of 12 m widening on one side and 6 m widening on both sides was established, and the horizontal displacement and vertical settlement variation of the subgrade under the two widening methods were comparatively analyzed, and the results are shown in Figure 3.
Figure 3 Subgrade deformation characteristic change curve Download the original figure
According to Figure 3, the horizontal deformation of the old and new subgrade using the unilateral widening method is quite different, and the reverse displacement occurs at the shoulder position of the new subgrade, and the maximum horizontal displacement of the subgrade surface occurs at the centerline position of the subgrade, and the maximum value is 2.73 cm. The horizontal deformation of the old and new roadbed using the double-sided widening method was basically symmetrical distribution of the centerline, and the maximum horizontal displacement appeared at the splicing position of the old and new roadbed on both sides, and the maximum horizontal deformation was 1.21 cm, which was nearly 55.6% lower than the maximum horizontal deformation of the single-sided widening roadbed. The maximum settlement value of the subgrade surface was -15.93 cm, while the difference between the vertical settlement of the old and new subgrade using the double-sided widening method was small, and the maximum settlement value was -11.38 cm, which was reduced by 28.6% compared with the maximum settlement of the unilateral widening subgrade. In summary, the double-sided widening method for widening the roadbed is better than the unilateral widening method for controlling the horizontal deformation and settlement difference of the old and new roadbed.
3.2 Subgrade height
In order to study the influence of different subgrade heights on the deformation characteristics of the widening subgrade, the calculation models of subgrade heights of 2.5 m, 5 m, 7.5 m and 10 m were established by software, and the widening width was 6 m by double-sided widening method, and the horizontal displacement and vertical settlement variation of the subgrade at different subgrade heights were compared and analyzed, and the results were shown in Figure 4.
Figure 4 Subgrade deformation characteristic change curve Download the original figure
According to Figure 4, with the increase of the roadbed height, the horizontal displacement of the surface of the old and new subgrade showed an increasing trend, and the maximum horizontal displacement of the old and new subgrade with subgrade heights of 2.5 m, 5 m, 7.5 m and 10 m was 0.39 cm, 1.10 cm, 1.93 cm and 2.71 cm, respectively, which showed that the change of subgrade height had a greater impact on the horizontal deformation of the old and new subgrades. With the increase of subgrade height, the vertical settlement of the surface of the old and new subgrade showed an increasing trend, and the maximum settlement of the old and new subgrade with subgrade heights of 2.5 m, 5.0 m, 7.5 m and 10.0 m was 8.02 cm, 11.56 cm, 14.37 cm and 16.71 cm, respectively, indicating that the change of subgrade height had a greater impact on the uneven settlement of the old and new subgrades. On the whole, the increase in the height of the subgrade increases the horizontal displacement and vertical settlement of the old and new subgrades, which is not conducive to the safety and stability of the old and new subgrades, so the height of the subgrade should not be designed too high in the actual project.
3.3 Subgrade width
In order to study the influence of different subgrade widths on the deformation characteristics of widening subgrade, the calculation models of subgrade widths of 4.5 m, 6.5 m, 8.5 m and 10.5 m were established by software, and the horizontal displacement and vertical settlement changes of subgrade widths were compared and analyzed, and the results are shown in Figure 5.
Figure 5 Subgrade deformation characteristic change curve Download the original figure
According to Figure 5, the horizontal displacement of the surface of the old and new subgrade gradually increased with the increase of the width of the subgrade, and the maximum horizontal displacements of the old and new subgrade with a width of 4.5 m, 6.5 m, 8.5 m and 10.5 m were 0.87 cm, 1.10 cm, 1.32 cm and 1.53 cm, respectively, and the maximum horizontal deformation occurred at the splicing position of the old and new subgrades, indicating that the change of the width of the subgrade had a certain impact on the horizontal deformation of the old and new subgrades. With the increase of subgrade width, the vertical settlement of the surface of the old and new subgrade showed an increasing trend, and the maximum settlement of the new and old subgrade widths of 2.5 m, 5.0 m, 7.5 m and 10.0 m were 9.59 cm, 11.46 cm, 12.93 cm and 14.44 cm, respectively, which showed that the change of subgrade width had a significant impact on the uneven settlement of the old and new subgrades. On the whole, the increase in the width of the subgrade increases the horizontal displacement and vertical settlement of the old and new subgrades, and the influence on the uneven settlement of the old and new subgrade is greater than the influence of horizontal deformation.
3.4 Subgrade modulus of elasticity
In order to study the influence of different subgrade elastic modulus on the deformation characteristics of broadened subgrade, the calculation models of subgrade elastic modulus of 5 MPa, 10 MPa, 15 MPa and 20 MPa were established by software, and the horizontal displacement and vertical settlement variation of subgrade with different elastic modulus of subgrade were compared, and the results are shown in Figure 6.
Figure 6 Subgrade deformation characteristic change curve Download the original figure
According to Figure 6, with the increase of the elastic modulus of the subgrade, the horizontal displacement of the surface of the old and new subgrade showed a decreasing trend, and the maximum horizontal displacement of the old and new subgrade with an elastic modulus of 5 MPa, 10 MPa, 15 MPa and 20 MPa was 1.69 cm, 1.11 cm, 0.87 cm and 0.73 cm, respectively, which showed that the elastic modulus of the subgrade had a greater influence on the horizontal deformation of the old and new subgrades. With the increase of the elastic modulus of the subgrade, the vertical settlement of the surface of the old and new subgrade showed a decreasing trend, and the maximum settlement modulus of the old and new subgrade with 5 MPa, 10 MPa, 15 MPa and 20 MPa was 13.48 cm, 11.46 cm, 10.71 cm and 10.32 cm, respectively, and the decrease in settlement was obvious, indicating that the elastic modulus of the subgrade had a greater influence on the uneven settlement of the old and new subgrades. In general, the increase of the elastic modulus of the subgrade can reduce the horizontal displacement and vertical settlement of the new and old subgrade at the same time, which has a significant effect on controlling the horizontal deformation and uneven settlement of the new and old subgrades, so the fill with high elastic modulus can be selected in the actual project to fill the subgrade.
4 Conclusion
(1) From the perspective of horizontal deformation and settlement difference, the control effect of the double-sided widening method is significantly better than that of the unilateral widening method. (2) The increase in the height of the roadbed increases the horizontal displacement and vertical settlement of the old and new subgrades, and the larger the subgrade height, the greater the horizontal deformation and uneven settlement of the new and old subgrades, which is not conducive to the safety and stability of the old and new subgrades. (3) The increase of the width of the roadbed increases the horizontal displacement and vertical settlement of the old and new subgrades, and the influence on the uneven settlement of the new and old subgrade is greater than the influence of horizontal deformation. (4) The increase of elastic modulus of the subgrade can reduce the horizontal displacement and vertical settlement of the old and new subgrade at the same time, which has a significant effect on controlling the horizontal deformation and uneven settlement of the new and old subgrade.
bibliography
[1] LIU Zhanrui, LIU Changxin, ZHANG Dingquan, et al. Numerical analysis of the effect of old subgrade replacement on stress displacement characteristics of widened subgrade[J].Construction Machinery, 2021(4):79-84,88.)
[2] CHEN Chao. Analysis of mechanical behavior under the change of subgrade fill parameters in the widening section of expressway[J].Fujian Communications Science and Technology, 2020(3):11-14.)
[3] ZHANG Tan, LI Youyun, XIE Jideng, et al. Study on uneven settlement characteristics of subgrade under different widening methods[J].Highway and Automobile Transport, 2020(2):86-90.)
[4] WEI Gaoming. Numerical analysis of the influence of highway subgrade widening on the deformation of pavement structure[J].Journal of Hubei Institute of Technology, 2019, 35(3):39-42.)
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