This study uses the finite element software Midas GTS NX (2019), combined with actual engineering projects, to establish numerical models and analyze the impact of different support types (pile-anchor support and double-row pile support) on the excavation of foundation pits near metro station tunnels. The results indicate that under both support methods, the vertical displacement of the tunnel is the greatest at the interface between the station and the tunnel, with greater vertical displacement occurring under double-row pile support. Under pile-anchor support, the horizontal displacement of the tunnel reaches its maximum value during the sixth excavation stage, while under double-row pile support, the horizontal displacement increases steadily, and the overall displacement is small. The horizontal displacement under pile-anchor support is significantly greater than that under double-row pile support. For the station, the maximum vertical displacement under pile-anchor support is smaller than that under double-row pile support. The horizontal displacement under pile-anchor support exhibits a linear change, while under double-row pile support, the displacement continuously increases from the end of the foundation pit farther from the excavation to the end closer to it. The model tests are consistent with the numerical simulation results, verifying the correctness of the numerical simulation. This study can provide references for relevant engineering projects to ensure the safety and stability of metro structures.
In the northwest, a lot of multi-stage high slopes with loess have been encountered in the construction of basic engineering. Slope engineering belongs to permanent project. So it is unavoidable to meet the conditions of rainfall. Under rainfall infiltration, the degree of saturation and mass of soil slope increase, which can further cause the change of slope matric suction and effective stress. As a result, the stability of the slope can be greatly influenced. In this paper, the coupling calculation model of seepage field and stress field is established. It considers the changes of the matrix suction as the rain water infiltration at the different depths of the slope body. Then, the stability of the multi-stage high slope with loess under the condition of rainfall infiltration can be analyzed. Then, according to an actual engineering and using the PLAXIS 3D geotechnical finite element software, the calculation model of slope stability is established. By setting the variation function of rainfall with the time and boundary condition, the stability calculation of multi-stage high slope with loess is carried out under the condition of rainfall infiltration. And then, The numerical calculation results are compared with the theoretical calculation results. According to the numerical calculation results, the changes of the deformation, matrix suction, effective stress, potential slip surface and safety factor of the multi-stage high slope with loess under the condition of rainfall infiltration are obtained. And the stability of the multi-stage high slope with loess under the condition of rainfall infiltration are analyzed. The study results can provide some guidance for the design of the multi-stage high slope with loess under the rainfall infiltration.
Abstract In this paper, the influence of space effect on soil pressure and deformation of deep foundation pit was considered, and the finite soil pressure calculation model was established. The soil pressure of deep foundation pit was calculated by assuming the slip surface and using the finite soil limit equilibrium theory. Then, PLAXIS 3D finite element software was used to establish finite element models of different plane sizes and depths. The distribution regulation of side wall soil pressure and deformation of deep foundation pit was calculated. Finally, the results of finite soil pressure calculation was compared with finite element method. The results shown that: The soil pressure of small deep foundation pit was affected by space effect, and the soil pressure and deformation decrease significantly along the foundation pit depth. Shear fracture Angle was related to the ratio of width to depth of foundation pit, and it was no longer a constant value of 45°+φ/2. Therefore, the spatial effect should be considered in the calculation of soil pressure of small deep foundation pit. The research results can provide some guidance for the design and calculation of similar small size deep foundation pit.
Abstract According to the deep foundation pit project of Xiaoxihu station on Lanzhou subway Line 1, the three-dimensional finite-element model of the half-cover excavation method of retaining structure is established to simulate the construction of the excavation of the foundation pit. This article analyzes the settling of the surrounding surface, the horizontal displacement and vertical displacement of the retaining pile, the vertical displacement of the shoring column, and the change of the axial force of the inner support and compares them with the actual monitoring data. The results show that for the collapsible loess strata in Lanzhou, the design of retaining pile and inner support is viable. The support form has a good control effect on the deformation of the foundation pit. It keeps the foundation pit stable. The numerical simulation results are more consistent with the actual monitoring data. It provides a basis for the scientific design and construction of a deep foundation pit in the Lanzhou metro station.
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