Complex Variable Solution for Stress and Displacement of Layered Soil with Finite Thickness

The static problem of a layered isotropic elastic body is a very useful research subject in relation to the analysis and design of foundation works. Due to the complexity of the problem, there is no analytical solution to the problem so far. This study provides an efficient analytical approach to accurately calculate the displacement and stress fields of the soil. The constraints of bedrock on soil, different soil layer thickness and the shear stress of the foundation on soil were all taken into account in the analysis. In this study, each layer is regarded as an isotropic elastomer with infinite width, and the layers are in complete contact. By using conformal mapping, each layer is mapped to a unit circle, and the two complex potential functions are expanded into Taylor series with unknown coefficients. These unknown coefficients are obtained by satisfying boundary conditions and continuity conditions. The boundary and continuity conditions were verified in this paper. As a validation step, we compared the analytical results for the settlement with the results of the ANSYS numerical simulations and found good agreement. Parametric analyses were also carried out to investigate the influence of different distribution forms of base pressure on surface settlement, and the effects of layered properties on the surface settlement and stress field.

Research on the Reuse of Discharged Soil from EBP Shield Tunnels in Synchronous Grouting Material

Great practical significance and engineering application value can be achieved when the large amount of discharged soil produced by EPB shield tunnels is recycled and comprehensively utilized. As one of the key processes of shield construction, synchronous grouting needs a large amount of bentonite, cement, fly ash, sand, and other materials. The research on the reuse of shield muck as synchronous grouting material is carried out based on Zhengzhou subway project. The physical properties and phase of the discharged soil from EPB shield tunnels are studied by using laboratory tests and XRD. The statistics show that the shield muck meets the performance requirements of bentonite and fine sand in synchronous grouting materials. The optimal grout ratio of the reused muck is obtained based on the optimization idea of multiobjective programming by MATLAB. Considering the combined effect of seepage field, stress field, and the timeliness of the grout, the influences of grouting pressure and the filling rate of synchronous grouting on surface settlement, plastic zone of strata, and segment deformation are analyzed by using finite difference method. The results prove that the surface settlement and segment deformation can be better controlled when the grouting pressure is at 0.18 MPa and the grouting rate is at 120%–150%.

Prediction of Ground Subsidence During Underground Construction of Metro Line 2, Section 1, Ben Thanh - Tham Luong

Urban metro line No. 2 from An Suong station to Thu Thiem is one of the six metro lines thatis planned to be built in Ho Chi Minh City (HCMC). The metro line goes through the area in which thestratigraphy consists of many units, distributed from 20-80 m. The hydrogeology mainly has 2 aquifers,namely Holocene, and Pleistocene which affecting the deep excavation. During construction, there willbe some problems that will affect the work on the surface such as settlement, cracking, and damage. Byfinite element method on Plaxis software, the article forecasts the surface settlement during this metroline No.2. The results show that the ground settlement is relatively large in areas with soft groundstructures. The settlement results depend on the geological structure characteristics, hydrogeologicalcharacteristics, and the shape and size of the tunnels.

Horizontal Wall Movement and Ground Surface Settlement Analysis of Braced Excavation Based on Support Spacing

Lateral supports, including walls and bracing systems on deep excavation, are generally required to prevent excessive horizontal wall movement and ground surface settlement which can cause damage to the excavation construction itself and adjacent structures. These criteria are influenced by the stiffness of the excavation system, including the spacing of vertical and horizontal supports (struts). This paper presents the parametric study using the variation of struts spacing in the vertical and horizontal direction to analyze the influence on horizontal wall movement and ground surface settlement. The analysis was carried out using finite element software, PLAXIS performed in 2D plain strain and 3D. This study shows that struts spacing in the horizontal and vertical direction is equally important and equally significant on the deformation that occurs with a maximum difference of about 0.06%. The maximum horizontal wall movement ratio computed by 3D analysis to the 2D analysis is defined as plain strain ratio (PSR). The PSR value decreases when the system stiffness is decreased. Meanwhile, when the system stiffness was higher, the PSR value will be higher and closer to 1, showing that the difference in the 3D and 2D models is relatively small.