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Taiwan is located at a junction of tectonic plates, which results in frequent earthquakes. Its terrain is mostly hilly, and its rainfall ranks among the highest in the world. Each of these elements affects the stability of slopes in various regions of Taiwan. Several slopes along Taiwan’s Freeway 1 and 5 have experienced landslides and rockfalls. It is imperative that the slope stability of these national freeways be analyzed to avoid future slope collapses brought on by precipitation or other outside factors. Thus, three sites on Taiwan’s Freeway 1 and 5 were chosen for numerical slope stability analysis in this study. PLAXIS 2D CE (Version: 24.02.00.1144) finite element software was used in this study to simulate and analyze the safety of freeway slope protection projects. Displacements induced by normal and high groundwater levels were discussed. Moreover, a pseudo-static study of slope displacements under seismic conditions was performed. According to the results of the numerical study, the force operating on the slope was centered on the sliding surface when the groundwater level was normal, and it extended to the top when the groundwater level was high. By comparison, under seismic conditions, the force acting on the slope extended to the whole slope. Furthermore, the slope safety factor of Site 1 was greater than the design specification value in three different scenarios. This confirms that the slope protection project at Site 1 is effective. Full article

Under weak geological conditions, soil deformation and surface settlement are the key factors affecting the success of shallow-buried rectangular excavation. To investigate this issue, an underpass of Zhongxiao East Road in Taipei City was used as a case study. The surface settlement and lateral deformation of an underground diaphragm wall caused by the excavation of a rectangular pedestrian underpass using the pipe-roof preconstruction method (PPM) were investigated by 3D finite element analysis. The numerical analysis results showed that the constructed numerical analysis model had considerable accuracy. The use of PPM combined with a box culvert structure to form a pedestrian underpass could effectively control the surface displacement above the box culvert. Under the condition of the same sectional area, the smaller the width of the pipe-roof structure, the more the impact on the ground surface was reduced. The maximum positive bending moment and maximum negative bending moment on the pipe roof produced by excavation at each stage were roughly inversely related to the height per the width of the cross-section of the pipe diaphragm structure. The results showed that the pipe-roof structure was suitable for underground excavation with shallow-buried depth in the soft soil of the Taipei Basin. Moreover, the shallow-buried box culvert was more sensitive to the subsidence caused by construction than the deep-buried box culvert. Full article