Numerical Study of Seismic- Soil-Structure-Excavation Interaction in Sand

The dynamic loads affecting earth retaining structures may increase in seismically active regions. Therefore, studying the soil-structure interaction between the soil, shoring systems, and adjacent structures is crucial. However, there is limited research on this important topic. This study analyzes the seismic performance of a deep-braced excavation and a nearby 10-story building in sandy soil formation. Sandy soil is modeled using the Hardening Soil model with small-strain stiffness (HS-small) using PLAXIS 2D software. The numerical model is validated against measured field data from a real case study of a deep-braced excavation in the central district of Kaohsiung City, adjacent to the O7 Station on the Orange Line of the Kaohsiung MRT system in Taiwan. After model validation, parametric study is conducted to investigate the impact of the foundation level of the building adjacent to the excavation on both the seismic behavior of the shoring system and the structure itself, using the Loma-Prieta (1989) earthquake record. The parametric study is further extended to assess the responses of the shoring system and the adjacent structure under the influence of the earthquake records of Loma Prieta (1989), Northridge (1994), and El Centro (1940). Analysis results show that the maximum lateral displacement of the diaphragm wall occurred at its top in all studied cases. The maximum bending moment in the retaining structure increased by more than three times of that calculated in the dynamic analysis compared to the static analysis. In contrast, the dynamic shear force is more than 2.85 times greater than the static one. In addition, the dynamic axial force in the 1st and 2nd struts increased by 1.38 and 3.17 times, respectively, compared to the static forces. Results also reveal that large differences in behavior of the shoring system and the adjacent structure are noticed between the used different earthquake records.