Numerical analysis of shaft excavation-induced rebound and soil disturbance in deep sand deposit

The analyses of the stress and deformation fields and soil disturbance at the bottom of a pit provide the guidance for the shaft design and construction, the geotechnical investigation and field testing in it. The small-strain hardening model (HSS) is widely adopted in numerical analysis of excavation problems due to its enhanced capability of considering the nonlinear stiffness-strain relationship of soils at small strain range. Existing research on HSS model parameters mainly focuses on typical soft soils, with limited studies on sandy ground. This study conducts a series of laboratory tests and calibrated the HSS model parameters for a deep sand ground, and then the shaft excavation-induced rebound and soil disturbance are analyzed by FLAC3D. The results illustrate that the HSS model parameters exhibit notable differences from typical soft soils and the depth dependency; the annular support system effectively restrains the structural deformation during excavation; the excavation-induced unloading effects develop nonlinearly with depth; and the rebound of the excavation predominantly occurs within the loosened zone in sandy layer and is also affected by the deformation of supporting structure. These findings provide valuable references for the evaluation of deep excavation-induced soil disturbance, and the design and construction of similar annular shaft in deep sandy ground.