Evolution mechanism of the dynamic excavation deformation of deep foundation pits with water-rich sand-pebble geology

Abstract This study focuses on the deep foundation pit with water-rich sand and gravel geology at the Southwest Jinfu Station of Chengdu Metro Line 6. A typical sand and gravel foundation pit standard cross-section is selected, and a plastic hardening constitutive model is employed. Considering the fluid-structure interaction during the excavation process, the study systematically analyzes the lateral displacement, bending moment variation, support axial force changes, as well as the evolution of surface settlement and foundation uplift of the underground continuous wall. The results indicate that as the excavation depth increases, the lateral displacement of the underground continuous wall gradually increases, with the displacement pattern transitioning from cantilever to bow, fish belly, and finally to a kick-foot shape. The bending moment increases with the excavation depth. The support axial force undergoes significant changes during excavation, especially during the steel support stage, where noticeable axial force loss occurs. Additionally, as the excavation depth increases, the settlement and uplift of the soil behind the wall also exhibit significant changes.