Development of surface settlement under the combined effect of foundation pit dewatering and excavation: Insights from experimental modelling

• Surface settlement, groundwater heads, and wall deflection in excavations were measured. • Settlement patterns during dewatering and excavation at key locations were analyzed. • Settlement patterns to the lateral displacement shapes of diaphragm walls were linked. To investigate surface settlement under the combined effect of foundation pit dewatering and excavation, a series of experiments was conducted using a scaled model of a deep foundation pit at a metro station. During experimental simulations of the dry excavation and dewatering processes, data were collected on surface settlement, water heads outside the pit, and deflection of the diaphragm wall. The characteristics of surface settlement were compared and analyzed under different conditions with a focus on the development of surface settlement during dewatering and excavation at key locations outside the pit. The combined effect of dewatering and excavation was found to increase surface settlement outside the pit and expand its area of influence. The insertion ratio of the diaphragm wall ( n ) significantly affected surface settlement; as the insertion ratio increased, surface settlement, along with its area of influence, decreased. For n < 1.25, the area beyond twice the excavation depth was considered a minor area of settlement influence. In contrast, for n ≥ 1.25, this area wasn’t classified as a minor area of settlement influence. As excavation depth increased, the surface settlement pattern outside the pit transitioned from triangle-type to groove-type, groove-type settlement occurred when A s ≥ 1.6 A c , whereas triangle-type settlement occurred under other conditions ( A s represents the area of the deep inward part of the convex deformation of the diaphragm wall; A c refers to the cantilever part of the diaphragm wall). This study provides insights into the development of surface settlement during dewatering and excavation and serves as a valuable reference for innovations in sustainable and resilient underground design.