In view of the issue of lacking clear standards for the foundation pit excavation limits of ship lock chamber expansions and the safety of existing ship locks being affected by adjacent expansion construction,an analysis method for finite soil on the basis of rupture surface characteristics is proposed to quantitatively define the critical control parameters for foundation pit excavation.Through generalized centrifuge physical model tests,the deformation mechanisms of the soil behind the wall and the distribution rules of earth pressure under different width-depth ratios are systematically analyzed.The critical width-depth ratio between semi-infinite and finite soil conditions is identified as k=0.75.When k≤0.75,the earth pressure distribution deviates significantly from the classical Coulomb theory.The active earth pressure coefficient decreases by 18%-35%,and the inclination angle of the slip surface increases until constrained by the fixed boundary.This method is applied to an actual second-line ship lock project.The schemes with 90 and 100 m centerline spacings (corresponding to width-depth ratios of 0.367 and 0.852,respectively) are compared,and validated by nonlinear finite element simulation and field monitoring.The results show that under the 90 m scheme,tensile stress appeares at the base of the existing ship lock wall,whereas under the 100 m scheme,all base stresses are compressive,with displacement reduced by 21.4%.The proposed analysis method and excavation limits control standard can provide a theoretical basis for revising relevant specifications and serve as a reference for similar projects.