Influence of Area Ratio on the Deformation Patterns during Pit-in-Pit Excavation: Experimental and Numerical Investigation

This study investigates the complex behavior of pit-in-pit foundation systems through integrated physical model tests and numerical simulations. The influence of key factors—including area ratio, pit toe coefficient, and asymmetric surcharge loading—on excavation-induced deformations was systematically evaluated. Experimental results indicate that increasing the area ratio and excavation depth led to greater lateral wall displacements, bending moments, and ground surface settlements, while reducing the active earth pressure behind the walls. Numerical analyses using PLAXIS 2D (version 24.02.00.1144) identified a critical area ratio threshold of 0.5: below this threshold, its effect on wall displacement was negligible; beyond this threshold, the influence increased markedly. Reducing the pit toe coefficient aggravated the horizontal displacement of the left wall and caused the backward movement of the right wall. Asymmetric loading also resulted in pushback displacement on the retaining wall of the unloaded side.