Experimental Study on Deformation and Passive Earth Pressure Behind Cantilever Pile Retaining Walls in Narrow Excavations

The deformation and displacement characteristics of narrow foundation pits supported by cantilever row pile flexible retaining walls exhibit notable compared to conventional foundation pits. Model tests were conducted using custom-made equipment to simulate the forward deflection and displacement modes of flexible retaining walls, such as cantilever pile rows, under various width-to-height ratios in narrow foundation pits. These tests aimed to investigate the deformation and failure characteristics of soil, as well as the distribution of passive soil pressure in non-viscous sand. The test results indicate that the soil mass in the passive zone of the excavation exhibits a symmetrical sliding fracture surface when subjected to forward bending deformation induced by the cantilevered pile row retaining wall. The lower section of the sliding fracture surface intersects with the zero displacement point of the wall, while the upper section exhibits a more pronounced penetrating fracture surface. The morphology of the sliding fracture surface can be described as a combination of a logarithmic spiral surface and two polygonal surfaces. The distribution of passive earth pressure along the retaining wall exhibits a nonlinear pattern. As the depth increases, the earth pressure gradually rises and then rapidly declines (approaching the static earth pressure at zero displacement). The smaller the width-to-height ratio, the greater the peak value of passive earth pressure. As horizontal displacement increases, the passive earth pressure above the zero point gradually rises, with a more pronounced increase in upper earth pressure compared to lower earth pressure. The ABAQUS finite element numerical simulation is utilized for the simulation of the narrow foundation pit. The strain cloud map aligns with the results of the experimental PIV analysis, showing a continuous sliding fracture surface formed in the limit state. The distribution of passive earth pressure under different aspect ratios is essentially consistent with the experimental results, and the peak value of earth pressure intensity closely resembles that of the experimental findings.