Spatial deformation effect of pile-diaphragm wall system in deep and large foundation pit in soft clay area

Significant spatial deformation effects are observed in deep and large foundation pits during soil excavation, which impacts the primary structure’s mechanical behavior. The deep and large foundation pit of the newly-built Suzhou South Railway Station was used as the engineering background, and the influences of the thickness of the diaphragm wall and the engineering piles were considered to establish a three-dimensional space finite element model based on ABAQUS. The modified Cam-clay model was used to consider the influence of the strain hardening characteristics of soft clay. This paper studied the deformation characteristics and spatial effects of the pile-diaphragm wall system in a deep and large foundation pit located in a soft clay area from three aspects: lateral displacement of the diaphragm wall, ground surface settlement behind the wall, and engineering piles and soil uplift at the bottom of the pit. The research results indicate that the lateral displacement of the diaphragm wall and the surface settlement behind the diaphragm wall in a deep and large foundation pit exhibit significant corner effects. For area A of the foundation pit (with a wall thickness of 1 meter and pile diameter of 1 meter), the influence range of the corner effect of the lateral displacement of the wall is 1.05 to 1.71 times the excavation depth. For area B of the foundation pit (with a wall thickness of 0.8 meters and pile diameter of 1.5 meters), the influence range of the corner effect of the lateral displacement of the wall is 0.91 to 1.48 times the excavation depth. The influence range of the corner effect on surface settlement for areas A and B of the foundation pit are 1.24～2.10 and 1.77～2.47 times the excavation depth, respectively. The spatial deformation corner effect of the deep foundation pit is related to the pile diameter and wall thickness, and has a greater effect on the long side of the pit than on the short side. The engineering piles effectively enhance the stiffness of the soil beneath the excavation surface, reducing the lateral displacement of the wall. The overall deformation of the foundation pit effectively decreases with increasing wall thickness. The engineering piles and the uplift of the soil at the bottom of the pit show a characteristic of being larger in the middle and smaller at the periphery. The soil around the engineering piles is constrained, resulting in a smaller uplift. Within a certain range, the suppressive effect of engineering piles on soil uplift is positively correlated with their diameter and negatively correlated with their spacing. In designing and calculating the deep foundation pit in soft clay areas, the spatial deformation effect of the engineering pile-diaphragm wall structure system should be emphasized. © 2024, Central South University Press. All rights reserved.