Impacts of pit excavation on foundation piles in deep silty soil by centrifugal model tests

The foundation pit excavation of a power plant located along the Yangtze River in Jiangsu province is selected to study the interaction mechanism between piles and soils during excavation of foundation pits in deep silty soft soil. Thus an indoor centrifugal model test with the similarity ratio of 1:50 is designed. The influence of foundation pit excavation on existing pile and surrounding soil in deep silty soft soil are analyzed from different aspects including the pile strain, pile displacement, pile top displacement, surface settlement and soil deformation influence range, pile bending moment and pore water pressure. Results from the centrifugal test and the excavation of the foundation pit in situ are compared and analyzed. It shows that when the shear strength of silty soft soil in the upper part of the layered foundation is relatively high, the pile foundation is subjected to a large force and it is prone to the breakage accident during the excavation process. Two extreme values of pile strain occur near the excavation depth and the interface between the silty soil and the underlying soil layer. Due to the influence of the pile, the pore water pressure of the soil near the excavation face changes smoothly, but the pore water pressure of the soil after the pile changes drastically with the excavation. The interaction between piles and soils mainly lasts 48 hours after excavation before the restoration of stability. The test results match with the field measured data, which can provide a reference for the design and construction process of the foundation pit in deep and thick soft soil.