Laboratory model tests on water inrush in foundation pit bottom

Numerous deep foundation pits were constructed in China in the course of urbanization. Water inrush is one of the most important causes of foundation pit accidents. At present, few images and detail courses of the water inrush have been recorded and reported. The evidences for the hypothesis of water inrush calculation are not enough. In this study, model tests were performed to verify the water inrush course in foundation pit bottom. The water inrush modes of foundation pits were analyzed for the aquitards that included clay and silty clay in Shanghai, China. The deformation and failure characteristics of the layers under different water pressures were obtained. The deformation course without water inrush was divided into three stages: continuous deformation, progressive deformation, and equilibrium stages. The deformation course with water inrush was divided into four stages: continuous deformation, progressive deformation, shear failure, and water inrush and sinking stages. The course included creep deformation and micro-cracks development before failure. It was not an instantaneous phenomenon but a time-depending one. The pore water pressure was the response of aquitard to boundary water pressure, which indicated the seepage in low-permeable aquitard and the development of micro-cracks. The water inrush formula was verified and tested using the model test results. The limit equilibrium method had larger safe reserves, and the prestressed homogeneous continuous-beam method was relatively accurately.