Prediction of drawdown and retaining structure deformation under the influence of foundation pit dewatering and excavation based on unsteady seepage

Existing theories for calculating the horizontal displacement of retaining structures do not simultaneously consider the effects of dewatering and excavation. The dewatering leads to drawdown and the seepage force, the excavation leads to the change of soil pressure. Under the combined effects of both factors, the distribution of water and soil pressure on both sides of the retaining structure is reassigned, resulting in the occurrence of horizontal displacement. This paper simultaneously considers the effects of dewatering and excavation, establishing a theoretical framework for predicting the drawdown and the horizontal displacement of the retaining structure. Firstly, a new method is established to calculate the drawdown caused by dewatering, deducing the numerical solution for the drawdown based on the unsteady seepage theory. Subsequently, a force balance equation for the water body element is established, based on the Rankine earth pressure theory, to derive a water and soil pressure calculation theory that takes into account seepage forces and drawdown. Meanwhile, this paper replaces the traditional Winkler foundation model with the Pasternak foundation model, deriving the bending differential equation and employing the finite difference method to calculate horizontal displacement. Compare the field monitoring data to verify the rationality of the theory. Analyze the calculation errors caused by neglecting drawdown and seepage forces, as well as the selection of foundation model. Additionally, further investigate the impacts of precipitation parameters and excavation parameters on the horizontal displacement and drawdown.