A general solution of consolidation for a double-layer foundation soil induced by pre-excavation dewatering with bottom reinforcement considering delayed responses of water table

Abstract

Precisely predicting soil deformation at each construction stage of foundation pit engineering is crucial for enhancing construction safety standards. However, the mechanics of ground settlement, both inside and outside foundation pits caused by pre-dewatering in an unconfined aquifer, remain unclear. Hence, this study proposes a semi-analytical solution that considers factors, such as soil stratification, pit bottom reinforcement, and unsteady pumping-induced flow in the unconfined aquifer, using finite Fourier transform and boundary transformation techniques. It verifies the acceptability of the proposed solution by comparing experimental and numerical results from COMSOL Multiphysics. A detailed parametric analysis is conducted to discuss how pit reinforcement parameters, specific yield, and soil stratification influence the behaviors of drawdown and deformation. The results indicated that increasing the reinforcement thickness at the pit bottom and reducing the permeability of the reinforcement layer can effectively mitigate soil deformation and drawdown. In contrast, the compression modulus of the reinforcement layer affects only the ultimate value of deformation. In addition, a larger specific yield significantly delays the rate of drawdown and deformation but does not impact their final values. For double-layer foundation soils, the final value of deformation and drawdown is reduced when the lower layer has higher permeability, resulting in less time for settlement completion. This study provides a theoretical reference for the engineering design of foundation pit projects.