Theoretical Model for Ground Subsidence Induced by Confined Aquifer Dewatering

Surface subsidence caused by the dewatering of deep confined aquifers substantially threatens infrastructure safety. In general, traditional monitoring methods can reflect settlement near observation points, but data are often captured only after soil deformation occurs. Furthermore, the field experiments may struggle to accurately reflect surface subsidence trends due to geological conditions, and existing models often ignore the influence of nonuniform aquitard deformation. Therefore, a new theoretical model is proposed in this study that focused on the spatially heterogeneous deformation of the aquitard caused by the seepage effect. This paper introduces a regional classification rule and links solid phase and liquid phase interactions through groundwater dynamics described by the Boussinesq equation. A formula for pore pressure distribution is also derived. The Mindlin solution is incorporated to calculate the subsidence. In addition, a subsidence transfer function is proposed, based on the subsidence mechanism, to improve the practical applicability of the theoretical model. Numerical simulations revealed significant seepage force between the cone of depression and the aquitard, leading to localized deformation. To more accurately reflect the deformation range of the aquitard caused by seepage forces, the aquitard was divided into a pressure-free zone (intense deformation) and a pressure zone (weak seepage effect). Sensitivity analysis showed that the elastic modulus, permeability, and specific storage significantly affected the subsidence behavior. The error of the proposed calculation model based on the Boussinesq equation under the condition of a deep aquifer was only 2%–14.49%, and the coefficient of determination (R2) ranged between 0.901 and 0.989. The model provided surface subsidence prediction for projects that require a reduction in the water level by pumping a large amount of confined water, such as tunnel excavation in deep confined aquifers.