Analytical Solutions for Nonlinear Consolidation of Aquitard Induced by the Dropping of Groundwater Table

The dropping of groundwater table by pumping may cause consolidation settlement of aquitard underlying aquifer, and the nonlinear compressibility and permeability of soils have evident influences on the consolidation deformation. Therefore, the nonlinear compressibility and permeability of soils have to be considered in the nonlinear consolidation model of aquitard caused by groundwater pumping, while difficulties exist in solving this consolidation model. Based on the analysis of the existing nonlinear consolidation models, an approximate analytical solution for the nonlinear consolidation of aquitard was derived, in which by adopting the classical nonlinear relationships and assuming a constant initial effective stress at different depths, an approximate analytical solution for one-dimensional nonlinear consolidation of soils caused by large area pumping of phreatic water layer were obtained using the method of separation of variables when the ratio of compressibility index Cc to permeability index Ck was not equal to 1. When Cc/Ck→1, the solution can be reduced to the existing one-dimensional nonlinear consolidation solution for the case of Cc/Ck =1. The solution was applied to the settlement analysis of engineering case, and the comparisons between theoretical and actual measurement results further showed that the solution is reliable for actual problems. Finally, taking the single-stage and constant-rate dropping of groundwater table as an example, the consolidation settlement curves of aquitard under different factors were calculated by using the above solution and the non-linear consolidation behaviors were analyzed. The results showed that when the value of Ck is constant, the larger Cc is (resulting in larger Cc/Ck), the slower the consolidation rate is, but the greater both the settlement at the same time and the final settlement are. When the value of Cc remains constant, the smaller Ck is (resulting in larger Cc/Ck), the slower the consolidation rate is, and the smaller the settlement at the same time during the consolidation process is, however it does not affect the final settlement of aquitard. The faster the dropping rate of groundwater table is, the faster the consolidation rate of aquitard is, while the final settlements under different dropping rate are same. The settlement rate grows with the increase in the final value of groundwater table (hc), whereas the influence of Cc/Ck on the consolidation rate becomes more evident. The larger the specific weight of soils (γ) is, the larger the settlement at the same time factor is, and the slower the dissipation rate of the excess pore pressure is, which indicates that γ has no influence on the final value of the excess pore pressure. Copyright ©2021 Advanced Engineering Sciences. All rights reserved.