An Analytical Method to Calculate Groundwater Released From an Aquitard Undergoing Nonlinear Consolidation

The estimation of groundwater released from aquitards is important for the groundwater resource management. In this study, a governing equation of drawdown variation within the aquitard, which undergoes nonlinear consolidation, was obtained based on the consolidation theory of Gibson et al. (1967, https://doi.org/10.1680/geot.1967.17.3.261). Then, analytical solutions of drawdown variations within an aquitard were derived for a single aquifer underlying an aquitard, as well as for the case when there are aquifers above and below an aquitard. Drawdown solutions were obtained for both the cases when there was a sudden hydraulic head decline in the confined aquifer(s). The characteristics of the groundwater dynamics and water balance in the aquitard have been analyzed with the analytical solution. A laboratory experiment was conducted to verify the analytical solution, and a type‐curve fitting method was presented to calculate the aquitard's hydraulic parameters. Our study revealed that the cumulative water released from the aquitard predicted by Gibson's theory (1967) is less than that obtained through Terzaghi's theory (1943). Groundwater released from the aquitard increases with increasing compression index, aquitard thickness, and drawdown of the adjacent aquifer, and with decreasing initial void ratio and initial effective stress. The time for the drawdown to reach steady state increases with increasing compression index, initial void ratio, and aquitard thickness, and with decreasing initial effective stress and hydraulic conductivity. Key Points New analytical solutions are derived that consider aquitard drainage undergoing nonlinear consolidation Factors affecting the cumulative water released over a unit area from the aquitard are obtained A type‐curve fitting method is proposed to calculate the hydraulic parameters of the aquitard undergoing nonlinear consolidation