Experimental study of one-dimensional nonlinear consolidation of an aquitard under multistage loading

Abstract

• Design of experimental instrument for simulating consolidation of aquifer system. • Monitor the parameters of aquitard and characterize their nonlinear distribution. • Conduct multistage loading to simulate complex and realistic loading conditions. • Reverse pore water pressure fluctuations occur in the thicker aquitard. • Calculate the curves of pore water pressure base on different hydraulic conductivities. Aquifer heterogeneity is critical for predicting processes involved in the dissipation of pore water pressure, consolidation, and rebound. The consolidation and rebound of aquifer systems should consider the spatiotemporal variation in the hydraulic and mechanical parameters of the aquifer and aquitard. In this study, a series of laboratory experiments was conducted to characterize the consolidation and rebound of the aquifer system and estimate the hydraulic conductivity of the aquitard. The experimental results revealed that under multistage loading, the compression in the upper part of the aquitard tended to decrease, while the compression in the lower part of the aquitard tended to increase. In addition, the variation in hydraulic conductivity and deformation of the aquitard were closely related and reasonably matched at each stage. Moreover, a one-dimensional consolidation model was developed to simulate the variation in pore water pressure and compare it with the experimental pore water pressure. Reverse pore water pressure fluctuations occurred within a part of the aquitard away from the drainage boundary. Compared to the theoretical curves, the experimental curves of the pore water pressure calculated from the initial and asymptotic hydraulic conductivities exhibited delayed and advanced effects. These findings can help elucidate the characteristics of consolidation and rebound of aquifer systems and the spatiotemporal variation in hydraulic conductivity.