查看更多>>摘要：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.
查看更多>>摘要：Porous media (PM) flow is essential in many natural and industrial processes. The PM can be either hydrophilic or hydrophobic, substantially affecting its imbibition and flow. As opposed to a decreasing infiltration rate with time (concave shape) in hydrophilic PM, an increasing rate with time (convex shape) has been observed in hydrophobic PM. A commonly accepted mechanism to explain the convex infiltration pattern is still lacking. The current study elucidates the latter by focusing on flow in hydrophobic capillary tubes under different boundary conditions. A convex-shape meniscus propagation in a hydrophobic capillary tube was observed for low ponded water depth at the tube inlet, whereas a concave shape propagation was observed for high ponded water depths. To the best of our awareness, such a finding is innovative. Once the meniscus reached the tube outlet, the hydraulic conductivity of the hydrophobic tube depended on the driving head for an open-to-air outlet while having a constant value for a submerged one. The saturated hydraulic conductivity for an open-to-air capillary tube depends on the ratio between ponded water depth and tube water-entry head,R-0 , and reaches a constant value measured for a submerged tube for R-0 > 20.8. While successfully predicting the wetting-front propagation for R-0 > 20.8, the modified Lucas-Washburn (LW) equation with slip boundary condition failed to predict the convex infiltration patterns. The observed infiltration patterns in hydrophobic porous media in general and soils in particular, seem inherent since capillary tubes are fundamental units in such media. Moreover, flow in PM has been frequently modeled using a bundle of nonuniform capillary tubes. The failure of the modified LW equation to predict the measured data for R-0 < 20.8 calls for a new approach to model water flow in hydrophobic tubes and PM.
NSTL
Elsevier