Experimental and numerical modeling of chemical osmosis in the clay samples of the aquitard in the North China Plain

Abstract

This study focuses on addressing the existence of chemical osmosis in the clay samples of the aquitard in the North China Plain (NCP). For this purpose, chemical osmotic experiments in the clay samples collected from the aquitard in the NCP were implemented to estimate the reflection coefficient or chemico-osmotic efficiency in clayey sediments. More specifically, under a certain chemical potential gradient, the reflection coefficients were, respectively, achieved by measuring the osmotic flow and the induced pressure in terms of the two sets of undisturbed clay core samples and their remolded clay samples equipped in a rigid wall permeameter. The measured reflection coefficient is the value of 0.023 for in situ clay sample, much smaller than that of 0.098 for remolded sample. Also, the constant-head tests for determining the hydraulic conductivity of clay samples were conducted before and after the osmotic tests. It is indicated that the permeability of the remolded sample is smaller than the undisturbed sample in both periods. Moreover, a chemical osmosis continuum model was used to fit the evolution of the osmotically driven hydraulic pressure in the clay samples where more intrinsic parameters of the samples were calibrated. Additional analysis demonstrates the sensitivity of the osmosis pressure to the different parameters input to the model for the in situ clay sample. This study could provide a reliable basis for further evaluating the role of clay sediments in the desalination of shallow saline groundwater and salinization of deeper fresh groundwater in the NCP.