Chemical osmosis test and numerical modeling of the clay samples in the North China Plain

Sediments with high clay content can act as semipermeable membranes, leading to osmotic flow and osmotic hydraulic pressure. The semipermeable membrane ability is usually quantified in terms of a reflection coefficient, σ, or chemico-osmotic efficiency, ω. In the previous studies, the osmotic transport was never taken into account in salt-rich region of the North China Plain. In a rigid wall permeameter, an undisturbed soil core sample drilled in this region and a remolded soil sample with the same clay content and porosity were subjected to a certain chemical potential gradient to estimate the reflection coefficient, σ, by measuring the osmotic flow and the induced pressure. Meanwhile, the constant-head tests for determining the hydraulic conductivity of soil samples were conducted before and after the osmotic test. It is indicated that the permeability of the remolded sample is smaller than the undisturbed sample in both periods. Also, the chemical osmosis was observed in both samples, and the measured value of σ for in-situ sampling (0.074) is much smaller than that value for remolded sampling (0.350). Moreover, a chemical osmosis continuum model presented by Garavito et al. (2006) 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. The results demonstrated in our tests can provide the reliable basis for the further study of clay sediments in the North China Plain.