Clay-based cutoff walls have been widely used as in situ barriers for contaminant isolation and controlling migration of the contaminated groundwater in landfills and site remediation engineering. With the interaction between CaCl2 solution and cutoff walls formed by mixing stratum of clays

what would happen to the permeability? To explore this problem

the Fujian standard sand is used to simulate sandy stratum and four different clays are selected as addition material

and the specimens are consolidated after mixing and pouring. Then the permeability coefficient and moisture characteristic curves of specimens are measured by the improved flexible-wall permeameters and the centrifuge test. The results indicate that at the 10% adding level of clay

all the final permeability coefficients are increased after the four sand-clay mixtures are permeated with 0.2 mol/L CaCl2 solution. Compared with the tap water

and the increases of permeability coefficients are less than 10 times their original values. In addition

the porosities of four mixtures decrease only slightly. The experimental results imply that calcium ions may substitute those monovalent cations on the surface of clay mineral particles

leading to a decreases in the thickness of diffuse double layer and bound water

and hence the increase of effective porosity.