EFFECTS OF Cu2+ CONCENTRATION AND CONFINING PRESSURE ON THE HYDRAULIC CONDUCTIVITY OF SATURATED CLAY SOILS

摘要

Hydraulic conductivity is a principal standard used to judge whether a clay liner is able to prevent leakage of leachates. The purpose of this investigation was to study the changes in permeability caused by two factors. One factor that regulates permeability of clay is the reaction that occurs between clays and chemicals when saturated clay soils are subjected to the permeation of heavy metal cations such as Cu2+. The other factor influencing the permeability of clay is the confining pressure exerted on clay samples. Hydraulic conductivity experiments were performed using a flexible wall permeameter in order to determine the effects of confining pressure and Cu2+ concentration on the permeability of saturated clay soils. The experiments were performed by varying one of two conditions in two sets of experiments: (1) In the first set of experiments, the soil samples were subjected to different confining pressures while the permeant concentration was kept constnnt; and (2) In the second set of experiments, the permeant concentrations were varied while the soil samples were subjected to the same confining pressure. It was observed that when the CuCl2 concentration remained constant (5.0g/L), the hydraulic conductivity of clay soil to water/CuCl2 mixtures was slightly greater than that to pure water. Meanwhile, when the confining pressure increased, there was a corresponding decrease in the reduction of hydraulic conductivity. Changing the properties of the permeant fluid had little influence on the permeability of soil samples when the confining pressure was over 600kPa. Under conditions where the confining pressure was kept constant while the concentrations of permeant were varied, the results showed that the void ratio and the hydraulic conductivity of soil slightly decreased when the solution concentration increased and when the CuCl2 concentration was less than 0.5g/L. However, the opposite effect occurred once the CuCl2 concentration increased over 0.5g/L. The test results showed that as the permeant concentration increased, both the void ratio and hydraulic conductivity values increased. Finally, a novel fitting formula was derived in order to describe the relationship among hydraulic conductivity, confining pressure and solution concentration.