Measurements of Unsaturated Hydraulic Conductivity Functions of Two Fine-Grained Materials

Abstract

Water unsaturated hydraulic conductivity (kw) functions of two remolded fine-grained materials were measured over a wide range of degrees of saturation (Sr) with two methods. The instantaneous profile method (IPM) was used for Sr>50%. An original vapor equilibration method (also known as the vapor equilibrium technique, VET) was used for Sr<50%. Both materials compacted at the standard Proctor optimum water content and maximum density, have saturated hydraulic conductivities (ksat)<10-7 m/s. The VET couples the total soil suction (s) control from desiccators with saturated salt solutions with water mass measurements from a digital laboratory balance. The kw measurements of the two techniques are consistent and complementary. The effect of hysteresis on the kw functions at higher s values was also investigated. The experimental results suggest that the hysteretic effect on the kw-Sr and kw-s relationships cannot be neglected, and that the measured kw are significantly dependent on the initial Sr. The VET tests on the specimens that were initially dried give the lowest values of kw and the tests on the specimens that were initially saturated give the highest values of kw. The relative hydraulic conductivity values are very small (krw<2×10-5) in this saturation range (Sr<50%) for the tested materials.