Standard Test Method for Hydraulic Conductivity Ratio (HCR) Testing of Soil/Geotextile Systems

Abstract

5.1 This test method is to be used for measuring the hydraulic conductivity of water-saturated soil/geotextile systems. 5.2 This test method is to be used as a design performance test, or as a comparative tool for evaluating the filtration behavior of soils with geotextiles. This test method is not intended for routine (index-style) testing, since the results will depend on the specific soil and hydraulic conditions that are evaluated. It is not appropriate to use the test results for job specifications or manufacturers’ certifications. 5.3 This test method applies to the permeation of porous materials with water. Permeation with other liquids, such as chemical wastes, can be accomplished using procedures similar to those described in this test method. However, this test method is intended to be used only when water is the permeant liquid. 5.4 The mathematical concepts (primarily Darcy’s law) used in this test method were originally developed for one-dimensional, laminar flow of water within porous materials, which is often the case with soil and geotextiles. When flow conditions are laminar and one-dimensional, the hydraulic conductivity is unaffected by hydraulic gradient. However, when flow occurs through some soil/geotextile systems, a change in hydraulic gradient could cause movement of soil particles, thereby changing the structure of the test specimen and hence, changing the hydraulic conductivity of the soil/geotextile system. The mathematical expressions given by Darcy’s law are still appropriate for application to this situation; however, it is therefore imperative that the hydraulic gradient be controlled carefully in the HCR test to simulate field conditions. 5.5 This test method provides a means of determining hydraulic conductivity at a controlled level of effective stress. Hydraulic conductivity varies with void ratio, which in turn varies with effective stress. The hydraulic conductivity of the test specimen will probably change if the void ratio is changed. It is therefore imperative that the effective stress (that is, the effective confining pressure) be controlled carefully in the HCR test to simulate field conditions.