New method quickly determines hydraulic conductivity of materials

Wang (left) and Benson with their newly patented hydraulic conductivity testing device. (28K JPG)

A newly patented method and apparatus for testing the hydraulic conductivity of materials such as clay, rock and soil means these tests can be completed in minutes, rather than weeks. Xiaodong Wang, the Department of Civil & Environmental Engineering's geotechnical laboratory manager, and Professor Craig Benson have devised an American Society for Testing and Materials-approved invention to improve hydraulic conductivity testing.

Current commercial technology places a sample between two openings (connected to burettes) that have different water levels, to create a pressure differential across the sample. This method has proven reliable; however, for media having very low hydraulic conductivity, such as tight rock cores, the time to reach a steady state flow of water across the sample can take upwards of nearly three weeks.

The new invention includes a constant head system and instruments for measuring the hydraulic conductivity of materials using a closed loop system. The geological sample is placed within a test fluid under a constant pressure and the fluid flow is regulated so that a constant volume of test fluid is within the sample. This invention eliminates variation in pressure difference, which is believed to cause errors in the calculation of hydraulic conductivity, and decreases the amount of time needed to reach a steady state flow of water across the sample. Advantages of this new, simpler process includes almost immediate results and a reduction in measurement variation.