Constant-Head Constant-Volume Hydraulic Conductivity Testing of Porous Materials

The constant-head constant-volume (CHCV) method for measuring hydraulic conductivity of less permeable (hydraulic conductivity <= 10(-6) m/s) saturated porous materials consists of a closed-loop of liquid that passes through the specimen, tubing, a mercury-water reservoir, and a capillary tube. Use of a closed-loop forces inflow to equal outflow throughout the test, resulting in faster equilibration. The closed loop contains two liquids: water and mercury. A constant head drop is applied by displacing a column of mercury and flow rates are measured by monitoring the rate of displacement of a water-mercury interface in a horizontal capillary tube. Tests were conducted on a variety of media having very different stiffness and hydraulic conductivity using the CHCV device and a conventional open system. Nearly identical hydraulic conductivities were measured using both methods, but much less testing time was required with the CHCV device.