Parasitic Head Losses During Laboratory Permeability Tests

Abstract

Parasitic head losses incurred outside the tested soil specimen may alter the results of laboratory permeability tests. They can be measured by running a blank test in an empty permeameter, and determining the flow resistance of the testing equipment. They can also be assessed by using the difference between a constant-head test, where the hydraulic heads are measured within the tested specimen, and a variable-head test, where the hydraulic heads are measured outside the specimen and include the parasitic head losses of the testing equipment. When not accounted for, they can lead to permeability values that are underestimated. An electric analog provides an analytical relationship between variable- and constant-head test results. The parameters in the analytical solution can be obtained via blank permeability tests. This article emphasizes the need to measure hydraulic heads inside the soil specimen during laboratory permeability tests.