Measuring unsaturated hydraulic conductivity in the laboratory and field

Fourteen methods to measure the hydraulic conductivity of unsaturated soils are described, including ten laboratory methods and four field methods. The methods can be classified as steady or unsteady, and range in complexity and cost. Methods of analysis are described for each test, as well as the advantages and disadvantages of the method. The traditional steady-state method is recommended if laboratory tests are to be conducted and the best possible estimate of K(psi) is needed. The method has few ambiguities, and the state of stress can be carefully controlled. However, this method is costly, tedious, and lengthy. Recommended alternative laboratory methods include the thermal method, instantaneous profile method, and the multi-step outflow method. The writers also recommend that field measurements be made whenever possible. The tension infiltrometer (or disc permeameter) is recommended for field testing surficial soils at lower suctions. The instantaneous profile method is recommended for testing fine-grained soils, or other soils where higher suctions are to be assessed. The cone penetrometer method shows promise for rapid testing of soils at depth.