Subsurface tension permeametry

A new method for determining subsurface unsaturated hydraulic conductivity in situ was developed. Steady state flow conditions were established from spheroidal cavities under subatmospheric pressure. Several borehole tension permeameter devices were constructed and field tested in four different soils. While the capillary length parameter (alpha) values were generally consistent with previously reported values, the estimates for saturated hydraulic conductivity (K-s) were, in some cases, 1 order of magnitude lower than reported values for the test soils. In part, this can be traced to the rigid log linear shape of conductivity to pressure head used by the Gardner [1958] model, which produces overly small intercept values (K(0) = K-s) when measured for drier conditions. Transformation of the estimated parameters to the Brooks and Corey [1964] model seems to extend the useful range of the parameters. A potential combination of near-saturation measurements [Shani and Or, 1995] with the proposed method could lead to improved characterization of subsurface K(h).