A SQUARE HOLE PERCOLATION TEST FOR DETERMINING THE FIELD-SATURATED HYDRAULIC CONDUCTIVITY OF UNSATURATED GRAVELLY AND STONY SOILS

A percolation test is presented for use in the field to measure the saturated hydraulic conductivity of unsaturated gravelly and stony soils. A square hole was used because a cylindrical hole is practically impossible to make in gravelly and stony soils. The test involves excavating a square hole, using a heavy duty spade, and carefully pouring in a slug of water which is then allowed to percolate. The theory of percolation, assuming a unit gradient, was employed to develop an equation to derive the field-saturated hydraulic conductivity. Results from measurements are presented and some comparisons made with results obtained by the tension infiltrometer method. The theory was used to calculate the field-saturated hydraulic conductivities equivalent to the 't' values derived from percolation tests to assess site suitability for the soil disposal of septic tank effluents. The test is likely to overestimate the true value of the field-saturated hydraulic conductivity as the assumption of unit gradient does not admit pressure potentials which exist. The test is easy to perform and can be repeated in the one hole and at different depths in trial pits. The method is feasible on stony and gravelly soils and appears to give realistic results.