FACTORS AFFECTING FIELD-SATURATED HYDRAULIC CONDUCTIVITY MEASURED BY THE BOREHOLE PERMEAMETER TECHNIQUE

The borehole permeameter method for measuring field-saturated hydraulic conductivity, K-fs is prone to variability due to soil smearing during borehole excavation, and swelling that results from differences in initial soil-water content. The Effects of borehole preparation techniques and initial soil-water pressure on Kr, were analyzed in this study. Eighty boreholes were studied in a strongly structured clayey soil (a fine, mixed, mesic Typic Hapludalf). A version of the borehole permeameter method was used to measure K-fs in soil that was initially at soil-water pressures of 0, -0.016, -0.050 and -0.080 MPa. Three different borehole excavation techniques were also studied to determine the effect on K-fs of soil smearing during borehole preparation. The treatments consisted of removing a uniform thickness of soil from the sides of the borehole with an ice pick, scarifying the sides of the borehole with a wire brush, and no treatment. Field-saturated hydraulic conductivity for the brushed treatments was similar to K-fs values obtained when no treatment was used. The ice pick method resulted in significantly higher K-fs. When K-fs values measured using the ice pick method were analyzed, no significant effect of initial soil-water pressure was evident. This could possibly be due to soil variability.