Using the borehole permeameter to estimate saturated hydraulic conductivity for glacially over-consolidated soils

摘要

The borehole permeameter (BP) method was developed in the 1950s by the United States Bureau of Reclamation to estimate saturated soil hydraulic conductivity (K-S) in shallow boreholes completed above the water table. The approach has been improved over the years, and now accounts for flow due to pressure, gravity and soil capillarity. However, the BP method is calibrated only for normally consolidated soils and ponding depth (H) versus borehole radius (r) ratios (H/r) <= 22. The primary objective of this study was to recalibrate the BP method for use in glacially over-consolidated soils withH/rranging from 0.05 to 200. Recalibration consisted of using numerically simulated steady BP flow for five representative glacially over-consolidated soils to update the BP shape function fitting parameters (Z(1),Z(2),Z(3)) for nine specifiedK(S)values and 15 test pit and borehole configurations. Four sets of fitting parameters were determined, which apply forH/r <= 20,H/r >= 20, soil with <12% silt content, and soil with >12% silt content. Relative to specifiedK(S), the updated shape function parameters yielded BP estimates ofK(S)with a maximum error of 13% and an average error of 3%, whereas the original shape function parameters (developed for normally consolidated soils andH/r <= 22) produced a maximumK(S)error of 94% and an average error of 23%. The numerical simulations were also used to develop criteria for estimating time required to achieve steady BP flow, and for correcting BP estimates ofK(S)where steady flow was not achieved.