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

Abstract

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 with H/r ranging 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 specified K S values and 15 test pit and borehole configurations. Four sets of fitting parameters were determined, which apply for H/r ≤ 20, H/r ≥ 20, soil with <12% silt content, and soil with >12% silt content. Relative to specified K S , the updated shape function parameters yielded BP estimates of K S with a maximum error of 13% and an average error of 3%, whereas the original shape function parameters (developed for normally consolidated soils and H/r ≤ 22) produced a maximum K 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 of K S where steady flow was not achieved.

Evaluation of infiltration testing methods for design of stormwater drywell systems

“…Although the infiltration rate is commonly considered to represent the vertical (gravity) flux out of the facility bottom, it measures the total flux out of the facility and includes the horizontal (pressure) flux and capillary flux (capillarity). As discussed by Kindreds and Reynolds [22], the importance of the pressure flux increases as the ratio of the ponded head (H) to the borehole radius (r) increases, and the importance of the capillary flux is greater for fine-grained soils than for coarse-grained soils.…”

Bias of stormwater infiltration measurement methods evaluated using numerical experiments

“…Values of K sat input to the numerical experiments would serve as an independent reference standard to assess bias. Such numeric simulations have been previously used to successfully evaluate individual infiltration measurement methods (Ahmed et al., 2014; Reynolds, 2010), unique soil conditions (Kindred & Reynolds, 2020), and SCM performance (Sasidharan et al., 2018). The limited scope of these previous studies does not allow for a simple comparison between methods.…”