Alternative Analytical Methods for Borehole Permeability Tests in Seepage Barrier Walls-Paper

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The paper evaluates analytical methods for estimating in situ permeability from borehole tests in seepage barrier walls. The commonly used Hvorslev equations assume an infinite, uniform permeable stratum, unlike a narrow, low-permeability wall bordered by more permeable ground. Because the actual flow path from the wall face to the borehole is shorter, Hvorslev analyses tend to overestimate wall permeability.<br /><br />The authors develop alternative line-source models for constant- and variable-head tests in unconfined and confined conditions. These models represent the two wall faces as constant-head sources and better reflect the wall’s limited thickness. Comparisons for typical test conditions show Hvorslev permeability estimates are about 1.3 to 2.5 times higher than estimates from the line-source models.<br /><br />When upstream and downstream water levels differ, the authors recommend using their average as the outside head in either model. If outside water levels are unknown, the borehole’s equilibrium water level can serve as an approximation. Although more representative, the line-source models still rely on simplifying assumptions, including negligible well-entry losses and restricted flow at the ends of the test zone; these can introduce biases.<br /><br />The authors emphasize that no analytical model fully captures the complexities of constructed barriers. Defects such as cracks or poorly treated zones may govern barrier performance and test results more than the permeability of the barrier material itself.

Keywords

permeability

borehole tests

seepage barrier walls

Hvorslev equation

line-source model

constant-head test

variable-head test

unconfined flow

confined conditions

analytical methods