Laboratory investigations of the strength, static hydraulic conductivity and dynamic hydraulic conductivity of glacial sediments

We report the first data on how effective pressure and deformation influence the hydraulic conductivity of glacial sediments. Fifty eight static hydraulic conductivity tests, 28 triaxial deformation tests and 25 dynamic hydraulic conductivity tests (in which hydraulic conductivity is measured simultaneously with deformation) have been undertaken on seven samples of glacial sediments recovered from the margins of Haut Glacier d' Arolla, Switzerland, and from Traeth y Mwnt, mid Wales. Testing reveals that hydraulic conductivity is inversely related to effective pressure, particularly at effective pressures below c. 100 kPa. Over the full range of effective pressures used (50-900 kPa), this relationship is best described by a negative power law above a base hydraulic conductivity value, termed K _o. The value of K _o varies between samples by over three orders of magnitude, from 10 ^-8 ms ^-1 to 10 ^-11 ms ^-1. These values vary directly, but weakly, with the square of the effective grain-size of the samples tested. Dynamic testing revealed a commonly repeated pattern of sample failure: axial stress approached a maximum value after which the sample deformed in a ductile manner from its initially cylindrical shape to a barrel shape. Most commonly, sample deformation and failure were accompanied by a decrease in hydraulic conductivity, although increases were also recorded. Dynamic testing also resulted in strongly linear relationships between effective pressure and the yield stress at failure. Such relationships are broadly consistent with a Mohr-Coulomb type model, revealing significant inter-sample variability in frictional resistance, and a cohesive term that is statistically indistinguishable from zero.