Field Investigation of Permeability Ratio of New Liskeard Varved Soil

The results are reported of an investigation to determine the in situ permeability ratio of a large body of varved soil near New Liskeard, Ontario. Permeability ratio is defined as the ratio of coefficients of permeability for flow parallel to and perpendicular to the varves. The method used was to measure with piezometers the pattern of water pressures within a natural slope and to determine by trial and error calculations the value of permeability ratio which would yield a similar pattern of water pressures. The value of this permeability ratio was found to be rK < 5.The in situ magnitudes of hydraulic gradient were appreciably smaller than unity and this brought into question the usual assumption that the flow obeyed Darcy's law. Comparisons between calculated patterns of water pressure based on Darcy flow and non-Darcy flow and measured patterns of water pressure indicated that the best fit was obtained based on the assumption of Darcy flow.It is hypothesized that soils consisting of distal varves have small values of permeability ratio and that soils consisting of proximal varves can have large values of permeability ratio.