Directional saturated hydraulic conductivity characterization in schist using laboratory tests

Abstract

In this study, the directional saturated hydraulic conductivity in weathered mica-schists from Embu Complex (Mauá/SP) was verified. Laboratory tests were performed in undisturbed rock samples using constant head permeameter under pressure to promote successive increments of hydraulic gradient, and analyses of grain size distribution, saturation degree and test of adsorption of Methylene Blue were carried out to characterize the investigated rock. Grain size distribution showed that the studied rock is composed by silt, clay and sand, with predominance of silt and sand fractions and absence of expansive clays. The results of hydraulic conductivity, 10^-09 m/s, showed an apparent isotropic condition in a strongly anisotropic rock, at least in higher hydraulic gradients. However, in lower hydraulic gradients, an apparent anisotropic condition is observed, considering that the responses for the rock samples in different directions are directly dependent to the hydraulic gradient applied. The experimental data herein demonstrate that rock samples with a higher saturation degree require lower hydraulic gradients to promote water flow through rock samples, and coincide with the parallelism observed between the flow direction and the foliation planes. On the other hand, rock samples with a lower saturation degree require higher hydraulic gradients to promote water flow through rock samples, and coincide with the larger angles observed between the flow direction and the foliation planes.