Stress-dependent flow through fractured clay till: A laboratory study

Stress-dependent hydraulic conductivities of weathered fractured clay till were measured in a flexible-wall permeameter. Measured conductivities were in the range 10(-7) to 10(-8) cm/s, of the same order as the clay matrix (10(-8) cm/s), and representing equivalent hydraulic apertures in the range 0-5 mu m. In general, the isolated fractures exhibited strongly nonlinear closure characteristics and hysteretic behaviour under stress reversal. Some fracture samples exhibited only weak stress dependency, representing observable features of only nominal conductivity. Results of the investigations suggest fractures are closed to residual aperture for an overburden load of the order of 12 m, this defining an effective closure depth and the degree of maximum useful compactive effort that might be applied to ''seal'' fractures and reduce fluid migration.