The effect of sample disturbance on laboratory properties of Lac du Bonnet granite

Abstract

Laboratory properties of Lac du Bonnet granite samples collected at depths ranging from near-surface to 1000 m were established. The laboratory properties indicated that either the in situ properties were changing with depth or the samples were changing with depth. Comparison of P-wave velocities in the samples and in situ confirmed the latter, i.e., sample disturbance was affecting the laboratory properties. The strength of the damaged samples indicated that sample disturbance affected the cohesion of the material, not the frictional properties, and that the cohesion loss cannot be accounted for, by applying a confining stress. Sample disturbance started to affect the laboratory properties of Lac du Bonnet granite when the maximum far-field in situ stress exceeded about 10% of the unconfined compression strength. Key words : sample disturbance, core discing, cohesion, brittle rocks, damage, microcracks, stress-dependent Young's modulus.