THE EFFECT OF SAMPLE DISTURBANCE ON LABORATORY PROPERTIES OF LAC DU BONNET GRANITE

Laboratory properties of Lac du Bonnet granite samples collected at de pths ranging from near-surface to 1000 m were established. The laborat ory properties indicated that either the in situ properties were chang ing 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 str ength of the damaged samples indicated that sample disturbance affecte d the cohesion of the material, not the frictional properties, and tha t the cohesion loss cannot be accounted for, by applying a confining s tress. Sample disturbance started to affect the laboratory properties of Lac du Bonnet granite when the maximum far-field in situ stress exc eeded about 10% of the unconfined compression strength.