Stress-Induced Micro-Cracking and Brittle Failure of Godhra Granite,Gujarat: A Laboratory Investigation Using Acoustic Emission

We carried out uniaxial compression tests and monitored the deformation and failure behaviour of a set of Godhra granites from Panchmahals district, Gujarat The testing was carried out by incrementing the stress at a constant rate on the test sample, and by recording the strain and acoustic emissions (AE) concurrently The static moduli have been computed from the stress-strain data, and the AE parameters, viz , hits, energy counts and peak amplitudes have been subjected to detaied analysis The results inferred from AE signatures of both medium grained and fine grained granites show that the stress-induced micro-cracking is stochastic during the early stages of rock deformation and it is followed successively by the on-set of dilatancy (inelastic volumetris strain) due to formation of new microcracks at = 65% failure stress, stable cracking, unstable cracking and crack coalescence leading finally,to the dynamic failure of the rock Owing to the preponderance of relatively high amplitude AE at stresses close to failure, the AE b value decreases quite sharply in accordance with the underlying physical processes of crack growth in both the medium grained and fine grained granite rock These observations agree well wlth those of accelerated increase in occurrence rate and energy counts of AE as the impending failure approaches in the rock.