Applications of Acoustic Mechanical Property Analysis in Deep Tunnelling Operations Under High Stress
One of the challenges of deep tunnelling through hard rock is the prediction of violent brittle failure along a blind alignment. In addition to high in-situ stress, geologic structures including faults, veins, and alteration zones cause stiffness transitions which can localize stress. The application of mechanical property assessment, using acoustic velocity measurement both at borehole scale and laboratory scale, are techniques to identify key zones of stiffness transitions. The results of borehole survey conducted at a deep exploration ramp in Sudbury Ontario, were examined and shown to be an effective method to identify shear zones and regions with pervasive hydrothermal alteration. Laboratory scale testing was conducted on samples of Cobourg limestone to determine the influence of small scale anisotropy. Results from the laboratory testing showed that variations in stiffness from interbedding structure could be detected, and mechanical property values were similar to results obtained from physical (static or mechanical) testing.