On wave and fracture propagation in Rock Media

Experimental-stress-analysis techniques were used to study wave and fracture propagation in rock media. Marble and granite plates were loaded explosively. Wave propagation was observed through isochromatic-fringe patterns on bonded photoelastic coatings and moiré-fringe patterns. These patterns were recorded with a Beckman and Whitley camera operating at rates from 250,000 to 1,000,000 frames per second. Dilatational, shear and Rayleigh wave velocities were determined. The leading part of the pulse is compressive and shows appreciable attenuation. The trailing part goes into tension, causing widespread tensile fracture. The velocity of propagation of this fracture zone in marble was nearly equal to the theoretical terminal velocity. In the case of induced cracks in marble and granite, the velocities of crack propagation were appreciably lower than the theoretical terminal values. Experimental results obtained were discussed and interpreted for their relevance to the rapid-excavation process in rock.