Crack coalescence in granite

Abstract

This thesis experimentally investigates crack coalescence in prismatic Barre Granite specimens with two pre-cut, open flaws under uniaxial compression. Using a high-speed video system, crack initiation, propagation, and coalescence are observed. Flaw geometries are chosen to allow one to compare the results with those of studies in other materials as well as to better understand fracturing and coalescence processes. Specifically, the effect of ligament length (L), flaw inclination angle (p3), and bridging angle (a) on coalescence is investigated. The same crack types as in other materials are observed. Coalescence patterns observed fit into a previously developed framework (for molded gypsum and Carrara marble) with the exception of one new coalescence pattern. Crack processes and coalescence patterns suggest a more tensile behavior as grain size increases from gypsum to marble to granite. Similar to previous work in marble and granite, white patches are observed during compression tests. These white patches can be categorized as either diffuse or linear, with linear white patches further subdivided into two more types, namely boundary-following and through-going. The white patches are essentially process zones. The effect of water pressure on coalescence pattern is also investigated. Flaw water pressure is seen to affect coalescence in granite, although further work is needed.