DETERMINATION OF ROCK PLASTICITY PARAMETERS BY INDENTATION EXPERIMENT
STANLEY, H. MARK, III
Master of Science
Indentation tests are performed on samples of Indiana Limestone and Berea Sandstone under confining pressures ranging from 0 to 2500 psi. The force-displacement data from these experiments are analyzed by comparing them to numerical results obtained for a simplified theoretical model which assumes (1) rigid-perfectly plastic behavior, (2) a Mohr-Coulomb linear yield envelope, and (3) negligible lip formation. In addition, indentation is assumed to be a quasi-static, equilibrium process. The two Mohr-Coulomb parameters cohesive strength (c) and angle of internal friction ($\phi$) are bounded by consideration of the following two heuristic conditions: (1) The force-displacement curve generated by a perfectly rough assumption must be an upper bound to the experimentally observed curve. (2) The frictionless solution must be a lower bound. These two conditions restrict $\phi$ and c to a narrow allowable region in $\phi$-c space, and are applicable to more realistic yield conditions, as well.