Indentation of rock by wedge-shaped tools

This paper presents the experimental results obtained with a two-dimensional indentation device controlled by a servo-hydraulic loading system and monitored with the nondestructive techniques of acoustic emission and electronic speckle pattern interferometry. The goals of this research were to evaluate the indentation pressure as well as the size of a damage (plastic) zone, and to study the initiation of tensile fracture at the intact rock-damaged rock boundary, that is, the elasto-plastic interface. The key factors controlling the failure process are (1) the mechanical properties of the rock including the elasticity and strength parameters, (2) the geometric features of the tool such as the wedge angle, and (3) the lateral confinement simulating the far-field stress. A good agreement with regard to indentation pressure and damage-zone radius was found between the experimental and theoretical analyses. Furthermore, the intrinsic crack length, critical in establishing tensile fracture, was estimated and correlated to the grain size.