NATURAL stone described as a microcracked solid

Experiments were performed on Charcoal granite to investigate the possibility of measuring the amount of damage present in the material. The results of 2D tensile tests on artificially cracked aluminum plates suggest that, if a random distribution of microcracks in a material is assumed, then the problem can be modeled using the approximation of non-interacting cracks even when interactions occur. The microcrack density of the virgin rock was estimated with the use of pressure-strain analysis, where linear strains were measured as a function of applied hydrostatic pressures. At large enough pressure, typically 50 MPa, all cracks closed and the measured response was due to the solids only. After transformation of the strain data, the volume strain was determined and the modulus of the solids was estimated to be 84 GPa (for Poisson's ratio of 0.25). The modulus of the granite in uniaxial tension was determined to be 46.5 GPa, so the granite in its natural state has a microcracked density of about 0.45. Further damage was then induced in the rock by slow, uniform heating. Results and implications of the additional microcracking are discussed.