Stress-wave Induced Fracture in Rock due to Explosive Action

Blasting is a complex phenomenon and many parameters affect the outcome of a blast. The process of rock fragmentation by blasting is not well understood yet. Therefore, as a first step, blast-induced dynamic fractures must be studied under highly controlled conditions. The whole cycle of conducting a series of laboratory-scale blast, analyzing the results, and using them to test the validity of an advanced numerical code is reported in this thesis. Initially, the respective contributions by both shock energy and gas energy fractions in an explosive in the blasting process are explained. Then, microstructural, physical and mechanical properties of Laurentian and Barre granites as the selected rock types are investigated. Explosively driven fractures in a blast are controlled by rock and explosive properties, coupling media and coupling ratio. Sample geometries, types of explosives and coupling media used in the experiments are explored in the next step. In order to isolate the effect iii of shock energy from the gas energy in explosively driven fractures, copper liners were installed in the blast holes to prevent gas penetration into the shock induced cracks. The aim of the experiments was to study exclusively the nature of shock-driven fractures, and to contain the dynamic fractures within the samples and avoid sample fragmentation. At the same time and in order to investigate the stress field as a function of distance from the borehole, pressure gauges were installed in the samples. The measured pressures were used in a numerical-experimental procedure to estimate the attenuation properties of the rocks. Blasted samples were cut and impregnated with a mix of epoxy and fluorescent dye. Next, dynamic fracture patterns were highlighted using a strong ultraviolet source. After taking photographs, fracture patterns were manually mapped and crack densities were calculated at different depths and distances from the boreholes. The parameters that affect the development of dynamic fracture patterns are also discussed and relation between crack densities and pressures applied by explosives are investigated. Finally, the dynamic fracture patterns and measured pressures will be used for calibrating the selected equation of state, strength and failure models implemented in AUTODYN. Governing equations, the procedure for obtaining the model constants, applicability of the selected model for predicting the blast experiments and its limitations are discussed in detail.Ph