| Summary: | Results of a rock deformation study designed to investigate the energy budgets of glass fragmentation under triaxial conditions are presented. This work comprises a series of room-temperature experiments designed to explore the fundamental mechanical behaviour of natural (obsidian) and synthetic glasses (Pyrex) under confining pressures of 0.1 - 100 MPa and at displacement rates of 40μm/s. The results quantify the amount of energy stored in the samples prior to failure, and establish a relationship between grain-size distributions of experimental-products (D-values) and the stress drop at failure. The relationship found for compressive fragmentation is significantly different from the relationship between D-values and energy densities established by previous authors for decompressive fragmentation. Furthermore, I show that natural glasses have less potential to store elastic energy after fragmentation than synthetic glasses. However, the stress storage capacity of natural glass can be enhanced (approaching synthetic glasses) through heat-treatment.
The evolution of the physical properties (strain, porosity, permeability and ultrasonic wave velocities) of conduit breccia deposits during compaction is addressed. Compaction produces strongly anisotropic materials, and the measured physical properties are controlled by this anisotropy. Measurements of permeability are up to two orders of magnitude higher and seismic wave velocities up to twice as fast along the direction of elongation. Measurements of physical properties are combined with models describing the timescales of porosity loss and from that, the timescales of permeability reduction and re-pressurization of the edifice are discussed.
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