Microcrack Network Development in Salt-Rock During Cyclic Loading at Low Confining Pressure

Abstract

Triaxial compression tests of synthetic salt-rock are conducted to investigate microfracture development in a semibrittle polycrystalline aggregate. The salt-rock is produced from uniaxial consolidation of granular halite at 150 °C. Following consolidation, the sample is deformed by cyclic loading at room temperature and low confining pressure (Pc = 1 MPa). Load cycles are performed within the elastic regime, up to yielding, and after successive increments of steady ductile flow. At the tested conditions, the samples exhibit ductile behavior with slight work hardening. The microstructure at different stages of deformation indicates that grain-boundary cracking is the dominant brittle deformation mechanism. Microcracking is influenced by the loading configuration and the geometric relationships between neighboring grains. These microcracks display a preferred orientation parallel to the load axis. With cyclic loading, microcracks increase in density and form linked arrays parallel to the direction of loading. As the linked arrays lengthen, grain contacts are progressively opened, which eventually leads to loss of cohesion along surfaces parallel to the loading direction. The observations of crack-network development in salt-rock can improve our understanding of progressive damage and spalling at salt cavern walls.