3D Experimental Studies of Temperature and Crystallographic Effects on Creep and Strength in Rock Salt

Salt domes utilization as storage reservoirs in the energy sector has led to extensive studies on rock salt’s mechanical and geothermal behavior. These important facilities’ safety and serviceability rely on understanding rock salt’s compressive strength and creep behavior under various loading directions, water contents, in-situ stresses, and temperatures. Despite numerous studies on rock salt’s mechanical behavior in the literature, there are still many unanswered questions about rock salt’s behavior. This dissertation was aimed at utilizing state-of-the-art experimental techniques such as 3D synchrotron micro-computed tomography (SMT) and 3D x-ray diffraction (3DXRD) along with hundreds of compression and creep experiments to enhance our understanding of crystal orientation and temperature’s influences on rock salt’s strength, creep behavior, and internal structural changes. Unconfined compressive strength (UCS) of natural single-crystal rock salt was observed to be lesser than synthetic single-crystal rock salt reported in the literature. Changing the loading direction from parallel to [1 0 0] crystal direction to 30^o to (1 0 0) in (0 1 0) direction resulted in higher UCS values. The same loading direction rotation in single-crystal rock salt’s creep decreased the accumulated axial strain and the transient and steady-state strain rates. During dry and wet 1D compressions of rock salt grains, unique critical porosity values of 32% and 37% respectively were established that caused a linear relationship between the porosity and logarithm of axial stress. Rock salt prepared in 1D compression exhibited a strong {1 1 1} texture and displayed a dominant {1 1 1}<1 >-1 0> slip system under unconfined compression, which contrasted with rock salt possessing a randomly distributed texture. Polycrystalline rock salt’s UCS was higher when the grain boundaries were nominally dry rather than wet (64.3MPa versus 16.2 MPa). Annealed polycrystalline rock salt regardless of its grain-boundary’s condition demonstrated a UCS of about 40 MPa and manifested a critical axial stress of 30 MPa and a critical porosity of 5.7% under compression where it developed a fully connected crack network indicating compromises to its impermeability. Increasing the deviatoric stress during polycrystalline rock salt’s creep increased transient and steady state strain rates and accelerated tertiary creep rupture.