A series of cylindrical intact and jointed rock-like specimens with single pre-existing cracks were prepared using high-strength gypsum by embedded thin sheet mica. Uniaxial compression tests, triaxial compression tests, and hydro-mechanical coupling triaxial tests (water pressure was applied inside the pre-existing cracks) were conducted to investigate failure behaviour of jointed specimens under hydro-mechanical coupling. Microscopic observation by scanning electron microscope (SEM) was employed to determine the crack nature, and X-ray computerized tomography (CT) scanning revealed the spatial geometric feature of internal cracks under hydro-mechanical coupling. The results suggest that the hydro-mechanical coupling significantly weakened the strength of the intact and jointed specimens. Nine types of cracks with various crack nature and spatial geometry in this experiment were summarized. Specimens under high confining pressure tended to shear failure, and specimens tended to tensile failure under high water pressure.

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