Experimental Study on Rock-Like Specimens with Single Flaw under Hydro-Mechanical Coupling

Abstract

Featured Application: To study the mechanical properties and cracking behavior of jointed rock mass under hydro-mechanical coupling, a series of uniaxial compression tests, and conventional and hydraulic coupled triaxial compression tests were carried out on cylinder gypsum specimens with a single pre-existing flaw. Based on X-ray computed tomography (CT) and scanning electron microscope (SEM) observation, the mechanical properties and crack behavior were analyzed. The results could provide a useful reference for rock mass under hydro-mechanical coupling that may be conceptually extended to the field scale.Abstract: In order to study the mechanical characteristics and cracking behavior of jointed rock mass under hydro-mechanical coupling, a series of uniaxial compression tests and triaxial compression tests were carried out on cylinder gypsum specimens with a single pre-existing flaw. Under different confining pressures, water pressure was injected on the pre-existing flaw surface through a water injection channel. The geometrical morphology and tensile or shear properties of the cracks were determined by X-ray computed tomography (CT) and scanning electron microscope (SEM). Based on the macro and micro observation, nine types of cracks that caused the specimen failure are summarized. The results of mechanical properties and crack behavior showed that the confining pressure inhibited the tensile cracks, and shear failure occurred under high confining pressure. The water pressure facilitated the initiation and extension of tensile crack, which made the specimens prone to tensile failure. However, under the condition of high confining pressure and low water pressure, the lubrication effect had a significant effect on the failure pattern, under which the specimens were prone to shear failure. This experimental research on mechanical properties and cracking behavior under hydro-mechanical coupling is expected to increase its fundamental understanding.Wong and Einstein [8,9] investigated the cracking behaviors in modeled gypsum and Carrara marble specimens with a single flaw under uniaxial compression by a high-speed camera. Seven different crack types were identified based on their geometry and tensile or shear propagation mechanism. Yang [10] analyzed the failure mode and cracking process of sandstone specimens containing a single flaw under uniaxial compression, and proposed nine different crack types based on their geometry and crack propagation mechanism (tensile, shear, lateral crack, far-field crack, and surface spalling). In addition to uniaxial or biaxial compression tests [2,[7][8][9][10][11][12][13][14], triaxial compression tests [15][16][17][18][19] are also used to study jointed rock masses. The cracking behavior is more complex and difficult to observe under three-dimensional conditions. However, many researches using three-dimensional conditions, judged the crack types by crack geometry [17][18][19][20][21]. They either refer directly to the crack types obtained by uniaxial or biaxial compression tests...

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