Experimental Study on Characteristics and Mechanism of Macrography and Mesoscopic Failure of Deep Granite from Beishan

Because of its good stability, high strength and low permeability, granite is considered as an ideal surrounding rock for geological disposal of high-level radioactive waste, which is also the main candidate surrounding rock for high-level radioactive waste disposal project in China. Rock mechanics is one of the important problems for site selection, design, construction and operation of geological repository. It is of great theoretical and practical value to study the failure law of rock from the microcosmic aspect, to link the microcosmic failure morphology characteristics with the mechanical mechanism of rock macro fracture failure, and finally to establish a bridge between microcosmic failure mechanism and macro fracture analysis of rock. We carried out uniaxial compression test, triaxial compression test under different confining pressures, Brazilian splitting test and direct tensile test for the deep granite from the core of No. BS28 hole in Beishan area with depth of 560–680 m. SEM and EDS was carried out for the fracture surface under different test conditions. The macro and micro failure characteristics of granite under different test conditions are analyzed: It is basically the splitting failure phenomenon dominated by tensile failure after the uniaxial compression test, while the failure of the triaxial test specimen are basically all form a large inclined failure surface which show the shear failure phenomenon. It shows obvious brittle tensile failure under direct tensile test, while not simply tensile failure under Brazil split test. The micro structure and mineral composition of rocks are closely related to their macro mechanical properties. Due to the existence of other impurities, Beishan granite has a certain degree of discreteness, and because of the different composition, its fracture presents different forms. These studies provide the necessary basis for the design and construction of the geological disposal of high-level radioactive waste.