Experimental and numerical studies of mechanical response of plate-shape granite samples containing prefabricated holes under uniaxial compression

Abstract

The uniaxial compression tests of plate-shape granite samples containing two prefabricated holes on each side, prepared from Iddefjord granite blocks in Norway, are carried out by Instron hydraulic servo control testing machine in laboratory. The axial stress, axial and lateral strain, acoustic emission(AE) counts and failure modes of the samples are monitored during the tests. The splitting cracks occur near the holes' vertical surface and parallel to the loading direction when the loading stress increases to a certain value. Some characteristics of rockburst phenomena such as rock block ejection and slabbing failure can be observed around the prefabricated holes under high compressive stress. The failure modes of samples always initiate from the splitting fractures around the holes under uniaxial compression. By observing the AE counts rate curve, it is shown that more jumping mutation points appear in the curve than that of intact rock samples. Based on the experimental studies, numerical models are validated by FLAC3D (3 dimensions fast lagrangian analysis of continua). The principal stresses distributions in the samples are obtained by the elastic model analysis, while the failure process is studied by the Mohr-Coulomb strain softening model. The modes of failure zones are monitored and characterized by the AE count events. Most failure zones are failed in tension and connected together to form as splitting fractures parallel to the vertical boundary of the holes. The numerical results are almost the same as the laboratory tests. The research results, to some degree, reveal the formation mechanism of slabbing fractures, which are usually parallel to the excavation boundary surrounding underground openings in hard rocks under high in-situ stresses.