Experimental Study of Three-dimensional Cracks Propagation Characteristics Under Uniaxial Compression

A series of uniaxial compressive tests were carried out on the rock-like brittle specimens with two parallel pre-existing three-dimensional(3D) cracks to investigate cracks spatial propagation and AE characteristics in 3D.AE monitoring technique and computerized tomography and reconstruction were used to assist the investigation.Three rock bridge failure modes were observed in the surface of specimens:anti-wing crack and wing crack failure mode, anti-wing crack and shear crack failure mode, wing cracks parallel propagation.Clear turning points were observed obviously in stress-strain curve which were caused by Mode I initiation and the rock bridge coalescence when the AE signals reached a peak value.The initiation energy of wing cracks is proportional to the loading time.Wing cracks were the dominant fractures, followed by a great number of shear cracks and secondary cracks.The number of shear cracks and secondary cracks was increased with different rock bridge angles between the pre-existing cracks, the failure modes were complicated.The wing cracks have an anti-symmetrical structure with the crack center line as the symmetry axis.The initiation angle of wing cracks increased with the depth into the specimens.With different rock bridge angles between the pre-existing cracks, the rock bridge failure can be divided into three modes:complete failure with anti-wing cracks and wing cracks; partial failure with anti-wing cracks and shear cracks; and partial failure with wing cracks parallel propagation. © 2019, The Editorial Board of Journal of Basic Science and Engineering. All right reserved.