Propagation of interactive parallel flat elliptical cracks inclined to shear stress

Abstract The propagation and interaction of parallel arrays of cracks embedded in rock mass have critical impact on the stability of rock mass subjected to earthquake. To investigate the propagation of these embedded cracks under shear stress, three-dimensional element partition method (3D-EPM) is used to model the pre-existing cracks in conjunction with the augmented virtual internal bond (AVIB) constitutive model to describe the rock matrix. By 3D-EPM, the contact effect of crack faces can be automatically accounted in the original mesh scheme. By AVIB, the failure criterion would be implicitly invoked by the micro fracture mechanism. It is revealed that the propagation pattern of embedded flat cracks to shear stress is related to the inclination of crack relative to the shear force. When the inclination is smaller than 90°, the father crack firstly propagates in wrapping wing pattern. Then, many parallel arrays of descendent cracks, which are vertical to the relative slip of the father crack faces, anti-symmetrically initiate on part of the upper and the lower father crack faces, respectively. With the inclination increasing, the distribution area of the descendent cracks moves from the lower to the upper part of the father crack face. With shear stress increasing, a prior propagation path, vertical to the father crack face, is formed near the middle transect of the father crack. Finally, these prior extended descendent cracks adjacent to different father cracks coalesce together in zigzag at rock bridges. However, when the inclination is bigger than 90°, the father cracks only independently propagate along their minor axis directions. The extended crack is coplanar with the father crack. In all inclination cases, no apparent tensile fracture propagates at the two major axis tips of the original crack. It is also found that the shear strength of the cracked specimen is strongly dependent on the inclination of embedded cracks. When the inclination varies from 0° to 40° or from 180° to 120°, the shear strength remarkably decreases while when the inclination varies from 40° to 120°, the shear strength changes very little. The features of crack propagation obtained and the conclusions drawn in the present paper are significantly valuable for the evaluation of jointed rock slope stability and landslide.

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