The Effect Of T-stress On The Crack Initiation Characteristics In Rock

Rock is a kind of natural material and have many joint, foliation, bedding and crack. It is a kind of typical inhomogeneous, discontinuous and anisotropic material. The rock instability and seismicity is mainly caused by initiation, propagation and coalescence of meso-crack in the practical engineering. So the crack initiation characteristic has been a hot research topic in rock engineering and now the research has already gained some achievements.In this paper, the new crack initiation fracture criterion is built by considering the secondary non-singular terms (T-stress) in the crack-tip stress field based on the traditional fracture mechanics. The crack initiation characteristic subjected to the far field stress and hydraulic pressure is analyzed. Besides, the study of the rock failure process of precast double cracks under different inclination bridge and the mechanism of coalescence is made with the help of Rock Failure Process Analysis. Major conclusions are as follows.(1) Under the far field of tension-compression stress, through the comparison with the experimental results, the crack initiation angle is more reasonable by considering T-stress modified theory than conventional theory. There is a transformation angle of compression and tension about crack surface stress with the the increase of crack inclination angle. In addition, the transformation angle increases with the increase of absolute confinement ratio and friction coefficient. The crack initiation angle decreases with the increase of crack inclination angle. When the crack surface stress is compression, the crack initiation angle increases with the increase of friction coefficient. Under the far field of compression-compression stress, the crack initiation angle increases with the increase of crack inclination angle. The singularity of the crack tip disappear in the region of smaller and larger crack inclination angle with the increase of friction coefficient, confinement ratio and dimensionless coefficient.(2) By considering the secondary non-singular terms (T-stress) in the crack-tip stress field, the crack initiation criterion subjected to hydraulic pressure is built, based on the maximum tensile strain criterion. And critical water pressure of crack initiation and crack initiation angle is calculated. The critical water pressure increases and crack initiation angle decreases with the increase of confining pressure, the radius of fracture process zone, and Poisson's ratio. Meanwhile, the critical water pressure and crack initiation angle are smaller by using the considering T-stress modified theory than conventional theory.(3) With the help of Rock Failure Process Analysis, the study of the rock failure process of precast double cracks is made. These models of precast double cracks have four types of coalescence trajectory. The initiation and propagation of wing crack and secondary crack are described. Three coalescence modes are verified and they are explained in the coalescence force and energy perspective. As acoustic emission figure shows, the macro-crack propagation is the result of microcosmic element damage.