Research On Cracks Initiation, Propagation And Anchoring Effect In Rock-masses

Many continuous internal structural planes distribute in rockmass internal, and many of the geotechnical engineering instability and failure is caused by cracks propagation. Crack propagation interaction and breakthrough mechanism is an important research subject in rock fracture mechanics. This paper uses single-dual axle press machine, which is self-researched by geotechnical engineering research institute in DLUT, to take tests on gypsum specimens containing central symmetry double cracks under uniaxial compression. By multy groups specimens, this paper analysed the effection of bridge angles to cracks propagation modes, initiation loads and peak strengthes. The result shows that:with bridge Angle increases, the crack coalescence patterns are tensile mode, tensile-shera mixed mode, and shera mode in turn; the samples peak strength gradually reduce.By using a particle flow code, PFC2D, numerical simulations on samples containing two parallel cracks with different bridge angles under uniaxial compression are conducted to research the cracks coalescence. The cracks propagation process and the number of microcracks have been tracked by functions in PFC. Comparation between the numerical simulated results with those of the experiment indicates that PFC can simulate the crack coalescence process properly. This means a lot to research crack propagation by discontinuous theory from the microscopic view.Using the SPRING elements to imitate the contact relationship between the anchor and the rock-mass. And using the Extended finite element method (XFEM), crack extension process of joint rock-mass with anchor bolts under uniaxial compression is presented. Multi-group simulations are made to analyse the effect of bolts with different positions and angles on cracks propagation. Results show that, with the increase of the distance, H, the initial loads decrease and gradually approach the case without anchoring; when a increases from0°to180°, the initial loads firstly reduce and then increase:45°<α<130°. the anchor appears negative effect; with the increase of anchoring force, both the potentiation and negative effect can be enhanced.