Numerical Simulation Of Mechanical Behavior Of Rock Mass With Cross-fractures

The rock masses in the natural geological environment undergo complex geological processes,and there are joints,cracks,faults,etc.in different distribution states.The relative positions of the spaces between these joints and cracks are also differently distributed.The cracks present in the rock mass tend to be spatially distributed or intersected at an angle.There are many researches on single-fractured rock mass at present,but few studies can be seen on cross-fracture,and the research on the influence of cross-fracture on rock mass engineering stability is rare.The fracture stress of rock specimens with single cracks at different angles is derived based on the maximum circumferential stress theory of fracture mechanics,considering the friction effect between closed fracture surfaces.The uniaxial and multi-axial numerical tests were carried out on the samples with cross-cracks using the RFPA numerical test system,and the stability analysis of the three-dimensional horseshoe-shaped tunnel with cross-fractures was carried out by the strength reduction method.Some results were reached in this thesis:?1?the crack initiation angle of open and closed crack specimens is derived based on the maximum circumferential theory of fracture mechanics,considering the stress intensity factor of crack tip with inclined closed or open cracks,considering the friction effect of closed crack surface.The theoretical solution formula of the cracking stress finally shows that the crack initiation stress of the specimen with closed fractures decreases first and then increases with the increase of the inclination angle of the fracture as the shape of“U”.The simulation results were well agreed with the physical test results.?2?The RFPA^2D finite element simulation software was used in the numerical simulation,and the single and double-axis loading numerical tests were carried out for the cross-crack samples of different working conditions.The effects of different angles and confining pressure on the mechanical properties such as failure mode,stress-strain curve,peak strength and elastic modulus of rock-like specimens were discussed.The influence of the curves under different fracture angles on peak strength and elastic modulus are obtained based on the numerical simulation results.The peak intensity changed like“U”as a whole trend,the elastic modulus increased first,then decreased and then increased with the increase of?.The law of change of stress-strain curves from brittleness to post-ductility occurs when the condition changed from uniaxial loading to confining pressure.?3?The three-axis loading was posed in the horseshoe-shaped tunnel.Then the strength reduction method was used to analyzed the stability of the tunnel.The effects of lateral pressure coefficient and intermediate principal stress on the stability and failure mode of horseshoe tunnel are studied to achieve the most dangerous triaxial loading mode.This loading state is applied to the horseshoe tunnel model with cross-fracture,changing the angle of?and?to analyze the safety factor,failure mode and the influence of the maximum principal stress distribution of the cross-fracture to the horseshoe tunnel under different working conditions and five different modes of failure are achieved.