Directional Failure And Control Of Surrounding Rock With Non-through Cross-type Jointed For Tunnels

Engineering rock mass is an anisotropic heterogeneous geological body composed of rock matrix and structural plane.During the period of excavation and service of tunnel engineering,joints development induced accidents such as roof fall and wall caving often occur,which cause serious casualties and economic losses.It is of great significance to investigate fracture mechanisms of jointed rock mass and directional reinforced supporting method of surrounding rock for stability of tunnel and safe and efficient mining.In this thesis,the jointed rock mass in-780m level tunnel of Sanshandao gold mine is taken as the research example.By means of mechanical test,theoretical calculation and numerical simulation,the mechanical behaviors including the mechanism of initiation and propagation under mining operation were studied,and the control methods of cross-type jointed rock mass were proposed,the following conclusions were obtained:(1)The variation rules of peak strength and initiation stress of cross cracked granite were obtained by uniaxial compression test.It was found that the strength of single cracked rock samples is generally greater than that of cross cracked rock samples.The strength of samples varies with the inclination of crack in a kind of"V" shape.When the dip angle of the crack is 60°,the strength reaches the lowest.The main crack has more obvious influence on rock strength and controls rock fracture development.(2)Based on the acoustic emission ringing count in the loading process,the crack initiation time and the corresponding initiation load were analyzed.When the intersection angle is fixed,the initiation stress decreases first and then increases with the increase of the main crack angle.The change of initiation stress of single crack rock sample with dip angle is more significant.When the dip angle of the main crack is 45°,the rock sample is more prone to fracture.(3)Based on the measured data of surface strain,the crack initiation law and the crack distribution pattern of the rock sample with cross cracks were studied.It reveals that the fracture of cracked rock has a significant direction,the initiation cracks are mainly distributed in airfoil or anti-airfoil,and are mainly tensile cracks.The main crack is the main controlling factor of initiation,and the secondary crack has a certain guiding effect on the crack.(4)A crack initiation model based on distortion energy theory was established.The initiation criterion based on this model was defined as follows:1)under uniaxial compression,the crack initiation is conducted in the direction with the maximum distortion energy at the crack tip.2)when the distortion at the crack tip reaches the maximum critical value of energy storage of rock materials,the crack expands.By means of theoretical calculation and numerical simulation,the applicability and accuracy of the maximum distortion energy criterion in determining the initiation of rock samples with single and cross cracks were verified.(5)A new method of directional reinforced supporting for the surrounding rock with jointed rock mass was proposed,which took into account the geological information such as the occurrence of the dominant structural plane and the direction of the tunnel.Crack criterion embedded in FLAC3D program,based on rock failure characteristics and the crack propagation path,the control method of single and cross crack structural plane was studied,the optimal method of directional reinforced supporting in jointed rock mass was determined.The peak strength of rock increased after anchoring,and the degree of rock fracture decreased under the same external load.The study on the control method provides scientific basis for the optimization of the supporting method on site.(6)A tunnel model considering the spatial distribution characteristics of ground stress and dominant structural plane was established.Based on the numerical simulation method,the deformation laws of surrounding rock under different supporting conditions are compared and analyzed.Taking the jointed rock mass of-780m tunnel of Sanshandao gold mine as the research object,the rock mass was supported by using the method of directional reinforced supporting,and the stability of the jointed rock mass was evaluated by using the monitoring data of mining stress,which verified the good anchoring effect of the directional reinforcement method.