Study On Fracture Characteristics And Damage Model Of Non-persistent Joints

The rock mass is a natural damage geological material that not only contains macroscopic defects but also contains microscopic flaws.The strength,stiffness and stability of the rock are influenced on these macro defects and meso-defects.Causing its discrete and great uncertainty of fracture mechanism and Macroscopic mechanical property.The anisotropic damage of rock mass is caused to macroscopic non-persistent joints and The isotropic damage of rock mass is caused mesoscopic flaws.It is proposed that the macro-defects and their effects must be taken into consideration in the analysis of mechanical properties of rock masses.The damage constitutive model of non-persistent jointed rock mass is established.The main research work carried out in this paper is as follows:(1)From the angle of elasticity and fracture mechanics,According to the difference of the mechanical properties of non-persistent jointed,two cases of non-persistent jointed opended and closed are discussed.The influence of transverse stress at joint tip should be considered for opened non-persistent jointed,and influence of deformation parameters of jointed introduced by closed jointed on stress transfer.For this reason,the calculation method of stress intensity factors for single non-persistent joint under two conditions is derived respectively.(2)The non-persistent jointed fracture forms are divided into two kinds of tensile and shear failure.According to the rock material parameters,the criterion for the failure forms of non-persistent jointed is established.Used to The maximum circumferential stress theory and the Mohr-Coulomb criterion,the crack angle of the jointed under the condition of tensile failure and shear failure were studied.The results are that the initiation path of the opened jointed rock mass are affect with the length,dip angle and transverse stress.The initiation angle of closed non-persistent jointed is related to jointed length,dip angle,internal friction angle,normal stiffness and tangential stiffness.(3)the damage variable calculation formula of the rock mass with a non-persistent joint is deduced based on the connection of the increment of additional strain energy in fracture mechanics and the emission of damaged strain energy in damage mechanics.The critical angle of joint damage is judged with the sliding driving force on the joint surface.considering the interaction between unconnected joints,the method of the stress intensity factor at the tip of a single row and a single group of multiple rows non-penetrating joints are obtained.And the corresponding macroscopic damage variable calculation method of non-persistent jointed rock masses are obtianed,useing MATLAB software to solve the macroscopic damage variables of non-persistent jointed rock masses.(4)The constitutive model for the damage of microscopic rock mass is deduced Based on the Weibull mesoscopic distribution function and the axial strain criterion.The distribution parameters of the meso-damage model were determined using the limiting properties of softened rock.a compound damage variable considering the coupling of macroscopic defects was deduced Based on the quantification of Lemaitre's strain-equivalent hypothesis.Finally,the damage constitutive model of jointed rock mass constructed in this paper is verified by experiments.The influence of macro and meso-defects on mechanical properties of rock mass is well considered in this model.