Study On Dynamic Characteristics Of The End Of Oblique Joints In Rock Plane Under Blasting Load

Rock mass usually show heterogeneity,anisotropy and discontinuity due to the existence of joints.The stress field will be readjusted after the exploaion stress wave acting on the rock mass with joints,resulting in damage or fracture of the rock.However,joints are usually distributed,disorderly and random in the space of rock.Therefore,it will not be universal to conduct research only on single joint or parallel joints.Based on the above considerations,the propagation equation of stress wave incident on oblique joints rock mass is deduced,and the variation characteristics of stress and displacement at the ends of oblique joints are analyzed.The blasting test and cyclic blasting test are carried out on cement mortar samples with oblique joints,and the crack propagation law is studied.Meanwhile,the method of joints rock mass blasting accumulaton is proposed.The main research results and contents are as follows:(1)The hyperbolic joint constitutive model(BB model)with normal nonlinear deformation and tangential linear deformation is introduced.Based on the theory of P-wave and S-wave incident joint,the propagation equation of P-wave incident oblique joints is deduced according to the wave theory,Snell theorem,conservation principle of wave front momentum,displacement discontinuity theory and superposition principle.(2)The mechanical model of oblique joints is established to calculate the expressions of the stress field and displacement field at the ends of oblique joints by the Westergaard complex analytic function.The auxiliary function of?function is selected as the incident wave function,and the MATLAB software is used to difine the mechanical parameters.Then,the characteristics of stress and displacement at the ends of oblique joints are analyzed.The results show that:When the stress wave is incident on oblique joints and the S-wave is totally reflceted,the stress field and diaplacement field at the ends of J₂ are not symmetrically distributed according to the interface of J₂,and rotate anticlockwise.The stress contour mpa at the ends of oblique joints is closed,and the displacement contour map is divergent,indicating that there is no displacement singularity at the ends of oblique joints.(3)The influence of dynamic response of joint length,incident wave amplitude and critical angle at the ends of oblique joints are considered respectively.When the joint length increases,the range of the stress field at the ends of oblique joints increases obviously,and the displacement field also accumulates.The peak stress of?_x,?_y and?_xy all increases,and the rate of increase is different.The peak displacement of u and v also increases,but the rate of increase is almost the same.Increasing the amplitude of incident wave leads to the peak time of P-wave transmission being advanced and the peak time of S-wave transmission being delayed.The peak stress of?_x,?_y,?_xy,u and v are all enlarged,and the expansion multiples are different at different positions,but the magnitude of the peak stress of?_x,?_y,?_xy,u and v is not changed.When the incident angle is less than the critical angle and the superposition of P-wave and S-wave is taken into accout,the peak stress of?_x and?_xyincreases or decays,or even changes direction,which leads to the change of the value of peak stress.However,the order of peak stress of?_y is:3^#>1^#>2^#>4^#,and the order of pedk displacement of u and v is not change.With the decrese of peak stress,the range of displacement field is reduced.When the stress is less than 0.05 MPa and r?300 mm,the displacment is less than 5.00?m at the ends of J₂.(4)Cement mortar samples with oblique joints are prepared through mix proportion design,compressive strength test,dynamci elastic modulus test and longitudinal wave velocity test.The influence of explosive quantity,epicentral distance and joint length on the expansion length and crack initiation angle of oblique joints is analyzed,as well as oblique joints rock mass under cyclic blasting.The results show that:With the increase of the joint length,the propagating crack also occurs at the interface,and the length of the propagating crack is more than 10 mm.The correlation between the epicentral distance and the value of stress-strain at the ends of oblique joints is negative,but the correlation between the explosive quantity and the value of stress-strain is positive.(5)The instantaneous energy spectrum of blasting vibration signal of sanlengshan tunnel on Beijing-Shenyang high-speed railway(Liaoning Section)is obtained by using the HHT principle.A method is proposed to ananlyze the cumulative damage effect of Joints rock by using the total energy of monitred points in any direction which obtained by summation of instantaneous energy spectrum.The particle vibration energy is used to analyze the strength effect of physical and mechanical properties of rock mass,to solve the dimensional puzzle of evaluating cumulative damage effect of rock based on area theory of vibration velocity waveform.Finally,the feasibility and applicability of the method are verified by numerical software.This paper has 111 pictures,27 tables and 168 references.