Viscoelastic Wave Propagation And Indced Damage And Failure Of The Rock

The occurrence of mining-induced dynamic disasters such as rockburst is closely related to the dynamic disturbance produced by drilling and blasting during mining.As the stress wave induced by dynamic disturbance propagates in the rock,the amplitude of the stress wave will attenuate and the waveform will dissipate,which can be characterized by the stress wave propagating in the viscoelastic materials.In fact,the propagation of stress wave may be not only influenced by the pre-existing structures in rock mass,but also inevitably affected by the secondary fractures due to the damage and failure induced by stress wave.Stress wave propagation in the jointed rock mass and the damage and failure of rock induced by the stress wave are usually investigated separately in the existing theoretical and numerical models.However,much greater efforts need to be made to study the interaction between the viscoelastic wave propagation in rock mass and the damage and failure of rocks induced by viscoelastic wave.The viscoelastic wave propagation in rock and the damage and failure process of rock induced by viscoelastic wave propagation was investigated under the unified framework in the paper.The split Hopkinson pressure bar(SHPB)experimental system driven by a pendulum hammer was developed and then the dynamic failure characteristics of rock under the intermediate strain rate were examined.The study includes:(1)By using the experimental apparatus driven by a pendulum hammer,the impacting tests for long viscoelastic bars of green sandstones and artificial ones were conducted,respectively.The characteristics of energy attenuation and waveform dissipation were analyzed during viscoelastic wave propagation,and the viscosity coefficient of green sandstone and artificial rock were subsequently determined.(2)Based on the theory of stress wave propagation in one-dimension viscoelastic bar and the elastic damage theory,an one-dimensional viscoelastic wave propagation analysis program was originally developed.The program was used to simulate the stress wave propagation in the long green sandstone bars and long artificial rock bars,based on which the measured viscosity coefficients are amended.(3)On the basic of the viscoelastic damage theory and the theory of stress wave propagation in one-dimension viscoelastic bar,the condition,position and time of the dynamic spalling induced by harmonic wave propagation in the viscoelastic bar were discussed,the influence of the amplitude and frequency of harmonic wave,the viscosity coefficient and length of the viscoelastic bar on the spalling number,position and time of the dynamic spalling were also analyzed in details.(4)The pendulum hammer driven split Hopkinson pressure bar was invented for testing the dynamic behavior of rock under the intermediate strain rate.The dynamic compression tests of green sandstone and artificial rock were conducted.The stress equilibrium of the rock specimen was analyzed,and subsequently,the dynamic constitutive behavior,strain rate dependence of dynamic compressive strength,failure pattern and energy dissipation in green sandstone and artificial rock were investigated,respectively.(5)The dynamic Brazilian disc tests of granite,green sandstone and artificial rock were performed to study the strain-rate dependence of dynamic tensile strength and failure patterns of rock under the intermediate strain rate.Besides,the contribution of the viscosity of rock specimen to the strain rate dependence of dynamic tensile strength was also analyzed.Then,based on the material parameters determined in the dynamic Brazilian disc tests,the numerical simulator RFPA-Dynamics was employed further to examine the dynamic failure characteristics of rock under the higher strain rates.