Mechanism Study On The Dynamic Response Of Rock Under Confining Pressure And Blast Loading

With the deep mining and national defense construction become more and more deeply,the dynamic response of deep rock under in-situ stress and blast loading is complicated.In the previous researches,the improved Split Hopkinson Pressure Bar(SHPB)and explosive experiment with passive confined pressure are used to study the dynamic characteristics of rock material,less researches has been done to explore the dynamic response under blast loading and active confining pressure.Thus,the systematic researches on the dynamic response of rock under confining pressure and blast loading will be conducted with a method combining theoretical analysis,experimental measurement and numerical simulation,and the main research contents and conclusions include:(1)The experiment system is set up,both the active confining pressure and blast loading are added in the system.Pressure system is adopted to provide the biaxial confining pressures for specimen,and the pressure sensors and transmission systems are selected with better pressure stability.The small diameter PETN charge and PETN cord are used for achieving blast loading,and the amplitude of blast loading is controled by non-coupling charge structure.The explosive stress wave propagation and size effect are analyzed,two parts compose the specimen for removing the effects of reflected wave in test surface.The high dynamic strain indicator,High-speed(HS)and Digital Image Correlation(DIC)method are used to obtain strain field and crack propagation under static and dynamic loads.(2)Researches on dynamic response process of rock under the uniform confining pressure and blast loading.The circumference compressive stress are formed by initial confining pressure,and it decreases the circumference tensile failure by explosive loading.The number and size of radial cracks and the broken radius significantly reduce with confining pressure increases.With the distance from borehole increases,the strength of shock wave reduces and confining pressure prevents cracks from propagating.The elastic mechanics and cylindrical elastic wave theory are selected to analyze the stress wave spreading,and found that compressive stress from initial confining pressure reduce the tensile failure in circumferential direction after blast loading,and this conclusion is the same as the experimental results.According to the results of numerical simulation,as confining pressure increases,the Von Mises stress increase and circumference tensile damage reduce.(3)Study on the dynamic response of rock under the nonuniform confining pressures and blast loading.The partly stress concentration is produced by nonuniform pressure.After blast loading,the radial cracks grow along the tensile failure caused by initial stress concentration and shock wave.When the coefficient of lateral pressure(K)is zero,the tensile stress concentration is obviously along the vertical direction under confining pressures,the vertical cracks appear on the stress concentration region and develop after blast loading.The number and size of vertical cracks decrease with K increases.When K>0.5,tensile stress is not obviously,and the crack propagation process is random under blast loading.Compared to the experimental results,the growth process and final shape of cracks are agree with the experimental results.(4)Researches on dynamic mechanical characteristic of rock subjected to confining pressure and cyclic blast loadings.After the first blast loadings,the elastic deformation is produced,the stress-time curve drop to zero after peak value.With blast loading times increase,the plastic strain increases when the strain exceeds the elastic limit strength of rock material,the irreversible deformation is accumulated due to plentiful fractures and pore spaces developed.The existing flaws or radial cracks run through specimen when the damage exceed the material's yield after the last blasting.(5)Taking the cyclic blast loading experiments results into the damage model of rock material,and the damage evolution is analyzed.The damage is successfully defined and described by strain variable.When the damage(D)is less than 0.4,a few internal micro cracks are generated by elastic plasticity deformation.When D is more than 0.5,cracks growth lead to the partial failure,but the rock specimen is not broken.As D increase to 0.6,the inner cracks develop and connect which cause the rock sample broken completely.During the initial blast loading process,the rock materials subject to less stress by elastic deformation.After the later stage of the cyclic loading,a large irreversible deformation appear,and the stress rapidly increased and droped at last.(6)When rock subject the stress wave from blast loading,both the initial intensity of rock and load time(or loading times)influence the rock failure process.Because the loading time is too short,the initial microcracks do not have enough time to develop into fractures under single loading.The fatigue-damage accumulate with loading times,and then brittle fracture is occurred by the last loading.In addition,because the compressive stress is formed by uniform confining pressures,the density and intensity of mineral particles increase by compressive stress.It also effectively prevents radial cracks growing,reduces the damage accumulation speed and increases the ability of rock against impact loading.