Research On Damage Model Of Rock Subjected To Coupled Static Loadings And Cyclic Impacts

During blasting excavation in many rock engineerings,the surrounding rock mass is subjected to repeated impact loads coupled with vertical and horizontal static stresses,which affect the dynamic fatigue properties of rock mass together.So far,The present study on constitutive models of rock under coupled static-cyclic impact loadings are still in blank field.In this paper,on the basis of combining statistic damage model and viscoelastic model,damage constitutive relations of viscoelastic model coupled static stress are obtained by theoretical analysis and mathematical deduction.Damage constitutive model of rock under coupled static-cyclic impact loadings is established through studying the relations between parameters in damage constitutive relations and numbers of cyclic impact,and the model is verified by experimental data of sandstone under coupled static-cyclic impact loadings.Finally,the effect of model parameters on fatigue dynamic mechanical properties of rock are discussed.The main contents and conclusions of the text are as follows:(1)Using a combination of static and dynamic loading test system for the cycle impact test of rock in different combinations of static stress,get some dynamic fatigue mechanical properties of rock,lay the foundation for the establishment and validation of dynamic constitutive model of rock.(2)On the basis of damage mechanics and statistical strength theory,the statistical damage variable is determined based on Weibull distribution in terms of micro and statistics,consider the rock specimen as combination which paralleled by viscous body and damage body,establish the constitutive relation of viscoelastic damage body which under coupled static loadings and cyclic impacts.And compare the resulting constitutive model curve and the measured curve to verify the rationality of the model.(3)On the basis of the established statistical damage constitutive model,launch a discussion of the constitutive model parameters,study on the variation of constitutive model parameters which subjected different static load.At the same time,analyze the impact of different changes of parameters to the model.During the cycle impact,the viscosity coefficient of rock are decreasing,the non-uniformity of rock gradually increases,its ability to resist the impact load are weakening.When the confining pressure is constant,the axial pressure increases,the degree of non-uniformity of rock is growing rapidly,the decreasing tendency of viscosity coefficient of rock is on the rise,the increased axial pressure acceleratethe destruction of rock.(4)The dynamic peak stress of rock is decreasing with the increased number of cycle impact,showing the fatigue characteristics.While the decreasing tendency of its peak stress is on the rise with the increased axial pressure.The peak stress degradation trend of rock under cyclic impacts load is steeper than in the cycle static load,especially in the last several shocks,the strength of the rock is most obvious decline.(5)During the cycle impact,the elastic modulus,viscosity coefficient and other parameters of rock are easily changed rock stress-strain curve shape,which have great influence on damage constitutive model,but the influence of friction angle and Poisson's ratio are small on damage constitutive model.