Study On Rock Constitutive Model And Mechanical Effects Numerical Simulation Of Underground Explosion

Underground explosions are widely used in the fields of civil engineering,national defense and scientific research.A constitutive model of rock is one of the key constituents in the study of the dynamic effects of underground explosions.In order to address the main issues in the numerical simulation of strong underground explosion,in this thesis,the rock constitutive models and several related aspects to the numerical simulation are studied.The main contents are as follows.1.Based on the previous damage constitutive models of rock,the plastic flow rule and the damage rate evolution equation are modified from the view point of the numerical continuity and computational stability.A widely ranged equation of state for granite is established.There into,the Thomas-Fermi equation of state is used for the high pressure region(over 100 GPa);in the intermediate pressure region(5?100 GPa),the Hugoniot data obtained from previous dynamic tests are used;in the low pressure region(below 5 GPa),the P-V relationships are taken mainly from both the static and the low-speed impact experimental data.The new elasto-plastic constitutive model can describe well the characteristics of the pressure strengthen and the damage softness of rock under strong dynamic loadings.Moreover,the pressure range of availability of the new elasto-plastic constitutive model,from 35 MPa to 4000 GPa,stretched over about 6 orders of magnitude,which can meet the requirements of the most numerical simulations for various mechanical effects of underground strong explosion under different conditions in the near,intermediate and far zones.2.The approaches to determine the rock parameters used in the equation of state under dynamic loadings are investigated.Based on the methods for determining the strength of both the intact and the jointed rock mass,a wave-velocity based approach for determining the strength of rock mass has been developed.Thus,according to the Byerlee law,in high pressure region(over 1.6 GPa),the Hugoniot data of the intact rock can be taken as the parameters of the rock mass in the equation of state,and,in lower pressure region(below1.6 GPa),the corresponding parameters can be fitted in an exponential function by the experimental results..3.The influence of the grid size,the fluid-solid coupling algorithm and time step on the numerical results are investigated systematically.The influencing mechanisms of these physical quantities on the grid size are also analyzed,and some conclusive regularities are obtained.It is found that the stable displacement is independent of the grid size.Moreover,a method for determining the appropriate mesh size based on the period of load and the medium wave-velocity is developed.4.The new elasto-plastic constitutive model is embedded in LS-DYNA via a user-defined material model,and,with a single collection of the model parameters,the mechanical effects of underground explosions are simulated numerically.The numerical results on the cavity size,the cavity pressure,the free-field attenuation rules,the damage zonings and the rules of stress cage for different explosion yields are in good agreement with the experimental data.Moreover,the calculated stress-waveform in both the intermediate and the far zones seems satisfactory,which can then be applied for the remote analysis of the ground motion.The methods and conclusions obtained in this thesis can be extended to further researches of the underground explosion effects.