The Study Of The Broken Model For Rock Mass Blasting Based On RHT Constitutive Equations

It is well-known that rock mass contains a large number of cracks, weak surface and structure which is different from rock. Its strength parameters have significantly weakened. Therefore, it is an obvious misconception to take the physical parameters of rock mass into rock in engineering and simulation, especially for more complex blasting problems. Whether the reflected tensile theory of stress wave or the explosive gas expansion effect are effected by the defects in rock mass.For the present, the most appropriate expression for the defects and the most simple method is damage theory, that is, through the introduction of damage variables into damage constitutive relation, the distribution and development level of defects in rock mass can be microscopically considered. So we could quantitatively evaluate the deterioration degree of rock mass. In this paper, the broken model of rock mass under blasting load is investigated mainly from the point of theory and simulation. In consideration of the purpose of the study and the current condition, we only takes rock mass with micro cracks and weak face into consideration, that is, excluding the structure plane such as joints, fissures in the rock mass. Thus, the rock mass can be simply treated as rock with initial damage.Rock(rock mass) as a brittle material is similar with concrete materials with characters such as the compression strength of pressure correlation, strain hardening, damage softening, and different tension and compression strain rate effect. Thus, it is feasible to apply the constitutive relation, which expresses the mechanic responses of concrete under dynamic, static load, into rock materials.Therefore, in this paper the most advanced RHT constitutive model at present is selected to study the blasting broken model of rock mass according to the above basic hypothesis and predigestion, by the method of theory analysis, combined with software programming technology extension, laboratory experiment and field trial, and numerical simulation.(1) Systematically analysis the equation of RHT constitutive model to the failure surface, the elastic limit surface and residual stress surface and research the relationship between the parameters in the equation and the meaning of each parameters. Summarizes the means of the p-? equation of state parameters and the way how to get it.At the same time, the 19 parameters of above equation are classified.(2) Apply the AUTODYN software to make the unit simulation test under different loading conditions(uniaxial compression, biaxial compression, and triaxial compression with confining pressure of 5MPa, 10 MPa and 20MPa; uniaxial tension, biaxial tension and triaxial tension with confining pressure of 10MPa) and different strain rates. The computational model is cubic of CONC-35 concrete material. Contrast the simulation test of stress-strain curve with the actual measurement and document literature in order to detailed analysis the RHT constitutive model`s advantages and shortcomings under the different dynamic and static load.(3) Detailed discussed the acquisition approach and importance of 19 parameters of RHT constitutive model and selected B, M, BQ, fs/fc, TENSRAT, D1 and Ef,min as investigation factors. Creativity point out using the projectile penetration concrete simulation orthogonal experiments to make the parameters sensitive analysis in order to determine the important degrees of various parameters.(4) The aforementioned unit test pointed out there are some defects in that RHT constitutive model for simulation of the explosion shock problems, and described its application in rock blasting crushing process need more necessary corrections. For this reason, by comparing the two-dimensional finite difference program is found that the SHALE as a development platform is feasible and scientific. Therefore, on the basis of the study of RHT constitutive model`s modeling ideas and stress update algorithm, combined with systematic research program on SHALE calculation principle and computing structures, processes, and through the establishment of data flow computing RHT constitutive model and its programming implantable SHALE program, through simulation SHPB impact process and comparison with experimental results verify availability and rationality of expanded program(5) Based on the RHT constitutive model`s limitation and deficiency which describe the broken process of rock mass blasting. The paper proposed the ideas as follows: Modify the tensile failure model from linear to bilinear; Modify the calculation formula of tensile and compression strain rate enhancement factor; Modify the calculation formula of residual stress and tensile to compression meridian; To the question of rock mass which contains a large number of fractures and weak plane, add the definition of the initial damage of RHT constitutive model.Update and recompile the modified model in the expanded SHALE program. Find the updated model for describing the tensile state mechanical response problem has obvious improvement through the biaxial compression, uniaxial tension and triaxial tensile unit simulation test once again. Using the SHALE program for simulating the impact loading the concrete pole with the triangle wave to intensive study the stress wave propagation, reflective stretching mechanism and the development of damage.(6) Systematically studied and summarized a set of method of rock mass mechanics parameters which is derived from the rock parameters. Estimate the rock mass parameters based on the wave velocity test of rock mass, physical and mechanical parameters of rock experiment, combined with 2002 Hoek-Brown strength criterion to confirm the geological strength index(GSI) and rock mass disturbance parameters D.Based on the above computational theory, using the single hole sound wave test the longitudinal(transverse) wave velocity of lime rock mass, using the ultrasonic wave test method detective the longitudinal(transverse) wave velocity of lime rock, using experiment test the uniaxial compressive strength and density of lime rock. Finally estimate the physical and mechanical parameters of lime rock.(7) Determine others model parameters except the lime stone`s physical and mechanical parameters, through make extensive use of the RHT constitutive parameters sensitivity analysis results and document literature. Finally laid a solid foundation for the simulate the crushing mechanism of rock blasting and its process based on the modified RHT constitutive model.(8) To simulate the blasting funnel test which 1m depth and 1.5kg dosage based on SHALE program embedded the modified RHT constitutive model and the model parameters correlative the lime stone. Through the stress-time cures and damage-time curves extraction, point out the funnel forming progress and the final depth and width. Contrast the field trial and simulation results using the AUTODYN software with identical parameters and computational model, discover that the modified RHT constitutive model which represent the broken process of rock mass blasting is effective and successful.