Study On Crack Evolution Mechanism And Damage Accumulation Effect Of Drilling And Blasting Excavation In Rock Mass

In mining engineering and tunnel engineering,drilling and blasting is still the main rock fragmentation method.When performing the excavation of rock blasting,the excavated zone of rock should be broken reasonably and effectively.It is necessary to minimize the damage in the surrounding rock and protect the stability of the remaining rock.At present,a variety of numerical methods were widely used in rock dynamics research.The finite element software LS-DYNA is widely applied in fields such as blasting and impact due to its high efficiency and accuracy.This study used biotite granite as the research object to study the accumulation process of blasting damage of rock mass.The main research contents and conclusions are as follows:First,the advantages and disadvantages and applicability of Holomquist-Johnson-Cook(HJC)model and Riedel-Hiermaier-Thoma(RHT)model are compared and analyzed based on single and cyclic blasting numerical experiments.The composite failure criterion of"maximum tensile stress+maximum shear strain"is used to improve the HJC model,but it cannot accurately describe the accumulative effect of damage under repeated blast loading.However,the RHT model can accurately describe the damage evolution of rock mass under both single and cyclic blast loadings.Then,the RHT model parameters were calibrated based on the test data of biotite granite.They were optimized and verified in turn,and applied to a high slope excavation project.At present,there is no clear calibration method for the RHT model.The more sensitive parameters are A_f,ε_p~m,F_s~*,B and G_c~*.Based on theoretical calculations and adjustment of sensitive parameters,the determined RHT model parameters can reproduce the compression failure behavior and dynamic crack growth of rock under impact and blasting loadings.In addition,a numerical simulation based on the high slope excavation project verifies the practical value of the RHT model.Finally,the effect of confining pressure on the cumulative damage of rock under repeated blast loadings is studied based on theoretical analysis,experimental validation,and numeral calculation.The shape of the crushed zone is hardly affected by the in-situ stress,and the tensile damage tends to evolve along the direction of the maximum principal stress.The accumulative rate of rock damage under high in-situ stress shows a decreasing trend with the increase of blasting cycles.It is difficult for repeated blasting to form a good excavation surface in the direction of the minimum principal stress.The pre-split blasting technology is beneficial to improve the stability of the remaining rock mass under blasting excavation.Even if the excavated rock mass is subjected to repeated blast loadings,the phenomenon of under-break may still occur under the action of in-situ stress.A plum-blossom-shape arrangement of blastholes and delayed initiation of production holes can promote the quality of blasting operations under pre-stress conditions.