| Granite is a kind of widely distributed rock.It is an igneous rock formed by the formation of magma below the surface.Its mechanical strength,deformation performance and damage mechanism are closely related to engineering stability and safety.In the construction of the project,such as dikes and tunnels,it is often necessary to experience multiple blasting.Therefore,through the in-depth study of the dynamic characteristics of granite and the experimental study of cyclic blasting,it is of great significance to judge and analyze the scope and evolution process of blasting damage.The research work and conclusions drawn in this paper mainly include:Firstly,the dynamic triaxial compression test was carried out on samples with different strain rates and different confining pressures using a high-pressure dynamic triaxial apparatus.The results show that with the increase of confining pressure,the failure mode of sample changes from axial splitting to shear failure.Under the same confining pressure,the fracture degree of sample increases with the increase of strain rate;The compressive strength increases with the increase of strain rate and confining pressure,but the growth rate decreases gradually after the strain rate exceeds 10-3s-11 and the confining pressure is greater than 60 MPa.In addition,the applicability of the classical Mohr-Coulomb strength criterion and its two improved forms have been analyzed comparatively at medium strain rate,result found that the Mohr-Coulomb criterion considering the average principal stress correction has a high degree of agreement with the experimental data,while the linear type Mohor-Coulomb criterion and the parabolic Mohr-Coulomb criterion have large fitting errors.Then,a small blasting test was carried out on the granite test block.The attenuation law of particle vibration and the evolution mechanism of cumulative damage of the granite subjected to multiple blasts were analyzed.The crack propagation and fracture morphology of the granite under different charge amount were analyzed comparatively.Results show that The Sadowski formula has good applicability to the blasting vibration attenuation law of indoor granite test blocks.The determinable coefficient are above 0.90;The blasting damage of granite increases with the number of blasting,and the damage value decreases as the distance from the core?explosion distance?increases,the damage value in the near zone decreases rapidly,while the damage in the middle and far regions decreases relatively slowly;The degree of destruction and the amount of charge have a high degree of correlation.When the amount of charge is low,the number of blasting required for cracking is greater,with the increase of the amount of charge,the number of broken pieces after the test piece exploded shows an increasing trend.Finally,the large-scale finite element software ANSYS/LS-DYNA and its restart technology were used,and the previous results were combined,the Holmquist-Johnson-Cook?HJC?parameters suitable for the granite in this paper were determined,the wave attenuation law,cumulative damage effect of rock,crack propagation and fracture of granite under multiple blasting were discussed.The results show that the restart technology can effectively realize the cyclic blasting process of granite and realize the accumulation of damage in the rock mass;The gradient meshing method is adopted to ensure the accuracy of calculation and the efficiency of calculation;The custom erosion criterion can effectively obtain the expansion of the internal crack of the rock with the number of blasting times;The vibration speed decrease quickly with the increase of the blasting distance,and the attenuation speed is slower away from the explosion source,and the vibration velocity test value is lower than the simulated value by about 20%;The area of damage continues to expand as the number of blasts increases,and there is no linear relationship between the accumulation of damage values and the number of blasts. |
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