Dynamic Fracture Behavior Of Fractured Rock Mass Under Dynamic And Static Loading

Before the final profile of rock mass blasting excavation is formed,a large number and a long length of blasting cracks are usually formed inside the rock mass.Under the action of blasting load and initial stress of rock mass,these first generated blasting cracks will affect the propagation of cracks in rock mass,thus affecting the stability and safety of rock mass engineering.In view of this,based on previous research results,a simplified crack relation configuration is established in this paper,which is used to study the influence of symmetric cracks on the dynamic fracture mechanical behavior of?type main crack under explosive dynamic load and under the combined action of initial stress and explosive dynamic load under different conditions.The main research contents and conclusions of this paper are as follows:(1)based on the explosive stress wave with a single crack coupling far end of the crack tip stress field and velocity field analysis found that the explosive stress wave is crack split into two mechanics parameters consistent stress wave,and the applied field at the crack tip,lead to the crack tip stress field and displacement field strength is greater than no crack in formation of the field intensity at one end.(2)A numerical model containing explosion loading holes and symmetrical cracks was established to analyze the distribution of stress field when the explosion stress wave and symmetrical crack acted on each other.It is found that the compressive stress field and the tensile stress field appear alternately between the symmetrical cracks under the action of explosion stress wave,and the compressive stress field always exists between the symmetrical cracks.(3)By verifying the rationality of the mesh size of the numerical model with the model diameter of 60mm(the diameter of the central loading hole is 4mm),it is found that when the mesh size changes within the range of 0.5mm?0.125mm,the number of meshes increases exponentially,the crack propagation range around the loading hole changes little,and the stress wave propagation has little effect.Therefore,considering the calculation cost and precision comprehensively,the mesh size is finally selected as 0.5mm.(4)A numerical model with a diameter of 600mm,a prefabricated crack length of 70mm,and different crack tip shapes and crack tip lengths was established.The crack initiation time and final propagation length of each model were compared and analyzed.It was found that both circular and square crack tips would form bifurcated cracks.The triangular crack tip propagates along a straight line after initiation and does not form a bifurcation crack.In addition,when the crack tip length varies from 1 mm to 2mm,the crack propagation length and crack initiation time fluctuate greatly with the crack tip length.However,the crack propagation length and crack initiation time only slightly change with the crack tip length when the crack tip length varies from 3 mm to 6mm.Based on the analysis of the above influencing factors,it is concluded that the numerical model parameters with the crack tip shape being triangle and the crack tip length being 3mm are more reasonable.(5)By analyzing the test data of the dynamic crack propagation velocity in the physical model experiment,it is found that under the condition of 0°,45°and 90°moving towards the secondary crack,with the decrease of the space between the secondary cracks,both the main crack propagation length and the average crack propagation velocity decrease.Under the condition of the same secondary crack spacing,the 90°strike secondary crack has the most obvious inhibition effect on the main crack growth,the 45°strike secondary crack is the second,and the 0°strike secondary crack has the least inhibition effect.(6)through the establishment of containing loading hole,crack and the crack front is different to Lord two numerical model of crack,comparison and analysis to two different crack under explosion load effect on the main crack found that three direction of the cracks will affect the expansion of the main crack,and the less crack spacing,the crack propagation length shorter;In the three strike secondary crack models with the same spacing,the order of the propagation length of the main crack is L_0°>L_45°>L_90°.Therefore,the three strike secondary cracks have different inhibitory effects on the main crack.The inhibition effect of the 90°strike secondary crack is the strongest,the 45°strike secondary crack is the second,and the inhibition effect of the 0°strike secondary crack is the least.In addition,some physical experiments show that the effect of crack propagation is similar to that of numerical simulation.By analyzing the?y and particle velocity vectors between three strike secondary crack at the same time,it is found that the compressive stress region between 45°strike secondary crack is larger than that between0°strike secondary crack,and the compressive stress region between 90°strike secondary crack is the largest and the relative value is the largest.The particle movement direction among the three strike secondary cracks is opposite to the direction of the main crack growth,which inhibits the main crack growth,and the order of velocity is V_90°>V_45°>V_0°.Comprehensive analysis shows that the 90°strike secondary crack has the strongest inhibitory effect on the main crack.(7)Based on the numerical simulation of dynamic fracture of fractured rock mass under explosive dynamic load,the specimen configuration with strike secondary crack spacing S=70mm was adopted as the numerical model,and initial stresses of 5MPa,10MPa,15MPa and 20MPa were applied around it through static calculation in Workbench.The results show that the initial stress inhibits the growth of the main crack,and the larger the initial stress is,the stronger the inhibition is.In addition,in order to study the influence of the direction of initial stress on the dynamic propagation of the crack,a prefabricated crack model with loading holes and a length of 70mm was established.The stress value of 10MPa was applied to the model,and the initial stress?with the prefabricated crack was 15°,30°and 45°,respectively.By comparing the final crack propagation morphology,it was found that:The larger the initial stress component relative to the crack propagation direction is,the stronger the inhibition effect on the crack propagation is.