Numerical Simulation Study On Open Bench Blasting With Combined Holes

In the open-air step blasting,complex geological conditions are often encountered.Under the condition of “upper hard and soft” rock formation,the joint layer hole(that is,the hole depth of the adjacent blasthole is inconsistent)is used to blast the rock layer of “upper hard and soft”geological conditions.This paper is based on the concrete model of making “upper hard and soft” lithology.The lower layer is filled with C30 concrete,and the upper layer is filled with C40 concrete.The mechanical parameters are determined separately.The main research contents are as follows:In the joint cloth hole mode,the high-speed camera technology is used to observe the instantaneous crack propagation process of concrete model blasting with different hole depth ratios,and the crack propagation law is observed.The blockiness generated by the blasting effect is analyzed.In the joint cloth hole mode,the super dynamic strain gauge test system is used to test the concrete strain model of different blasthole hole depth ratios.The main findings are as follows:(1)Using high-speed camera to observe the crack propagation at the moment of blasting,the main crack is in the “ ? ”line.First,the transverse crack appears at the stratification,and the longitudinal crack appears in the middle of the upper concrete.The underlying concrete appears inclined at an angle of 50 degrees to the transverse crack.To the crack,the secondary crack propagates around the main crack,and many irregular cracks appear one after another during the throwing process.(2)Using ultra-dynamic strain gauge to test the strain law of concrete at the moment of blasting,the measuring points are arranged at the same position of each model,the strain law curve is consistent,the compressive strain peak appears at 20 places,the tensile strain peak appears at 31,and the small peak appears at 87 There is a difference in strain peaks.The strain law is similar to the numerical simulation strain law,and the time variation is almost the same.(3)Using ANSYS/LS-DYNA software,using fluid-solid coupling algorithm,setting mechanical parameters,establishing concrete numerical model,using joint hole method,concrete blasting,observing the stress and strain law;When the depth ratio of the adjacent blasthole is 0.4,the free blasting formed by the shallow hole blasting has a guiding effect;when the hole ratio of the adjacent blasthole is 0.5,the depth is deep.The stress generated by the hole blasting is concentrated in the middle hole;when the depth ratio of the adjacent blast hole is 0.6,the stress distribution generated by the shallow hole blasting freely faces the deep hole blasting has no effect,and the stress does not aggregate.The numerical simulation strain law is similar to the measured strain strain law,and the time variation is almost the same.(4)Comparing the blasting effect of each group model,it is feasible to use the joint cloth hole method under the condition of “upper hard and soft”,which can blast the rock and make full use of the explosive.When the hole depth ratio of adjacent blasthole is 0.6,it is large.The block rate is the lowest and the blasting effect is the best.