Zonal Inversion Simulation And Prediction Of Blasting Fragmentation In Jointed Rock Mass

Deep-hole bench blasting is generally used in the exploitation of grading materials of rock-fill dams in water conservancy and hydropower engineering.The rock exploited by blasting should not only meet the requirements of maximum particle size,but also meet the corresponding gradation.How to obtain good grading ingredients is a difficult problem in academic and engineering circles.In this paper,considering the joint distribution of rock mass,combined with theoretical analysis and numerical simulation methods,the prediction of blasting fragmentation was studied and calculated.The main conclusions are as follows:?1?.The existence of structural planes will affect the propagation of explosive stress waves,thus affecting the effect of rock fragmentation.During the propagation of explosive stress waves,when the joint surface containing filling medium is encountered,multiple transmission and reflection occur at the junction of the two joint surfaces.The total stress at the joint surface near the explosion source is the superposition of incident stress,reflection stress and multiple transmission stress,so the rock mass between the joint and the explosion source is more fragmented under the interaction of reflected wave and incident wave.The stress at the joint interface far from the explosion source is the superposition of the incident stress after multiple transmission on the side.Due to the obstruction of filling medium,the total energy of stress wave decreases,which makes the joint easy to produce large blocks.?2?.The zoning characteristics of blasting fragmentation of jointed rock mass were introduced.The development process of near-blasting zone was explained.The formula of distribution range of small-size materials,which combines theoretical solution with blasting test,was put forward:=₀.It is found that thevalue of the same project does not change much.Therefore,value can be obtained from a small number of tests for the same project,and small-size materials of the certain fragmentation can be predicted.?3?Based on the blasting funnel theory,the critical fracture resistance line is calculated.When the fragmentation of natural joints is larger than the maximum size of transition material in hydraulic and Hydropower projects,by adjusting the size of the resistance line,when the resistance line is smaller than the critical resistance line,the blocks cut by primary cracks will be re-fragmented under the action of stress wave,so as to meet the gradation requirements.?4?.Small-sized materials are mainly distributed in the crushing zone.When strong shock wave acts on rock mass,under the condition of high strain rate,the crushing of rock mass is mainly determined by shock waves and dynamic strength index of rocks.Although the structural plane will affect the propagation of shock waves,the structure of rock mass will be destroyed before the penetration and reflection process of structural plane in the crushing zone.From engineering phenomenon and numerical simulation of blasting prediction model based on continuum medium,it is also proved that the correlation between rock mass discontinuity and small-size fragmentation is not obvious.The structural plane mainly affects the formation of blasting fragmentation in medium and distant areas.?5?.Because the fragmentation and piles by blast are typical discontinuous processes,the blasting area of rock mass is divided into two parts:the smashing area and the crushing area.A prediction method for fragmentation of bench blasting was established.The method includes calculating the fragmentation proportion of the upper and lower envelopes of the grading materials of rock mass proposed by the design,converting the particle size into the corresponding two-dimensional area,generating the two-dimensional joint network of rock mass before blasting,determining blasting parameters,establishing a two-dimensional joint network after blasting,counting the gradation of fragmentation after blasting and simulating the shape of the blasting pile with DDA.Through calculation and analysis,the gradation prediction results of the jointed rock mass model generated by the lower envelope more accord with the actual screening results than those generated by the upper envelope,and the shape of blasting pile simulated by DDA also accord with the actual requirements of the site.The forecasting method can provide reference for similar projects.