Study On The Effect Mechanism Of Accurate Millisecond Time Delay Between Charge Holes On Fragmentation In Blasting Mining

With the increasing popularizing of digital electronic detonators in hydropower rockfill dam batching blasting mining,the optimization of the delay time between charge holes in the deep hole bench blasting excavation is imminent.The previous studies on the delay time between holes tends to reduce blasting vibration and disturbance to the surrounding environment,while the issue on the influence of the delay time between the holes on the distribution of blasting fragmentation has not been studied in depth.Regarding the problem above mentioned,three methods,including theoretical analysis,numerical simulation,and field test,were used to study the influence of the delay time between holes on the mining of hydropower engineering grade ingredients and to further optimizes the delay time between holes.The main content of this thesis is summarized as follow(1)The rock breaking mechanism of delayed blasting in recent years was summarized and divided into new free surface hypothesis,residual stress hypothesis,rock collision hypothesis,seismic wave interference hypothesis,stress wave superposition principle,and minimum resistance line principle.Based on the rock blasting process and crushing mechanism,the impact of rock physical and mechanical properties,rock blastability,and rock joint development on the blasting effect was explored,and the influence of blasting parameters(such as step height,aperture,hole depth and ultra-depth,chassis resistance line,Hole row distance,step slope angle,blockage length,explosive unit consumption)and network structure on the blasting effect and its value were summarized and studied.(2)Based on the secondary development module of LS-DYNA,the predictive model of blasting grade ingredients was compiled into a calculable program,which realized the simulation calculation of grade ingredient distribution,and the validness and accuracy of the modelling method was verified by actual screening results.The dynamic finite element analysis software ANSYS/LS-DYNA was used to simulate the blasting process with different time delays between holes.The effects of different blasthole delays on the propagation of stress waves in rock masses were analyzed.The effects of mutual interference in the propagation of stress waves were analyzed based on the results of particle vibration induced by different time differences;the statistics of distribution of fragmentation in the numerical simulation was carried out.Based on statistics,a gradation curve was drawn,and the influence of delays between different holes on the distribution of block size was analyzed,and it was determined that when the blast hole delay is 5-20 ms,the crushing effect is better.(3)Relying on Lianghekou blasting and excavation test,the geological conditions and blasting parameters of Lianghekou quarry and Wazhigou quarry were studied,and the distributions of fragmentation under various delay time intervals between different holes were measured through on-site screening and Wip Frag fragmentation scanning.By establishing the grading curve of blasting material corresponding to delay time=0ms,5ms,10 ms,20ms,30 ms,and 50 ms,the law of fragmentation distribution was analyzed.Separate statistical analysis was performed for three intervals of 0mm～10mm,10mm～80mm and above 80 mm,and it was found that the delay between holes had a greater impact on the ingredients under interval=10mm～80mm.The relationship curves between average fragmentation and delay time,the unevenness coefficient and the delay time,the qualification index and the delay time were established for the two quarries,and the influence of the delay time between the holes on the rock fragmentation,unevenness,and qualification degree was studied.The rock breaking mechanism of millisecond blasting was analyzed based on test conditions and analysis results and three hypotheses,i.e.,stress wave superposition,new free surface,and rock collision.Based on the data analysis of this experiment,the best delay time for hydraulic grade batching blasting mining was determined: the best delay time between holes is 10ms～20ms.Based on the results of numerical simulation and blasting test,it was found that when the delay time between holes is 10ms～20ms,the rock fragmentation effect is more in line with engineering needs,and that it is more reasonable to set delay time increment to 2～5ms/m with the change of the hole row spacing distance.