Study On Blasting Mechanism And Blasting Effect Evaluation Of Burnt Rock In Open-pit Mine

The bench blasting of open-pit mine is the primary link of open-pit mine.The blasting effect directly affects the efficiency of mining and loading operation,and then affects the production efficiency,safety and cost of open-pit mine.The factors affecting the blasting effect of open-pit mine mainly include the lithology of blasting rock mass,rock mass structure,borehole parameters,explosive performance,charge structure and detonation mode.Lithology is the basic factor affecting the blasting effect of open-pit mines.Especially in some open-pit mines in Xinjiang,Inner Mongolia and Ningxia,a large number of burnt rocks have a great influence on the blasting effect.The joint fissures in the burnt rock mass are developed,and the anisotropy of the rock mass is significant.After blasting,it is easy to produce umbrella eaves,hard sides and roots.The rock block is not uniform,the powder rate and the block rate are high,and the blasting effect is poor.Therefore,how to improve the blasting effect of the open-pit mine fire area and make a scientific and reasonable evaluation of the blasting effect is an urgent problem to be solved in the current open-pit mine burnt rock blasting.In this paper,the mechanism of blasting fragmentation of burnt rock is studied by means of theoretical analysis,laboratory experiment,numerical simulation and industrial field test.The physical and mechanical parameters of burnt rock and the change of mineral composition of rock after high temperature were tested by the experiment.The blastability grade of burnt rock was determined to be more explosive rock,and the matching degree between burnt rock and mixed emulsion explosive was verified.Combined with ANSYS / LS-DYNA and PFC2 D numerical simulation software,a burnt rock model with multiple joint cracks and irregular distribution was constructed by inserting random cracks obeying weibull distribution through self-compiled FISH language.The blasting fragmentation process of burnt rock under the combined action of stress wave and detonation gas was simulated.Based on the conventional rock blasting fragmentation mechanism,the influence of joint cracks in burnt rock on blasting effect was analyzed,and the blasting fragmentation mechanism of burnt rock was clarified.The damage factor in damage mechanics is introduced to determine the mechanical properties of burnt rock mass and the attenuation law of stress wave.Combined with the Mises criterion,the calculation formula of the radius of the crushing zone and the fracture zone of burnt rock under the combined damage of explosive gas and stress wave with different charge structures is derived.Based on the fuzzy comprehensive evaluation method,the weight determination method is improved by the combination of analytic hierarchy process and entropy weight method,and the evaluation model of bench blasting effect of burnt rock in fire area is constructed.The blasting design of burnt rock in burnt area of the second mine of Dananhu in Xinjiang is studied.The parameters of perforated blasting are optimized.The industrial test is carried out and the blasting effect is evaluated.The results show that the optimized blasting scheme improves the bench blasting effect of burnt rock obviously.The research results have been successfully applied in the bench blasting of burnt rock in the fire area of Dananhu No.2 Mine.The research results have important reference value for the bench blasting of open-pit rock under similar conditions.There are 87 figures,53 tables and 146 references in this paper.