Study On Improvement Of Open-pit Bench Blasting Quality Under The Condition Of Extremely Hard Rock

This paper mainly Studies on improvement of blasting quality under the condition of extremely hard rock, Takes Jiangxi Jinding tungsten and molybdenum mine as the research background, the key technical problems in the process of mining were as follows: high blasting boulder yield, a large amount of secondary breakup and high explosive consumption.In this paper, optimization methods of blasting parameters and the application and development trends of numerical simulation in blasting simulation in actual mine in recent years were summarized. According to the rock mechanics test, mechanical parameters of the ore rock were as follows: the uniaxial compressive strength, 241MPa; the elastic modulus, 62GPa; Poisson’s ratio, 0.38 which proved that this rock belongs to extremely hard rock. Based on the rock mechanics parameters, the finite element software ANSYS/LS-DYNA was used to conduct research on blasting simulation. The main research results were as follows:(1)The rock mechanics parameters in this paper were got by rock mechanics test.First, the rock mechanical properties were found by conventional triaxial experiments, and estimated through Hoek-Brown strength criterion, at the same time, the previous estimates were tested by compared with the results got from the uniaxial compressive strength test, point load strength test, and the Mohr circle comparisons. Finally,the high precision rock mechanics parameters of Jin ding tungsten and molybdenum ore were determined after comprehensive analysis.(2)In the experimental study,it was found that the tensile strength and cohesion of rock estimated through Hoek-Brown strength criterion were very different from the measuring results, so the method of Hoek-Brown strength criterion is not suitable to estimate the tensile strength and cohesion of rock.(3)By the comparative analysis of simulation on pore size of diameter is 11 cm, 15 cm, and 20 cm, the result was that value of blasting stress was the maximum when the diameter was 20 cm.Experiments show that the application of large diameter borehole is helpful to improve the blasting effect in open-pit blasting in high bench. Diameter of 20 cm was chosen in this design.(4)By the comparative analysis of simulation on explosive consumption of 0.60kg/ m3、0.65 kg/m3、0.70 kg/m3,the result was that value of blasting stress was the maximum when explosive consumption was 0.70 kg/m3, the rock at the top and bottom of the steps can be well damaged. So explosive consumption in this design is 0.70 kg/m3.(5)By the comparative analysis of simulation on bore hole compression coefficient of 1.2、1.5、and 1.8, the research found that, when the bore hole compression coefficient was 1.5 or 1.8,blasting stress value can damage the rock at the top and bottom of slope, when it was 1.8,it produced greater stress value, and the blasting effect will be relatively better, but it maybe lead to more serious blasting vibration,so in this paper, the density coefficient of 1.5 will be chosen.(6)In the simulation scheme, after selecting the suitable blasting aperture and explosive consumption, on the basis of above, the density coefficient of holes as variation was simulated, establishing the double-row and four-hole model, and also considering the interaction between holes, more in line with the actual situation of the mine blasting.(7)According to the numerical simulation of the selection of blasting parameters, practice were taken in Jiangxi Jinding tungsten and molybdenum ore 96 m level. Blasting effect have greatly improved, and it coincided numerical simulation, which proved the feasibility of the numerical simulation.According to the effect of blasting simulation, the blasting parameters were selected, which can lead to better blasting effect and correspond to the mine’s actual situation.