Distribution of Blasthole Fracture in Eccentric Charge Under In-situ Stress
Received date: 2019-09-16
Revised date: 2019-12-09
Online published: 2020-05-07
Drilling and blasting is widely used in mining and tunnel excavation as an economical and efficient method of excavation.Among them,smooth blasting is the most common.The theory of smooth blasting theory is based on the concentric uncoupled charge structure.In the actual smooth blasting,the charge structure will change due to the existence of its own gravity, forming eccentric uncoupled charge.The change of the charge structure has made the previous theory no longer applicable,and the earth stress is a problem that cannot be ignored as the depth of the excavation changes.Therefore,in the presence of in-situ stress,the fracture area formed by eccentric blasting is determined to provide a theoretical reference for blasting construction.Because of the eccentricity effect,the uncoupling coefficient of the blasthole is different after charging.According to the definition of the concentric uncoupling coefficient,the equivalent uncoupling coefficient of each point of the eccentric uncoupled blasthole is given.Then based on the theory of blast stress wave and explosive gas,considering the effect of earth stress and the initial damage of rock,combined with the theory of maximum circumferential stress in fracture mechanics,the calculation formula of initial crack and extended fracture under eccentric uncoupling charge was derived.The No.2 rock emulsion explosives and three kinds of rocks were selected as examples to calculate the initial fracture range of the marble,shale and sandstone under the eccentric uncoupled charge,drawing with Origin software.By observing the difference between the coupled side and the uncoupled side,and exploring the influence of the ground stress on the initial crack caused by the explosion stress wave,we compared and analyzed the variation of the initial crack range under different ground stresses.The results show that the uncoupling coefficient on the wall of the blasthole is related to the difference between the deflection angle α,the blasthole and the radius of the lap.The equivalent uncoupling coefficient on the wall of the blasthole hole results in a very uneven distribution of the eccentric uncoupled charge structure,and there is a large difference between the length of the coupling side and the uncoupled side.With the increase of ground stress,the range of cracks around the blasthole is gradually decreasing,and the angle α of the shortest crack on the uncoupled side gradually increases,and its range gradually approaches the radius of the smashing zone.The presence of visible ground stress inhibits the expansion of the crack.The higher the ground stress,the smaller the crack range.When high geostress is encountered in the selected three types of rock blasting constructions,it is necessary to consider the fact that the cracks on the non-coupling side are short or non-existent.The blast holes are arranged in a triangle and the hole spacing is controlled between 0.45 and 0.70 m.
Honglu FEI , Yu LIU , Qifei QIAN , Qiang SU , Xiaoyu SUN . Distribution of Blasthole Fracture in Eccentric Charge Under In-situ Stress[J]. Gold Science and Technology, 2020 , 28(2) : 228 -237 . DOI: 10.11872/j.issn.1005-2518.2020.02.154
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