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Gold Science and Technology ›› 2020, Vol. 28 ›› Issue (2): 228-237.doi: 10.11872/j.issn.1005-2518.2020.02.154

• Mining Technology and Mine Management • Previous Articles    

Distribution of Blasthole Fracture in Eccentric Charge Under In-situ Stress

Honglu FEI1(),Yu LIU1(),Qifei QIAN1,Qiang SU2,Xiaoyu SUN1   

  1. 1. Institute of Blasting Technique，Liaoning Technical University，Fuxin 123000，Liaoning，China
    2. CCTEG Shenyang Research Institute，Fushun 113000，Liaoning，China
  • Received:2019-09-16 Revised:2019-12-09 Online:2020-04-30 Published:2020-05-07
  • Contact: Yu LIU E-mail:feihonglu@163.com;nameliuyu@163.com

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Abstract:

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of its own gravity, forming eccentric uncoupled charge.The change of the charge structure has made the previous theory no longer applicable，and the earth stress is a problem that cannot be ignored as the depth of the excavation changes.Therefore，in the presence of in-situ stress，the fracture area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.

Key words: eccentric uncoupled charge, explosive gas, crack range, ground stress, blasting effect

CLC Number: 

  • TD235

Fig.1

Eccentric uncoupled charge structure"

Fig.2

Diagram of the variation rule of the uncoupled coefficient K "

Fig.3

Stress distribution map of surrounding rock outside the cavity"

Fig.4

Crack propagation model driven by explosive gas"

Table 1

Physico-mechnical properties of different rocks"

岩石类型 μ ρ m /（kg·m-3） C p /（m·s-1） a/（m·s-1） b S t d /MPa
大理岩 0.20 2 730 4 420 4 000 1.32 10
页岩 0.31 2 350 3 970 3 600 1.34 8
砂岩 0.25 2 450 4 050 3 600 1.43 10

Fig.5

Distribution map of crocks in three types of rocks with and without ground stress"

Fig.6

Distribution map of cracks in three types of rocks under in-situ stress"

Fig.7

Distribution map of tangential force"

Fig.8

Fracture distribution map under different ground stresses"

Fig.9

Distribution map of fracture range and comminution zone under high ground stress"

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80项成果获得中国黄金协会科学技术奖
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[3] Xiaohan LI,Kewei LIU,Jiacai YANG,Xudong LI. Analysis of Blasting Vibration Effects Under Different Ground Stress [J]. Gold Science and Technology, 2019, 27(2): 241-248.
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