Crack propagation behavior of empty hole defects under blast load
ZHANG Zhaoran1, ZUO Jinjing2, GUO Yixian3
1.School of Civil Engineering, North China University of Technology, Beijing 100141, China;
2.School of Mechanics and Civil Engineering， China University of Mining and Technology(Beijing)， Beijing 100083， China;
3.BGI Engineering Consultants LTD., Beijing 100038, China
Abstract：Empty holes play an important role in straight-hole-cut blasting of rock tunnel.Here, in order to study propagation behavior and action mechanism of empty holes and defects under blast load, PMMA was used to replace rock material, and a prefabricated crack was used to replace an empty hole defect.Dynamic caustic line system and theoretical analysis were taken as means to study dynamic propagation laws and mechanism of prefabricated cracks and blast induced ones at holes’ position with different spacing, and analyze the relation between different ratios of diameter to distance and cutting effect.The results showed that when charge quantity is certain, blast induced cracks propagation distance increases while prefabricated cracks’ decreases with variation of distance between blast hole and empty hole, but both of them have extreme values; when distance between blast hole and empty hole is smaller, blast induced cracks and prefabricated ones’ propagation and interaction are the most complicated; blast induced crack propagation is mainly caused by compressive stress wave, its earlier stage propagation reveals a straight line; its medium stage propagation under combined action of compressive stress wave and stress wave emitted by empty hole diverges the connection line between blast hole center and empty hole one; its later stage propagation offsets in the direction of empty hole due to action of empty hole’s stress concentration area; pre-fabricated crack propagation is caused by stress concentration at empty hole, its earlier stage propagation reveals a straight line, and its later stage propagation develops to blast induced crack due to action of reflected tensile wave at blast induced crack; when distance between blast hole and empty hole is larger, reflected stress wave and stress concentration effect reduce blast induced crack propagation and pre-fabricated one, and their propagations only have an earlier stage of straight line; "ratio of diameter to distance" has a larger impact on blasting effect, straight-hole-cut blasting should take the optimal "ratio of diameter to distance" as a basis for design of hole-cut blasting parameters.
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