爆炸载荷下空孔缺陷与爆生裂纹扩展行为研究

Crack propagation behavior of empty hole defects under blast load

空孔在岩石巷道直眼掏槽爆破中具有重要作用,为研究空孔及其缺陷在爆炸荷载作用下的扩展行为和作用机理,以PMMA代替岩石材料,利用预制裂纹代替空孔缺陷,借助动态焦散线系统和理论分析为手段,研究不同间距下空孔、空孔处预制裂纹、爆生裂纹动态扩展规律及机理,分析不同“径距比”与掏槽效果的关系。研究结果表明:在装药量一定的情况下,随着炮孔与空孔距离的变化,爆生裂纹扩展距离呈现递增而预制裂纹扩展距离呈现递减的趋势,但都存在极值;当炮孔与空孔距离较小时,爆生裂纹和预制裂纹扩展及相互作用最复杂,爆生裂纹扩展经历由压缩应力波为主,表现为直线的前期扩展;由空孔处发射应力波和压缩应力波共同作用下,爆生裂纹偏离炮孔与空孔连心线的中期扩展,以及由空孔应力集中区作用使爆生裂纹向空孔方向偏移的后期阶段;预制裂纹扩展经历由空孔处应力集中作用下,表现为直线的前期扩展,以及由爆生裂纹处反射拉伸波作用使其向爆生裂纹发展的后期阶段;当炮孔与空孔距离较大时,反射应力波及应力集中效应对爆生裂纹和预制裂纹扩展在减弱,爆生裂纹与预制裂纹扩展行为仅有前期直线扩展阶段。“径距比”的大小对爆破效果影响较大,直眼掏槽爆破应以最优“径距比”作为掏槽爆破参数设计的依据。

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.