The formulation of blasting plans frequently necessitates consulting the experiences of similar pro-jects to enhance the execution of blasting operations.However,the application of blasting techniques in exca-vation activities is frequently accompanied by challenges such as rock damage,over-excavation,and under-ex-cavation.These issues can compromise the stability of the rock mass,consequently impacting the overall safety and reliability of the project.A widely adopted technique for effectively managing the directional propagation of cracks during blasting operations,thereby ensuring the desired blasting outcome,involves the strategic place-ment of guide holes surrounding the blast hole.To further investigate the variations in the guiding efficacy of different types of guide holes,this study employs the *MAT_JOHNSON_HOLMQUIST_CERAMICS cons-titutive model within the LS-DYNA software for simulation,building upon prior research.The objective of this model is to forecast the mechanical behavior of brittle materials,including ceramics and polymethyl metha-crylate,under extreme conditions such as high strain rates,elevated pressures,and impact loads.This model facilitates the analysis of crack propagation effects in polymethyl methacrylate plates subjected to explosive loads,specifically examining the influence of varying guide hole configurations.Additionally,it enables a more in-depth investigation into the guiding effect on crack propagation by altering the spacing between blast holes and guide holes.This study investigates the influence of various guide hole configurations on crack propagation control by analyzing the morphological differences of blasting cracks and examining the temporal stress history curves at multiple measurement points on the walls of different guide holes.The findings indicate that polymethyl methacrylate with guide holes facilitates crack penetration more effectively than those without,with grooved guide holes demonstrating superior penetration efficacy compared to circular guide holes.A detailed examination of the stress alterations surrounding the guide hole reveals the presence of a stress concentration phenomenon in this region.Compressive stress manifests on both sides of the line connecting the guide hole and the blast hole,facilitating the extension of cracks around the guide hole.The stress levels on either side of a grooved guide hole are notably higher compared to those of a circular guide hole,thereby exerting a more pronounced influence on crack propagation.Additionally,the circular guide hole demonstrates a superior guiding effect on crack propagation compared to scenarios lacking a guide hole.Similar to the indoor test results,the feasibility of this simulation method has been verified.
钻爆法因具有成本低、适应性强等优点,而在隧道开挖施工中被广泛应用,但该方法容易出现围岩损伤、超挖和欠挖等现象,使岩体的稳定性遭到破坏(戴俊,2002;王建秀等,2013;陈鑫,2024)。为了确保爆炸损伤达到使用要求,国内外学者提出了多种解决方案。常见的方法有4种,即:药卷形状法、炮孔形状法、切缝药包法和导向孔法。其中,药卷形状法和炮孔形状法均是通过改变药卷或炮孔的形状,以影响爆炸能量的传播路径和作用效果(杨树仁等,2012,2020;岳中文等,2016);切缝药包法通过在药包上安装预先切槽的套管,使得爆炸时较多的能量向切槽方向集中,能够更有效地作用于周围的岩石,实现定向断裂(Fourney et al.,1978);导向孔法由Mohanty (1990)提出,该方法是在不改变炮孔和药卷形状的情况下,采取在炮孔周围设置空孔的方式,使得爆炸时在空孔周围出现应力集中,从而引导爆生裂纹向空孔延伸,降低裂纹延伸的随机性,实现对裂纹延伸方向的控制。
为了进一步研究导向孔对爆炸应力波传播和裂纹扩展的影响,通过采用动态焦散线法(姚学锋等,1998)观察应力波对空孔的作用过程,发现导向孔与炮孔之间的距离对导向孔的导向效果起关键作用,当炮孔与导向孔之间的间距较小时,周围岩体损伤严重无法充分发挥导向孔的导向作用;当炮孔与导向孔之间的间距较大时,两侧炮孔裂纹贯通效果较差(张召冉等,2022,2023;田国宾等,2024)。同时,在一定范围内增大导向孔的直径,也能够提升导向孔的导向效果(杨仁树等,2017),但随着导向孔直径的增加,其反射回来的拉伸应力波会降低主裂纹的延伸速度(岳中文等,2016)。在设计爆破参数时还需要考虑岩石的岩性,软岩在空孔效应影响下形成的片裂区明显大于硬岩(张召冉等,2023)。江俐敏等(2022)将数值模拟、理论分析与现场试验相结合,研究空孔对爆炸应力波传播和裂隙扩展规律的影响,优化了空孔参数。在研究圆形导向孔的基础上,Nakamura et al.(2004)进行了带有切槽导向孔对裂纹扩展的影响研究,并通过试验与数值模拟相结合的方式加以验证(魏炯等,2013;蒲传金等,2022)。
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