A layered rock mass is a special type of geological body. The existence of a bedding surface may lead to a poor cutting effect (over/under-excavation of the surrounding rock), falling of blocks, or collapse, thereby affecting most constructions in areas with such rocks. Given the lack of a proper quantitative analysis method for surrounding rock damages, the construction process of layered surrounding rock tunnels becomes difficult. To address these problems, three types of cut blasting models with single, double, and four holes are studied in this paper. With this, the LS-DYNA program is used to analyze the behaviors of stress wave propagation, crack propagation, and fracture modes, as well as fracture mechanisms of mudstone, sandstone, and layered rock. Using the image processing technology and fractal theory, the fractal dimension change trend and progressive damage evolution behavior of the three types of rocks under different cut blasting conditions are determined. Also determined is the corresponding relationship between the fractal dimension and the rock damage degree. The results indicate that crack initiation, propagation, bifurcation, and fractal dimension evolution are more closely related to the phenomenon where the compression wave is ahead of the tension wave, and the∖incompatible deformation of the bedding under single-hole blasting. Under double-hole and four-hole blasting, the phenomena, such as spalling, bedding crack penetration, and fracture connection between the explosive holes are caused mainly by the effects of stress concentration, reflected tension waves, and stress wave superposition. Moreover, under different blasting conditions, the rocks exhibit a similar progressive damage process, i.e. a rapid increase at first, then a slow rise, and finally a stabilization phase. The dynamic damage degree of the rock exhibits a linear increasing trend under different blasting holes. The study results provide a useful reference for blasting scheme design and optimization of underground engineering projects.

中文翻译：

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隧道施工爆破致层状围岩损伤分析

层状岩体是一种特殊类型的地质体。层理面的存在可能会导致切割效果不佳（围岩超挖/欠挖）、块体掉落或坍塌，从而影响大多数有此类岩石的地区的建筑。由于缺乏合适的围岩损伤定量分析方法，层状围岩隧道施工难度加大。针对这些问题，本文研究了单孔、双孔和四孔三种切割爆破模型。有了这个，LS-DYNA程序被用来分析应力波传播、裂纹扩展和断裂模式的行为，以及泥岩、砂岩和层状岩石的断裂机制。利用图像处理技术和分形理论，确定了三种岩石在不同切割爆破条件下的分形维数变化趋势和渐进损伤演化行为。还确定了分形维数与岩石破坏程度的对应关系。结果表明，裂纹的萌生、扩展、分叉和分形维数演化与压缩波先于拉伸波的现象密切相关，∖单孔爆破下层理的不相容变形。双孔和四孔爆破下，爆破孔之间的剥落、层理裂纹贯穿、断裂连接等现象主要是由于应力集中、反射张力波和应力波叠加的影响。此外，在不同的爆破条件下，岩石呈现出相似的渐进破坏过程，即先快速上升，然后缓慢上升，最后进入稳定阶段。不同爆破孔眼下岩石动态损伤程度呈线性增加趋势。研究结果为地下工程爆破方案设计和优化提供了有益的参考。