Abundant engineering practice shows that coal and rock dynamic disasters often occur in fault zones; hence, the detection of faults in coal mines is important. As an essential branch of seismic tomographic application, research shows that ultrasonic P-wave velocity can detect mine faults and provide technical support for dynamic disaster prewarning systems. Traditional P-wave testing mostly takes rock or raw coal as the research object, which has some shortcomings in controllability, homogeneity and comparability. This paper compares the difference in ultrasonic P-wave propagation velocity in jointless and jointed briquettes through laboratory research, focuses on the effect of macro-joints on P-wave velocity and makes a preliminary theoretical analysis. The results show that: (i) the three-dimensional P-wave velocity throughout a jointless briquette specimen is similar, which reflects the high homogeneity of this medium and avoids the influence of the random distribution of primary bedding, joints and structural planes; (ii) the P-wave velocity in jointless and jointed briquettes is positively correlated with density and forming pressure, and is negatively correlated with the angle between the ultrasonic wave and the joint surface in a sample and (iii) when the P-wave encounters the macroscopic joint surface, it may reflect and refract, changing the propagation direction and inducing wave mode conversion. This study provides the necessary technical support and a theoretical guide to optimise acoustic property analysis of coal and rock as well as a field application for seismic tomography technology.

中文翻译：

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人工节理煤球的超声P波传播特性

大量的工程实践表明，煤和岩石的动态灾害经常发生在断层带。因此，检测煤矿的断层非常重要。作为地震层析成像应用的重要分支，研究表明，超声波纵波速度可以检测出矿山断层，并为动态灾害预警系统提供技术支持。传统的P波测试大多以岩石或原煤为研究对象，在可控性，均质性和可比性方面存在一些不足。本文通过实验室研究比较了无接缝煤球和接缝煤球的超声波P波传播速度的差异，着眼于宏观接头对P波速度的影响，并进行了初步的理论分析。结果表明：（i）整个无接缝型煤样品的三维纵波速度是相似的，这反映了这种介质的高度均一性，并且避免了主要层理，节理和结构面的随机分布的影响；（ii）无接缝煤球和接缝煤球的P波速度与密度和成形压力呈正相关，与样品中超声波与接缝表面之间的夹角呈负相关；以及（iii）当P波遇到在宏观的关节表面，它可能会反射和折射，改变传播方向并引起波模转换。这项研究为优化煤和岩石的声特性分析以及地震层析成像技术的现场应用提供了必要的技术支持和理论指导。