岩石二氧化碳相变致裂技术，目前已经被广泛应用于边坡工程和岩石开采等相关工程领域，显示了二氧化碳破岩稳定性的显著优势，但在地下开采领域的技术理论研究仍处于初步探索阶段。围绕“双碳”目标，针对二氧化碳的相变储能、封存和合理利用的研究，已经成为当前岩石力学研究的热点。为此，本文针对二氧化碳相变定向破岩问题，采用物理实验、理论分析、数值模拟、现场试验相结合的方法，对二氧化碳岩石致裂机理和二氧化碳定向破岩裂纹扩展规律进行了研究，结合工程背景开展了工程验证。主要取得以下研究成果：

（1）通过室内实验测试了岩石的物理力学性能，得到了岩石的抗压、抗拉和抗剪强度参数，利用R-K-S气体状态方程分析计算二氧化碳致裂岩石的所释放的能量、当量和爆容，为理论分析和数值模拟参数的选取提供了依据。

（2）对液态二氧化碳致裂过程中产生的聚能冲击波和低温高压二氧化碳气体联合作用下的破岩过程进行了分析，总结了液态二氧化碳致裂破岩机理。根据线弹性理论，分别得出了在高压二氧化碳气体作用下裂纹尖端以及岩体内部的应力场。引入损伤理论推导得出了在高压二氧化碳气体作用下裂纹尖端有效应力强度因子的表达式，并推导了在高压二氧化碳气体驱动下岩体内裂纹的开裂准则，结合损伤理论分别分析计算得出了在冲击波与应力波作用下粉碎区、裂隙区半径。

（3）利用LS-DYNA软件建立岩体致裂损伤模型，模拟单孔、双孔、导向孔以及孔内多点定向致裂的液态二氧化碳致裂岩体裂隙形成过程，研究了单孔岩体二氧化碳致裂裂纹形成与扩展机理，根据单孔致裂岩体模拟结果确定了二氧化碳相变岩石致裂半径。研究了孔间相互作用致裂岩体裂纹形成与扩展规律，分析计算出了双孔致裂合理孔间距。通过研究导向孔对裂纹的导向作用机理，分析了导向孔对裂纹扩展的影响。研究了不同致裂点间距下的孔内多点致裂岩体效果，确定了孔内多点致裂的合理致裂点间距，分析了多点致裂时孔内岩壁致裂裂纹的扩展贯通规律。

（4）通过大采高综采工作面顶板岩层相变定向致裂卸压现场试验表明，二氧化碳相变致裂顶板岩层卸压的实际效果显著。通过钻孔窥视法对孔内裂缝连通情况进行考察，经顶板岩层定向致裂后，卸压区相比于未卸压区煤柱应力平均降低了约22.2%，巷道顶底板变形量平均减小了46.4%，两帮变形量平均减小了51.8%，有效地控制了巷道围岩。

Rock carbon dioxide phase change cracking technology has been widely used in slope engineering and rock mining and other related engineering fields, showing the significant advantages of carbon dioxide rock breaking stability, but the technical theory research in the field of underground mining is still in the preliminary exploration stage. Focusing on the goal of "dual carbon", the research on phase change energy storage, storage and rational utilization of carbon dioxide has become a hot spot in the current research of rock mechanics. Therefore, this paper studies the cracking mechanism of carbon dioxide rock and the crack propagation law of carbon dioxide directional rock breaking by combining physical experiments, theoretical analysis, numerical simulation and field experiments, and carries out engineering verification based on the engineering background. The following research results have been achieved:

(1) The physical and mechanical properties of the rock were tested through indoor experiments, and the relevant physical and mechanical parameters were obtained, and the energy, equivalent and explosive volume released by the constant pressure shear sheet with a release pressure of 270MPa were calculated by the analysis of the R-K-S gas equation of state, which provided a basis for theoretical analysis and the selection of numerical simulation parameters.

(2) The rock-breaking process under the combined action of concentrated energy shock wave and low-temperature and high-pressure carbon dioxide gas generated during the cracking process of liquid carbon dioxide is analyzed, and the rock breaking mechanism of liquid carbon dioxide cracking is summarized. According to the linear elastic theory, the stress fields of the crack tip and the interior of the rock mass under the action of high-pressure carbon dioxide gas are obtained. The expression of the effective stress intensity factor of the crack tip under the action of high-pressure carbon dioxide gas is derived by the damage theory, and the cracking criterion of cracks in the rock under the drive of high-pressure carbon dioxide gas is derived, and the radius of the crushing zone and the fracture zone under the action of shock wave and stress wave are analyzed and calculated respectively combined with the damage theory.

(3) LS-DYNA software was used to establish the rock mass cracking damage model, simulating the fracture formation process of liquid carbon dioxide fracturing rock mass with single-hole, double-hole, guide hole and multi-point directional cracking in the hole, and the formation and propagation mechanism of carbon dioxide cracking in single-hole rock mass was studied, and the cracking radius of carbon dioxide phase change rock was determined according to the simulation results of single-hole fractured rock mass. The crack formation and propagation law of the fractured rock mass of the interaction between the pores were studied, and the reasonable pore spacing of the double-hole cracking was analyzed and calculated. By studying the guiding mechanism of the guide hole on the crack, the influence of the guide hole on crack propagation was analyzed. The effect of multi-point cracking rock mass in holes under different cracking point spacing was studied, the reasonable cracking point spacing of multi-point cracking in holes was determined, and the propagation law of cracking cracks in rock walls in holes during multi-point cracking was analyzed.

(4) The field test of phase change directional cracking and pressure relief of the top slate layer of the large-scale mining and comprehensive mining face shows that the actual effect of pressure relief of the carbon dioxide phase change fracture roof slate layer is remarkable. After directional cracking of the roof rock layer, the stress of the coal column in the pressure relief zone was reduced by about 22.2%, the deformation of the roof and floor of the roadway was reduced by 46.4% on average, and the deformation of the two groups was reduced by 51.8% on average, which effectively controlled the surrounding rock of the roadway.

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