基于中间主应力效应和采动卸荷应力路径的低渗煤岩变形破坏及渗透特性研究

The problem of the sudden gas emission caused by the excavation of coal and rock layers is essentially the influence of the intermediate principal stress and the mining unloading stress path within the influence range of the coal wall. Therefore, in this project, research methods such as experimental research and theoretical analysis and numerical simulation are undertaken, considering the effect of intermediate principal stress and unloading stress path on the deformation and failure and permeability of coal and rock, the effects of intermediate principal stress and maximum principal stress loading rate and minimum principal stress unloading rate on strength and energy evolution and dilatancy and damage deformation and failure modes and permeability characteristics of coal and rock are studied. Based on the strength theory, the failure criteria of coal and rock under true triaxial unloading conditions are proposed. Combining with the crack strain theory, the effects of intermediate principal stress and unloading rate on crack volume strain and crack initiation stress and damage stress and permeability of coal and rock at different stages of deformation and failure are analyzed, and the relationship between Crack strain and permeability variation is explored. The influence mechanism of the intermediate principal stress effect and the unloading stress path on the permeability and deformation and failure of coal and rock is revealed. The permeability calculation model under true triaxial unloading condition is proposed and the gas migration model is established considering the combined effect of the intermediate principal stress and unloading stress path. The research has an important theoretical and field guidance on coal mine dynamic disaster control and the development of clean energy.

煤岩层开挖时导致的瓦斯急剧涌出问题，其实质是煤壁影响范围内中间主应力与采动卸荷应力路径产生的影响。因此，本项目以试验研究、理论分析与数值模为主要研究手段，综合考虑中间主应力效应和采动卸荷应力路径对煤岩变形破坏和渗透率的影响，研究中间主应力、最大主应力加荷速率、最小主应力卸荷速率对煤岩强度特征、能量演化特征、扩容特征、损伤变形特征、破坏模式及渗透率的影响，结合强度理论，提出真三轴卸荷条件下煤岩的破坏准则，结合裂纹应变理论，分析中间主应力和卸荷速率对煤岩变形破坏不同阶段裂纹体应变、起裂应力和损伤应力及渗透率等的影响，并探明裂纹应变和渗透率变化量之间的关系，揭示中间主应力效应和卸荷应力路径对煤岩变形破坏和渗透特性的影响机制，提出真三轴卸荷条件下煤岩的渗透率计算模型，建立考虑中间主应力效应和卸荷应力路径综合影响的瓦斯运移模型。该研究对矿井动力灾害控制及清洁能源开发有重要的理论和现场指导意义。

煤岩层受到开采扰动影响的采动卸荷应力路径表现为最大主应力增加的同时最小主应力减小的综合过程。项目以试验研究、理论分析与数值模为主要研究手段，综合考虑中间主应力效应和采动卸荷应力路径对煤岩变形破坏和渗透率的影响。通过开展真三轴采动卸荷煤岩的力学与渗流特性试验，研究中间主应力、最小主应力、卸荷条件、最大主应力加荷速率、最小主应力卸荷速率对煤岩强度特征、能量演化特征、扩容特征、损伤变形特征、破坏模式及渗透率的影响。结合强度理论，分析中间主应力、初始最小主应力对砂岩卸荷破坏时峰值强度的影响；采用粒子群算法对其初始权值和阈值进行优化，将粒子群算法良好的全局寻优能力与BP算法良好的局部寻优能力相结合，开展PSO-BP神经网络对岩石强度进行预测；对比考虑初始最小主应力和未考虑初始最小主应力的非线性Mohr-Coulomb准则的拟合结果，从而对非线性Mohr-Coulomb准则进行改进，建立考虑初始最小主应力影响的非线性Mohr-Coulomb准则。结合能量变化理论，分析中间主应力和卸荷对砂岩变形破坏不同阶段的影响，探究中间主应力和卸荷作用对砂岩扩容行为和能量演化的影响。引入平均弹性应变能转化率和平均耗散能转化率表征出中间主应力和卸荷应力路径的作用形式，分析砂岩的变形扩容历程。模拟不同开采深度的实际工程情况，对砂岩的应力-应变过程、力学特性、裂纹的变化过程以及渗透率演化过程进行研究分析。分析开采过程中应力-裂隙-渗流耦合效应，推导岩样在渐进破坏过程中裂纹体应变、损伤变量、渗透率变化量之间的关系式，揭示中间主应力效应和卸荷应力路径对煤岩变形破坏和渗透特性的影响机制，提出真三轴卸荷条件下煤岩的渗透率计算模型，建立考虑中间主应力效应和卸荷应力路径综合影响的瓦斯运移模型。该研究为矿井动力灾害控制及清洁能源开发提供重要的理论和现场指导意义。