三轴蠕变扰动作用下含瓦斯煤岩损伤模型研究
A damage model of gas-bearing coal under triaxial creep disturbance
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摘要: 为研究不同应力状态下蠕变煤岩在开采扰动下的瓦斯渗流变化规律, 采用自主研发的RRTS-IV型岩石蠕变扰动效应试验系统, 开展三轴蠕变扰动渗流试验, 基于扰动损伤影响下的Burgers蠕变模型和改进的加速蠕变元件, 建立煤岩蠕变模型, 并进一步推导应力−渗透率关系公式。试验结果表明: ①瓦斯压力不变时, 围压增大使渗透率降低, 轴压超过应力阈值后渗透率迅速增大, 该阈值介于稳定与加速蠕变阶段之间, 低于长期强度; ②围压不变时, 随着初始瓦斯压力增大, 煤样初始渗透率降低, 此时应力对渗透率的影响弱于煤样的解吸、吸附对煤样内部膨胀变形的作用, 但随着有效应力的增大, 有效应力的作用将会占据主导作用; ③静态应力不变时, 持续扰动引起煤岩损伤并最终破坏, 并经历减速蠕变、稳定蠕变、加速蠕变3个阶段, 且静载应力水平影响初始蠕变状态及抗扰动能力; ④基于蠕变扰动试验, 将Burgers体模型与改进的加速蠕变模型元件串联, 考虑扰动损伤, 联立渗透率−应变关系, 建立了一种包含损伤的应力−渗透率模型(蠕变模型), 通过拟合数据对比R2均在0.9以上, 验证了模型的合理性。Abstract: To investigate the variation laws of gas seepage in creeping coal rock under mining disturbance at different stress states, triaxial creep disturbance seepage tests were conducted using the self-developed RRTS-IV Rock Creep Disturbance Effect Test System. Based on a Burgers creep model and considering disturbance-induced damage and an improved accelerated creep component, a coal rock creep model was established, and a stress-permeability relationship formula was further derived. The experimental results show that when gas pressure is constant, an increase in confining pressure reduces permeability, while permeability increases rapidly after the axial pressure exceeds a stress threshold. This threshold lies between the stable and accelerated creep stages and is lower than the long-term strength. When confining pressure is constant, the initial permeability of the coal sample decreases with increasing initial gas pressure. At this stage, the influence of stress on permeability is weaker than the effect of desorption and adsorption on the internal swelling deformation of the coal sample. However, the effect of effective stress becomes dominant as effective stress increases. Under constant static stress, continuous disturbance causes damage and eventual failure of the coal, undergoing three stages: decelerating creep, stable creep, and accelerated creep. The level of static stress affects the initial creep state and anti-disturbance ability. Based on the creep disturbance tests, a damage-containing stress-permeability model (creep model) was established by connecting the Burgers model in series with an improved accelerated creep component, considering disturbance damage, and combining it with the permeability-strain relationship. Comparison of fitted data showed R2 values all above 0.9, validating the model.