实时高温三轴压缩下砂岩强度及破裂特征研究

Study on the Strength and Failure Behaviors of Sandstone Specimens at Elevated Temperature under Triaxial Compression

深部岩石处于高地应力及高温环境中, 使得深部资源开采面临很大挑战, 因此研究高温作用下岩石三轴力学行为具有重要意义。本文综合采用室内试验与数值模拟方法, 分析了实时温度和围压对砂岩强度及破坏特征的影响, 揭示了岩石热裂纹演化规律。首先, 对砂岩试样进行了不同实时温度作用三轴压缩试验, 获得了温度和围压对砂岩试样力学特性的影响规律。其次, 采用三维颗粒流程序 (PFC3D) 构建了砂岩三维数值模型, 通过与常温条件下三轴试验结果对比, 标定了一组能够反映砂岩力学特性的细观参数, 在此基础上开展了砂岩实时高温三轴压缩数值模拟, 模拟结果与室内试验结果相吻合。数值模拟结果表明, 当温度不超过150℃时, 砂岩试样内无微裂纹产生, 峰值强度变化不明显; 当温度超过150℃后, 砂岩试样内开始萌生微裂纹, 低围压条件下峰值强度随温度升高而降低, 高围压致微裂纹的闭合降低了温度对砂岩强度的弱化作用。砂岩破裂形态受温度和围压共同作用, 低围压下高温砂岩呈轴向劈裂破坏, 高围压下呈剪切破坏。

Deep rocks are in high geostress and high temperature environment, which makes the exploitation of deep resources face great challenges, so it is of great significance to study the triaxial mechanical behaviour of rocks under high temperature. This paper comprehensively adopts indoor test and numerical simulation methods to analyze the influence of real-time temperature and peripheral pressure on the strength and damage characteristics of sandstone, and reveals the law of rock thermal crack evolution. Firstly, triaxial compression tests on sandstone with different real-time temperatures were conducted and the influences of temperature and confining pressure on the mechanical properties of sandstone were obtained. Secondly, a three-dimensional numerical model of sandstone was constructed using PFC3D, and a set of microscopic parameters reflecting the mechanical behavior. of sandstone were calibrated by comparing with triaxial compression results at room temperature, on the basis of which a numerical simulation on sandstone under realtime high temperature triaxial compression was carried out, and the numerical results were consistent with the laboratory experimental results. The numerical results show that no microcracks are generated in the specimen and the peak strength changes were not obvious when the temperature does not exceed 150℃; when the temperature exceeds 150℃, microcracks begin to sprout in the sandstone specimen. Under low confining pressure conditions, the peak strength of sandstone decreases with increasing temperature. The closure effect of high confining pressure on microcracks reduces the weakening effect of temperature on peak strength of sandstone. The fracture pattern of thermal sandstone is influenced by both temperature and peripheral pressure. The thermal sandstone exhibits axial splitting failure under low confining pressure, and shear failure under high confining pressure.