Wang Chong, Li Shuangyang, Zhang Tongwei, You Zhemin
School of Civil Engineering and Mechanics, Lanzhou University, Lanzhou 730000, China.
Key Laboratory of Mechanics on Disaster and Environment in Western China, MOE, Lanzhou University, Lanzhou 730000, China.
Materials (Basel). 2019 Mar 26;12(6):992. doi: 10.3390/ma12060992.
The thermomechanical behavior of coal and sandstone during excavation using the freezing method is a new challenge for coal mining and geotechnical engineering. In this paper, the influence of temperature on the mechanical characteristics and fracture patterns of two types of saturated rocks (coal and sandstone) were investigated. A series of laboratory tests, including the Brazilian tensile strength (BTS), uniaxial compressive strength (UCS), and triaxial compressive strength (TCS), were conducted at temperatures of 20, -4, -10, and -15 °C. The results indicated a significant increase in their strength when the temperature was reduced from 20 to -15 °C, especially near the phase-transition point. Then, a theoretical model was proposed to predict rock strength change with temperature, based on the phase-transition theory. To evaluate this model, the predicted results were compared with experimental data, where a good correlation was identified. In addition, four failure patterns were observed in indirect tensile tests (i.e., layer activation, central fracture, noncentral fracture, and central and layer activation), and three types of failure modes in compression tests (i.e., axial splitting, shearing along a single plane, multiple fracturing). The evolution of the rock damage was divided into four stages: Crack closure, fracture initiation, critical energy release, and rupture. These results could be applied to evaluate and predict the mechanical behavior of saturated coal and sandstone during excavation using the freezing method.
冻结法开采过程中煤和砂岩的热机械行为对煤矿开采和岩土工程来说是一项新挑战。本文研究了温度对两种饱和岩石（煤和砂岩）力学特性及断裂模式的影响。在20、-4、-10和-15℃的温度下进行了一系列实验室试验，包括巴西劈裂抗拉强度（BTS）、单轴抗压强度（UCS）和三轴抗压强度（TCS）试验。结果表明，当温度从20℃降至-15℃时，其强度显著增加，尤其是在相变点附近。然后，基于相变理论提出了一个预测岩石强度随温度变化的理论模型。为评估该模型，将预测结果与实验数据进行了比较，发现二者具有良好的相关性。此外，在间接拉伸试验中观察到四种破坏模式（即层激活、中心断裂、非中心断裂以及中心和层激活），在压缩试验中观察到三种破坏模式（即轴向劈裂、沿单一平面剪切、多重破裂）。岩石损伤演化分为四个阶段：裂纹闭合、断裂起始、临界能量释放和破裂。这些结果可用于评估和预测冻结法开采过程中饱和煤和砂岩的力学行为。
