This paper described an improved multi-layer computational method based on fully coupled thermal-mechanical ordinary state-based peridynamics (OSB-PD), which enables simulating fracturing in granite under coupled thermal-hydraulic effects. Four computational layers, i.e., pre-treatment thermal layer (PTL), mechanical loading layer (MLL), interactive thermal layer (ITL), and hydraulic mechanical layer (HML) were included in this method. PTL was used to simulate the heterogeneity of granite materials by creating initial pre-existing microcracks. MLL was utilized to apply borehole pressure, while ITL was designed to generate real-time thermal forces. HML was employed to apply equivalent hydraulic pressure to cracks, and distinguish between thermal-induced and hydraulic-induced damage. Two verification cases, including hydraulic fracturing and sleeve fracturing of granite specimens at different pressurization rates, as well as the steady-state heat conduction of a hollow cylindrical specimen, were simulated to investigate the convergence, capability and accuracy of the numerical method. The proposed method was then applied to the hydraulic fracturing of granite under high temperature and high pressure (HTHP) treatment. The complex interactions among natural pre-existing microcracks, thermal-induced microcracks and hydraulic-induced cracks was properly predicted. The effect of cold water (temperature gradient) on the fracture morphology and breakdown pressure of granite specimens was also discussed. A systematic comparison with the experimental results shed lights to the failure mechanisms of granite specimens subjected to HTHP hydraulic fracturing tests.

本文描述了一种基于全耦合热力-机械普通态近场动力学（OSB-PD）的改进多层计算方法，能够模拟热-水力耦合作用下的花岗岩破裂。该方法包括四个计算层，即预处理热层（PTL）、机械加载层（MLL）、交互热层（ITL）和液压机械层（HML）。PTL 用于通过创建初始预先存在的微裂纹来模拟花岗岩材料的异质性。MLL 用于施加钻孔压力，而 ITL 旨在生成实时热力。HML 用于对裂缝施加等效液压，并区分热致损伤和水力致损伤。两个验证案例，模拟了不同加压速率下花岗岩试件的水力压裂和套筒压裂，以及空心圆柱试件的稳态热传导，以研究数值方法的收敛性、能力和准确性。然后将所提出的方法应用于高温高压（HTHP）处理下的花岗岩水力压裂。正确预测了自然预先存在的微裂纹、热致微裂纹和水力致裂纹之间的复杂相互作用。还讨论了冷水（温度梯度）对花岗岩试样断裂形态和击穿压力的影响。