基于PFC3D的高温后不同冷却方式下石英砂岩力学特性模拟研究

Simulation Study on Mechanical Properties of Quartz Sandstone after High Temperature under Different Cooling Conditions Based on PFC3D

摘要: 隧道火灾会使围岩经历高温环境，而消防水冷却会导致高温岩石快速降温，这种骤冷过程产生的热冲击会加剧岩石的损伤。本研究采用PFC3D离散元方法建立石英砂岩的平行黏结模型，通过正交试验与单因素敏感性分析标定细观参数。模拟设置自然冷却与水冷却两种方式，涵盖20℃、200℃、350℃、500℃、650℃和800℃六个温度点，通过参数调整系数间接反映热损伤效应。模拟结果复现了文献中的宏观试验规律：水冷却比自然冷却造成更大的强度损失，在500℃时峰值强度额外劣化率达到16.43%；水冷却使张拉裂纹占比从83.8%升至93.6%，降低了起裂应力门槛值，削弱了能量储存能力。研究建立了细观参数调整系数与损伤指标之间的定量关联，并反演得到了不同温度及冷却方式下细观参数的定量退化系数，为火灾后隧道围岩的离散元模拟提供了参数调整依据。

Abstract: Tunnel fires expose surrounding rocks to high temperatures, and the subsequent firefighting process often involves rapid cooling of hot rocks by water. The thermal shock induced by such rapid cooling can significantly aggravate rock damage. In this study, a parallel bond model for quartz sandstone is established using the discrete element method (PFC3D). The mesoscopic parameters are calibrated through orthogonal experiments and single-factor sensitivity analysis. Two cooling paths—natural cooling and water cooling—are simulated at six temperature levels (20˚C, 200˚C, 350˚C, 500˚C, 650˚C, and 800˚C), and the thermal damage effect is indirectly represented by parameter adjustment coefficients. The simulation results successfully reproduce the macroscopic experimental trends reported in the literature. Water cooling causes greater strength loss than natural cooling, with an additional deterioration rate of peak strength reaching 16.43 % at 500˚C. Moreover, water cooling increases the proportion of tensile cracks from 83.8 % to 93.6 %, lowers the crack initiation stress threshold, and reduces the energy storage capacity of the specimen. This study establishes a quantitative relationship between mesoscopic parameter adjustment coefficients and damage indicators, and provides a set of degradation coefficients for mesoscopic parameters under different temperatures and cooling conditions. These coefficients can serve as a direct reference for parameter calibration in discrete element simulations of tunnel surrounding rock after fire exposure.