传导加热下花岗岩中热冲击因子试验测定与演变规律分析

Thermal shock factor measurement and its evolution in granite under conduction heating

岩石热破坏过程中,传热、细观破裂、宏观力学3个因素密切相关,热冲击因子是能够定量表征热对岩石破坏强度的重要物理量,基于热冲击因子可计算获得岩石内某一时刻的动态热应力,进而确定热破坏的具体时刻和热破坏程度。为了研究获得热传递过程中热冲击因子的演变规律,对传导加热下花岗岩内温度场、温度梯度、热冲击因子进行试验测定,研究结果表明:(1)花岗岩在恒定热源传导加热下经历快速升温、缓慢升温、温度相对稳定3个阶段;(2)温度梯度在升温阶段变化较大,温度梯度与热源温度和时间密切相关,单位时间内温度梯度的变化率不同;(3)花岗岩体内热冲击因子具有分布非均质性和无规律性,对岩体结构变化的敏感性,以及传导加热过程中波峰动态移动性;(4)循环加热造成花岗岩体破坏的实质在于矿物颗粒在动态热应力的频繁作用下发生分离,裂隙逐渐萌生、扩展、延伸,形成裂缝贯通岩体,导致岩体热破坏。热冲击因子演变规律的试验测定与研究,以及基于热冲击因子的动态热应力计算和岩石热破坏判别准则,可促进岩石热破坏理论的进一步发展。

Heat transfer,meso-fracture and macro-mechanical properties are closely related to each other during the thermal damage of rocks. Thermal shock factor is an important physical quantity that can quantitatively characterize the strength of thermal damage to rocks,based on which the dynamic thermal stress in rock at a certain moment can be calculated to determine the time and degree of thermal damage. In order to study the evolution of the thermal shock factor during the heat transfer process,the temperature field,temperature gradient and thermal shock factor in granite under conductive heating were experimentally determined. The results show that granite undergoes three stages of rapid temperature increase,slow temperature increase and relatively stable temperature under constant heat source conduction heating,that the temperature gradient closely related to the temperature of the heat source and time changes greatly during the heating stage and the changing rate of the temperature gradient per unit time is different,and that the thermal shock factor in granite is heterogeneous and irregular in distribution and sensitive to rock mass structure and the peak of the thermal shock factor in the conduction heating process is dynamically mobile. The essence of the granite damage caused by cyclic heating is that mineral particles are separated under the dynamic thermal stress and cracks gradually present,expand and penetrate through the rock mass. The experimental determination of the thermal shock factor and the study of its evolution law,as well as the calculation of the dynamic thermal stress and the criterion of rock thermal damage based on the thermal shock factor,can promote the development of rock thermal damage theory.