不同冷却模式下花岗岩强度对比与热破坏能力表征试验研究

Experimental investigations of compressive strength and thermal damage capacity characterization of granite under different cooling modes

不同冷却模式下热对花岗岩的破坏能力不同,其细观破裂程度和宏观力学特性表现也不同。在20℃空气中自然冷却和20℃恒温水中热冲击急剧冷却2种模式下花岗岩单轴抗压强度和表面降温规律的对比试验研究的基础上,引入"热冲击因子",建立不同冷却介质环境下热传递数值模拟方法,从传热角度探究不同冷却介质对花岗岩强度劣化机制,找到能够清晰描述热对岩石破坏能力的物理量,从而对热的破坏能力做进一步的定量划分。研究结果表明:(1)2种冷却模式下,因热冲击急剧冷却模式的换热系数远大于自然冷却的换热系数,热冲击因子数值变大,动态热应力相应也随之变大,试件内部破裂严重,裂隙密度增多,力学强度劣化更严重;(2)20℃恒温水中热冲击冷却模式下,花岗岩的抗压强度仅为20℃空气中自然冷却模式下的抗压强度的85%~90%;(3)不同冷却模式下热传递过程中,花岗岩试件内部形成的温度梯度、热冲击因子、热应力的演化过程和规律一致,其最大值总是出现在靠近试件表面的位置;(4)热冲击因子能较好地表征热破坏能力,花岗岩的单轴抗压强度与最大热冲击因子具有很好的相关性;(5)根据热冲击因子的演化规律,可以确定花岗岩试件内部破裂最严重的具体时间,热冲击因子可以实现对热破坏能力的定量表征。

The thermal damage capacity for granite is different under different cooling modes,and the microfracture degree and macroscopic mechanical properties are also different.Comparative tests of the uniaxial compressive strength and surface cooling law of granite were carried out under two cooling modes of natural cooling in 20℃air and cooling in thermostatic water of 20℃,and a heat transfer numerical simulation method under different cooling medium environments was established by introducing a thermal shock factor which can describe the damage ability of heat to rocks.Strength degradation mechanisms of granite with different cooling media were discussed from the perspective of heat transfer,and quantitative classification of thermal damage capacity is made according to the thermal shock factor.The results show that,due to that the heat transfer coefficient of thermal shock sharp cooling mode is much higher than that of natural cooling,the values of the thermal shock factor and the dynamic thermal stress under the former mode are larger than those under the later mode,which results in more serious cracking,larger density of cracks and worse deterioration of the mechanical strength of the specimen.In the thermal shock cooling mode in constant temperature water of 20℃,the compressive strength of granite is only 85%-90%of that in the natural cooling mode in 20℃air.For different cooling modes,the evolution process and law of temperature gradient,thermal shock factor and dynamic thermal stress formed inside the granite specimen are consistent,and the maximum values always occur near the surface of the specimen.The thermal shock factor can well characterize the thermal damage ability,and the uniaxial compressive strength of granite has a good correlation with the maximum thermal shock factor.According to the evolution law of the thermal shock factor,the specific time of the most serious internal fracture of granite specimens can be determined,and the thermal shock factor can realize the quantitative classification of thermal damage capacity.