冻融循环作用下岩石疲劳损伤计算中关键问题的讨论

 利用疲劳损伤理论来研究冻融循环条件下岩石的损伤累积在理论上是可行的。主要分析冻融疲劳损伤模型在计算自然条件下岩石冻融损伤时面临的主要问题，包括复杂多变的自然条件下如何简化、近似冻融循环作用，如何选取合适的物理量来计算损伤变量，及如何计算多种机制作用下岩石的冻融损伤。经过分析认为：研究自然条件下的昼夜循环和年度循环对人类工程活动意义最大，根据岩石中饱和度的高低和岩石中未冻水迁移速率的快慢，可分别将昼夜循环和年度循环划分并等效为高周或低周疲劳荷载；冻融循环条件下岩石孔隙率的变化可直接反映冻融损伤的特征，利用缺陷面积和残余应变定义的损伤变量其本质是相同的，均可用孔隙率计算得来；建立冻融循环作用下砂岩的高周疲劳损伤模型和低周疲劳损伤模型，利用模型进行分析表明，在计算自然条件下岩石的冻融损伤时高周疲劳荷载的作用是不可忽略的，并且低周疲劳和高周疲劳荷载的作用顺序具有显著的影响。

Discussion of the key issues within calculation of the fatigue damage of rocks subjected to freeze-thaw cycles

The fatigue damage theory has been proven to be practical in estimating the damage of rock subjected to the repeated action of freezing and thawing. The application of the established frost fatigue model in the calculation of rock damage in the natural environments still faces several challenges，for instance，how to simplify the complicated natural freezing and thawing action，how to define the damage variable reasonably and how to calculate the frost damage of rock caused by the joint action of multiple mechanisms. In this paper，analysis is carried out corresponding to the above challenges. The results indicate that the diurnal and annual freeze-thaw cycle should be the research focus in the engineering activities，which could be classified into the low-cycle or high-cycle fatigue loads according to the saturation degree of rock and the flow rate of unfrozen water in rock respectively. The change of the porosity of rock reflects the underlying frost mechanism，and the damage variables are thus defined by the flaw area and residual strain. The damage generated by high-cycle loads is comparable to that generated by low-cycle loads according to the fatigue damage model. Moreover，the effect of the action sequence of low-cycle and high-cycle loads should be taken into account.