岩体冻融疲劳损伤模型与评价指标研究

 岩体冻融损伤模型与评价是研究岩体经历冻胀力萌生、发展与消散反复作用后物理力学性质劣化的主要内容，现有对岩体冻融循环后的损伤评价指标主要有孔隙率、纵波波速、静动弹性模量等物理参数。冻胀力对于岩体可等效为三轴拉伸应力，首先基于三向等效拉应力建立岩体冻融疲劳损伤模型，该冻融损伤演化方程与单轴循环拉应力下的疲劳损伤方程虽然具有同样的形式，但物理意义不同。基于动弹性模量的定义，以孔隙率和纵波波速为参变量推导出了统一的损伤变量表达形式，该损伤变量不仅考虑了双物理参数的影响，还能对不同冻融循环次数下岩石的单轴抗压强度进行较好预测，可作为岩体冻融损伤的评价指标。定义动弹性模量损失40%为岩石冻融破坏临界值，利用该临界值可避免通过试验确定最大冻融循环次数，进而结合统一损伤变量对冻融疲劳损伤演化方程进行求解，最后通过2个实例说明该冻融疲劳损伤模型与评价方法的正确性和实用性。

STUDY OF FATIGUE DAMAGE MODEL AND EVALUATION INDEX FOR ROCK MASS UNDER FREEZE-THAW

Frost heaving pressure in rock mass undergoes a process of initiation，development and dissipation under the freezing-thawing condition，which results in the fatigue degradation of the physical and mechanical properties of rock. The freezing-thawing damage model and the damage evaluation method are the key problems for the rock mass in cold regions. There are many evaluation indexes of freezing-thawing damage including the porosity，the longitudinal wave velocity and the elastic modulus. The frost heaving pressure was considered to be equivalent to the triaxial tensile stress for frozen rock mass. A freezing-thawing fatigue damage model was established based on the equivalent triaxial tensile stress. The equation describing the freezing-thawing damage variation has the same expression but the different physical meaning with that obtained under repeated uniaxial tensile stress. A new unified damage variable depending on the p-wave velocity and the porosity was deduced based on the definition of the dynamic modulus of elasticity. The damage variable includes the effect of dual physical parameters，and is a better prediction index for the uniaxial compressive strength under different freeze-thaw cycles. The loss of 40% of dynamic elastic modulus was defined as the damage threshold. With the damage threshold，the maximum failure freeze-thaw cycle was determined. The freezing-thawing damage model was solved in combination with the unified damage variable. Finally，the validity and applicability of the freezing-thawing fatigue damage model were illustrated through two examples.