冻融循环作用下危岩体稳定性劣化机制及敏感参数分析

Stability Deterioration Mechanism and Sensitive Parameter Analysis of Dangerous Rock Mass Under Freeze-thaw Cycles

寒区危岩体常因温度起伏而受到冻融循环作用,使其力学性能劣化;而危岩体失稳破坏的实质是主控结构面的起裂和扩展问题,建立考虑断裂韧度劣化的危岩体稳定性分析方法能为寒区危岩体工程的长期稳定性评价提供理论依据。首先,根据断裂力学及冰冻结分离压力理论,考虑冻融循环作用对岩石Ⅰ型断裂韧度的劣化和结构面冻胀力,构建冻融循环作用下危岩体稳定性评价模型;其次,基于圆孔扩张理论分析冰的冻胀力作用对岩石内部微孔洞的细观劣化机制,建立冻融循环作用下抗拉强度的细观劣化模型;再次,通过理论分析Ⅰ型断裂韧度与抗拉强度、断裂过程区扩展半径的关系,得到Ⅰ型断裂韧度在冻融循环作用下的演化方程;最后,通过危岩体工程算例,分析冻融循环作用下危岩体稳定性的劣化规律,同时利用算例讨论了敏感参数对危岩体稳定性系数和冻胀力的影响规律。结果表明:危岩体在冻融环境下的稳定性与岩石的抗拉强度、弹性模量、孔隙率、岩屑流失比等因素相关;在冻融循环作用下,半径较小的孔洞产生的冻胀力更大,对危岩体稳定的劣化作用更显著;岩石的弹性模量与冻胀力呈正相关关系,岩石抗拉强度越小更易发生冻胀破坏;当岩屑流失比大于0.8时,冻融循环作用对危岩体的长期劣化作用较强,控制冻胀破坏产生的岩屑流失对寒区危岩体长期稳定至关重要。

The mechanical properties of dangerous rock mass in the cold region are often deteriorated by freeze-thaw cycles due to temperature fluctuation. The establishment of stability analysis method of dangerous rock mass considering fracture toughness deterioration can provide a theoretical basis for long-term stability evaluation of dangerous rock mass engineering in the cold region. The essence of unstable failure of dangerous rock mass is the crack initiation and expansion of the main structural plane. Firstly, according to the theory of fracture mechanics and freezing separation pressure, considering the deterioration of rock of mode Ⅰ fracture toughness caused by freeze-thaw cycle and the frost heaving force of structural plane, the stability evaluation model of dangerous rock mass under freeze-thaw cycle was established. Secondly, based on circular cavity expansion theory, the meso degradation mechanism of ice frost heaving force on micropores in rock was analyzed, and the meso evaluation model of tensile strength under freeze-thaw cycle was established. Thirdly, the evolution equation of mode Ⅰ fracture toughness under freeze-thaw cycles was obtained by theoretical analysis of the relationship between mode Ⅰ fracture toughness and tensile strength, fracture process zone expansion radius. Finally, the deterioration law of the stability of dangerous rock mass under freeze-thaw cycles was analyzed based on an engineering example, and the influence of sensible parameters on the stability coefficient and frost heaving force of dangerous rock mass was discussed. The results showed that the stability of dangerous rock mass in the freeze-thaw environment was related to the tensile strength, elastic modulus, porosity, debris loss ratio and other factors of rock. Under the action of the freeze-thaw cycle, the hole with a smaller radius produced more frost heaving force and had a more significant deterioration effect on the stability of dangerous rock mass. There was a positive correlation between the elastic modulus of rock and the frost heave force, and the smaller the tensile strength of rock, the more likely the frost heave failure as to occur. When the debris loss ratio was greater than 0.8, the effect of the freeze-thaw cycle on the long-term deterioration of dangerous rock mass was stronger. Therefore, it is important to control the debris loss caused by frost heave failure for the long-term stability of dangerous rock mass in the cold region.