裂隙冻胀压力及对岩体造成的劣化机制初步研究

Preliminary study of frost heave pressure and its influence on crack and deterioration mechanisms of rock mass

岩体在冻融循环下裂隙中会经历冻胀力的萌生、发展与消散,裂隙冻胀扩展和岩体冻胀损伤程度受冻胀力控制,基于热力学、渗流理论、界面力学和弹性理论建立了柱形封闭裂隙中冻胀力演化模型,对考虑水分迁移和不迁移两种情况下的冻胀力量值进行了研究。结果表明:不考虑水分迁移作用下冻胀力随裂隙饱和度g和岩石弹性模量sE增加而迅速增大,当sE>10 GPa且g>94%时产生的冻胀力超过15 MPa,足以驱动任何岩体冻胀开裂,不同岩石裂隙冻胀开裂存在一个对应的临界饱和度ming;考虑岩石的透水性,渗透率低于5×10^(-14) cm^2的低渗透性岩石中裂隙水冻结会产生较大的冻胀水压力,容易引起裂隙冻胀扩展;而在渗透率大于10^(-12) cm^2的高渗透性岩石中,饱和裂隙水冻结难以形成有害的冻胀水压,裂隙冻胀开裂主要是冻结后期在冰-岩界面间的微观未冻水膜中产生的分离压力引起。

It is known that frost heave pressure goes through the process of initiation, development and dissipation when rock cracks under freeze-thaw cycles. Moreover, both the frost extension of cracking and the degree of frost damage of rock depend on frost heave pressure. Therefore, an analytical model is established for frost heave pressure in an idealized cylindrical closed crack, based on the theory of thermodynamics, seepage mechanics, interfacial mechanics and elastic theory. Besides, the effect of moisture migration on the value of frost heave pressure is investigated. Without considering the moisture migration, the results show that the frost heave pressure increases rapidly with the increase of water saturation g in crack and rock elastic modulus Es. Under the condition of Es〉 10 GPa and γ〉 94%, the frost heave pressure exceeds 15 MPa, which is high enough to drive rocks to initiate cracking. In addition, the rock starts to crack once the water saturation reaches its own critical value, ming. For rocks with the low permeability below 5×10^-14 cm^2, a high frost heave pressure can be produced by frozen water in the crack, which easily leads to frost crack propagation. However, for rocks with the permeability above 10^-12 cm^2, the frost heave water pressure could not cause any damage. The main reason for crack frost propagation in high permeability rock is the disjoining pressure in a microscopic unfrozen water film between ice and rock interface after water frozen.