低温饱和岩石未冻水含量与冻胀变形模型研究

Study of unfrozen water content and frost heave model for saturated rock under low temperature

寒区岩石在季节性温度变化下会经历冻胀融缩过程,研究低温岩石中未冻水含量以及冻胀变形规律是进行寒区工程数值仿真和稳定性分析的关键问题。岩石是不同于土体的脆性多孔介质材料,孔隙中的未冻水含量还无法通过实验直接测量;基于累计孔隙体积分布规律,考虑孔隙水的冻结点变化和未冻水膜的影响建立低温岩石未冻水含量理论表达式,实例证明该计算式具有较高的可靠度。假定岩石为弹性孔隙介质,基于孔隙冰与岩石孔隙间的膨胀耦合关系可计算冰压力;利用应变等价原理将孔隙中的冰压力等效为岩石表面的三向拉应力,从而根据弹性理论建立了有效冻胀力下低温饱和岩石冻胀变形模型。结果表明饱和岩石低温冻胀变形与岩石基质的力学参数、岩石孔隙率以及未冻水含量等因素有关。最后通过与2个已有的室内冻胀变形实验对比,说明本文冻胀变形模型的正确性以及实用性。

Seasonal temperature variation induces cyclic frost heaving and shrinkage of rock in cold regions. The unfrozen water content and frost heave in rock under low temperature are the key problems for numerical simulation and stability analysis of engineering in cold regions. Because rock,different from soil,is a brittle porous medium,its unfrozen water content cannot be directly measured experimentally. Considering the existence of unfrozen water films and the freezing point depression of pore water at low temperature,a theoretical expression of unfrozen water content in frozen rock was established with the assumed distribution function of accumulative pore volume,and the expression was validated to be reliable with examples. Assumed rock as the elastic porous medium,the ice pressure was derived on the condition of volume equality. The ice pressure in pores was considered to be equivalent to the triaxial tensile loads on the surface of rock and a frost heave model was thus established based on the elastic theory. The results show that the frost heaving strain in saturated frozen rock is a function of the mechanical parameters of rock matrix,porosity and unfrozen water content. Finally,the frost heave model was validated to be correct and practical by comparison with two existing frost heave experiments.