单向冻结时开放条件下饱和砂岩冻胀试验及THM耦合冻胀模型

为研究寒区岩石在梯度温度场中补水条件下的冻胀变形规律,进行了单向冻结时开放条件下饱和砂岩冻胀试验。试验结果表明,单向冻结时开放条件下饱和岩石冻胀过程中,沿冻结方向的冻胀位移变化过程可分为冷缩阶段、原位冻胀阶段、分凝冻胀阶段3个阶段。分凝冻胀阶段冻结锋面趋于稳定,冻胀变形持续增长,与时间基本呈线性关系。此外,分凝冻胀阶段补水量换算的迁移水分凝冻胀位移与冻结方向冻胀位移比较接近。随着平均温度梯度增大,分凝冻胀变形速率增大,且分凝冰位置与平均温度梯度线性相关。然后,建立了考虑孔隙水原位冻胀与迁移水分凝冻胀的THM耦合冻胀模型。模型中,孔隙水原位冻胀计算基于未冻水含量,并引入约束系数表征岩石骨架对孔隙水冻胀约束程度;迁移水分凝冻胀计算基于分凝势理论,水分迁移速率与冻结缘处的温度梯度成正比。模型计算结果与试验结果对比表明,建立的THM耦合冻胀模型能够比较准确地计算单向冻结时开放条件下饱和岩石冻胀位移,并能够模拟出分凝冻胀时分凝冰层引起的位移突变及分凝冰位置,可用于寒区冻胀敏感性岩石开放条件下冻胀变形计算。

Frost heave experiments on saturated sandstone under unidirectional freezing conditions in an open system and coupled THM frost heave model

To study the frost heave of rocks in cold regions under temperature gradient with water supply, the frost heave experiments on saturated sandstone under unidirectional freezing conditions are conducted in an open system. The results show that the variation process of the frost heave parallel to freezing direction can be divided into three stages during the freezing process of rocks under unidirectional freezing conditions in an open system, namely, thermal contraction stage, in-situ frost heave stage, and segregation frost heave stage. During the segregation frost heave stage, the frost front tends to be stable, and the frost heave increases continuously in an approximately linear relationship with time. Moreover, the frost heave calculated by water migration amount is close to the measured frost heave parallel to freezing direction during the segregation frost heave stage. The segregation frost heave rate increases with the increase of the average temperature gradient, and the location of the segregation ice is in a linear relationship with the average temperature gradient. Furthermore, a coupled THM frost heave model considering the in-situ frost heave of pore water and the segregation frost heave of migrating water is proposed. In the model, the calculation of the in-situ frost heave is based on the unfrozen water content, and a constraint coefficient is introduced to consider the constraint extent of the rock skeleton to the frost heave of the pore ice. Besides, the calculation of the segregation frost heave is based on the segregation potential theory. Comparisons between the experimental and calculated results show that the proposed THM frost heave model is reliable to calculate the frost heave of rocks under unidirectional freezing conditions in an open system, and to simulate the displacement mutation due to segregation ice layer. Therefore, the proposed THM frost heave model is applicable to the frost heave calculation of rock with frost susceptibility in cold regions.