正冻土中冰透镜体形成力学判据的分析讨论

Review of mechanical criterion for formation office lens in freezing soil

冻结缘是正冻土中从未冻区向冻结区过渡、并且非常薄的冰水共存带.由于冻结缘在正冻土中位置的特殊性和其对冻胀的重要性,从其概念的提出并在试验中得到证实后,基于冻结缘的第二冻胀理论得到了快速发展.通过分析近些年冻结缘的研究现状及冻结缘内冰-水压力关系基本可以发现,由于受到现有观测和测试技术的限制,描述冻结缘的很多参数大多来自于经验.土体在冻结过程中,在温度梯度小的情况下,可以形成不连续的多层分凝冰.只有了解冻结缘的特性才能更深刻了解分凝冻胀.但关于分凝冰的形成判据却有很多种,主要分为两类:一类是以热物理方面作为判据;另一类是以力学方面作为判据.通过对分凝冰形成的各种判据的综合分析和比较,发现用冰压力和未冻水膜压力判断分凝冰形成是比较合理的,而用孔隙压力则因为水压力概念的不清而显得模糊.这些分析将为冻土冻胀理论的研究提供科学参考.

Freezing fringe is a very thin transition zone between the unfrozen zone and the frozen zone,and water coexists with ice. After the freezing fringe was defined,and verified by experiment,the second frostheaving theory based on the freezing fringe developed rapidly because of its special location in the freezing soil and its importance for the frost heaving. By reviewing recent research of freezing fringe and water-ice pressure relation in freezing fringe,we found that many parameters about freezing fringe were almost from experience due to the limited observation and test technologies. It is found that multiply discontinuous ice-lens layers can be formed during freezing when the temperature gradients are small. Frost heaving caused by segregated ice lens can be understood more deeply by analyzing the characteristics of freezing fringe. However,there are many criterions for the formation of segregated ice lens,which can be mainly divided into two categories： one is determined by thermophysics; another is by mechanics. In this paper,through analyzing and comparing various criterions,we find that it is more reasonable by using ice pressure or unfrozen water interface stress to determine the formation of segregated ice lens,and not clear by using pore pressure because of the controversial concept of hydraulic pressure. This will provide a scientific reference for the study of frost heaving theory.