土体冻胀过程中的物理化学效应

Frost heave has been infesting for long the infrastructure and its development in the cold regions. Although extensive research efforts have been made to gain insights into the problem, many issues related to the ice lens formation and moisture migration during the frost heave remain to be unresolved. Current research results indicate that the microscale physiochemical interactions in the soil pores can exert important controls on the ice lens formation and moisture migration in a freezing soil. The current theories of frozen soils, however, fail to address these complicated physicochemical interactions to a sufficient extent. This research is proposed to investigate the effects of the physicochemical interactions on the ice lens formation and moisture migration during soil freezing processes. Experiments are carefully designed and performed to characterize the effects of the physicochemical interactions on the frost heave under various thermal gradients and freezing rates. Based on the continuum theory of porous media, a chemo-mechanical coupling theory is developed, which can be used to describe effectively the freezing and thawing processes of soils. In this context, explicit mathematical formulations are developed for flagging the initiation of ice lens and describing the moisture migrating process. The proposed formulations are then calibrated and validated using the experimental data. Based on the proposed theory, a FEM-based numerical procedure is developed for analyzing the initial and boundary value problems related to frost heave and soil freezing and thawing processes. A series of model tests are conducted to simulate the frost heave under various conditions, and the results are used to validate the proposed numerical procedure. Expectably, the proposed research will have strong theoretical and practical bearings on resolving the issues related to frozen soils.

土冻胀问题长期困扰着我国寒区工程建设活动。尽管人类对土冻胀机理有了较为深入系统的认识，但有关土冻胀过程中冰透镜体的形成条件以及水份的迁移机制问题仍然悬而未决。最新研究表明，正冻土中微观物理化学作用对冰透镜体形成与水份迁移有着决定性的影响，然而目前的冻土理论仍无法充分描述这些物理化学效应。本项目重点研究土体在冻胀过程中物理化学作用对冰透镜体形成以及水份迁移过程的影响机制与规律。在前人研究基础上，基于室内试验，研究不同温度梯度和冻胀速率下物理化学作用对土冻胀过程的影响机理与规律；基于多相多组份岩土介质力学理论，建立能描述土体冻融过程的多过程耦合理论模型，提出反映冰透镜体形成条件以及描述水份迁移过程的数学表达式，并对所建的理论模型进行校正和验证；建立有关土冻胀问题的数值模型与分析方法，并基于模拟土冻胀过程的小型模型试验，验证所建的模型和方法。为我国寒区工程建设以及地下环境保护提供理论依据。

随着我国西部大开发战略的实施，在青藏高原的多年冻土区，许多重大工程正在不断地实施。而困扰这些工程建设的主要问题之一就是在扰动下地下永久冻土层的破坏以及地表土的冻胀-融沉问题。因此阐明冻胀机理及其过程机制是解决寒区有关土体胀融问题的关键。本研究通过开展室内试验和理论分析，阐明了土颗粒与孔隙水之间的物理化学作用对土体冻胀过程的影响机制及规律，研究了温度梯度、冻结速率、土样高度和压力对冻胀的影响并识别出影响冻土中冰透镜体形成及其空间分布的关键影响因素；在此基础上建立了能描述土体冻融过程的多过程耦合理论模型，提出反映冰透镜体形成条件以及描述水份迁移过程的数学表达式；推导出冻土的有效应力或粒间平均应力的数学表达式，建立反映冻土平衡状态的温度、压力、含冰量、未冻水盐浓度等参量间的数学关系；并提出有关土冻胀问题的数值分析方法，为解决寒区的土体冻胀融沉问题提供理论依据与技术支持。