基于土体破裂驱动力变化的冰透镜体形成机制研究

Frost heave, which caused by the formation of ice lens, is the main damage form to the building during the soil freezing process. As always, the mechanism of ice lens is an important content in both the frozen soil physics and frozen soil engineering. However, the current research lacks a good explanation on the mechanism of ice lens formation. As a result, there exist some shortcomes on the frost heave assessment and prediction. In this project, a self-designed device will be used to carry out the ice lens growth tests, and the ice lens growth process will be measured accurately. Combined with the acoustic emission parameters, the internal connection between the formation of ice lens and soil failure will be studied. Based on the formation mechanism of the crystallization stress during the freezing process, the driving force of the soil failure during the ice lens formation are expounded, and the ice lens forming criterion can be established from the macro level. This project is hope to solve two scientific problems:1) clarify influence machine of the crystallization stress on the driving force of soil failure ; 2) explore the mechanical behavior during the ice lens formation. Through the innovation of the test methods and theoretical, we strive to have a breakthrough on the mechanism of ice lens formation. The results will not only deepen the knowledge on the mechanism of frost heave, but also can applied to frozen soil engineering in regard to the frost heaving evaluation and prediction

冻胀变形是土体冻结过程中对建筑物造成危害的主体形式，而冰透镜体是导致冻胀的核心物质。一直以来，尽管冰透镜形成机制是冻土物理学及冻土工程学都十分关注的重要内容，但已有研究未能对冰透镜体形成过程中的力学行为进行很好的解释，从而造成在冻胀量评估与预测方面存在不足。项目将利用自行设计的冰透镜体生长试验装置开展试验研究，通过准确测定冰透镜体生长过程信息，结合声发射参数揭示冻结过程中的土体破裂与冰透镜体形成之间的内在联系。基于冻结过程中结晶应力的形成机制，阐述冰透镜体形成过程中土体破裂驱动力的变化特征，进而从宏观层面建立冰透镜体形成准则。主要解决两个科学问题：1）明确微观结晶应力对宏观土体破裂驱动力的影响机理及规律；2）探究冰透镜体形成过程中的力学行为。通过测试方法和理论的完善与创新，力争在冰透镜体形成机制上有所突破。项目成果不仅能深化对冻胀机理的认识，而且可应用于冻土工程关于冻胀影响的评价与预测。

为了更好地揭示冰透镜体形成过程中复杂的力学机制，发展与完善冻胀基础理论，本项目以冻结过程中土体破裂驱动力为研究对象，通过对国内外在土体冻结过程中土体破裂驱动力方面的研究进行综合评述，指出了各研究结果之间的异同点，并采用试验监测与理论分析相结合的方法，对不同条件下土体破裂驱动力的变化进行了较为系统的研究，探究了冻结过程中土体孔隙介质中结晶应力的形成和发展过程，建立了微观结晶应力与宏观土体破裂驱动力间的联系。依据冰透镜体形成过程中土体破裂驱动力的变化特征，以及微观结构理论中应力的变化过程，阐明了在土体冻结过程中影响冰透镜体形成的力学机制及主要影响因素，并提出了冰透镜体生长和发展的综合判据。研究表明：冰透镜体形成温度集中在-0.5~-1.5℃。随着温度的降低，土体破裂驱动力逐渐增大并趋于稳定。将孔隙壁上的微观结晶压力与孔隙基质上的均化应力进行了转化，得到了理想状态下，孔隙内所产生的宏观拉力。不同初始含水量的试样内，晶体的结晶应力与均化应力均随着孔径的增大而逐渐降低，随着温度的变化而逐渐增大；当孔隙半径大于某一孔径时，初始含水量的不同对均化应力的影响较大；当孔隙半径小于某一孔径时，初始含水量的不同对于均化应力的变化起次要作用或可能不起作用。研究成果可用于修正冰透镜体形成准则，为建立准确冻胀预报模型提供基础。