人工冻融软土微观结构与融沉特性内在机理研究

Large-scale subway construction and operation are facing the problem that when connected aisle is constructed with artificial freezing method the long-term thawing settlement of the soft soil layer is hard to control.However, the internal mechanism between microstructure and thawing settlement characteristics of freezing and thawing soil is the critical scientific issue for controlling the long-term settlement.It is by laboratory test and theoretical analysis that the project will be implemented.And through this project thawing settlement characteristics and its macro model,physical and mechanical properties differences between undistorted soil and thawing soil,microstructure differences and its rule before and after free-thaw of strong frost heave and thawing soil in different freezing and thawing conditions. Needs to be emphasized,soil texture includes silt clay and muddy clay, besides, the different conditions includs different tempareture and virous thawing conditions.For the purpose of researching the affection that microstructure parameters to macro thawing characteristics (thawing settlement coefficient and compression coefficient) the grey relevance theory and rough set method are taken as the main analysis methods, and macro thawing characteristics will be revealed by change rules of microstructure. More over,based on the above methods relevance between microstructure parameters and macro thawing characteristics (thawing settlement coefficient and compression coefficient) could be estimated.Comprehensively considering the microstructure affection to thawing settlemnt nonlinear thawing settlement model with microstructure parameters as variables can be established for sake of providing theoretical basis on predicting and controlling long-term settlement of collection aisle constructed by artificial freezing method and road embankment settlement in seasonal frozen soil region. At last but not least, the model will enrich the theory of freezing and thawing soil mechanics.

大规模地铁建设、营运将面临在软弱土层人工冻结法施工联络通道等地下工程的长期融沉控制难题，而冻融土微观结构与融沉特性内在机理是解决长期融沉控制的关键科学问题。本课题拟通过室内试验、理论分析，研究具有强冻胀、强融沉特性的软土（粉质黏土、淤泥质黏土）在不同冻融条件下（温度、解冻条件）冻融土的融沉特性、宏观融沉模型，冻融前后宏观物理力学及微观结构的差异性与变化规律；运用灰色关联度分析和粗糙集理论，研究各微观特征参数对宏观融沉特性（融沉系数、压缩系数）的影响，以微观结构变化揭示宏观融沉特性内在机理，评价微观结构参数与宏观融沉特性（融沉系数、压缩系数）间的关联性；综合考虑土的微观结构对融沉的影响，建立包含微观结构参数的非线性融沉模型。为预测和控制人工冻结法施工的联通道等地下工程长期融沉，以及季节性冻土地区道路路基融沉提供理论依据，并丰富冻融土力学理论。

大规模城市地下工程（如地铁联络通道、盾构进出洞）及矿山井筒利用冻结法施工，面临软土地层人工冻结长期融沉和工后沉降控制难题。为研究软黏土融沉变形的微细观变化机制，从微细观角度揭示人工冻融软黏土融沉特性内在机理，本课题改制了一套基于温度梯度控制、模拟单向冻融的冻胀融沉试验系统，研究了原状软黏土人工冻融特性、压缩系数、热物理特性与水分迁移研究，分析了含水率及应变速率对冻结软黏土强度特性的影响，通过SEM、压汞等方法对软土冻融前后微观结构差异性研究，研究了冻融对软黏土孔隙与颗粒的平均直径、定向性、平均圆形度、丰度、分维的影响规律，基于X-CT技术，研究了人工冻融软黏土细观特性，首次发现了软黏土封闭系统单向冻融条件下，靠近暖端位置出现的冻融颈缩现象，提出用冻融体积收缩率评价融沉变形量，分析了冻融前后含水率、孔隙比和干密度变化与CTI之间的相关性。研究成果对解决软土地区人工冻结法融沉控制具有重要的理论、实践和学术价值。