中文摘要：

研究目的：冻结法施工以其止水性好、强度高等优点广泛应用于软土地区地铁联络通道施工，但是冻结法施工后，冻融循环作用将影响地基土的工程性质，因此有必要针对地铁冻结法工后融土进行深入研究。基于地铁联络通道冻结法施工背景，本文对冻结法工后冻融软土的微观结构进行电镜扫描试验，定性描述饱和软土经历冻融循环后微观结构的孔隙特征、颗粒特征和结构连接方式，同时基于Image—ProPlus图像分析软件对冻融软土微观结构中孔隙直径、孔隙面积等微观结构参数进行分析。研究结论：（1）冻融循环后，微孔隙（d〈0．5μm）含量减小，较大尺寸孔隙（d≥1μm）数量增加，面孔隙比有增大趋势；软土经历冻融后孔隙结构变得更为复杂，表现为孔隙平均分形维数的增加；（2）随着冻结温度的降低和冻融循环周期的增加，颗粒间孔隙体积增加，絮凝结构更加明显，结构连接作用受到一定程度的弱化；（3）冻融土微观研究成果可以解释其宏观动力特性的变化，为控制冻结法施工后的长期沉降提供依据。

英文摘要：

Research purposes ： Freezing method is applied to the construction of cross passage of metro tunnel in coastal soft soil area, which highlights its good sealing performance, high strength and other advantages. However, in the construction of metro tunnel with freezing method, the freeze - thaw circulation will affect the engineering properties of soil. The further study on dynamic properties of frozen -thawed soil is necessary. Based on the freezing method construction of the subway connecting passage, this paper scanned the microstructure of artificial frozen - thawed soil through electron microscope, qualitatively described the pore characteristics of the microstructure, particle characteristics and structure mode of connection of the saturated frost - thawed soft soil, and analyzed the pore diameter, pore area, and other microstructure parameters of artificial frozen - thawed soft soil under microstructure based on Image - Pro Plus analysis software . Research conclusions： （ 1 ） After the freezing and thawing, the content of micropores （ d 〈 0.5μm） decreased, the number of larger pore size （d ≥1μm ） increased, surface porosity ratio had developing trend; after freezing and thawing, the pore structure of soft soil became more complex, the performance of the average pore fractal dimension increased. （2） With reduction of the freezing temperature and increase of freezing thawing cycles, the inter - particle pore volume increased, the flocculent structure was more obvious, the role of structural connection had a certain degree of weakening. （3） The macroscopic dynamic characteristics can be explained from the microcosmic angle, which can provide the basis for controlling long term settlement after the construction of freezing method.