冻结作用对青藏红黏土及兰州粉土微观结构的影响分析

冻土微观孔隙特征是决定冻土体一系列物理、力学性质的基本参数，冻土中存在的冰晶体其体积受温度影响发生变化会影响到冻土的土体微观结构及孔隙特质发生变化。利用可用于负温冻土观测的新型扫描电镜，通过对青藏红黏土及兰州粉土不同初始条件下的土样冻结前后微观结构进行研究分析。结果表明：冻结作用发生后，冰晶生长对周围土颗粒产生挤压作用，导致周围土颗粒的移动和结构破坏，土中大孔隙的数量增多，加之周围小孔隙补给大孔隙中的冰晶进一步生长，出现局部个别大孔隙体积增大，小孔隙体积缩小的现象，表现在孔隙率上为土体在冻结后孔隙率减小；此外，对于粒径级配不同的土体而言，冻结作用对细颗粒土的土体孔隙的尺寸、形态以及排列方式等方面的影响均大于粗颗粒土；同样，初始含水率决定了冻结作用发生后参与改变土体微观结构的冰晶体生长的"量"的大小，在冻结作用对土体结构性破坏的过程中起重要作用。研究成果定量揭示了冻结作用对不同初始条件下的土体微观结构的影响，为研究冻土宏观力学特性和冻胀机制等提供了理论基础与和试验支撑。

Effect of freezing on the microstructure of Qinghai-Tibet red clay and Lanzhou silt

The microscopic pore characteristics of frozen soil are the basic parameters for determining a series of physical and mechanical properties of frozen soil. The volume of ice crystals in frozen soil changes with temperature, which will affect the microstructures and pore characteristics of frozen soil. Using the newly scanning electron microscope (SEM), which can be used for the research of frozen soil, to analyze the microstructure changes of Qinghai-Tibet red clay and Lanzhou silt before and after freezing under different initial conditions. It was found that ice crystal growth squeezing the surrounding soil particles when freezing. As a result, the surrounding soil particles moved and the original soil structure was damaged, the number of large pores in the soil had increased. In addition, the surrounding small pore replenished water to the ice crystals in the larger pore and made it continue to grow, due to the volume of some individual large pores increasing. After freezing, the porosity decreased and the average diameter of pores increased. In addition, for the soils with different gradations, the effect of freezing on pore size, shape and arrangement in fine-grained soils was greater than that on coarse-grained soils. Similarly, the higher the initial water content was, the greater effect of freezing on soil microstructure was. The initial water content determined the amount of ice crystals which participate in changing soil microstructures during freezing. This results reveal the effect of freezing on soil microstructures under different initial conditions, provide theoretical basis and experimental support for the study of the macro-mechanical properties and frost heave mechanism.