新疆伊犁属典型的季节性冻土区，常年冻土面积比较大，以伊犁谷地压实黄土为地基的建筑物在工程建设期和运行阶段都应将冻融作用的影响考虑在内。因此本文以伊犁谷地压实黄土在冻融循环作用下的水力特征为切入点，通过对不同冻融循环次数下的伊犁谷地压实黄土开展室内试验，得到了土体的无侧限单轴抗压强度、渗透性能参数和微观结构变化规律。主要研究内容及研究成果如下：

（1）针对伊犁谷地压实黄土开展不同冻融循环次数下的无侧限抗压强度试验，结果表明：不同含水率、干密度压实黄土应力-应变曲线表现出相似的形态特征和走势，均可定义为弹塑性-应变软化型曲线，随着含水率的升高应力-应变曲线由强软化型转变为弱软化型；不同含水率、干密度压实黄土的极限强度随冻融次数的增加持续减小，而弹性模量随冻融次数的增加呈波浪式变化，总体表现为衰减趋势；基于损伤力学理论和推广后的Lemaitre等效应力假定原理建立了冻融循环作用下压实黄土冻融损伤模型，并验证了其合理性。

（2）以伊犁压谷地压实黄土为研究对象，开展不同冻融循环次数下的GDS固结渗透试验，结果表明：渗透性受含水率和干密度影响显著，含水率越大渗透系数越大，干密度越大渗透系数反而越小；随着冻融循环次数的增加渗透系数和自重湿陷性系数均增大，含水率越高土体受冻融影响持续时间越长；一般来讲其对应的孔隙比也应该不断增加，但却出现了孔隙比降低，渗透系数反而增大的情况，分析其原因可能是由于冻胀融沉作用使得土中形成了微小裂隙，进一步扩展为裂缝，这就形成了优势流动通路，因而虽然试样孔隙比减小了，但并不影响其渗透性的增强。

（3））以伊犁谷地压实黄土为研究对象，开展不同冻融循环次数下压汞试验和扫描电镜试验，从定量和定性两个方面对土体的微观结构进行分析，结果表明：冻融循环使得土体孔隙向大中孔径孔隙演化，提高土体孔隙体积百分比；冻融循环次数的增加丰富了颗粒间的接触方式，由面-面接触发展为点-面接触和点-点接触甚至出现粒间接触方式，从而增大了粒间孔隙；土中水相变成冰晶体，体积增大，形成冻胀力，挤压周围土颗粒，骨架颗粒产生错动，形成一定的通路，同时骨架颗粒间的胶结作用减弱，为后续渗透作用提供通道；经过冻融作用后，大的骨架颗粒遭到破坏形成中小粒径的土颗粒，同时伴随微裂纹的产生，压实黄土强度也逐渐衰减。通过上述研究方面将黄土力学强度和渗透性与其微观结构联系起来，系统的阐述了伊犁谷地压实黄土冻融劣化机理。

Yili in Xinjiang is a typical seasonal frozen soil area, and the perennial frozen soil area is relatively large. The influence of freeze-thaw action should be taken into account in the construction and operation stages of buildings based on compacted loess in Ili Valley.  Therefore, this paper takes the hydraulic characteristics of compacted loess in Yili Valley under freeze-thaw cycles as the starting point. Through the indoor test of compacted loess in Yili Valley under different freeze-thaw cycles, the unconfined uniaxial compressive strength, permeability performance parameters and microstructure variation of soil are obtained. The main research contents and results are as follows :

(1) The results show that the stress-strain curves of compacted loess with different water content and dry density show similar morphological characteristics and trends, which can be defined as elastoplastic-strain softening curve. With the increase of water content, the stress-strain curve changes from strong softening type to weak softening type. The ultimate strength of compacted loess with different water content and dry density decreases continuously with the increase of freeze-thaw times, while the elastic modulus changes in a wave-like manner with the increase of freeze-thaw times, showing an overall attenuation trend. Based on the damage mechanics theory and the generalized Lemaitre equivalent stress assumption principle, a freeze-thaw damage model of compacted loess under freeze-thaw cycles was established and its rationality was verified.

(2) Taking the compacted loess in Yili valley as the research object, the GDS consolidation permeability test under different freeze-thaw cycles was carried out. The results show that the permeability is significantly affected by water content and dry density. The larger the water content, the larger the permeability coefficient, and the larger the dry density, the smaller the permeability coefficient. With the increase of the number of freeze-thaw cycles, the permeability coefficient and the self-weight collapsibility coefficient increase. The higher the water content, the longer the duration of the soil affected by freeze-thaw. Generally speaking, the corresponding void ratio should also increase, but the void ratio decreases and the permeability coefficient increases. The reason may be due to the formation of micro cracks in the soil caused by frost heave and thaw settlement, which further expands into cracks, thus forming a dominant flow path. Therefore, although the void ratio of the sample is reduced, it does not affect the enhancement of its permeability.

(3) The compacted loess in Yili Valley was taken as the research object, and the mercury intrusion test and scanning electron microscope test under different freeze-thaw cycles were carried out. The microstructure of the soil was analyzed from both quantitative and qualitative aspects. The results show that the freeze-thaw cycle makes the soil pores evolve to large and medium pore size pores, and increases the percentage of soil pore volume. The increase in the number of freeze-thaw cycles enriches the contact mode between particles, from surface-to-surface contact to point-to-surface contact and point-to-point contact and even inter-particle contact, thus increasing the intergranular pore. The water phase in the soil becomes ice crystal, the volume increases, the frost heaving force is formed, the surrounding soil particles are squeezed, the skeleton particles are displaced, and a certain path is formed. At the same time, the cementation between the skeleton particles is weakened, which provides a channel for subsequent infiltration ; after freezing and thawing, the large skeleton particles are destroyed to form small and medium-sized soil particles. At the same time, with the generation of micro-cracks, the strength of compacted loess gradually decreases. Through the above research, the mechanical strength and permeability of loess are related to its microstructure, and the mechanism of freeze-thaw deterioration of compacted loess in Yili Valley is systematically expounded.

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