干湿循环下滑带土强度特性与微观结构试验研究

库区水位周期性波动，巨大的水位变幅使库岸滑坡滑带土处于干湿循环变化之中，而干湿循环作用影响土体的强度特性。基于此，以三峡库区某典型库岸滑坡滑带土体作为研究对象，对经历不同干湿循环次数的土样进行环剪试验、扫描电子显微镜（SEM）试验和核磁共振（NMR）试验，分析干湿循环作用下滑带土强度特性和微观结构变化规律，并初步探讨干湿循环对滑带土强度影响的微观机制。试验结果表明：干湿循环作用下，滑带土残余强度的劣化特性十分明显，且前3次干湿循环导致土体强度衰减幅度较大，之后衰减趋势减弱，土体强度逐渐趋于稳定，同时，黏聚力的劣化效应大于内摩擦角；随干湿循环次数的增加，以叠聚状、凝块状为主的团粒逐渐分散、解体，颗粒间连接由面?面接触逐渐向面?边、面?角接触演化，表现为土体内孔隙数量增多，土颗粒形态变化，粒间距离增加，微小孔隙逐渐向大孔隙演变；干湿循环作用下，滑带土内亲水性黏土矿物吸水膨胀、失水收缩而引发土颗粒、孔隙及胶结物等微结构变化是导致滑带土残余强度劣化的内在原因。

Strength properties and microstructure characteristics of slip zone soil subjected to wetting-drying cycles

Large hydro-fluctuation and periodical water level changes in the reservoir have caused the slip zone soil of the banks to experience drying-wetting cycles, which has a great influence on strength characteristics of soil. In this paper, a series of drying-wetting cycle tests on the slip zone soil from an ancient landslide is carried out. The soil samples after different runs of drying-wetting tests are then used to conduct the ring shear tests, scanning electron microscope (SEM) tests and nuclear magnetic resonance (NMR) tests. The results of these tests can be used to analyze the changes of soil microstructure and strength properties during drying-wetting cycles, and to investigate the microscopic mechanism of changes in strength properties. The research indicates that the deterioration of the residual strength of soil is obvious in drying-wetting cycles. The first three drying-wetting cycles result in a larger attenuation of soil strength, then the decay trend weakens and the soil strength gradually stabilizes. At the same time, the deterioration effect of cohesion is greater than the internal friction angle. Besides, the results also show that the clump-like aggregates are gradually disintegrated with the increase of drying-wetting cycles, and the way of connection of soil particles changes from plane-plane to plane-edge and plane-angle. Meanwhile, under the drying-wetting cycles, the number of pores in the soil increases, the morphology of the soil changes, the distance between the grains increases, and the small pores gradually change to the large pores in soil. The pore and cement microstructure changes of soil particles caused by clay mineral swelling and shrinkage are the causes of deterioration of the residual strength of slip soil under the drying-wetting cycles.