STUDY ON MECHANICAL PROPERTIES AND MICROSCOPIC DAMAGE OF UNDISTURBED LOESS UNDER DRY AND WET CYCLES

Humidification-dehumidification cycle is one of the main causes of engineering diseases in the loess area. It is of great theoretical and engineering significance to explore the mechanism of the humidification-dehumidification cycle to damage the loess structure. In this paper, the loess in Yan'an area is taken as the research object. The undisturbed loess humidification-dehumidification cycle tests with different water contents and different times are carried out to analyze the change rules of porosity, shear strength and parameters of loess induced by dry and wet cycles. NMR technology is used to obtain the damage evolution of crack development in loess. The results show that with the increase of the times of dry-wet cycling, the soil exhibits a gradual increase in porosity, a decrease in the liquid limit and plasticity index, and a basically constant plastic limit. The reason is the dynamic changes in the internal particles loess damage. The increase of dry-wet cycling times and water content weakens the cementation of the soil particles, which reduces the shear strength, cohesion, and internal friction angle. When the water content of the sample exceeds the plastic limit, the decline becomes more obvious. The NMR of the loess shows that with the increase of the times of dry-wet cycling, micropores smaller than 0.025 μm inside the sample gradually transits to small pore groups of 0.025~0.63 μm and new pores begin to occur.