Compression behavior and structure of undisturbed Q2 loess under wet-dry cycles

Abstract

In the Loess Plateau of China, the undisturbed Q2 loess is in a state of wet-dry cycles due to seasonal rainfall and groundwater level fluctuations. The root cause of large deformation and poor stability of engineering foundation caused by wet-dry cycles or load compression lies in the distinctive structure of loess. In this paper, the effects of wet-dry cycles and initial water content on the compression deformation and compression coefficient of undisturbed Q2 loess were analyzed. Based on the structural parameter at the macro-level and the microscopic morphology and pore size distribution at the micro-level, the effects of wet-dry cycles and initial water content on the structure were analyzed from two aspects, and the influence mechanism was discussed. Meanwhile, based on the relationship between microstructure and unsaturation, the impact of wet-dry cycles on the soil–water characteristic curve was determined. The results show that the wet-dry cycles and initial water content were positively correlated with the compression deformation and compression coefficient of the undisturbed Q2 loess, but negatively correlated with the structural parameter and water retention. These parameters were stable under the 2 wet-dry cycles. With the increase in initial water content, the sensitivity of wet-dry cycles to the compression deformation, structural parameter, and water retention gradually decreased. The sensitivity of initial water content to the compression deformation, structural parameter, and water retention gradually reduced with the increasing wet-dry cycles. Moreover, the influence mechanism of wet-dry cycles and initial water content on the macro-parameters and structure was mainly weakening the particle cementation strength. With the increase in initial water content, the decreasing range of the inter-aggregate cementation strength and intra-aggregate cementation strength under the influence of wet-dry cycles decreased. With the increase in wet-dry cycles, the decreasing range of the inter-aggregate cementation strength and intra-aggregate cementation strength under the influence of initial water content decreased.