Abstract

This research examined the drying–wetting cycles induced changes in undrained triaxial shear strength parameters and microstructural changes of Yili loess. The drying–wetting cycles were selected as 0, 1, 3, 5, 10, 20 and 30. Then, we collected Yili loess samples and performed unconsolidated-undrained (U-U) triaxial shearing tests to ascertain the variation in shear strength parameters with drying–wetting cycles. Additionally, we investigated the microstructural changes of Yili loess samples under drying–wetting cycles simultaneously via nuclear magnetic resonance (NMR) and scanning electron electroscopy (SEM). Finally, we established a grey correlation model between shear strength and microstructural parameters. Under U-U conditions, the prime finding was that the loess’s shear strength parameters changed overall after drying–wetting cycles; in particular, the internal friction angle φ dropped significantly while the cohesion c changed only slightly during cycles. For all the cycles, the first cycle gave the highest change. Soil morphology deterioration was evident at the initial stage of cycles. During the entire drying–wetting cyclic process, pore size distribution showed progressive variance from two-peak to a single-peak pattern, while both porosity and the fractal dimension of pores increased gradually towards stability. Soil particle morphology became slowly simple and reached the equilibrium state after 20 drying–wetting cycles. Under cyclic drying–wetting stress, the shear strength parameter changes were significantly correlated to microstructural modifications. This investigation was related to loess in the westerly region. The findings were expected to provide new insight into establishment of the connection between microstructure and macro stress–strain state of loess. To some extent, it provided a theoretical basis for the prevention and control of loess engineering geological disasters in Yili, Xinjiang and other areas with similar climate and soil types.

Highlights

  • The relation curves between principal stress different and axial strain of Yili loess samples after varying numbers of drying–wetting cycles at a confining pressure of 300 kPa (Figure 5)

  • Wetting cycles, we found that: (a) mean pore diameter imposed almost no effect on internal friction angle; (b) as the number of drying–wetting cycles increased, the correlation coefficient increased; mean pore diameter began to be correlated with internal friction angle; (c) mean pore diameter was well correlated with cohesion under cyclic drying–wetting action; (d) the fractal dimension of pores were highly correlated with shear strength parameters during the whole cyclic process

  • The existing studies regarding the change of soil mechanical properties under drying–wetting cyclic action have mainly focused on red soil in southwestern China and loess on Loess Plateau

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Summary

Introduction

Yili basin is located in Yili, Xinjiang, China, which is adjacent to the western border of the Republic of Kazakhstan. It is characterized by low hilly areas, piedmont slopes, and the marginal zones of the desert, with varying thickness from several to nearly 100 m [2,3,4]. The Yili area has abundant precipitation events and has the characteristics of a humid continental mesotemperate climate. The precipitation in this area is mainly concentrated from April to July, accounting for about 51.5–80% of the whole year.

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