Investigation of Changes to Triaxial Shear Strength Parameters and Microstructure of Yili Loess with Drying–Wetting Cycles

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.

Experimental Study on the Triaxial Compression Properties of Coarse-Grained Filling Soil under Drying–Wetting Cycles

“…Diameter and height of the specimens is Ф300 mm × 600 mm. The samples were prepared via compaction in 10 cm layers, with the density controlled at 2.3 g/cm 3 . According to the volume of the forming cylinder, the coarse-grained soil materials were weighed and placed into the forming cylinder covered with a rubber film.…”

“…The drying-wetting cycle process reflects the cyclic water loss and water-saturation process of the soil. Many studies [1][2][3][4][5][6][7][8] have been conducted on indoor drying-wetting cycle tests and simulation methods. However, there is no one uniform test method at present as a result of the many types of rock and soil, their various properties, and the difficulties associated with drying-wetting treatments, as well as other reasons.…”

Effect of Mica Content on Mechanical Properties of Yili River Valley Loess under the Impact of Freezing and Thawing

“…The impact of freezing and thawing on the properties of the Yili loess focused on its physical, mechanical, and hydraulic properties. Hao et al studied the micro process corresponding to the macro change in the Yili loess shear strength under the dry-wet cycle process [29]. Lv et al investigated how FTCs affected the permeability of Yili loess and conducted a quantitative study of its microstructure [30].…”

Study on the Unified Mechanical Properties of Ili Undisturbed Loess under the Influence of Soluble Salt

“…[22][23][24][25][26][27]. At present, there are many studies on the loess in the monsoon area in the reports [28][29][30][31], and the research on Ili loess mainly focuses on the mechanical properties under cycling test conditions of dry-wet [32,33] and freeze-thaw [34,35], respectively. However, there are few studies on the mechanical properties of Ili loess under the change of soluble salt content.…”