Shear Strength and Microstructure of Intact Loess Subjected to Freeze-Thaw Cycling

Kuan Liu,Wanjun Ye,Hongjun Jing,Kenji Kaneko

doi:10.1155/2021/1173603

Abstract

In the Loess Plateau, seasonal freeze and thaw cause great damage to the mechanical behavior and microstructure of soil, which leads to frequent geological disasters during winter and spring. To investigate the influence of freeze-thaw (FT) cycling (FTC) on the shear strength and microstructure of intact loess, triaxial shear, nuclear magnetic resonance, and scanning electron microscope tests were carried out on soil samples after target FT cycles. The results indicate that the FTC has limited changes to the soil stress-strain curve, but has a significant attenuation effect on the peak deviatoric stress. The peak deviatoric stress was attenuated by FTC but changed insignificantly after ten cycles. The cohesive force decays exponentially with the number of FT cycles, while the internal friction angle increases slightly. Moreover, under FTC, the T2 hydrogen spectra of soil samples showed a multimodal distribution, with the main peak appearing to have two obvious upward shifts that occurred at 6 and 10 FT cycles. Indeed, a depolarization phenomenon related to the directional frequency of soil particles was observed, and the mass fractal dimension of the pore network increased slightly. In an FT environment, the shear strength declines due to accumulated internal microstructural damage. These findings contribute to a better understanding of the response of loess to FTC and provide novel ideas for the prevention of frost damage in loess areas.

Highlights

Loess is a type of Aeolian Quaternary sediment with loose structural features found between Western Europe and East Asia and from North America to South America [1, 2]
After six FT cycles, the morphology of the soil particles became significantly fragmented with mostly edge-to-face or pointto-face intergranular contact forms arranged in the form of overhead structures into wider through-pores
FT tests were performed on intact loess specimens with different water contents. e specimens were tested by triaxial apparatus, nuclear magnetic resonance (NMR), and scanning electron microscopy (SEM). e potential relationships between FTC and soil physical-mechanical behavior and microstructural characteristics and their mechanisms were discussed. e following conclusions are drawn

Summary

Introduction

Loess is a type of Aeolian Quaternary sediment with loose structural features found between Western Europe and East Asia and from North America to South America [1, 2]. Due to differences in test materials and conditions, Advances in Materials Science and Engineering the mechanisms of change in soil shear strength properties due to FTC have not been completely unified [8]. Understanding these properties is important to engineering in seasonally frozen areas. In terms of shear strength parameters, several studies have reported that soil cohesion is reduced after FTC, while the friction angle increases slightly or does not change much [16, 18, 19]

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Discussion

Conclusion