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

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.

Destabilization Mechanism and Stability Study of Collapsible Loess Canal Slopes in Cold and Arid Regions

“…During FT cycles, the fragmentation and reorganization of loess particles lead to structural damage, and the development of internal pore space in the soil. With increasing cycles, the loss of the peak strength of loess gradually increases, and the shear strength continues to decrease and eventually approaches a residual value [12,13]. Due to extreme cold and abnormal drought, loess in Northwest China is always under the coupling action of alternating dry and wet and repeated freeze-thaw cycles.…”

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

“…[20,21]. Liu et al showed that the FTCs had a limited impact on the change in the soil stress-strain curve, but they significantly attenuated the peak deviation stress [22]. Li et al studied the changes in the stress and strain before and after freezing and thawing and believed that the interior strength of the soil structures was significantly affected by the FT impacts [23].…”

Seasonal freeze-thaw characteristics of soil carbon pools under different vegetation restoration types on the Longzhong Loess Plateau

“…However, in the context of global climate change, influenced by geographical location, soil texture, and climate, the region exhibits significant seasonal FT from late autumn to early spring each year (Bo et al, 2021). Numerous studies have revealed that the effects of FT cycling processes on soil properties in different areas of the Loess Plateau vary depending on the type of vegetation (Ye and Li, 2018;Wang et al, 2019;Bo et al, 2021;Liu et al, 2021a). Studies have shown that arboreal land soils freeze later than bare land (Bo et al, 2021) and that dam farmland was better able to retain soil moisture during FT, resulting in higher water migration and increment in the soil than slope farmland (Wang et al, 2019).…”

“…Studies have shown that arboreal land soils freeze later than bare land (Bo et al, 2021) and that dam farmland was better able to retain soil moisture during FT, resulting in higher water migration and increment in the soil than slope farmland (Wang et al, 2019). Other studies have shown that FT cycling processes weaken soil shear strength (Liu et al, 2021a) and disrupt the internal soil microstructure (Ye and Li, 2018;Liu et al, 2021a), which in turn affects soil carbon stocks and carbon cycling processes in the region (Bo and Brandt, 2003;Li et al, 2019;Xiao et al, 2019). Over the past few decades, a project known as "the Conversion of Farmland to Forests and Grasses Program" has been put into place in this region to efficiently manage soil erosion and realize ecological restoration and its virtuous cycle (Yang et al, 2022a).…”