Large-amplitude shear tests trace how loess mudflows shift from solid-like to fluid-like behavior

A new laboratory study combines large-amplitude oscillatory shear (LAOS) and Fourier-transform rheology to track how loess slurry responds as deformation increases. Tests across three water contents and frequencies of 0.1–10 Hz identify four strain markers that distinguish the linear regime, nonlinear yielding and the solid–liquid crossover. Water content and loading frequency jointly shape these thresholds. Under the tested conditions, the slurry with 36% water content remained solid-like at 5–10 Hz. The findings provide a strain-resolved framework for studying mudflow behavior, while field-scale thresholds still require validation.

Loess mudflows can evolve from solid-like to fluid-like behavior as they deform. This shift is important to their movement, but it is not necessarily a single, instantaneous change. Conventional steady-state measurements can miss how a soil’s internal structure and energy dissipation evolve during yielding.

In a study published in Continent and Life Evolution, researchers examined loess samples collected from the source area of a liquefaction landslide in Caotan Village, Gansu Province. They prepared slurries with water contents of 28%, 32% and 36%, then tested them at oscillation frequencies from 0.1 to 10 Hz using large-amplitude oscillatory shear (LAOS). Fourier-transform rheology and scanning electron microscopy were used to characterize the samples’ mechanical response and microstructure.

The team identified four characteristic strains that mark stages in the material’s response: the limit of the linear viscoelastic region, the nonlinear transition strain, the nonlinear limit strain, and the strain at which the storage modulus (G′) and loss modulus (G″) cross. Together, these markers track the progression from near-linear behavior through solid-like nonlinearity and toward fluid-like response.

Loading frequency and water content both influenced the transition. As frequency increased, the linear-region limit and nonlinear transition strain generally decreased, while the nonlinear limit and solid–liquid transition strains increased. The measurements also showed a pronounced change around 1 Hz. Higher water content weakened the nonlinear response but could increase the strain required for complete fluidization. At 36% water content and 5–10 Hz, G′ remained above G″ throughout the tests, with no solid–liquid crossover observed.

Microscopy showed a more dispersed soil structure as water content increased, consistent with weaker particle interactions and the delayed fluidization observed in the rheological tests.

“These findings provide a strain-resolved characterization of the solid-liquid transition in loess mudflows and offer theoretical support for hazard assessment and early warning,” the authors conclude.

Key findings include:

1. LAOS and Fourier-transform rheology identify four characteristic strains that track the progression from linear response to yielding and fluid-like behavior.
2. Water content and loading frequency jointly affect the strain thresholds.
3. At 36% water content and 5–10 Hz, the tested slurry remained solid-like, with no G′–G″crossover.

This paper ”Research on nonlinear rheology perspective of loess mudflows based on large amplitude oscillatory shear (LAOS)” was published in Continent and Life Evolution. 

Wang D, Wang X, Wang J, Jia P, Sun D, et al. Research on nonlinear rheology perspective of loess mudflows based on large amplitude oscillatory shear (LAOS). Cont. Life Evol. 2026(2):0012, https://doi.org/10.55092/cle20260012.