Accumulation and permeability characteristics of inverse grading deposit in high-speed and long-distance landslide

Abstract

Earthquakes and other disasters can lead to the formation of a large number of inverse grading landslide deposits, which can cause secondary disasters such as landslides and debris flows under rainfall conditions. It is of great value to study the accumulation and permeability characteristics of the landslide deposits in order to reduce the risk of piping and slumping. This paper classifies and statistically analyzes the accumulation characteristics of typical high-speed and long-distance landslides inverse grading deposits around the world, and obtains their layered accumulation characteristics. On this basis, an experiment was conducted to investigate the permeability characteristics of inverse grading stacking structures, considering the factors of seepage time, fine particle content, and discontinuous gradation. The results indicate that the inverse grading deposits can be classified into three distinct layers, i.e., carapace, body facies, and basal facies. The cumulative distribution curve of particles is shifted from the left to the right, with the content of coarse particles rising in a sequential manner, with no crossover between the curves. The slope of each layer is distinct, and the phenomenon of particle size reduction occurs. It was found that the permeability coefficient varied with seepage time and was negative exponential correlation and closely related to fine particle content. When the content of fine particles in the basal facies is less than 40%, the permeability coefficient of the body facies and the carapace increases by up to 21.4 % with time. Conversely, they all begin to decline over time, with decreases of up to 50% or more. In the context of discontinuous gradation, the sensitivity of the permeability coefficient to the time factor is positively correlated with the fine particle content, exhibiting a discontinuous range of up to 7.01 times. Regression analysis indicates that the permeability coefficient of the inverse grading deposits is highly linearly correlated with the mean particle size and exhibits a negative exponential correlation with the uniformity coefficient.