Experimental study on the change law of internal erosion and seepage characteristics of inverse grading sand accumulation

Abstract

Inverse grading deposits are commonly found in circulation and accumulation areas of high-speed and long-distance landslides. Due to its special structure of large particle size at the top and small at the bottom and strong permeability, the accumulation is highly susceptible to unstable failure. In this study, using a self-designed device, seepage erosion tests were conducted on seven sets of inverse grading soil samples with continuous and discontinuous particle gradation of particle size 0.075-20 mm to investigate the parameter changes and fine particle migration patterns and laws during seepage erosion of inverse grading sand mass. The results show that the fine particle content and nonuniformity coefficient have an important influence on the seepage erosion of the inverse grading soil samples. The higher the fine particle content, the greater the nonuniformity coefficient and the lower the initial seepage coefficient. After the occurrence of cross-layer tube surge particles, the bottom layer of particle loss is the most, and the particle size of 0.075-0.125 mm particle loss ratio is the largest.The seepage capacity of the inverse grading sand mass depends mainly on the content of fine particles at the bottom. The higher the content of fine particles is, the greater the critical hydraulic gradient will be.In continuous graded soil samples, the relationship between the hydraulic gradient is quadratically related to the percolation coefficient.Soil samples with discontinuous particle gradation are stabilized when the content of fine particles exceeds 45%.After tube gushing occurred in the reverse grain sequence accumulation body, the particles show a migration pattern of stripping-precipitation-stripping-precipitation alternately eroded particles in the middle and lower layers. The study has theoretical and practical significance for the formation mechanism and prevention of such disasters.

Keywords

• inverse grading
• sand accumulation
• fine particle content
• particle migration
• piping
• seepage and erosion