Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Internal erosion in gravel soils and the particle deposition simulation
Zhuomin Li, Pingfan Wang, Xianqi Luo
School of Naval Architecture, Ocean and Civil Engineering
Shanghai, P.R. China

evident reveal; and numerical simulations should be more adjusted forreal engineering scales with the random and heterogeneous propertiesof soil particles fully regarded.
In this research, first, the percolation analytical method wasemployed to evaluate the deposition rate during the internal erosion
process, and the modified constitutive model of internal erosion wasproposed; and then, 6 sets of internal erosion tests of different types ofgravel soils were carried out to investigate the hydraulic behaviors
under seepage flow; after then, the internal stabilities of testing
specimens were analyzed, and for each set of tests its erodible particle
sizes were evaluated; at last, the finite element method (FEM)
paralleled with the percolation method was conducted to study themodified model, and the simulations were analyzed and compared tothe test results. This research provides a fresh view of internal erosion
from microscopic to macroscopic, and it reveals the interactive
mechanisms between particle erosion and deposition. The random andnonlinear characteristics of soil particles are well considered, thus thismethod shows more advantages in application to broadly graded, gap
graded, and nonlinearly graded soils. By means of the percolation
analytical method, the relationships between erosion and deposition canbe determined and regarded in finite element models, and it aids inmore complex and changeable engineering issues of internal erosion.

ABSTRACTInternal erosion is a common damage form occurred in extensive gravel
soils. During the erosion process, the mechanism of particle deposition
exists, but is difficult to survey or evaluate. In this research, first, thedeposition rate of transported soils was studied, and the modified
constitutive model for internal erosion was proposed; second, internal
erosion tests were conducted for gravel soils of different grading
properties; third, the percolation analytical method is adopted toevaluate the internal stability of tested soils, and a modified model ofinternal erosion was verified by the tests.

KEY WORDS: Internal erosion; deposition; seepage; piping test;
numerical modeling

INTRODUCTION
For broadly graded granular soils in hydraulic structures such asembankments dams, levees, downstream drains, and natural granularaccumulations, internal erosion causes a lot of engineering problems
and property loss. Researches (Foster et al. 2000; Xu and Zhang 2009)have investigated several dam failures and determined internal erosion
to be a major contributor. Under a long-term hydraulic condition, fineparticles can be eroded through larger pores; while, some of theliquefied particles can be deposited at the narrower pores; the latter isdifficult to observe and measure by traditional experimental ornumerical methods, but cannot be ignored to some certain
circumstances.
A lot of researchers have carried out piping tests to evaluate theinternal stability of soils (Skempton and Brogan 1994; Kenney and Lau
1985; Chang and Zhang 2014); internal stability criteria have beenproposed considering the gradations and hydraulic conditions of soils(Kézdi 1979; Wan and Fell 2008; Kenney and Lau 1985); various ofnumerical simulations of internal erosion process have been conducted
and analyzed to study the influencing factors (Yang et al. 2019; Jiang etal. 2015; Bi et al. 2021; Zhang et al. 2017). Although there areextensive investigations of internal erosion, the properties oftransported particles need further exploration. The grading
characteristics of soil particles are not comprehensively considered; thedeposition effect during particle migration process requires more

GOVERNING EQUATIONS OF COUPLED SEEPAGE AND
INTERNAL EROSION
Mass-conservation Equations for Internal Erosion
In a represented element volume of the saturated gravel soil, as Fig. 1
shows, the soil matrix can be separated into solid phase and fluid phase;
while, the solid phase can be divided into soil skeletons and erodible
soil particles, and the fluid phase can be classified into water andliquefied particles. For the 4 components, the liquefied particles and theerodible particles can transfer into each other at a certain hydrauliccondition; and the soil skeletons are fixed and not erodible, watertransfers the seepage pressure to other components.
The erodible particles can be separated from the soil skeletons andstart to move at a certain hydraulic gradient. If the velocity oftransported particles is regarded equal to the seepage velocity, themass-conservation equation of the liquefied particles can be expressed

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