Influence of Non-Cohesive Soils with Induced Structural Heterogeneities on Internal Erosion Due to Suffusion

Research Article

Ann Materials Sci Eng. 2024; 8(1): 1051.

Influence of Non-Cohesive Soils with Induced Structural Heterogeneities on Internal Erosion Due to Suffusion

Ouaga Jean-Bruce Gboga; Athanas Konin*

Civil engineering laboratory, Institut National Polytechnique Félix Houphouët-Boigny (INP-HB), BP 1093 Yamoussoukro, Ivory Coast

*Corresponding author: Athanas Konin Civil engineering laboratory, Institut National Polytechnique Félix Houphouët-Boigny (INP-HB), BP 1093 Yamoussoukro, Ivory Coast. Email: athanas.konin@inphb.ci

Received: June 11, 2024 Accepted: July 03, 2024 Published: July 10, 2024

Abstract

This paper presents an experimental study focused on the behavior of non-cohesive soils presenting structural heterogeneities subjected to internal erosion due to suffusion. The suffusion tests were performed by applying a downward seepage flow under multi-staged hydraulic gradient. Experiments were carried out at the scale of a soil sample. Soil samples with structural homogeneity and soil samples with structural heterogeneities were tested. Homogeneous soil samples were used for comparison. Two heterogeneity configurations based on fines content (15% and 25%) and density index (ID = 0.1 and ID = 0.4) were tested. measurements of flow velocity, total eroded mass and erosion rate were carried out.

The analysis of results obtained has shown that soils with induced structural heterogeneities are more erodible than soils with homogeneous structure, independently of the fines content and the density index. The specimens with low density index (ID = 0.1) are more erodible than those with medium density index (ID = 0.4).

Introduction

Earthen hydraulic structures, such as dams and dikes, present a high risk of failure due to internal erosion. According to Foster et al. [1], 46% of embankment dams failure is due to internal erosion. Moreover, during ERINOH project [2], it was shown that internal erosion is the main mechanism of failure of embankment dams. In addition, these structures were mostly built based on the hypothesis of homogeneity of soil layers [3-6]. However, earth dams sometimes present heterogeneities created during their construction due to particle segregation or during their rehabilitation/reinforcement due to the addition of new soil layers to existing ones [7]. The study of the effect of soil heterogeneity on internal erosion therefore appears to be essential to better understand and predict the behavior of earthen hydraulic structures.

Thus, several research on suffusion based on laboratory tests have been carried out by subjecting soil samples to different levels of hydraulic gradient under ascending or descending water flows [8-13]. The main results highlighted the impact of different factors on the internal stability of soils, such as geometric conditions (granulometric distribution, grain size, constrictions size, etc.) and hydraulic conditions (hydraulic gradient, direction of flow, etc.). Most of this research has focused on homogeneous samples.

Few research has been devoted to studying the influence of soil structural heterogeneity on suffusion. Luo et al. [14] carried out laboratory tests to study the influence of discontinuous grain size gravel in a soil layer on the suffusion process. The results showed that the presence of gravel in the soil led to a significant reduction in the hydraulic gradient, and an increase in soil porosity. This facilitated the migration of fine particles. Oueidat et al. [15] studied the effects of structural heterogeneity and fine particles content of soil on suffusion initiation. The results showed that the central heterogeneity configuration (coarser particles in the middle of the sample) is more susceptible to suffusion than the downstream one (coarser particles in the lower part of the sample). Deng et al. [16] investigated the internal erosion of gap-graded sandy gravels with different gap ratios, fines contents, and coarse particle morphologies. They founded that increasing the gap ratio could reduce the internal stability of soil and promote the mechanical instability. Fines content affected the permeability and internal stability of soil by altering the filling state of inter-granular pores and the constraints on fine particles.

This paper aims to investigate the influence of non-cohesive soils with induced structural heterogeneities subjected to internal erosion due to suffusion. To do this, homogeneous soil samples and soil samples with structural heterogeneities are tested.

Materials and Methods

Characteristic of Tested Soils

The tested soil samples consisted of Hostun sands commonly used in erosion tests [13,17]. Two types of Hostun sands served as basic material were used to prepare homogeneous and heterogeneous specimens. Sand 1 (fine fraction) noted HN34, is composed of particles with a diameter less than 500 mm. Sand 2 (coarse fraction) noted HN1/2.5, is made up of particles with a diameter greater than 800 mm. The particle size distribution curves are given in Figure 1 and their characteristics in Tables 1.