Experimental investigation on hole erosion behaviors of chemical stabilizer treated soil

Highlights

• Reproduce the erosion progression in chemical treated soils.

• Reveal the relationships of stabilizers and the erosion behaviors.

• Compare the anti-erosion performances of different stabilizers.

Abstract

Soil erosion plays a vital role in the performance of hydraulic projections such as earth dams and embankments. To improve the erosion resistance of the soil is crucial for preventing the dam break and assuring the safety of the hydraulic projections. In this study, three chemical stabilizers, i.e., sodium silicate (SS) solution, lignosulfonate (LS) powder, and sodium polyacrylate (PAANa), are used to treat the sandy soil. A set of hole erosion tests to investigate the erosion behaviors in treated and untreated specimens. The experiments collect flux and the mass of eroded particles during the erosion process. These data then yield the relations between hydraulic shear stress and erosion rate. Erosion coefficients, i.e., the critical shear stress (CSS), and the erosion rate index (ERI), are acquired from linearly fitted relation curves between the hydraulic shear stress and the erosion rate. During the erosion experiments, we observe that the erosion continues in untreated specimens and leads to the collapse of the specimens if the experiment is not stopped. On the other hand, erosion in treated specimens stops automatically after a long erosion time, even if the hydraulic gradient is maintained. These results indicate that the stabilizers improve the anti-erosion capability of the soil specimen. The improvement becomes significantly noticeable if the stabilizer content and the curing time increase. Among the three stabilizers tested in the experiments, PAANa performs best in treating the sandy soil since the rate of increase in CSS and ERI reaches 214.4% and 85.4%, respectively, when 1.5% PAANa is added into the specimen. The rates of increase in CSS and ERI are 23.2% and 43.8%, respectively, for the specimens treated with lignosulfonate, given the same other conditions. Based on the results, the choice of the stabilizer is discussed and suggested.

Introduction

Soil erosion generally includes internal erosion and surface erosion. The internal erosion is a common cause of concentrated leak erosion, backward erosion piping, contact erosion, and suffusion, which ultimately lead to the failures of earth-rock fill dams and levees (Fell and Fry, 2013, Liang et al., 2019, Liang et al., 2017, Richards and Reddy, 2007, Van Beek, 2015). In a survey, Foster et al. (2000) reported that approximately half of all dam failures and incidents in their surveys were attributed to internal erosion. In addition to the safety issue, the erosion exacerbates the loss of soil nutrients and water in the ecosystem, sedimentation buildup of surface waterways, deforestation, and others, which ultimately contributes to global change, and the reduction of agricultural and environmental productivity (Panagos et al., 2015, Zuazo and Pleguezuelo, 2008).

Remediating the erodible soil is an approach to prevent soil loss and failures of the hydraulic engineering projects. The erosion resistance of soils dictates their erodibility, governed by interparticle friction, electrochemical, and biological forces (Lundkvist et al., 2007, Tolhurst et al., 2006). Applications of chemical stabilizers to soils have been utilized to improve the frictions and bonding forces between particles, and in turn, the soil erosion resistance. The commonly used chemical stabilizers include lime, cement, gypsum, and fly ash (Lu et al., 2018, Oza and Gundaliya, 2013, Rahardjoh, 2013). These stabilizers are effective for controlling erosion but not readily acceptable since they may lead to the environmental issues such as changing the soil chemistry and groundwater pH, affecting the growth of the vegetation and the quality of the water, et al. (Indraratna et al., 2013, Sunil et al., 2006). Therefore, many research has explored alternative soil stabilizers which not only increase the erosion resistance of the soil but also are eco-friendly (Chen et al., 2015, Farooq et al., 2020, Indraratna et al., 2008, Koohpeyma et al., 2013, Vakili et al., 2018b).

Among the new chemical stabilizers, lignosulfonate has drawn much attention since it is an environmentally friendly, non-corrosive, non-toxic chemical, and does not alter the soil pH (Vinod et al., 2010). For example, Indraratna et al. (2008) proved the effectiveness of lignosulfonate in stabilizing erodible silty sand collected from Wombeyan Caves, NSW, Australia. Vinod et al. (2010) reported that the robust performance of the lignosulfonate is owing to its reduction of the clay double layer thickness by the neutralization of surface charges of the clay particles and the formation of more stable particle clusters by polymer bridging. More recently, Koohpeyma et al. (2013) demonstrated that lignosulfonate improved the erodibility of the clayey sand specimen and reported that adding a few of lignosulfonate to clayey sand can dramatically reduce the coefficient of soil erosion.

The effectiveness of stabilizers may vary in treating different kinds of soils and are also influenced by the content of the stabilizers added and the curing time in the treatment. In this study, we carry out a set of experiments with three commonly used eco-friendly stabilizers, i.e., the sodium silicate solution, the lignosulfonate, and the sodium polyacrylate to investigate their effectiveness. In particular, we prepare the specimens with different contents of the three stabilizers with varying durations of curing. We then examine the erosion resistance of the treated soils under a given stress state in a stress-controlled apparatus.