Characterization of biopolymer-treated soils considering soil-water-hydrogel interaction

Abstract

Microbial biopolymers have recently been introduced as a new material for soil treatment and ground improvement. The engineering properties of biopolymer-treated soil are determined by the soil-water-hydrogel interactions, which allows biopolymers to show excellent performances in soil strengthening, reduction in hydraulic conductivity, dust control, reduction in surface erosion, and so on. Typical applications of biopolymer are for surface treatment and building materials, which are sensitive to weathering conditions such as rainfall and temperature. Weathering conditions determine the water distribution in biopolymer-soils as well as the relationship between water content and strengthening effects of biopolymer-soils. Furthermore, with biopolymer-soils’ controllability of water flow, it may be suggested as a hydraulic barrier or grouting material.

The aim of this study is to have an understanding of the water-related properties of biopolymer-treated soil, considering the effects of external conditions on the soil-water-hydrogel interaction. To meet the objective of this study, xanthan gum and gellan gum were used for this study. Soil-water characteristic, pressurized hydraulic conductivity, heavy metal adsorption were main laboratory tests conducted in this study. In order to introduce the applicability of biopolymer-treated soil, additional testing on vegetation growth in a controlled chamber and numerical modeling on rainfall-induced slope failure retention were carried out. Furthermore, based on the experimental data, a potential as a landfill material using of biopolymer-treated soil was also provided. Through the study, biopolymer types and optimal content were suggested for different geotechnical engineering purposes.

The drying and wetting soil-water characteristics show that biopolymer can improve the water storage in soil and reduce the capillary conductivity of soil via water absorbing and holding capacity. The presence of clay admixture can render different wetting behavior of biopolymer-treated soil corresponding to clay types. Even under a high water pressure, the water absorbing and holding capacity of thermo-gelatin biopolymers, allows the treated-soil to be able to hold its structure and restrict the water movement through the soil system. The biopolymer-kaolinite matrix enhances the hydraulic reduction performance of biopolymer. Furthermore, ion adsorbability of biopolymers enhances the heavy metal removability of soil. The metal removability from a contaminated flow increases proportionally with biopolymer concentration.

In general, the water-related properties of biopolymer-treated soil brings a promising future of using biopolymer to improve drought survivability of vegetation and rainfall-induced slope stabilization. In addition, the water flow controllability and ion removability of biopolymer allow biopolymer-treated soil can be used as a hydraulic barrier.