Mechanisms of compacted soil deterioration in biopolymer-treated sands under cyclic wetting and drying

Abstract

Biopolymers have received research attention for improving the erosion resistance and strength of coarse-grained soils. Unlike cement-treated soils, however, no standardized tests have been developed to assess the durability of biopolymer-treated soils under cyclic drying and wetting conditions. Therefore, questions remain on their long-term stability. The main goal of this study is to examine the performance of biopolymer-treated sandy soils both over time and with cyclic drying and wetting. This work focuses on Xanthan Gum (XG) as a model biopolymer for treating sandy soils. Compacted biopolymer-treated specimens were subjected to cyclic drying/wetting according to the ASTM code designed for soil-cement mixtures. The specimens were dissected after each cycle to study the mechanism and progression of failure. Furthermore, the biopolymer pore fluid was extracted and studied using rheology and infrared spectroscopy (FTIR) to investigate the effects of drying and wetting on the physical and chemical properties of the biopolymer gel. It was found that the low hydraulic conductivity of the biopolymer-treated sand creates a unique distribution of moisture in the compacted specimens. Rheological investigations indicated a reduction in the yield stress of the pore fluid in the “crust” of the specimens, which played the main role in the failure of the specimens under cyclic drying and wetting. FTIR tests showed evidence of biological degradation of the biopolymer. Cyclic drying and wetting tests were also performed on pure biopolymer gels to further investigate the degradation of biopolymers independent of the soil.