Biopolymer stabilization of clayey soil

Abstract

This study investigates the efficacy of sodium alginate (SA), xanthan gum (XG), guar gum (GG) and chitosan (CS) — each applied at five different solid biopolymer-to-water mass ratios (or dosages) and cured for 7 d and 28 d — on the unconfined compressive strength (UCS) performance of a high plasticity clayey soil. Moreover, on identifying the optimum biopolymer-treatment scenarios, their performance was compared against conventional stabilization using hydrated lime. For a given curing time, the UCS for all biopolymers followed a rise–fall trend with increasing biopolymer dosage, peaking at an optimum dosage and then subsequently decreasing, such that all biopolymer-stabilized samples mobilized higher UCS values compared to the unamended soil. The optimum dosage was found to be 1.5% for SA, XG and CS, while a notably lower dosage of 0.5% was deemed optimum for GG. Similarly, for a given biopolymer type and dosage, increasing the curing time from 7 d to 28 d further enhanced the UCS, with the achieved improvements being generally more pronounced for XG- and CS-treated cases. None of the investigated biopolymers was able to produce UCS improvements equivalent to those obtained by the 28-d soil–lime samples; however, the optimum XG, GG and CS dosages, particularly after 28 d of curing, were easily able to replicate 7-d lime stabilization outcomes achieved with as high as twice the soil's lime demand. Finally, the fundamental principles of clay chemistry, in conjunction with the soil mechanics framework, were employed to identify and discuss the clay–biopolymer stabilization mechanisms.

Keywords

• Soil stabilization
• High plasticity clay
• Biopolymer dosage
• Hydrated lime
• Curing time
• Unconfined compressive strength (UCS)