Effect of Biopolymer Inclusion and Curing Conditions on the Failure Strain and Elastic Modulus of Cohesive Soil

Abstract

This article presents detailed analyzes of the effect of biopolymer(s) inclusion on the mechanical properties of a cohesive soil. The effects of biopolymer type and dosage, curing time and curing conditions on the failure strain, and elastic modulus of soil are studied. Two biopolymers, xanthan gum (G1) and guar gum (G2), were selected, and their dosages were kept at 0.5, 1, 2, and 4% by weight of dry soil mass. To evaluate the effectiveness of biopolymer inclusion under different field conditions, the treated specimens were subjected to two types of curing conditions, i.e., controlled and natural curing for a period of 7, 28, and 60 days, respectively. In controlled curing, specimens were kept inside desiccators maintaining constant temperature and relative humidity; whereas, for natural curing, the specimens were kept outside exposed to daily variations in atmospheric temperature and relative humidity values. Stress–strain curves obtained from unconfined compressive strength tests indicate that biopolymer inclusion leads to more ductile behavior compared to untreated case. Secant modulus values increased with an increase in biopolymer dosage and curing period up to 28 days for natural curing, and no notable variation is observed for controlled curing. Physical binding of the soil particles with the biopolymer gel leads to an improvement in the adhesive strength which results in an increase in secant modulus (Es) values. Desiccator cured specimens exhibited an increase in failure strain values with increase in biopolymer dosage and curing period. Whereas, specimens subjected to natural curing exhibited a reduction in failure strain values with an increase in curing period due to faster dehydration rates. The mechanisms responsible in improving the mechanical properties are described in detail relying on scanning electron micrographs (SEM) of biopolymer treated soil which reveals the distribution and binding of XG/GG strands within the soil mass.KeywordsFailure strainGuar gumSecant modulusXanthan gum