Recycling of paper/wood industry waste for hydromechanical stability of expansive soils: A novel approach

This article presents a sustainable solution to repurpose paper/wood industry waste as a geotechnical construction material. A novel lignosulphonate (LS)-based composite admixture (CA) was used in this study to cope with construction problems pertaining to expansive soils. Surface water infiltration in terms of rainfall and surface water irrigation are the prime factors that cause volumetric change behavior and a drastic reduction in shear strength due to loss in suction that eventually causes failure in expansive soils. Such failures are comprised of complex hydromechanical phenomena and their remediation requires special attention. In this context, this study for the first time deals with the use of LS-based CA as a remedy to such failures in expansive soils considering the hydromechanical properties. To better understand the hydraulic response, the specially designed soil-column model tests (SCMTs) were conducted. Besides, different geotechnical experiments and microstructural analyses were carried out to analyze the hydromechanical behavior of CA treatment against the varying degree of saturation (S_r). The results showed that LS-based CA treatment increases the water holding capacity over a suction range of 78.4 kPa and air entry value (AEV) by 33%. Also, the SCMT showed that the wetting-front depth (WFD) at full saturation in CA treated expansive soil was 4–10% quicker than untreated expansive soil. In addition, for the increase in S_r from optimum to 100%, the decrease in cohesion (c) value for untreated and treated soil was found to be 88% and 39.8%, and the increase in compressibility was 37% and 17%, respectively, highlighting better resistance against S_r. Whereas, the swelling potential was completely eradicated with a significant reduction in volumetric shrinkage by 43% compared to untreated soil. The microstructural analyses showed the development of apparent aggregation with the S_r in untreated expansive soil, whereas the CA treatment-induced better structure with bigger size particles with disrupted inter and intra assemblage pore spaces. The results showed that LS-based CA manifests substantial hydromechanical stability against variation in S_r. Overall, this study provides the scientific basis to the practitioners for the pragmatic use of LS-based CA in treating expansive soil problems.