Collapsible Soil Stabilization Using a Novel Crosslinked Biopolymer Binder: A Multiscale Evaluation

In this study, soy protein isolate, a renewable protein-based biopolymer containing a minor carbohydrate fraction, was formulated into a polymeric binder using polyvinyl alcohol (PVA) and oxidized glucose and applied to improve the hydro-mechanical behavior of collapsible soils. The resulting soy protein–PVA-based binder (CSP) was evaluated against chitosan through laboratory tests including collapse potential, unconfined compressive strength (UCS), consolidated drained triaxial testing, permeability, and microstructural characterization using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). CSP substantially improved the engineering performance of the treated soils. For Soil C, the collapse potential decreased from 9.3% for the untreated soil to 3.0% with only 0.25% CSP. At 1.5% CSP and 9 days of curing, the UCS reached 2367 kPa for Soil C. In consolidated drained triaxial testing, the cohesion of soil C increased from 5 kPa in untreated soil to 734 kPa with 1% CSP, while the corresponding friction angle increased from 24° to 28°. FTIR and SEM observations indicated changes in the chemical environment and composite microstructure after treatment, although FTIR alone does not establish covalent crosslinking. Overall, the results demonstrate the potential of the CSP-based binder to improve the mechanical and collapse behavior of collapsible soils under the investigated laboratory conditions.