Geotechnical properties of problematic expansive subgrade stabilized with guar gum biopolymer

This article presents a comprehensive study on the geotechnical behavior of problematic expansive subgrade stabilized by guar gum (GG) biopolymer. In this regard, many geotechnical tests were conducted (such as consistency limits, Proctor compaction, unconfined compressive strength (UCS), California bearing ratio (CBR), and resilient modulus tests) on expansive soil treated with varying GG contents (i.e., from 0 to 5%) and aging periods (0–60 days). The results show that GG treatment increases soil consistency and optimum moisture content, whereas the maximum dry density decreases. The stress–strain behavior, UCS values, and CBR tend to increase with the increase in GG content and aging period, highlighting that GG induced better load-carrying capacity against the imposed loading while retaining the ductile behavior. At 60 days of aging the UCS value at 1.5% GG was found to be increased by 342%, elastic modulus by 309%, energy absorption capacity by 250%, and soaked CBR by 176%, transforming the soil into a better-quality subgrade for pavement construction. The stabilization mechanism showed that the inclusion of GG results in the formation of hydrogels which induce a covering effect, that not only clogs the pore spaces but also binds the soil particles in the soil matrix upon hardening, thus reducing the swelling potential and greatly enhance the soil’s strength parameters. Besides, the GG biopolymer exhibits resistance to degradation and exhibits slight improvement considering the long-term aging effects of up to 365 days. Overall, the GG treatment provides a green sustainable approach to mitigate the adverse expansive subgrade problems.