Harnessing biopolymers for sustainable soil improvement in geotechnical engineering: a state-of-the-art review

This study comprehensively evaluates the principles of using biopolymers for soil improvement in geotechnical engineering and the current literature. First, biopolymers are defined and classified, and their potential as an environmentally friendly, sustainable alternative to traditional improvement materials is emphasized. The interaction mechanisms with fine and coarse-grained soils are explained in detail; the microscopic examination methods used to observe these mechanisms (e.g., SEM, FESEM, ESEM, FTIR, and XRD) are briefly discussed. According to laboratory studies, the mixing method, temperature, biopolymer concentration, curing time, and water content directly affect soil behavior. The literature reports that xanthan gum (XG), a particularly widely used additive, can increase the uniaxial compressive strength (UCS) of clay soils by approximately 400–600% and improve the elasticity modulus by up to 5 times under appropriate curing conditions. In addition, a decrease in permeability coefficient from 10−4 to 10−6 m/s (between 10 and 100 times) and a 60–80% reduction in compression and swelling indices have been achieved. In durability studies, it was determined that more than 60% of the initial strength was retained after 5–10 wet–dry or freeze–thaw cycles. While applicability in field conditions is discussed in numerical and physical modeling studies, data on field applications, long-term performance, and dynamic soil behavior are still limited. This situation highlights the need for interdisciplinary and holistic research to fully evaluate the potential of biopolymers in engineering applications.