Xanthan Gum-Stabilized Soils as a Sustainable Material for Coastal Restoration: Mechanical and Erosion Performance

This study evaluates the feasibility of 1% xanthan gum-treated sandy soils (natural sand and recycled glass sand) as sustainable materials for coastal restoration applications. The long-term durability and water erosion resistance of treated soils were systematically investigated through wet–dry cycling, pH durability testing, Erosion Function Apparatus (EFA) tests, and rainfall simulation experiments. Particular attention was given to the combined use of xanthan gum and recycled glass sand (RGS) as an environmentally friendly alternative to conventional geomaterials. The results demonstrated that soil gradation and soil type significantly influenced the performance of the xanthan gum–soil matrix. Xanthan gum-treated pure recycled glass sand specimens lost their structural integrity within one day of water immersion, whereas xanthan gum-treated natural sand specimens resisted water erosion for up to 20 days. In contrast, xanthan gum-treated mixed sand (XTMS), prepared using RGS and natural dredged sand, exhibited significantly improved durability and erosion resistance. Although the unconfined compressive strength (UCS) of XTMS decreased by approximately 70% after three wet–dry cycles, accompanied by only 0.21% soil loss, the specimens maintained structural integrity throughout the testing period. The UCS results further indicated that XTMS exhibited relatively good durability under artificial seawater conditions but experienced significant degradation under acidic and alkaline environments. EFA results classified XTMS as having medium erodibility, representing a substantial improvement in water erosion resistance compared to untreated sand. In addition, rainfall simulation tests demonstrated that XTMS specimens were capable of withstanding very heavy rainfall conditions (120 mm/h) with minimal soil loss. Overall, the findings suggest that the combined use of xanthan gum and RGS provides a promising, sustainable, and environmentally friendly approach for improving soil stability and erosion resistance in coastal restoration applications.