Enhancing strength and ductility of xanthan gum–stabilized clayey sand: Impact of polypropylene fiber content and length

The use of Xanthan Gum (XG) as a sustainable, eco-friendly biopolymer stabilizer has recently attracted significant interest in geotechnical engineering. Although XG improves soil cohesion and compressive strength, it often leads to brittle stress–strain behavior with a sudden post-peak strength loss, especially in surface-stabilized soils under low confining pressure. This study aims to enhance the brittle behavior of XG-treated clayey sand by adding Polypropylene (PP) fibers. Three XG contents (0.25 %, 0.50 %, and 0.75 %) and two PP fiber lengths (6 and 12 mm) were tested at two dosages (0.4 % and 0.8 %) to explore how fibers of different lengths and contents reinforce the soil. Unconfined compressive strength (UCS) tests were used to evaluate stress–strain behavior, secant modulus (Esec), modulus at 50 % strength (E50), absorbed energy, post-peak stress ratio, and failure patterns. Microstructural analyses with scanning electron microscopy (SEM) were also conducted to examine the reinforcement mechanism and fiber–matrix interaction. Results showed that adding fibers of various lengths and dosages increased compressive strength, absorbed energy, and post-peak stress ratio, while decreasing initial stiffness. At a fixed fiber length, doubling the fiber content significantly increased the UCS; the optimal dosages were 0.8 % for short fibers and 0.4 % for long fibers. SEM images confirmed uniform fiber distribution and strong bonding among fibers, the XG matrix, and soil particles. The combined use of XG and PP fibers offers a practical, sustainable way to improve the ductility of surface-stabilized soils.