To address the need for enhanced geotechnical performance in gravelly soil stabilization, this study investigated the synergistic effects of guar gum as an additive in enzyme-induced calcium carbonate precipitation (EICP) treatment. Through systematic experimentation combining unconfined compressive strength (UCS) tests, carbonate content quantification, and triaxial analysis, the mechanical behavior of treated soils was evaluated under varying EICP solution concentrations (0–2 mol/L) and curing durations. Results demonstrated that a 1.5 mol/L EICP solution achieved peak strength and carbonate precipitation before subsequent decline, while a 1% guar gum dosage optimized mechanical properties by balancing initial strength enhancement and precipitation efficiency. Scanning electron microscopy revealed microstructural mechanisms wherein guar gum provided heterogeneous nucleation sites for calcite crystals, while its interaction with EICP enabled dual-phase pore filling and interparticle bonding. This synergistic effect created a three-dimensionally reinforced matrix, significantly improving both UCS and unconsolidated undrained shear strength compared to native and EICP-only specimens. The findings establish a theoretical framework for regulating calcite precipitation patterns and enhancing cementation mechanisms in gravelly soil improvement, offering practical guidelines for foundation engineering applications through the combined use of guar gum and EICP.