Objective To address geohazards such as earthquake-induced soil-slope instability and landslides, an environmentally friendly biopolymer, xanthan gum, was introduced to construct a new biopolymer-geogrid composite reinforcement unit with the aim of synergistically improving slope seismic performance and overall stability.

Methods Based on the extended Newmark sliding-block analysis principle, and considering the additional chemical bonding provided by xanthan gum and the interface friction correction factor, a limit-equilibrium rotational-control differential equation for slopes under seismic loading was established. Analytical solutions for earthquake-induced slope rotation and displacement were obtained. Experimentally, xanthan-gum-improved clay was combined with geogrids to construct composite reinforcement units. Five groups of scaled shaking-table model tests with different reinforcement lengths, together with unreinforced slopes and conventional geogrid-reinforced slopes, were conducted. Acceleration response, crest settlement, horizontal displacement, and final instability modes were analyzed under stepwise increasing excitation amplitudes.

Results The settlement evolution at the slope crest predicted by the theoretical model agrees well with the experimental measurements. The tests show that soil deformation under seismic loading has a clear elevation effect, and the slope-crest area is most prone to sliding. Under 0.5 g excitation, the crest settlement of the unreinforced slope reaches 81 mm, and an integral deep sliding surface extending to the slope toe develops internally. In contrast, for the slope reinforced with a 70 cm new biopolymer-geogrid composite unit, crest settlement decreases to 16.23 mm, corresponding to a deformation reduction of 74.07%-87.93%. The reinforced slope still maintains nearly 70% deformation-confinement capacity in the complex stress zone in the middle part of the slope, showing better reinforcement performance than the conventional geogrid-reinforced slope.

Conclusion The new biopolymer-geogrid composite reinforcement unit provides both synergistic confinement and damping energy dissipation. Through lateral hoop confinement and polysaccharide-network crosslinking, it restricts soil-particle slip and flow and suppresses upward transfer of seismic energy. This composite reinforcement system can change the slope instability evolution path, transforming the overall deep sliding of an unreinforced soil slope into controlled rear deep deformation, and can provide a reference for seismic reinforcement of slopes.