"EXPERIMENTAL AND NUMERICAL EVALUATION OF RECYCLED TIRE CHIPS AS BACKFILL MATERIAL FOR RETAINING WALLS

Recycled tire chips have the properties needed to function as a lightweight retaining wall backfill: low compacted density, high permeability, measurable shear resistance, and the capacity to reduce lateral stress through mass reduction and internal deformation. The reported studies associate tire chips, alone or mixed with sand, with static reductions of approximately 50–60 percent in lateral earth pressure and wall displacement. Under dynamic loading, reported displacement reductions reach approximately 50–65 percent and dynamic earth pressure reductions reach approximately 70–80 percent. The material's engineering behavior is not uniform. Friction angles of 19°–25°, cohesion intercepts of 8–11 kPa, permeability of 1.5–15 cm/s, and K₀ values of 0.26–0.47 describe ranges rather than fixed design constants. Initial compressibility is the key behavior requiring control, while reduced compressibility during subsequent unloading and reloading cycles may improve performance after the first loading stage. Recycled tire chips are therefore best treated as an engineered backfill whose performance depends on material type, placement, confinement, drainage, wall movement, and loading history. With these factors incorporated into design and construction verification, tire-chip backfill can provide a technically credible approach for reducing retaining wall pressure and seismic response while diverting used tires into beneficial geotechnical use.  

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