:

Liquefaction of saturated sandy soils is a major geotechnical hazard during earthquakes. This study experimentally evaluated the effect of adding 0, 10, 15, and 20% crumb rubber by weight on the liquefaction potential of Firoozkuh 161 standard sand using a cyclic simple shear device. All tests were conducted under saturated conditions (B≥0.96), effective vertical stress σ′v = 100 kPa, relative density Dr = 30%, and cyclic stress ratio CSR = 0.15 (τ_cyc = 15 kPa) at 1 Hz frequency. Excess pore water pressure (Δu) was continuously recorded, and the liquefaction criterion was defined as Δu reaching 95% of initial effective stress (Δu ≥ 95 kPa). Results showed that the pure sand sample liquefied after 12 cycles, while samples with 10, 15, and 20% crumb rubber liquefied after 22, 31, and 29 cycles, respectively. The normalized maximum pore water pressure (Δu/σ′v) decreased from 0.98 in pure sand to 0.85 in the 15% rubber sample. The rate of pore pressure buildup decreased by an average of 40% in rubber-amended samples. The 15% rubber sample exhibited the best performance with a 2.6-fold increase in cycles to liquefaction. Increasing rubber content to 20% did not provide additional significant improvement due to a severe reduction in shear modulus (53% loss compared to pure sand). Overall, crumb rubber effectively reduces liquefaction risk in Firoozkuh sand through pore pressure control and energy absorption mechanisms.