Effect of Relative Density on Liquefaction Resistance of Sand Under Simulated Earthquake Loading

Soil liquefaction threatens structures in seismic zones, reducing bearing capacity and causing damage. This research examines how relative density affects Firuzkuh sand’s liquefaction resistance under conditions that replicate the 1999 Kocaeli earthquake. Soil samples with relative densities of 0.30 (loose), 0.40 (medium-dense), and 0.50 (medium-dense) underwent 1-g shaking table tests with scaled building models. Cement-stabilized sand columns arranged in a triangular configuration were employed for ground enhancement. Measurements of acceleration, pore-water pressure, and settlement were conducted. Results indicate that increased relative density markedly enhances liquefaction resistance. The peak pore pressure ratio (ru) decreased from 1 in loose sand to 0.55 in dense sand under similar conditions. Foundation settlement was reduced from up to 9 mm in the most critical configuration to under 0.5 mm in the best-performing configurations. The density–settlement relationship was not monotonic: medium-dense sand (Dr = 0.40) produced the largest settlement in some configurations, while loose sand (Dr = 0.30) performed well when column length was sufficient. This study advocates for a minimum relative density of 0.50 for clean sands in regions anticipating strong, prolonged shaking akin to the Kocaeli earthquake. The results furnish empirical backing for performance-based ground improvement design in seismically active regions like Turkey’s Marmara area.