Experimental investigation of sediment suspension during earthquake-induced sloshing in water distribution tank

Abstract This study investigates the suspension of sediments accumulated in water distribution tanks during seismic sloshing. Shaking‑table tests were conducted using a small rectangular tank to examine how internal water flow and sloshing amplitude influence sediment uplift. Two experiments were performed under identical vibration conditions: one using tracers to visualize flow patterns, and another using actual sediments to evaluate suspension and resulting turbidity. When sinusoidal input at the tank’s primary sloshing frequency was applied, tracers near the bottom wall rose to the surface once the water level reached the ceiling. Sediment tests similarly showed increased suspension and turbidity. For a water depth of 600 mm, turbidity remained below the water quality standard of 5 mg/L as long as the water level rise did not exceed 126 mm. Turbidity peaked not during shaking but after oscillation ceased. The study also examined the effect of internal columns, finding that sediments beneath column bases were rapidly disturbed, producing turbidity more than twice that observed without columns. Because the seismic motions used correspond to observed ground motions, the results suggest that uncleaned distribution tanks may pose a risk of water supply interruption during earthquakes.