Evaluation of overburden correction factor (Kσ) of pond ash for liquefaction analysis under earthquake loading

The present experimental study evaluates the overburden correction factor (K<inf>σ</inf>) of different pond ash samples under earthquake loading for liquefaction analysis. A series of 54 stress-controlled cyclic simple shear tests was conducted on pond ash specimens at different overburden pressures and cyclic stress ratios. Cyclic resistance ratio (CRR) was evaluated for each pond ash sample at different overburden pressures using two criteria based on maximum excess pore water pressure and double amplitude shear strain to evaluate the K<inf>σ</inf>. The K<inf>σ</inf> values obtained for the pond ash were compared with the K<inf>σ</inf> values for natural soils (clean sand and sand-silt mixtures). The cyclic resistance ratio (CRR) and K<inf>σ</inf> values were observed to decrease with an increase in overburden pressure from 50 kPa to 100 kPa, and a further increase in overburden pressure to 150 kPa led to an increase in CRR and K<inf>σ</inf> values for pond ash specimens with fine particles dominated matrix. However, an opposite trend was observed for pond ash specimens with coarse particles-dominated matrix. The unique response of K<inf>σ</inf> values for pond ash was found to be significantly different from the already available K<inf>σ</inf> response for natural cohesionless soil (clean sand and sand-silt mixtures) as it unavoidably included the effect of OCR and void ratio along with the vertical overburden pressure.