Effects of Fly Ash on Liquefaction Characteristics of Ottawa Sand

This paper presents the results of effects of non-plastic fines (Class F fly ash) on liquefaction behavior of Ottawa sand. Stress-controlled cyclic triaxial tests were performed on clean Ottawa sand, fly ash, and sand–fly ash mixtures containing 10, 20, 25, 30, 50, and 70% of fly ash. For the evaluation of the effects of confining pressure on liquefaction resistance, three series of tests were conducted at 34.48, 68.96, and 103.42 kPa initial effective confining pressures, except for pure fly ash. In the case of pure fly ash, tests were conducted only at an effective confining pressure of 34.48 kPa. The reversible shear stress was applied systematically by varying Cyclic Stress Ratio from 0.1 to 0.5. Addition of fly ash to sand resulted in decrease in liquefaction resistance initially and then increase in liquefaction resistance for fly ash contents up to about 20–25%. Increase in fly ash content beyond 25% was seen to decrease the liquefaction resistance.