Abstract: Cyclic properties of fly ash under earthquake load are crucial for the safety of stock yard and filling bodies. In this paper the cyclic deformation, cyclic pore pressure, failure mode and modulus degradation of fly ash under earthquake load were investigated via triaxial test under effective consolidation stress of 50-200 kPa and three different cyclic stress levels. The cyclic shear stress was calculated based on Seed-Idriss's equation. Results revealed that under large cyclic stress level, fly ash failed under the criterion of dual-amplitude axial strain; under medium cyclic stress level and 50 kPa consolidation stress, fly ash failed under the criterion of accumulative axial strain, while when consolidation stress exceeded 50 kPa, fly ash failed under the criterion of dual-amplitude axial strain; under low cyclic stress level, cyclic deformation failure did not occur. At the same cycle, pore pressure ratio decreased with the rising of consolidation stress; pore pressure in fly ash was far below liquefaction criterion when deformation failure occurred. Modulus of fly ash degraded rapidly under large stress level until 10 cycles; under medium cyclic stress level, the modulus degradation index decreased swiftly when cycle number was beyond critical value; degradation of modulus was very small under low cyclic stress level.

Key words: fly ash, earthquake, cyclic deformation, failure mode, pore pressure, modulus degradation