Permanent deformation response of coal ash under long-term cyclic loading

Abstract

This study presents the experimental investigation on the effect of loading frequency on the long-term cyclic response of coal ash under as-compacted conditions by performing cyclic triaxial testing. The specimens were prepared using the moist tamping method at 95% MDD (maximum dry density) and OMC (optimum moisture content) of coal ash. The frequency varied from 0.1 to 9 Hz at a cyclic stress ratio (CSR) of 0.15. The effective confining pressure was kept as 70 kPa for all the cyclic triaxial tests. The specimens were cyclically loaded for 20,000 loading cycles simulating long-term cyclic loading conditions. Initially, a static stress of 30 kPa in addition to the confining pressure (70 kPa) was applied before the application of cyclic loading. The cyclic loading was applied in the sinusoidal waveform in purely compressive mode. Total vertical deformation was determined as the summation of elastic/resilient and permanent deformation due to the application of long-term cyclic loading under cyclic triaxial conditions. Permanent deformation is defined as the accumulated plastic strain, which is non-recoverable on the application of cyclic loading. The dynamic modulus and stiffness degradation ratio were also evaluated with respect to the number of loading cycles. The results indicated that permanent vertical strain was found to reduce with frequency from 1 to 9 Hz for all the loading cycles. Dynamic modulus decreased with increasing number of loading cycles for all the frequencies (1−9 Hz), but became constant at a larger number of loading cycles.