Monotonic Behaviour of Pond Ash

Abstract

The monotonic behaviour of pond ash was comprehensively investigated under the critical state soil mechanics (CSSM) framework using an extensive triaxial testing programme. In order to investigate the influence of specimen reconstitution, two techniques were employed in the reconstitution of pond ash. One was a newly developed paste deposition (PD) technique aimed at simulating the wet disposal of pond ash in ash ponds, and the other the moist tamping (MT) technique which has been widely used for the reconstitution of sand and sand with fine. The particle size distribution of the pond ash was analysed by a laser particle analyser before and after triaxial testing to investigate particle breakage. Also, the tested pond ash was reused for triaxial testing, aiming to investigate the influence of particle breakage on its behaviour. Test results indicated that the pond ash generally exhibited similar monotonic behaviour to that of sand and other granular geo-materials, and the CSSM framework is applicable to predicting the behaviour of pond ash, irrespective of reconstitution technique and drainage condition. However, the behaviour of pond ash was also found to be highly dependent on the reconstitution technique. Specifically, the critical state line (CSL) of the MT pond ash in the e-logp' plane was located statistically higher than that of the PD pond ash, whilst the MT pond ash exhibited a higher strength and more dilative/less contractive behaviour than its PD counterpart. Moreover, both the PD and MT pond ash underwent particle breakage during shearing, and irrespective of reconstitution technique, drainage condition and stress history, the amount of breakage, as quantified by the increase in specific surface area, exhibited a unique correlation with the total input energy per unit mass (E), in which the effects of stress and strain could be combined. Although particle breakage introduced bias into the measurement of the void ratio, the bias was so small that the interpretation of the test results was not affected. Furthermore, the CSL of the reused pond ash in the e-logp' plane was located distinctly below that of the original pond ash, and under a given E, the increase in the specific surface area that newly occurred on the reused pond ash was lower than that on the original pond ash.