Fly Ash as Structural Fill

Field and laboratory tests on fly ash from power plant disposal areas are presented with parameters for design and construction of fly ash embankments. Controlled compaction permits 20% more storage in disposal area and, with proper drainage and slope design, structures can be safely supported on spread footing type foundations. Eight direct shear tests and sixteen triaxial shear tests show ϕ angle related to dry unit weight. The ϕ angle varied from 30° to 40° in the range of 60 pcf to 80 pcf. Unconfined compression on moist fly ash showed a maximum cohesion of 500 psf under ideal conditions, but no cohesion when dry or saturated. Nine consolidation tests showed an average compression index of 0.2 in the range of 2 tsf to 20 tsf. Five series of vibratory field compaction tests relate dry unit weight to number of equipment passes and show that higher frequencies (up to 2,000 vpm) are more effective and compacted density is independent of initial water content.