What is the steepest slope that can be created using PFA as a fill material?
When fly ash is excavated from lagoons and stockpiles, vertical faces can be created without failures occurring. However, this is an extreme and couldn’t be considered safe for normal construction applications. The maximum slope used in recent construction projects, to our knowledge, has been 45°, which was used at the Black Country Route in the West Midlands. The moisture content, the source, the degree of compaction and the shear strength of the PFA all effect the possible slope. As PFA gains strength with time, due to the pozzolanic reaction, the shear strength increase very significantly with some ashes. Typical values for shear strength are given in Technical Datasheet No. 2. Vertical faces are possible by the use of geogrid for reinforced earth applications. Such grids have to be resistance to the high alkalinity of PFA. For further details of suitable geogrid materials contact Tensar who produce such products.
