Behaviour of trial embankment on hydraulically placed pfa: Fid-Bau Portal

Behaviour of trial embankment on hydraulically placed pfa

Cousens, T.W. / Stewart, D.I.

Much of the electricity generation in Great Britain is currently, and has been historically, produced by the combustion of coal. By-products of the process are fine ashes from electrostatic precipitation (pulverised fuel ashes, pfa) and coarser furnace bottom ashes. A large percentage of pfa is disposed of by producing a water-based slurry and pumping it into lagoons where settlement occurs. Such areas have potential for development but there are difficulties constructing on the hydraulically deposited pfa. The paper describes the performance of a 5,3-m trial embankment constructed on approximately 45 m of hydraulically placed pfa. It is planned to redevelop the 17-ha lagoon containing the pfa as a landfill. There is little variation in the particle size distribution of the uniformly graded silt sized pfa over the lagoon. However, the density of the pfa varies with depth with loose material underlying a denser surface layer, in a pattern that probably results from the water level in the lagoon during pfa deposition. Settlement under the trial embankment was apparently largely complete by the end of the construction period (17 days), with approximately 300 mm of settlement under the crest of the embankment. The embankment settlement is significantly affected by compression of the loose layers within the deposit. Analysis of the problem using the conventional one-dimensional settlement method, and a profile determined by CPT calibrated against laboratory tests gave a reasonable prediction of the embankment crest settlement.