Remediation for housing
Fallon were contracted by Partner Construction to remediate a site in Witney for the construction of 68 houses. Topographical levels reduced from an existing development in the south towards the River Windrush to the north of the site by approximately 12m resulting an escarpment and lower plateau. The lower plateau had been formed historically from the quarrying of limestone in two locations and backfilling with quarry waste. More recent activity had resulted in relict foundations, a cesspit, garden nursery rubbish, chrysotile asbestos, and a layer of made ground that extended across the majority of the site area.
The works commenced with a general vegetation strip and excavation of the made ground layer to reveal underlying natural soils and quarry backfill. The made ground was screened to produce a fill material but found to be too organic and determined as unsuitable by the client’s consultant. The two areas of quarry backfill were excavated to full depth with the garden nursery rubbish and chrysotile asbestos being separated from the bulk limestone quarry waste. The excavation proceeded from west to east in parallel rows with the first arising being side cast to reveal undisturbed basal material. The next row was excavated with the material being placed immediately as fill in the adjacent void.
Approximately 8000m3 of quarry waste was placed and compacted in layers of engineered fill to achieve a minimum CBR value of 5% in the mass of fill and 15% at formation.
The escarpment was cut to finished level to produce approximately 2000m3 of topsoil, and limestone and clay. The topsoil was screened and stockpiled for subsequent re-use as garden soils. The clay was used a general fill material and the limestone crushed to produce a 6F2.
All unsuitable wastes were segregated and disposed of off-site.