The former Veolia Water Central Ltd offices and water treatment works at Three Valleys Way was to be redeveloped for housing. The site covers an area of approximately 4.2 hectares and required excavation, remediation and soil improvement in places down to the 7m depth of fill. The work included the breaking out of former water treatment works infrastructure, including nine underground reinforced concrete softening tanks and associated pipe work. The tanks had previously been backfilled with made ground that was to be removed and processed for re-use as engineered fill. The project involved very deep excavation of soil, backfill, encapsulation and stabilisation.
Cognition was contracted by Persimmon Homes to develop the backfill design and testing and then carry out the earthworks. In accordance with the design. The objective was to process and re-use existing fill to save on disposal and import of materials and produce a geotechnical suitable platform for piling and construction. The key elements of the works included;
Cognition's strategy enabled 60,000m3 of soil to be processed for re-use, delivering considerable savings on disposal and import and minimising traffic and disruption in the local area. The heavily reinforced concrete water tanks were broken out and the concrete crushed and re-used. The stabilisation design mix was developed to optimise backfill and compaction. The geotechnical testing proved the backfill would not be subject to long-term settlement and the site was able to be re-used for a large residential housing scheme.