THE CHALLENGE:
Historic waste operations had left significant stockpiles of waste soils as well as waste materials including creosote-treated timbers across the site. Extensive concrete aprons, variable thicknesses of geotechnically poor made ground and significant in-ground concrete was also identified to depths of up to 5mbgl. To provide an additional challenge, ~40% of the site was confirmed to overly soft to very soft alluvial deposits that created unacceptable settlement risks to the main road corridor and external areas.
Regulatory consultations also presented challenges—the EA deemed all stockpiled materials to be ‘waste’ and required a Deposit for Recovery (DfR) Permit for re-use, whilst the NHBC did not recognise the best practicable option for ground improvement (Bi-modular Columns) in their approved list. Soilfix therefore developed a phased surcharging solution jointly with Redrow’s engineer (Coffey Geotechnical), with band drains installed to accelerate consolidation across areas of deeper alluvial deposits .
OUR SOLUTION:
Soilfix implemented a sequential, phased programme of site preparation and ground improvement works ahead of construction works, using a hybrid approach for materials re-use under a DfR permit (imported stockpiles) and CL:AIRE DoWCoP (site of origin). Works included:
- Screening / sorting over 47,000m3 of Made Ground;
- Breakout / processing of 20,000 tonnes concrete / brick to a 6F2 specification;
- Site-wide cut & fill regrade, with cement stabilisation carried out on 35,000m3 cohesive soils for geotechnical improvement (including construction of hybrid pile platforms);
- Remediation of large quantity of AIB as licensable works in accordance with CAR-SOIL;
- Excavation of shallower alluvial deposits across a key construction area (below main spine road), stabilisation and re-use of material;
- Installation of vertical band drains and sequential placement of fines material for surcharging; and,
- Removal of surplus made ground arisings and segregated deleterious materials.
In spite of many significant ground / regulatory challenges faced during the project, Soilfix completed all preparatory works in line with Redrow’s ongoing construction programme, with zero lost time accidents over the course of these logistically challenging works.
