THE CHALLENGE:
The enabling works involved ground improvement of 2nr areas of historic landfill covering a total 4Hectares beneath car parking/open space areas of the College site to reduce the risk of settlement (in particular differential settlement) outside proposed piled structures. Site preparation also required extensive stripping of surface materials— this process, together with ground improvement, required an approach that minimised generation of landfill materials that would require a Permit for re-use with a prohibitively long application process.
OUR SOLUTION:
To achieve the client’s objectives and improve ground conditions in a sustainable and cost—effective manner, Soilfix delivered a ground improvement and development platform preparation strategy to satisfy NHBC requirements for settlement control and the Environment Agency to work under CL:AIRE DoWCoP for non-landfilled material:
- Controlled strip of surface topsoil, capping subsoil, tarmac/concrete surfacing and made ground / sub-base materials—screening, sorting & crushing to produce site-won aggregates and subsoils for site regrading / capping purposes;
- High Energy Impact Compaction (HEIC) treatment across the 2nr landfill areas to achieve maximum settlement without requiring any excavation. Detailed monitoring was carried out during these works to produce real-time data of the compaction process;
- CPT and plate testing following HEIC works, to measure the settlement and improved ground conditions. Independent verification of this data was provided that showed targets had been achieved;
- Importation of 15,000 tonnes of naturally occurring soils as a Direct Transfer arrangement under a Materials Management Plan to raise levels across site;
- Construction of multiple ‘Hybrid’ pile mats across the 4Ha area using site won and imported aggregate. CBR plate tests on the pile mats to ensure design criteria met FPS requirements.
Soilfix successfully achieved the required ground improvement criteria (settlement potential <25mm in treated areas), achieving hand over of all pile mats to the programme with zero lost time accidents / incidents.
