The Challenge
An extensive history of site investigation works identified the widespread presence of trace asbestos fibres and PAH’s across the site within varying thicknesses of Made Ground. Remediation works were required in order to address planning conditions pertinent for unlocking this brownfield site for residential redevelopment. However, finished development levels necessitated a significant reduced-level excavation to be carried out, potentially resulting in >6,000 HGV movements onto the local highways and risk the scheme becoming commercially unviable.
Our Solution
A detailed Remediation Strategy & Method Statement was formulated by Soilfix to satisfy a pre-commencement condition, primarily based upon a clean capping ’Inversion’ based approach to achieve required finished levels with a layer of clean subsoil across all external areas and roadways. Processed Made Ground was utilised to backfill excavated voids and construct ’Hybrid’ Pile mats using stabilised fill. Works included:
- Removal of redundant buried ductwork containing process pipes & remnant drainage;
- Excavation and processing of ~56,000m3 of Made Ground soils to remove deleterious materials and incidental asbestos fragments;
- Selective excavation of ~18,000m3 underlying natural subsoils for re-use as clean service corridors and inert capping across the site following rigorous validation testing;
- Removal of segregated geotechnically unsuitable (pure sand/ballast) materials to off-site facilities for recovery into usable construction products (~14,000m3);
- Backfilling excavated voids with processed Made Ground (using lime/cement stabilisation, as required) in accordance with Series 600 SHW;
- Construction of ‘hybrid’ piling platforms (consisting cement stabilised, processed Made Ground and a site-won crushed concrete running layer).
Soilfix successfully achieved all objectives for the project (including phased handover to CALA) ahead of a 40-week programme with zero lost-time accidents. An effective materials management strategy compliant with CL:AIRE Code of Practice achieved significant cost savings on disposal off-site, whilst significantly reducing the number of HGV lorry movements.
