THE CHALLENGE:
Prior investigation of the 0.9Ha size site had identified various contaminants in the made ground, mostly associated with historical demolition activities. Licensable asbestos containing materials (ACM’s) including asbestos insulation board (AIB) fragments were identified within Made Ground below a former car park area. Widespread fragments of other non-licensed ACM’s, principally cement sheet fragments, were also present across the site – giving rise to significant concerns over unforeseen asbestos contamination including significant quantities fused to underside of slabs and on foundations. Only limited investigation was possible around the supermarket building, which created uncertainty on the true extent of ACM’s as well as remnant in-ground obstructions associated with historic buildings.
The developer (A2 Dominion) and their Main Build Contractor (Higgins Construction) required a comprehensive solution with a fully enabled Development Platform site that was free from impediments, including no in-ground obstructions or hazardous classified soils & stones during ongoing construction works. the site location also presented a significant challenge for temporary works, owing to a 4-storey building situated directly adjacent to the site, with a deep foundation ring beam requiring grubbing out and removal to facilitate piled foundations clashing with these.
OUR SOLUTION:
A Detailed Remediation & Enabling works Strategy was developed by Soilfix to remediate asbestos contamination, remove significant in-ground obstructions and allow future unimpeded redevelopment of the site. Works included:
- Targeted excavation and removal of visible AIB fragments and other fibrous ACM’s from Made Ground as Licensed Works – contaminated fines strategically utilised as general fill in an area not to be disturbed during future construction;
- Controlled breakout of 3,200m³ slabs and sub-structures, including 2 drainage interceptors – hardcore processed to 6F2 specification for re-use;
- Implementation of Temporary Works along a site boundary adjoining a 4-storey high building to the satisfaction of Party Wall Surveyors;
- Hand-picking of non-licensed ACMs during controllled excavation and turnover of the made ground;
- Mechanical screening of 5,100m³ of soils to render suitable for re-use on site;
- Re-grading site to required construction formation levels, with cement stabilisation of remediated soils to install sustainable ‘hybrid’ working platforms for piling works – lower layers comprising cement stabilised fill capped with a protective running layer of crushed aggregate;
- Strict implementation of environmental monitoring & controls to satisfaction of LB Hounslow. Including continuous boundary PM10 dust monitoring and frequent reassurance air testing for respirable fibres.
All works were completed under the supervision of Higgins acting as Principal Contractor with no lost time accidents to the required construction programme, in full compliance with CAR-SOIL guidance for asbestos and CL:AIRE Code of Practice (DowCoP), with >95% materials re-use achieved during the works.
Soilfix successfully achieved all remediation goals for the project, and environmental monitoring data confirmed the works were carried out safely with regards to potential liberation of asbestos fibres.
