THE CHALLENGE:
Willmott Dixon were constructing a 94 unit residential care home in partnership with LB Hounslow, on the site of a former infilled gravel pit. Investigations confirmed the presence of up to 6.0m of made ground fill containing significant quantities of Asbestos Containing Materials (ACMs) including cement and insulation board fragments. To enable safe construction and achieve required development platform levels, wholescale excavation and disposal of circa 11,000m3 was estimated to cost >£4.5m which would have rendered the scheme commercially non-viable. Significant disturbance to the local road network from more than 1,300 HGV movements was also a concern.
OUR SOLUTION:
Soilfix devised a ‘suitable for use’ remediation and development platform preparation scheme that optimised the volume of site-won soils and aggregates within the site, fully in accordance with the Control of Asbestos Regulations (CAR) 2012 and CL:AIRE Code of Practice. Works included:
- Soil Excavation: Controlled reduced level excavation to required formation levels under watching brief of a qualified Asbestos Supervisor. Over-excavation also carried out along the line of deeper drainage runs, proposed footprints of attenuation tanks, lift pits and crane bases.
- Modular Processing : Soils screened/sorted to separate soils fines & aggregates, with ACM fragments hand-picked by certified operatives and removed off-site as hazardous waste.
- Environmental Monitoring & Controls: to satisfy the clients Environmental Health Dept, including dust / fibre suppression and real-time PM10 monitoring.
- Laboratory Testing & Trials: Comprehensive chemical / geotechnical testing was carried out, including w/w determination of asbestos in soils. Laboratory trials included use of a ‘dustiness’ test to determine the respirable fibre release potential of cement stabilised soils.
- Development Platform Construction: Soils were cement stabilised to “lock in” any potential residual asbestos fibres & render soils geotechnically suitable for the construction of the working platform in combination with site-won processed aggregates. Excavated service corridors lined with hi-visibility marker layers and backfilled with selected fill.
Soilfix successfully achieved the required aims of the project on programme and below budget. A total of 86% materials recovery was achieved, with the vast majority of surplus materials de-categorised to non-hazardous for more cost effective disposal to a more local facility.
