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- ►CS01 Nell Lane, Manchester
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Other Services
►CS03 Manchester Road, Tyldesley
| Development: | 141 Residential properties |
| Year: | 1999-2004 |
| Clients: | Rivermead Homes and Wainhomes |
| Development Value: | £16 million (approximately) |
Site History
Coopers were commissioned to investigate a 14.8 acre (6 hectare) parcel of land for a mixed low rise residential development. The historical use of the land was the former Yew Tree Colliery and associated colliery spoil mound. At the time of the commission, the superstructure of the colliery building had been removed and the stockpile of colliery spoil had been levelled across the site.
Ground Investigation
An extensive ground investigation comprising of trial pits, cable percussive boreholes and rotary boreholes was undertaken to determine the true extent and nature of fill strata, the potential for the presence of ground gas as well as the presence of shallow mine workings beneath the site.
Caol Mine Shaft Capping and Shallow Mine Workings Investigation
2 No. disused mine shafts were noted on site and were drilled using rotary boreholes from a safety platform to confirm that both had been filled and that no voids were present. The boreholes/shafts were grouted up and the shafts were subsequently capped. The diameters of the shafts were 3.2m and 4.5m, with reinforced concrete caps having diameters of 6.4m and 9.0m which were designed by Coopers Structures Department. Additional investigation was also undertaken on conjectured mine entries to confirm these features were either drawing errors on old plans or staple pits (shafts at depth linking seams).
Coopers supervised the tendering procedure for drilling and grouting of shallow mine workings as well as the backfilling and capping of the mine shafts. Due to geological faults being present within the site, and the presence of shallow mine workings, raft foundations were specified and designed by Coopers for this site. These works were approved by the Local Authority, the NHBC and the Coal Authority.
Ground Gas Monitoring
A ground gas monitoring programme was undertaken by Coopers. It was noted that areas with low pH values were generating significant concentrations of carbon dioxide. We designed mitigation measures for those properties within close proximity to areas with significant concentrations of carbon dioxide consisting of a granular blanket underlying the plots, proprietary gas membrane and passively vented under slab voids.
Remediation and Combustibility Assessments
The depth of colliery spoil was recorded to vary between 0.5m to 5.6m, and was noted to have contamination as well as the presence of combustible materials (coal fragments) requiring an inert cover to be utilised throughout the site.