RITCHIES HAS started on the bulk infiling phase of a £2.7M mine treatment contract in south Wales.
Work is part of an £11M site preparation of a brownfield site near Methyr Tydfi for the Trago Mills retail store. The scheme is being carried out by the Wales region of Edmund Nuttall for Charles Robertson Developments. Consultant is CD Gray Associates and cost consultant is Chandler KBS.
The site is in an old industrial area typical of the south Wales valleys and was the former home of a brickworks. There are a number of old coal and ironstone tips on the site.
Ritchies' work comprises investigation and treatment of abandoned mine workings by infilling with grout.
Work began in March this year and will continue until April 2006.
Ground treatment is being carried out in two phases. The first was the search for, and treatment of, a number of mine entrances. Initial work involved probing by drilling to locate the 18 shafts and adits thought to be on the site.
The current second phase, to treat development areas by bulk infill grouting, is the main element of the contract.
A number of ironstone and coal seams may be encountered during treatment including the Gellideg and Garw coal seams and the Rosser and Big Vein ironstone bands. In some places up to five worked seams could be intersected.
The contractor is using four Boart Deltabase drill rigs and a Casagrande M9 machine, all equipped with hydraulic top hammers. Holes up to 45m deep are being drilled with up to 24m of casing needed to get through the made ground, overburden and boulder clay on the site.
About 4,500 holes will be needed - about 148km of drilling. Perimeter holes are 110mm diameter and infill holes 89mm diameter. Water flush is being used wherever possible.
A bespoke grouting station using sealed silos, transfer conveyor and mixing units has been designed and built by Ritchies to minimise environmental nuisance to nearby residents.
About 24,000t of grout will be injected to stabilise the workings under the new store. The grout is cement and PFA in varying proportions between 5:1 and 10:1 depending on whether it is perimeter or infi l grout. The PFA is processed and supplied from Aberthaw near Barry, south Wales.
The treatment programme is complex because of site conditions, multi-seam geology and the sensitive environmental considerations.
Ritchies and Edmund Nuttall have a comprehensive regime in place to monitor and control the various environmental risks and to minimise effects of the work on the local community.
Extensive control measures deal with airborne dust and ground borne pollution. Part of these measures includes the use of dried processed PFA and cement both supplied by tankers direct into silos, to ensure all dust is contained within a sealed system throughout.
There is no anticipated displacement of groundwater but even so the local streams and watercourses are regularly monitored for any signs of pollution.