Woodhouse Ancient Mine Workings Stabilisation
Woodhouse is a former farming and coal-mining village, now a suburb and housing estate in the south-east of Sheffield. Infrastructure links include a railway to Sheffield and a station on the Sheffield–Lincoln railway line.
As an area of historic mining activity, the potential for near surface voiding exists, which can pose a significant risk to the railway. Following an assessment of the mine workings by ground investigation, any significant voids and broken ground identified, is required to be stabilised by bulk infilling.
Central Alliance (part of the RSK Group) initially undertook a programme of ground investigation works at Woodhouse, which was completed successfully ahead of budget and programme. As a result of this, Central Alliance was commissioned by AmcoGiffen to work collaboratively with them to complete the drilling for grouting works at the same site.
The stabilisation works were required in order to stabilise the ancient mine workings that were identified during the investigations and posed a risk to the railway. The programme of works was not without its challenges, having to be completed on weekend nights, with only limited mid-weeknight working every 6 weeks. A grid pattern of holes was drilled in accordance with the design and specification produced by WSP, which meant works had to be well planned and organised in order to maximise the very limited working window for the two Fraste PLG rigs employed on the project.
With the additional issue of site access constraints, road-rail vehicles were used to transport the drilling equipment the site, for each shift. The rigs and relevant drilling equipment and plant were lifted on to RRV trailers and mobilised to site, before being lifted on to a temporary drilling platform. Temporary drilling platforms were constructed with rail sleepers to avoid any disturbance of the railheads (tracks) and to position the drilling rigs in the correct orientation for drilling operations.
Specifically, a combination of inclined and vertical holes was sunk in the cess, the four-foot and the six-foot to form a curtain wall, a total of forty-five boreholes ranging from 6-18 meters were drilled at 3-metre spacings, to form the curtain wall. A total of fifty vertical infill holes were then drilled
at 6m spacings inside of the four-foot and six-foot, to target the ancient mine workings and the High Hazel seam.
Inclined holes were drilled to circumvent known services and drainage channels. Each borehole was drilled to 100mm in diameter, using open hole drilling techniques. Boreholes were installed with perforated 89mm UPVC pipe, to allow the AmcoGiffen team to inject liquid cemented grout into the mine workings and broken ground.
In addition, three fully cored investigation boreholes were sunk to thirty metres, to provide further information on the area surrounding the original site. Validation boreholes for “permeability by grout acceptance testing” were also drilled to provide confirmation that the workings had been successfully infilled within the site. Despite the restricted working time and access, the works were completed on programme and within budget safely, and without incident.
Central Alliance and AmcoGiffen have a long history of collaboration to deliver complex investigation and remedial works on the railway infrastructure.