CAN were contracted to deliver rock stabilisation work on an unstable face above a busy single carriage way at Livox, on the A466 between Tintern and St. Arvans. CAN acted as Principal Contractor for Monmouthshire County Council to undertake regrading, rock bolting and installation of rock fall netting to the unstable face.
CAN’s initial approach was to install the GEWI solid bar rock bolts by DTH drilling 90mm diameter holes and installing anchors in batches for post grouting. However the rock encountered was unexpectedly highly fractured and voided, resulting in grout loss into the surrounding rock, with limited grout return and uncertainty over the volume of grout retained in the boreholes. This led to CAN changing the installation methodology, assembling the bolts with pre fitted grout socks as a grout containment system to ensure they could be fully grouted.
With the relatively small 90mm diameter boreholes, issues with tearing in the grout sock were encountered and the borehole diameter was also increased to larger 115m holes to avoid this. The new methodology was successful in allowing the rock bolts to be fully grouted, and was used for all 5m and 6m length bolt.
The unforeseen ground conditions resulted in the programme extending, however CAN were able to increase labour resource and mobilise additional drilling equipment to site to mitigate delays. On completion of drilling Geobrugg’s TECCO G45 mesh was installed over the rock face, with additional 1m profiling bolts installed to assist contouring the mesh over the undulating face.
Duration: 12 weeks
Client: Monmouthshire County Council
Location: Chepstow, Wales