This steep sided railway cutting on the Vale of Glamorgan line in South Wales had a history of instability, with weathering of the chalk faces causing loose rock to regularly fall to track level. CAN undertook a previous phase of works in 2015 at the Western end of the cutting and were contracted again to address the remainder of the cutting in the next phase of works. This larger scheme required vegetation clearance and rock scaling over both sides of the remaining 700-yard length of the cutting, following by installation of a series of rock netting systems and catch fences to protect the line.
In total this required over 10,000m2 of vegetation clearance using rope access techniques to access the face, with loose rock cleared as this progressed. A total of 4800m2 of passive rock netting was then installed in targeted areas, requiring over 200 rock bolts to be drilled into the crest and toe, with concrete head blocks cast around the top bolts.
Road rail vehicle mounted drill rigs were used to drill the rock netting and catch fence bolts at the base of the cutting, with smaller excavators used for crest bolts in restricted access areas. A long reach mounted drill rig was utilised where mid face bolts were required in one of the areas of netting, allowing these to be drilled without the need for face mounted drill rigs.
The bespoke catch fence consisted of vertical posts drilled and grouted into the bedrock, with additional bolts drilled into the face beyond the fence, allowing tie back cables to be fixed from the top of the fence into the cliff face. Sections of rock netting were then fixed to the posts and strung from horizontal cables to complete the detail.
With a significant amount of the work requiring possessions to complete, a complex programme was developed to utilise 4 long blockades on subsequent weekends to undertake as much of the vegetation clearance and drilling as possible at the start of the programme, with shorter Saturday night possessions used for the remainder of the programme to complete remaining possession works. Midweek daytime working ran concurrently to this, undertaking work from the crest to install upper bolts and netting.
Duration: 18 weeks
Location: Porthkerry, South Wales