CIVILS, TUNNELS & EMBANKMENTS
protected 3mm high-tensile wire in a 65mm diamond aperture interlocking mesh. This mesh is tensioned on to the face when the rockbolt head plates are torqued up, but the design also calls for horizontal cables on every row of bolts. Vertical cables are also required every 10 metres each side along the cutting length. Some 10,732 square metres is required.
Work took place both in possessions and during normal train operations, which include about four trains per day. Every weekend was worked. Up to three road/rail units were deployed, giving good outputs for the bolting of the areas that they can reach.
Nuttall/BAM Ritchies team on the combined WAL7 & 11 (Up and Down) lines between 3m 77ch – 4m 05ch on both sides of the cutting, on the approach to the tunnel between a road bridge and the tunnel portal.
Initially vegetation was cleared, a tactile inspection carried out and a topographical survey completed. As a result the type of remediation was agreed to be very similar to that adopted for Pentwyn Farm Cutting. Vegetation removal has also included mature trees close to the crest of the cutting.
Again, the design is based upon the robust standard Network Rail active meshing and rock bolting details. Annotated photographs and topographical survey have been used to present the design solution in each area. The rock bolt design is reliant on suitability testing done in advance of the permanent works and acceptance testing on 10% of the working bolts.
Drilling on the upper sections has been used as a guide to determine the depth of soil overlying the rock, which in turn is used to fine-tune the construction design. Construction methods, materials and personnel are all similar to that of Pentwyn Farm.
Llangyfelach Cutting
Llangyfelach Cutting is at the eastern approach to Llangyfelach Tunnel, near Morriston, having been designated as having a risk of failure by Network Rail’s earthworks examiner. As a result this second scheme was run concurrently to the work at Pentwyn Farm Cutting, although it started a bit later.
Stabilisation works for Network Rail using a TGP design were undertaken, also by a BAM
In total, 604 rock bolts were installed, securing approximately 4,400 metres of high tensile mesh.
Both projects had a completion date of the end of April 2014.
Both schemes are being delivered for Network Rail very much as a team effort with the joint BAM Nuttall and BAM Ritchies civil engineering and geotechnical skills working seamlessly together, combined with a flexible Tony Gee design that takes the actual ground conditions and topography into account while being true to Network Rail’s standard guidance for rock face stabilisation using high tensile meshes.
Project engineer Ian Bannerman said during the final stage of the works: “It is the first time I have been so far west into Wales and the weather has certainly lived up to its reputation.
“Nevertheless we are making good progress and it is really pleasing that we are well advanced to complete our third and fourth cutting stabilisation schemes for Network Rail in Wales and the west in the last few months.”
He added: “I have the utmost respect for the workforce, who are working lots of weekends, on steep hard rock cutting slopes, in some pretty awful weather conditions. Hopefully now the weather is improving and the daffodils are out, we can swiftly move to completion of the
square
project.”
Site agent Jonathan Bryant added: “BAM Nuttall Ltd and BAM Ritchies have worked in unison and overcome many challenges to deliver these projects, foremost of which is the fact that this is the first time rock bolts have been installed along a solid rock railway cutting whilst trains have been running ALO (adjacent line open) without firstly installing a dedicated catch net for falling debris.
“This has been achieved through the adaptation of the drilling rigs to incorporate a small catch net and BAM Nuttall’s tireless efforts to assure the ‘buy-in’ of the Network Rail management team.”
About the companies BAM Ritchies, which
started business in
Scotland in 1963, is the specialist geotechnical division of BAM Nuttall Ltd,
employing
approximately 360 staff. Its turnover is just under £60m, and it is based in Kilsyth near Glasgow with other offices at Wigan, Clevedon near Bristol, Erith in Kent and Dublin.
BAM Nuttall Ltd had a turnover of £680m in 2012 and operates throughout the country from a network of regional centres. Both are part of Royal BAM, one of Europe’s largest construction contractors, with a turnover of 7.6 billion EUR in 2011.
Tony Gee and Partners LLP has been providing specialist civil, structural and geotechnical engineering
consultancy services to the construction industry worldwide since 1974.
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rail technology magazine Jun/Jul 14 | 55
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