You’ve got to start somewhere. Such were the timescales involved in delivering it, there was a clear logic behind engineer James Mathias’ choice of turning the first sods of the Pembroke & Tenby Railway at either end of its greatest engineering enterprise – a tunnel of 480 yards under Golden Hill, on the line’s approach to its terminus at Pembroke Docks.
Whilst miners drove headings to create a pilot tunnel, others were engaged on the mammoth task of excavating the approach cuttings. This was 1863 – no plant, no machinery – just hand drills, explosives and elbow grease. And yet 500 tons of arisings were despatched daily to form an embankment further down the line. Just pause for a moment to consider those logistics in an era when bulk haulage involved horse power in its purest sense.
The miners’ efforts fractured the porous Welsh sandstone through which the railway was laid. So it’s only to be expected that 150+ wet winters later, the accompanying freeze-thaw action – aided by the odd badger – will have loosened rock in the approach cuttings and caused pieces to dislodge periodically. One of these weighed 400kg.
Dealing with such fall hazards is part and parcel of the railway’s routine asset management regime. In the cutting at the tunnel’s south end, the accompanying obligations recently prompted a 19-day blockade to facilitate the installation of stainless steel netting and more than 1,200 rock bolts.
The project first appeared on the radar of Alun Griffiths (Contractors), holder of a Geotechnical framework for Network Rail’s Wales & Western Region, in the summer of 2016 when its workforce spent 16 weeks deveging the site. The work revealed the soil mantle to be deep whilst the underlying rock was soft and weathered, insight which helped an in-house team from Network Rail to develop the design for a stabilisation project.
At this time, a housing development was springing up on land to the north and west of the cutting, a constraint which influenced the delivery approach for the main scheme. Although the hours available were comparatively generous, the option of using Rules of the Route possessions was soon dismissed as this would have involved 26 weeks of overnight working, imposing intolerable disruption and disturbance on lineside neighbours as a consequence of the noise and light pollution. The inefficiencies were also apparent.
Instead, a blockade was agreed between Whitland Junction and Pembroke Dock, closing the single-track branch for 19 days from 23:00hrs on Sunday 19 January through to 05:45hrs on Saturday 8 February. This allowed the drilling to be restricted to the period between 07:00hrs and 23:00hrs, with only the bolts, grout and netting put in overnight. Buses replaced trains on the route to the west of Carmarthen, although services to Fishguard Harbour and Milford Haven continued to stop at Whitland.
Alongside the Pembroke work, the blockade facilitated vegetation management activities along several stretches of line. Amongst these was another Griffiths site encompassing 570 linear yards at either end of Narbeth Tunnel, the felled timber from which went to fuel a local biomass power plant. There was also track replacement work and geotechnical surveys of some earthworks and foundations.
The methodology manual
Rock drilling on the higher part of a slope comes with obvious challenges. Historically, rope access teams would use a skid rig – effectively a sledge with a drill mounted to it which would be lowered down the bank on cables anchored at the crest, with the workforce man-handling it into the desired position assisted by winches or tirfor rigs.
The drilling itself was carried out by hand – using kit much like a jack hammer – bringing considerable implications around HAVS (Hand-Arm Vibration Syndrome). So acute was the potential impact that each man was typically limited to 20 minutes per day on the drill.
Except ‘historically’ is not the right word here – some contractors still use these methods. But not so Griffiths. In 2017, it made a commitment to bring the work in-house, buying two Ripamonti drills and mounting them on road-rail excavators sourced from Total Rail Solutions, their plant supplier.
As well as bringing huge efficiency improvements, almost all hand-drilling has been eliminated. The past two-and-a-half years has seen around 12,000 rock bolts installed by the firm as part of several schemes across Wales and the south-west; more than 99 per cent of these have been achieved through mechanised means. The workforce health benefits cannot be overstated.
Taking the strain
At Pembroke, Network Rail’s design required the installation of 1,154 stainless steel rock bolts, typically in an offset diamond pattern at two-metre centres, as well as 68 spot bolts at identified vulnerable locations. Each was between 2.5 and 3 metres in length. Additionally, around 3,700m2 of 3mm diameter steel netting had to be fitted, together with spike plates and associated components. The system actively holds the rock in place; the alternative – a passive system – has bolts at the top and bottom, and only contains the rock pieces as they fall.
Delivering the programme within the available time window relied on meticulous planning and the collaborative relationship Griffiths enjoys with Total Rail Solutions. Deployed on site were five machines fitted with Ripamonte EX170TH/THV drills: a 13-tonne excavator with nine metres of reach and a 36-tonne excavator with 20 metres of reach worked above the tunnel portal and along the west-side crest, whilst on-track were two Doosan 270 RRVs, one with a purpose-built 10-metre dipper arm offering 19 metres of reach, and the other with a 5-metre dipper arm and 11 metres of reach.
It was possible to install around 92% of the bolts using these four machines. The remainder – numbering about 100 – were located towards the top of the east-side cutting slope, the crest of which was inaccessible to plant due to adjacent properties. So there were two options here – reverting to manual means or developing an innovative solution involving a different machine. Enter Total Rail Solutions.
In the latter half of 2019, Total Rail Solutions’ fleet was boosted by the arrival of a new piece of kit – the UK’s first Sennebogen 643 crane with its 30-metre telescopic boom. It offers enhanced opportunities for the firm’s rail clients, with a 40-tonne lifting capacity and 24-metre maximum radius. But where this machine really scores over its competitors is the ability to fit attachments to the boom, a feature which offered a potential means of overcoming the issue Griffiths faced at Pembroke.
By evaluating the technical specification of the Ripamonte drill against the capabilities of the crane under the relevant operating conditions, it was determined that the drilling requirements for the upper two rows of bolts – between 16 and 21 metres above track level – could be fulfilled. Beyond this, site visits were undertaken to ensure the machine’s swept envelope would not conflict with any railway furniture such as signage, signal posts or drainage catchpits.
GOS Tool & Engineering Services, who have a positive track-record of converting machinery for rail use, were engaged to engineer the bespoke high-spec adaptor between the crane and drill. It was designed and fabricated within a week, including the need to modify the hydraulics on the machine to divert high-pressure oil to the end of the boom to drive the drill. A three-day period of testing followed before the assembled kit was taken to Pembroke.
Understandably, as this was a first for the UK and therefore a new experience for both Total Rail Solutions and Griffiths, the approach taken to the crane’s initial use was cautionary. Moving it took longer than the conventional RRVs as it’s stabilised by jacks, but that reflects the unique nature of the role it was taking on. Confidence grew as the methodology proved itself.
Mention must be made of the crew working with and alongside the crane whose skills and collaborative effort were equally important as its mechanical capabilities, effectively controlling exclusion zones and recognising the manoeuvrability limitations within a constrained worksite.
“From our point of view, the project went very well”, reflects Paul Clancy from Total Rail Solutions. “We were there to do the out-of-reach holes that the other machines couldn’t do and we did them 100% without issue.”
Overall, the project asked many questions of the Griffiths team, confronted by difficult terrain, the impacts of prolonged wet weather and the close proximity of housing. This was a job very much within the community. A workforce of 130 – mostly from Wales – contributed to its successful delivery, working 24/7 and clocking up more than 16,000 man hours. Jackie and Nyree kept them fuelled with hot food on demand, whilst seven local guest houses – normally closed through the winter – benefited from unexpected income.
And as for the outcome? “We have exceeded our expectations by successfully delivering all 1,154 bolts, some 24 hours ahead of the planned programme and installed 3,700m2 of mesh”, Jason Shannon, Griffiths’ Contracts Manager, makes clear. You can’t say fairer than that.