An unexpected inclusion in Network Rail’s work programme for Christmas 2012 was the relaying of both lines through Shugborough Tunnel.
The tunnel, 777 yards long and dating back to 1846, lies on the West Coast Main Line just north of Colwich Junction, south of Stafford. It is on the Shugborough estate of the Earls of
Lichfield, the site is of special scientific interest, and its portals are both Grade 2 listed.
The project’s late inclusion in the Christmas programme stemmed from the imposition of a temporary speed restriction (TSR) through the tunnel in 2011. This was caused by the restricted clearances in the tunnel resulting from years of track maintenance works lifting the tracks. The speed restriction on this critical section of the West Coast route could not be tolerated for any length of time. In consequence it was decided that the renewal and lowering of the tracks through the tunnel should be added to the work programme for Christmas 2012, even though this challenged the normal planning timescales.
Once the project was added to their workload as a ‘reactive renewal’ in March 2012, Network Rail’s project manager Patrick Vallely and his colleagues were compelled to enter into negotiations with the train operators concerned, particularly Virgin Trains, in order to agree the necessary possessions. This was quite a task in itself as normally Patrick and his colleagues work on a rolling three year work bank. This project was to be planned and delivered in roughly half that time.
After discussions with all concerned, Adrian (Ade) Brookes concluded an agreement which granted Network Rail a possession of both lines for a period of eight and a half days between 21:00 on 24 December 2012 and 07:00 on 2 January 2013.
Planning for success
What was eventually to become a £2.5 million project required very careful advanced planning by Patrick and his Network Rail colleagues, including Paul Eamonson (scheme project manager) and Ian Marks (construction manager). They worked in alliance with other company people and colleagues from suppliers. A critical issue, recognised early on, was the importance of having the necessary engineering trains, and the haulage for them, during the Christmas period. It became clear that this haulage would not be available unless some special arrangements were made, and in the end Network Rail had to cancel some less critical works elsewhere to free up the resources required.
At first, few details of the structure of the tunnel or of the existing track construction were available to the project team, and without this information it was difficult to develop a plan or specification for the works. Detailed desktop structural investigations were undertaken along with surveys to confirm the arrangements of track and drainage within the tunnel.
Many historic drawings were located but, as with many projects of this era, these were largely aspirational rather than as-built.
One mystery surrounded the tunnel ventilation shafts. It was known that the tunnel had been constructed with nine of these but, at some past time, they had been sealed and their locations were no longer known. The details of other relevant infrastructure, particularly cable routes and overhead line equipment, were also needed and were obtained similarly by desk study and/or site survey.
It was established that the OLE was on the limits of its adjustment and that the drainage was not functioning correctly. Moreover, it was clear that the cable routes, one in each cess, were going to be in the way of the track and drainage works and additionally there were hard materials below ground which were sometimes too high for the necessary depth of excavation for the new track and drainage.
With excavation depths of around one metre there was the possibility that the stability of the tunnel structure could be put at risk by the work – but the depth could not be reduced because of the need to lower the tracks to restore the clearances to normal standards, one of the key project objectives. As a result, Network Rail’s structures team, along with consulting engineers Donaldson Associates, assessed the safety of the tunnel structure in relation to the proposed works and advised on what should be done.
All of these issues had to be accounted for in the plans for the works. It was decided that during the main possession the OLE should be released from its supports sufficiently to permit tying it back out of the way of the track relaying machines (TRMs) to be used for the track works. The cable routes also needed to be moved clear, and it was agreed that this would be done by diverting the cables to new routes hung on the tunnel walls. If all this was not enough, the drain in the six foot required complete renewal and the drainage outfall some way outside was found to be obstructed and in poor condition.
It was quickly established that significant enabling works would be needed prior to the main possession, and so a number of smaller track occupations were used in the preceding six months. The drainage outfall was cleared and repaired, the cable route diversions were completed and a number of other preparatory tasks were got out of the way.
The advice of the structures experts was that the excavations could not be carried out all at once, and that there should be a real time monitoring system in place to watch for any movements in the structure throughout the works. The track and drainage excavations were therefore planned to be staged accordingly.
Datum Monitoring, specialists in the monitoring of structural movements, were engaged to design, install and implement the tunnel monitoring system which they installed using a high accuracy laser distometer and targets fixed on the walls at 10-metre intervals throughout the tunnel.
This system was manned and monitored throughout the excavation works, but thankfully no movements of the structure were observed.
OLE contractor for the main possession was Bourne Rail, who undertook the work of tying the overhead wires out of the way of the track renewal and reinstated it to the new design afterwards.
Main contractor for the works was Amey Colas, who used contingent labour from various suppliers including SkyBlue. Network Rail encouraged an ‘alliance’ approach to the project, so Amey Colas’ permanent way engineer Tom Dwyer and construction manager Tim D’Arcy were heavily involved in planning the successful outcome of the job. It was critical to ensure that the morale and motivation of staff on the site was maintained at all times during the possession. People working in a tunnel far from their families and friends through Christmas might well be demotivated. A good deal of thought and effort was therefore given to ways in which this problem might be alleviated. The phasing of the work shifts was planned with special care, for example.
During the main possession the drainage renewal was undertaken in a rather unusual fashion. As the hard spots limiting easy excavation could not be removed in the time available, conventional catchpits could not be used in all the locations where they would normally have been. Instead, rodding eyes were used at locations where the level of the hard material obstructed the excavation for catchpits.
Track relaying machines (TRMs) were used to lift out the old track in panels, loading these onto an engineering train for removal from site. Though no longer good enough for further use in the WCML, the old panels are perfectly serviceable for use on lower category lines or sidings and will be reused accordingly. After excavation and removal of the old ballast, new ballast and new track were installed.
Once the first line was completed and ‘fettled’ to a suitable standard, everything was swapped over to allow the other line to be renewed in the same fashion. The track was tamped in preparation for the reopening of the line.
Keeping things fresh
The tunnel was regarded as a confined space and so forced ventilation was needed. This was provided by specialist contractor Factair which provided six of their modular 1220mm diameter fans to force air to flow through the tunnel and ensure 17 changes of air per hour inside the structure. The air current reached speeds up to 2.7m/s. This may sound like overkill, but the specialist contractor points out that the tunnel has an air volume of almost 33,000 cubic metres, and that this volume of air weighs in the region of 39 tonnes at normal pressure and temperature. The fans were placed in the cess adjacent to a tunnel portal, clear of the line, permitting unrestricted use of both tracks. Factair staff attended to the equipment throughout the possession.
Factair also supplied air-fed respiratory protection for staff involved in particularly dusty operations such as ballast tipping. The kits supplied for this are sophisticated incorporating hard hats and both eye and ear protection in the one system.
Finally, Factair provided an air quality monitoring service during the works. Staff were on duty throughout, monitoring oxygen levels and checking for toxic and pollutant gases including carbon monoxide. They also recorded temperatures, air speeds, dust concentration and more, taking over 3,000 readings in all. Their reports provided their client with evidence that the appropriate duty of care had been exercised in respect of their staff, sub-contractors and others who might be affected.
Some 7,200 tonnes of new ballast, 2,300 new sleepers and 3,304 metres of new rail were used in the project, together with 840 tonnes of pea gravel and 660 tonnes of sand and the renewal of 1000 metres of drainage. A total of 1,800 yards of track were relaid, 850 on one line and 950 on the other.
The project’s critical path was closely monitored by the project team throughout the possession and corrective action was taken immediately when necessary to keep the works on time. Network Rail had an operations delivery manager (ODM) on site throughout to assist when there were any railway operational issues, and this proved to be a valuable contributor to the successful achievement of the work and the handback of the possession nearly two hours early on Wednesday 2 January.
An additional challenge for Patrick and his colleagues was a planned visit by the Secretary of State for Transport, the Right Honourable Patrick McLoughlin, accompanied by Network Rail’s CEO Sir David Higgins and track programme director Steve Featherstone. This too went well and the visitors were apparently suitably impressed.
The TSR has now been removed as the clearances have been restored to the norms required for the route. The new track and drainage will ensure better track quality, now and for the foreseeable future, with a reduced maintenance requirement and greater reliability.
Shugborough is well and truly sorted.