The last Rail Engineer article (issue 132, October 2015) on the progress of the £2.8 billion electrification of the Great Western main line (GWML), now planned to be completed in 2019, focussed on the east of the city of Bath, between Bathampton Junction and Box Tunnel. The work started on Saturday 18 July last year, and was completed on 1 September. During this time, trains to London were diverted via Bristol for six weeks whilst the work was underway.
As you would expect, preparation for this work required detailed planning and consultation which started at least three years ago. Andy Haynes, Network Rail’s project director for the West of England, explained that this involved detailed discussions with primarily Great Western Railway (GWR) and many other groups including Historic England, Victorian Society, Georgian Society, Bath Heritage Trust and Bath & North East Somerset Council, to name just a few.
Normally, a six week line closure would be referred to as a “blockade” but during the consultation process the use of the word “blockade” became a very sensitive issue as it implied that Bath was not accessible, which wasn’t the case. Therefore, to ensure that tourists were not put off travelling to Bath, it was suggested that Network Rail should use a different description for the closure. As a result the acronym TPOD (Temporary Period of Disruption) was created, so the above happened in TPOD1!
Moving on to TPOD2
Moving on, at 01:30 2 April 2016, through to 05:00 11 April 2016, Network Rail embarked on their second phase of intense engineering work, valued at £7.5 million, spanning over nine days. This phase is known as TPOD2 and – guess what? – detailed plans are now in place for TPOD3, but more about that later.
TPOD2 involved the closure of the main line from Bath Spa station to Bristol Temple Meads which, as well as being the main corridor for GWR trains travelling from London to Bristol, is also used by thousands of commuters making local train journeys every day.
This phase of work started at Bath Goods loop, which is located east of Oldfield Park station. Network Rail has renewed the nearly “life expired” existing layout that consists of eight sets of switches and associated plain line. The work was carried out by the S&C Alliance – Network Rail and Colas Rail – which removed the old S&C and plain line track panels and the supporting track ballast in three planned phases. A new ballast formation was reinstated then the new S&C was brought to site using the now familiar and very efficient tilting wagons. Rail mounted cranes off loaded and placed the S&C which was then aligned and consolidated using S&C tamping machines.
Skill and drama
The final step was to carry out the testing and commissioning of the new layout and the associated signalling system. This process, coming as it does at the end of the work, always evokes a sense of drama even though it is normally fairly straightforward, albeit requiring a high degree of technical ability.
However, in this instance it included a little additional frisson since the testing involved signals in the Bath station area, which remained open throughout the works. The testing could only start at 00:30 on the final day when handback was due at 05:00. This gave a very narrow margin of error after a nine-day closure. Should anything have happened, Network Rail and GWR would have enacted their pre- planned contingency and continued running buses to and from Bath and Bristol.
Fortunately, effective planning and skilled execution ensured that the testing and commissioning was completed without incident and in time for the station to accept its first train of the day.
Moving on west, there is a steel girder overbridge at Keynsham station which carries the busy A4175 as well as a number of key services over the railway. The clearances for electrification would have required the bridge to be lifted by approximately 500mm or, alternatively, the track to be lowered.
The latter option was chosen to minimise the disruption that bridge work would have caused to the A4175, with Babcock as the principal contractor for this track lowering. This involved the removal of 1000 metres of plain line track and ballast through and beyond the station platforms. The formation was lowered to the required level and then a geotextile track blanket was installed throughout before laying the new ballast and track.
Whilst this work was in progress, Hochtief removed the old platform copings and replaced them with new ones. These were positioned at a height and level which ensured that they complied with rigorous gauging tolerances and were ready for operational service. In addition, Hochtief also extended the waiting room on the Up side platform and built a new waiting facility on the Down platform. A pleasant addition for the patiently waiting commuter!
Andy Haynes was keen to point out the excellent cooperation as the contractors coordinated their activities, shared plant where appropriate and subsequently managed to complete the work in a very confined space ahead of programme and without incident.
Finally, moving yet further west to North Somerset Junction at Bristol Temple Meads, the Bristol Area Signalling Renewal and Enhancement (BASRE) programme of works, designed to replace the 1960s signalling systems in the area, is in progress. This project was able to benefit from the TPOD2 and the main contractor Alstom replaced two signalling structures that would have fouled electrification clearances. Also, an under track crossing (UTX) was installed for routing cabling and services.
Network Rail will have to drive 15,000 piles to complete electrification throughout the GWML route. Many will be routine and straightforward but some have been, and will continue to be, quite challenging. To make best use of the line closure, around 30 piles were driven by contractor Hochtief in locations with unpredictable ground conditions.
Preparing for TPOD3!
So far, TPOD1 and 2 have proved to be very successful for Network Rail with more than 500 skilled operatives contributing to the nine day TPOD2. As was hinted earlier, there is going to be a TPOD3, planned for Easter 2017.
Firstly, there are a number of locations where there is a requirement to lower the track to create adequate clearances for overbridges, work that requires a high degree of skill and planning. In addition to the track lowering, there is a need to increase the height of the parapet walls on overbridges to protect people from the 25kV catenary cables that provide power to the electric trains.
One of these locations is Pixash Bridge, a Grade 2 listed structure and one of a group of architecturally similar overbridges on the section between Bath and Bristol designed by I K Brunel. The bridge includes a chamfered four-centred arch and stepped buttresses in a Tudor-Gothic style erected over a cutting in 1840.
It also has a distinctive parapet and other important architectural features.
Retaining Brunel’s design integrity
Detailed designs are being carefully prepared for review with stakeholders such as the Bath Preservation Society and will be subject to final approval by Historic England and Bath and North East Somerset Council. For the Pixash Bridge, an iron railing barrier is likely whilst plans for two Grade1 bridges in the Bath Sydney Gardens area are likely to include glass screens to minimise impact on these rare structures. Final approval is yet to be given.
Work is being planned at Oldfield Park station which will include track lowering and associated adjustments to platform levels and, of significant importance, a package of work is being planned in TPOD3 at Bath Spa station.
At this historic location, to ensure adequate electrification clearances are created, either the platform canopies have to be cut back or the platforms brought forward. Fortunately, there is redundant space between the tracks through the station so, to keep the canopies intact, the two platforms are going to be extended outward by around two metres, thus ensuring that the distance from the canopy to the 25kV wires is adequate.
In addition, the Down platform needs to be lengthened to accommodate the new Hitachi trains but, at each end of the station, there is a rail bridge that spans across the River Avon which meanders around the station. At present, the options available are being considered but, inevitably, the eyes of the heritage world will be watching very closely. So the work is progressing, the many engineering challenges are slowly but surely being addressed and agreement is being made with regard to ensuring that the railway’s engineering heritage is being protected without unduly hindering progress. The bi-mode electric/diesel Hitachi trains will be operational by late 2017, offering longer trains with more spacious carriages. The engineering work is planned to be completed in 2019, at which time there will be a railway service that will be worth all the effort.
Meanwhile, let’s enjoy the success of TPODs 1 and 2 and look forward to the fascinating challenges that will be posed during TPOD3.