Phase four of Railtrack's Severn Tunnel refurbishment project will start in July this year to detailed plans being drawn up by Birse Rail.
Careful programming and coordination of resources is crucial and progress of the scheme suffered at the outset, albeit under a previous contractor. But during the past two years Birse Rail has developed an effective strategy for managing the difficult logistics of getting resources to the tunnel's remote location in a short space of time.
The 155 year old single bore Severn Tunnel is 7km long and takes two tracks below the Severn Estuary between Caldicot on the Welsh side and the English portal north of Bristol.
Effective maintenance of the tunnel is vital as it forms a key link in the Great Western rail network. But insufficient maintenance had left the structure in a poor state of repair before Railtrack let the first contract in 1998, aiming to address the problem.
Refurbishment work includes cleaning and repairing a 600mm diameter brick culvert which runs below the gap between the tracks. Precast concrete inspection chambers at 20m intervals are being cleaned and reset, and the tunnel's nine-skin brick lining is being repaired together with management of water ingress through the brickwork.
This involves fixing guttering and down pipes to the tunnel perimeter with carrier drains to transfer water to the existing culvert.
Tunnel maintenance was carried out from July to the end of March during Saturday night possessions between 22.20 and 08.55 during the winter timetable.
'The first phase of refurbishment work was not a success because we lacked an effective strategy and system of work, ' says Railtrack project manager Jane Austin. 'We were not getting value for money due to the time being taken to get resources from the access point to the workplace. Less than 1km of culvert was cleaned during the first phase.'
The project was retendered early in 1999. Birse Rail took on the contract as principal contractor and began looking for ways to make it work. At this stage Railtrack was one quarter way through its four year programme with much less than 25% of the work completed.
'We needed to shorten the loading time to increase productivity, ' says Birse Rail project manager Mark Peters. 'The tunnel's emergency access ramp close to the Bristol portal was being used to get resources onto the track once the possession period had started, but safety regulations prevented it from being used at any other time. It also restricted the quantity of men, materials and plant that could be transferred to site in the time available.'
Birse solved this problem by procuring a 150m length of redundant siding at Severn Tunnel junction, about 2.5km from the Welsh portal. This infrastructure has become the lynchpin of Birse's strategy. Up to eight road/rail excavators with flat bed trailers are stored in the sidings and loaded with necessary plant and materials for the next possession period. Everything is ready to go and deployed to where it is needed as soon as the possession begins.
Birse works throughout the week to prepare for the following Saturday night's work. Monday and Tuesday are spent stripping down and servicing plant from the previous possession and carrying out detailed planning. The road/rail trains are then pieced back together before checks are carried out on the Friday ahead of the following night's possession.
'Detailed planning and checking to ensure everything is in place and in the right order in the sidings is essential, ' says Peters.
'We have to move quickly as soon as the possession starts and once the resources have been deployed, they cannot pass each other or come back out again. Time is tight and we are usually blocked in by other contractors possessing the track immediately adjacent to the tunnel entrance.
'Even one missing breaker can cause big problems because one man then has to walk a round trip of at least 5km to retrieve it, which stops an operation for most of the possession.'
Clearing up and exiting the tunnel also has to be carefully co-ordinated. Train delay penalties for any contractor failing to hand backtrack on time vary from £20 to £100 per minute and accumulate throughout the day if the delay has knock-on effects on the timetable.
As possession manager and principal contractor, Birse Rail has awarded a drainage subcontract to Garth Plant Hire and brickwork to DQMA. Owen Williams Railways is providing essential skilled personnel for taking the possession.
'Maintaining continuity of men and subcontractors is important for keeping the whole operation smooth. We have up to 120 men working in various places at one time and standard procedures for operating safely on Railtrack infrastructure have to be followed. There is very little flexibility because we have a fixed length of siding and quantity of Railtrack approved equipment and experienced men. All of this is key to productivity, ' says Peters.
Despite these constraints, Birse Rail appears to have solved Railtrack's Severn Tunnel refurbishment problem and the contractor was retained for phases three and four after it had completed its first year of work.
'Birse took the initiative and the work has gone very well so far, ' says Austin. 'Maintenance of the Severn Tunnel has been reactive for 20 years and deterioration of the structure has been running away from us due to short possession times and lack of an effective strategy. 'But the backlog is now being cleared and the system of work developed by Birse Rail will be worked into future routine maintenance contracts.'