Coal miners are back in the Southeast of England. Twenty three years after the closure of the Betteshanger, the last pit in the Kent coal field, miners from Wales and the North-East are once more beneath the rolling countryside. But this time they’re not looking for coal.
Amalgamated Construction has its roots in mining. It was born from the engineering division of the former National Coal Board and many of its personnel have direct experience of pit work. They are Network Rail’s main contractor for the extensive works being carried out to stabilise and secure the future of Ore Tunnel.
Thomas Cowie is Network Rail’s Project Manager looking after, amongst other things, the Ore tunnel project which is being undertaken during a nine week blockade between Hastings and Rye. This blockade enables a long list of other infrastructure works. But more on this later….
Distorted profile
Thomas explains that the tunnel, a Victorian structure, was constructed almost certainly by drill and blast methods as it passed through a mix of clay beds and inclined stratified layers of limestone and sandstone. The parabolic, brick lined tunnel was smashed out through the rock.
The profile is distorted, particularly around the crown and it is believed that packing is poor between the rock and the lining in the drilled and blasted sections.
Over generations there have been many repair exercises in various parts of the tunnel. All the repairs have been short term due to the previously limited possession times available. They are at the end of their life so it is time to replace them with something more permanent.
Shotcrete lining
The tunnel is extremely wet. As Thomas observes, “It’s really unbelievable how much water comes through it! And that’s primarily one of the reasons for the deformation. The water is taking the mortar out from the bricks.”
To put matters right some sections will have sprayed shotcrete linings applied to the roof of the tunnel. These will be held in place and strengthened using rock meshing over the top of the new lining, with carbon fibre ground anchors or dowels installed between the new lining, through the brickwork, into the rock above.
They are there to hold the weight of the lining so that it causes no additional load to the existing tunnel structure.
Hidden shafts
There are many other minor works within the tunnel such as renewing previous water catchment systems, especially in the huge ventilation shaft in the middle which is like a flume. There are four hidden shafts and strengthening work will be carried around their bases as they’re adding pressure to the walls.
Sections of brickwork throughout the tunnel that have been damaged through grout loss are being repaired or stitched. There are some fractures of the walls which need to be repaired and there is a significant section of the roof which is bulging which is going to be cut out and strengthened with a shotcrete lining.
There are several areas of the tunnel where injection grouting behind the lining will eliminate voids. With these and other measures, it is hoped to manage some of the water which is doing the damage to the tunnel and to the track.
Preparatory work
Work started on Monday 9 January, but before that there was an element of “softening up”.
Thomas recalls that, to minimise the time needed for the blockade, they did a considerable amount of preparatory work in advance. “Anything practical that could be done before the blockade was done. So, for example, we set up our accesses, our compounds, installed lighting systems, water mains and emergency telephone systems.
“We spent most of November and December working night shifts installing ventilation systems. We have at least two very large Factair fan systems which will provide flowing air through the tunnel, and all the machinery in use has been thoroughly serviced to ensure that emissions are at a minimum. Expensive catalytic converters have been fitted to every machine. These new filters, which are changed weekly, are meant to remove some 95% of particle solids from the air. The fans are really a precaution because we are trying to remove most of the problems at source.”
Logistical problems
“Ore tunnel is a double line bore but with a single line which leads to many logistical problems. Although complex, by working with our delivery partner, everything has been managed very successfully. We did several shifts of trial work to see what to expect and to practice some of the movements because the single line meant that once setup for the day then that’s it! We have to make sure everything’s in the right order in the tunnel as we can’t drive through each other!”
At the end of the tunnel work there will be a full track renewal including the ballast subgrade and the track drainage. As part of the project, geotechnical drainage that runs through the tunnel from cuttings and embankments will be renewed.
Access issues
Access to the tunnel could have been a serious problem but the project was extremely fortunate. The local area was quite industrial in the past and it’s now a massive redevelopment area. Very near to the railway there is the site of a former coal fired power station and this has been secured for access. Even the old sidings have been found. In fact the access at the west end is fantastic – it couldn’t be better. At the other end there were some difficulties because the best places were reached either through bogs or marshy land, but access has been secured.
Journey time improvements
But the tunnel is not the whole story. With a nine week blockade available, just about everyone wants to take advantage of this extraordinary opportunity.
Murray Motley is a Senior project sponsor with Network Rail. As sponsor for a longer term scheme to improve journey times between Ashford and Brighton he has a great interest in the blockade.
Murray explains that, “The journey time improvement scheme had been developed to a point where we knew what we needed to do and what it would cost – but the costs were fairly high and, given that this is a rural railway, we were struggling to justify it. But what has actually happened is that much of what we were going to have to do is being picked up as part of routine maintenance.
“So, for example, if track has been relayed then that’s part of a normal renewal maintenance cost rather than a discrete scheme cost and so the actual money we have had to provide is just the incremental cost of putting the track back at a higher speed. The line is currently 60mph throughout with permanent speed restrictions in various places, but the aspiration is to get it up to 75mph.
“Although we won’t be able to open at the higher speed because we still have work to do on some structures and level crossings, the track will be ready for it because we will have done a substantial part of the overall scheme.”
The line’s not completely shut because there’s still the traffic to and from the Dungeness nuclear power station. Trains run two or three times a week with nuclear flasks. But Network Rail have worked with DRS to concentrate their period of operations so that they could get longer periods of blockage of up to five days at a time.
Bridgeworks
Elsewhere in the blockade Network Rail are renewing two overbridge decks, repairing about 18 footbridges and several culverts. An embankment is being repaired and there are about six areas with major track renewals. In amongst all this the track maintenance organisation is doing the maximum it can within the constraints of everyone else working including a mile’s worth of relaying.
The two overbridges are at Three Oaks and Doleham and were not planned to be renewed until fairly late on in 2013. They had to be fast-tracked. There’s a bit of risk because both bridges are covered in services. But, even in a worst case, they won’t affect the blockade if they’re not finished. As a result road closures have been reduced from six months to just three weeks, drastically hacking the costs by up to 50%. The existing superstructures will be reconstructed by contractor Dyer and Butler with repairs carried out to the wing walls and abutments to give a design life of 120 years, maintenance free for the first 25 years. Precast concrete bridge beams are being installed at both sites in series as each bridge acts as a traffic diversion route for the other. All this work, including re-instatement of the highway, will be complete by 1 April 2012.
Stockpiles
Of course, everyone wants to get their trains in. To get the most from the blockade there’s an Ore blockade coordination meeting every two weeks to thrash out details. In parallel, Orpington Maintenance teams led by Helen Warnock, the Infrastructure Maintenance Engineer, have spent months dropping equipment and materials around the line in secure locations so that it’s there ready for the blockade. Also trains and road-railers have been parked up in various locations along the line so that they’re in position and don’t get in each other’s way.
A new coalfield?
The blockade ends on 11th March. But there will be a subsequent weekend possession to mop up works that can’t be done before the track renewal work in the tunnel, such as work on manholes. The fabric of Ore tunnel will be secured for at least 20 years.
The Kent coalfield was discovered during an early attempt to drive a channel tunnel – at least that’s what it says on the internet so it must be true. This time miners will emerge from Ore tunnel probably with not one piece of coal – but who knows?
