My question still stands once NR had decided how Farnworth was to be tackled how long was planned, allowed for by discussion with operators and how long it will take in practise. If NR didn't know how Farnworth was to be tackled in terms of the tunnel before discussing with opeartors then that sounds like sheer incompetence.
I'll be honest, I don't have the first idea what information you actually want or expect.
Network Rail gauged the two Farnworth Tunnels first of all, and determined that no overhead catenary could fit within the two tunnels without the tunnels being modified.
The civil engineers had a look at the data we have on the tunnels and initially decided the work needed would be a trackbed lower in one tunnel and slab track in the second tunnel (I forget which one is which) and went about checking the lining of the tunnel to see what implications a track bed lower and slab track installation would have on the lining, what work would be needed at the base of the tunnel, and checking to see where the catenary would be installed on the roof of the tunnel.
The civil engineers very quickly came to the realisation that the tunnels were effectively life expired, and would need significant work to rehabilitate the fabric of the structure, even then, additional work and additional monitoring would be needed.
The question was asked - what if we build a new tunnel, would that help, and a business case was built around re-boring the larger tunnel, improving the alignment, increasing the line speed to make full use of the 100mph capability of the rolling stock, and removing some of the maintenance requirements that would come from monitoring and repairing the old tunnels continually.
The four month closure that was originally mentioned 3 years back was before detailed design work was done, that was based on other tunnel repair work that Network Rail has had to contend with, experience from looking after structures like Box Tunnel, the Severn Tunnel and planning works concerning repairs to Bowshank Tunnel and electrification of Winchburgh Tunnel.
The decision was made to re-bore the large tunnel thank to the business case that was developed, and that's where the current plan comes from.
The current plan was based on the tunnelling company working on the geophysics data they generated and from lots of work going on between the civils contractor, electrification contractor, tunnelling contractor and the TBM manufacturer to decide on the machine needed, the progression the machine would have with each ring fitted and what sort of tunnelling rates could be achieved given the ground conditions presented at the site, with the actual tunnel requirements dictated by Network Rail's requirements for gauge and track alignment.
There was also the requirement to keep one track open if possible, whilst the work was ongoing, so additional works were then planned to reinforce the remaining tunnel and to work out if any additional requirements would be needed to maximise the safety and stability of the remaining tunnel. There was lots of work with TOCs to see what we could do for them too, so they could offer less frequent but more capacious services. There's Schedule 4 and Schedule 8 payments to take into account too.
That all fed in, with other aspects of the electrification program, so we knew how long the tunnel would take to re-bore, what other works were necessary for the alignment changes, track upgrades for the speed and so on, with the result that a timetable was drawn up and with a little extra padding to cope with small problems - bad weather, machinery failure, that sort of thing, it was intended that the tunnel would have been re-bored and completely ready for traffic on the 5 October 2015.
There's none of this incompetence that you like to accuse Network Rail of time and time again. Network Rail are not tunnelling engineers, that's why specialist contractors have been appointed. This is not an overrun like the Kings Cross debacle at Christmas, it's a very well planned operation being screwed over by some really bad corner cutting and bodged tunneling work from the 1830s.
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The Engineers / Experts said four months required.
I'll see what I can dig out later in the week (when I should have a bit more time!)
