Less than five weeks into the project to bore out the Farnworth tunnel on the Manchester-Bolton line, Network Rail admitted on September 2 that “exceptionally poor ground conditions” meant that completion had been delayed from the planned October 4 “possibly until December”.
The ‘Up’ (Manchester-bound) bore is being increased in size to accommodate twin tracks and overhead electrification.
However, soon after boring started on August 1, engineers came across “large swathes of sand” said NR.
Between August 1 and September 2, 45 metres of the 276m tunnel had been excavated. Network Rail says that was at a rate of 2.8m per day (indicating that boring only took place on 16 days in August).
“On the assumption that the rate of tunnelling stays as it is now, completion will be December,” said NR.
The 9m-diameter ‘Fillie’ boring machine was expected to be able to tunnel 5.6m to 7m every 24 hours.
Network Rail Route Managing Director Martin Frobisher said: “We first hit an area of running sand on August 14, when our engineers saw it suddenly pouring from the working face. This has slowed progress and created big voids, the largest of which needed filling with around 35 tonnes of grout.
During the tunnel work, a very limited Preston-Bolton-Manchester service continues to operate each way through the ‘Down’ tunnel.