S&C VIADUCT
PAUL STEPHEN commends Network Rail’s project to protect the Settle-Carlisle Line at Eden Brows from future landslides
On March 31, the iconic SettleCarlisle Line (S&C) is due to reopen as a through route following a 14-month closure. The date marks the completion of a long and costly engineering project to put right the effects of the 500,000-tonne landslip that occurred near Eden Brows in February 2016 ( RAIL 794, 795).
The railway will also be protected from any future geological instability, with Network Rail spending £ 23 million on shoring up the compromised embankment in the Eden Valley, eight miles south of Carlisle.
The area has a history of failure. An even more catastrophic landslip occurred during construction of the line in 1873, delaying the opening of the S&C by a full two years.
The Victorians opted to make rudimentary repairs by hastily replacing the lost material and then managing any further movement, but 143 years later NR engineers opted for a more permanent fix.
They decided to build a concrete slab 1.5 metres thick and 100 metres long, held in place just below the railway by two rows of steel piles filled with concrete, driven up to 20 metres into the ground.
By anchoring the new structure so firmly within the surrounding bedrock of the gorge, it has effectively isolated it from the embankment. So even if the earthworks should give way again, the alignment would remain unaffected ( RAIL 810).
But what will passengers see at Eden Brows? Inevitably with so much of the new structure supporting the tracks from beneath, almost nothing - presenting something of an anticlimax to the end of NR’s largest ever landslip repair project.
To help RAIL readers visualise the size and scale of the subterranean structure, it is useful to think of it as a viaduct complete with bridge deck and supporting columns, but buried beneath ground (unlike the S&C’s other 22 more traditional viaducts).
NR stresses that it is technically more of a wall rather than an underground viaduct, despite appearances, but it will be assigned its own structure number in recognition of its scale.
In imperial units, the Eden Brows ‘viaduct’ measures 79 feet deep and 82 yards long, making it comparable in size to four other S&C viaducts.
Ais Gill viaduct is the closest match at 75 feet tall and 87 yards long. But as it crosses a steep ravine its height is mainly in the middle, unlike at Eden Brows where its concrete pilings are of uniform depth.
High Stand Gill viaduct is 60 feet high and 91 yards long, but trees obscure much of it, while Crowdundle viaduct is 55 feet tall and 86 yards, making it a similar length but not as high as the piles at Eden Brows.
Lastly there is Dry Beck viaduct, 80 feet high and 139 yards long. It is the nearest of the four viaducts to Eden Brows, making its comparison a little more interesting.
Here RAIL presents images of two of these viaducts, to illustrate the enormity of the Eden Brows subterranean structure.