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Allt-na-Slanach Viaduct, Moy
Allt-na-Slanach burn, Moy, Highland
Allt-na-Slanach Viaduct, Moy
associated engineer
Murdoch Paterson
date  1897, 23rd November 2002
UK era  Victorian  |  category  Railway Viaduct  |  reference  NH760349
ICE reference number  HEW 601 / 02
photo  Paul Steen
Allt-na-Slanach Viaduct is the last timber viaduct left on the Scottish mainland rail network — a rare and substantial survivor of a once fairly common bridge type. It is situated approximately 24km south of Inverness.
The viaduct carries the Perth to Inverness line over the Allt-na-Slanach burn, originally as a single line of track, though provision was made for a double one. Timber was chosen for its construction in order to keep the weight of the bridge down, for the land is marshy.
The trestle viaduct crosses the small valley in five spans of 7m, the centre one spanning the burn. It is a Grade A listed structure.
Timber beams run lengthwise supported on the trestle structures. Each trestle consists of four vertical posts across the width of the bridge and bracing raked posts at each end. Angled support struts from each post to the beams above reduce the beam spans to about 3.3m. Below thethe structs is further bracing and longitudinal members at a low level.
Investigations in 2001 found that the timbers had been seriously damaged by fungal decay and work engineered by Arup Scotland was planned to protect the timber and strengthen the bridge.
The central track-supporting structure was replaced at deck level, supported by concrete columns with independent foundations. This design allowed the majority of the original timbers to remain in place, keeping the appearance of the bridge in tact, but putting no railway loading on the original structure, though it does still support the side gangways.
To carry out this work, the contractors had possession of the bridge for only one week. They inserted the new, multi-span steel deck into the heart of the structure. Work was completed on 23rd November 2002.
Contractor: John Ross & Son (1897)
Associated engineer: Arup Scotland (2002)
Contractor: Carillion Rail (2002)
Research: JJ
Arup Scotland ... www.arup.com
reference sources   CEH SHI

Allt-na-Slanach Viaduct, Moy