Railway viaduct arch repairs:

Edinkillie Viaduct

Dunphail, Moray · 2009

Our role: Principal contractor, masonry repairs
Client: Private estate trust
Engineer: A F Cruden Associates, Inverness
Grant body: Historic Scotland
Value: Under £0.5m
Programme: October 2008 to March 2009
Scope: Designed suspended scaffold, sandstone voussoir indents, stone stitching, lime repointing, cleaning of lime deposits, parapet repairs, deck joint resealing

Edinkillie Viaduct, also known as the Divie Viaduct, carries the former Inverness and Perth Junction Railway across the valley of the River Divie near Dunphail in Moray. Built between 1861 and 1863, it has seven arches of about 13 metres span, rubble piers and spandrels and dressed sandstone voussoirs, and stands around 14 metres high. The line closed in the 1960s. We were appointed by the trust that owns the structure, working to the consulting engineer's design under a Historic Scotland grant scheme, to repair the worst affected arch and the parapets.

Edinkillie Viaduct: drone flyover, October 2024

Edinkillie Viaduct, River Divie, Dunphail, Moray — photograph 1

Edinkillie Viaduct, River Divie, Dunphail, Moray — photograph 2

Edinkillie Viaduct, River Divie, Dunphail, Moray — photograph 3

Edinkillie Viaduct, River Divie, Dunphail, Moray — photograph 4

Edinkillie Viaduct, River Divie, Dunphail, Moray — photograph 5

Edinkillie Viaduct, River Divie, Dunphail, Moray — photograph 6

The challenge

The viaduct had leaked from its track bed for most of its life. Water draining through the granular fill had washed lime out of the mortar beds and redeposited it as thick calcite streaks across the arch soffits and piers, and the sandstone voussoirs of the second arch from the south were cracking, splitting along their bedding planes and spalling, with blocks falling from the soffit. The dense, almost impermeable rubble of the piers meant the masonry could only dry through its joints. Access was the other difficulty: the arch is 14 metres above a steep, wooded riverbank, with no ground from which a conventional scaffold could reach the soffit.

Our solution

The arch was reached from an engineer designed suspended scaffold hung from an anchor scaffold built on the viaduct deck, with the parapets protected in hessian while materials were passed over the wall. From the platform we raked out the eroded joints across the arch soffit and spandrels to a minimum depth of 50 millimetres and repointed them in lime mortar, cleaning the calcite deposits from the stone as we went. The delaminated voussoirs were cut back and faced with new sandstone indents, each dowelled to the sound stone behind with a stainless steel resin anchor, washer and nut, then bedded and pointed in lime to the engineer's detail. A temporary timber support system held the intrados while the indents were set, and two delaminated stones were cross stitched rather than replaced. A fabric assessment with core sampling identified the voussoirs as a Hopeman type sandstone and confirmed that water from the deck, not driven rain, was the main cause of decay. The works were therefore extended to the top of the structure: the expansion and drainage channel joints in the concrete running slab were cut out and sealed with a two part polysulphide sealant, the parapet to deck junction was sealed, and the parapets were repointed with fallen stones rebuilt.