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Lothian Bridge
Tyne Water, Pathhead, Midlothian, Scotland, UK
Lothian Bridge
associated engineer
Thomas Telford
date  1827 - 1831
UK era  Georgian  |  category  Bridge  |  reference  NT390645
ICE reference number  HEW 892/01
photo  © Kim Traynor and licensed for reuse under this Creative Commons Licence
Lothian Bridge, or Pathhead Bridge, is a striking five arch masonry viaduct that carries the A68 Edinburgh to Morpeth road over the Tyne Water valley. It features the arch and pilaster detailing that its engineer later used to good effect on Dean Bridge in Edinburgh. Lothian Bridge is still in use, with a speed restriction.
The 19th century improvements to the road between Edinburgh and Morpeth were commissioned by the districtís convenor of roads, Sir John Hamilton Dalrymple (1780-1835, 5th baronet). To cross the wide valley of the Tyne Water north of Pathhead, engineer Thomas Telford (1757-1834) designed a five span viaduct between large approach embankments. Resident engineer Henry Welch (1795-1858) supervised the construction by stonemason James Lees.
Problems were encountered with the foundations. The supposed bedrock 4m below the surface was actually a deposit of "large round stones". Piling was not an option, as during site investigation an iron rod was driven some 17m without impediment. At the direction of Telford, James Jardine (1776-1858) and others, the piers were founded on platforms consisting of two tiers of Memel timber (softwood) logs, and three tiers of stones from Craigleith quarry. This added an extra £2,000 to the cost.
Constructed in sandstone ashlar masonry, the viaduct stands 25m high and cost about £8,500 in total. The abutments are rectangular in plan, with curved wing walls helping resist thrust from the embankments. The interior of each abutment is divided into four hollow cells by longitudinal and transverse walls.
The superstructure is supported on four piers, 2.4m by 8.5m in section. They are also hollow, with cross walls dividing each into three equal-sized cells. Five semicircular arches of 15.2m span spring form the piers, with soffits 22.6m above the river bed. The bridge carries a two-lane roadway.
The narrow footpaths that flank the bridge are supported by 'ascititious', or supplemental, arches ó five to each elevation. They project 610mm from the superstructure. Each is a shallow segmental arch of 16.5m span and 2.4m rise, springing from a pilaster detail at the midpoint between the main arch springing and the top of the parapet wall.
Telford intended that the supplemental arches and pier pilasters would make the bridge appear less massive and more slender. Though successful to some extent here, he refined the approach further for Dean Bridge (1829-31) in Edinburgh where the external arches are 1.5m forward of the main spans.
In January 1971, Lothian Bridge was Category A listed. It now carries the A68 and has an imposed speed limit of 48kph (30mph).
Resident engineer: Henry Welch
Contractor: James Lees
"Mechanics' Magazine", Vol.2, July-December 1833, New York, 1834
reference sources   CEH SLBBDCE1Smiles2

Lothian Bridge