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Aberdeen Harbour South Breakwaters
Greyhope Road, Aberdeen, Scotland, UK
Aberdeen Harbour South Breakwaters
associated engineer
Thomas Telford
William Dyce Cay
Hugh R. Barr
date  1812 - 1815, July 1869 - 1873, 1938 - 1965
era  Georgian  |  category  Breakwater  |  reference  NJ962057
ICE reference number  HEW 1377/04-05
photo  © Richard Webb and licensed for reuse under this Creative Commons Licence
Aberdeen Harbour is a major British port. Its mouth on the River Dee is protected by solid breakwater arms constructed in stages during the 18th and 19th centuries. The first, Old South Breakwater (mapped and shown in the foreground above), was shortened after the second was completed. The structures require ongoing maintenance.
Aberdeen Harbour has been trading since at least the 12th century, and Aberdeen Harbour Board is the oldest existing company in Britain (established 1136). The harbour is protected by its North Pier and two South Breakwaters.
The 782m long granite and concrete North Pier was constructed in three stages, to the designs of three successive engineers: John Smeaton (1724-1792) in 1775-80, Thomas Telford (1757-1834) in 1810-15 and William Dyce Cay (1838-1925) in 1874-7.
The first South Breakwater was constructed in 1812-5, under the superintendence of the harbour board’s resident engineer John Gibb (1776-1850) in consultation with Telford. The structure was built to protect Telford’s North Pier extension and to restrict the harbour entrance channel, the depth of which also increased as a result of scour.
The breakwater follows a north-south alignment and was originally almost 244m long. When completed, its northern end was only 76m from the North Pier. It was constructed of stone quarried at Greyhope Bay and cost Ł14,675.
During 1869-79, many harbour entrance improvements were undertaken at the direction of Dyce Cay, who had succeeded Gibb as the board’s resident engineer. Further protection from south easterly gales was deemed necessary and, in addition to extending the North Pier for a third time, a new South Breakwater (NJ967056 to NJ967060) was constructed.
The second structure lies some 384m to the east of the first and was constructed between July 1869 and 1873. It too runs north-south, and is 320m long from high water mark with a maximum height of 14.3m above the seabed. An 18.9m tall concrete lighthouse sits at its seaward (north) end.
The seabed under the second breakwater is irregular, with areas of hard granite near the shore and a mix of boulders, gravel and clay at the seaward end. Rather than trying to shape the bedrock to fit the breakwater, Dyce Cay decided to adapt the structure to suit the rock by forming its foundation with bags of concrete. Jute bags filled with wet concrete were deposited from skips holding from 5.1 to 16.3 tonnes of concrete, by opening the skip hopper once it was in the right place. The bag dropped out and was tamped into position by divers.
Where the bedrock was of softer material, the outer end of the breakwater was protected from wave action undermineing using a concrete apron toe. The apron consisted of 101.6 tonne bags of concrete tipped from a timber hopper.
Precast mass concrete blocks weighing from 7.6 to 25.4 tonnes were laid over the bag foundations in horizontal courses 1.2m thick. They were lowered into position by a 25.4 tonne steam crane mounted on a temporary wagon way constructed on timber staging 3m above the sea. Divers prepared the sea bed for the foundation bags and also guided the blocks into place.
The blocks were built up to 300mm above low water neap tides, and the remaining 5.5m of the breakwater’s height was constructed in large pours of in situ mass concrete. The unmortared blocks are kept in place by the weight of the structure above them.
The clear distance between the North Pier head and the South Breakwater head is 335m. The cost of the new breakwater was Ł68,100 and when it was finished, the timber staging was sawn off level with the top of the concrete. Dyce Cay went on to use a similar construction method, relying on concrete bags and blocks, for his 1874-7 extension to the North Pier.
The old South Breakwater was shortened to 91.4m long (tip truncated to NJ963058) once the new one had been completed.
Within a couple of years of the second breakwater’s completion, the corners and faces of its concrete blocks exposed to the sea had begun to break away as immersion caused the concrete to swell. Investigation revealed that salt water caused a chemical reaction with the Portland cement in the concrete, resulting in the formation of magnesium hydroxide and calcium sulphate, which weakened and softened the concrete.
The deterioration was noted by William Smith, the harbour board’s resident engineer from 1880 to 1895. In a paper published in 1892, he recorded that voids had formed in the concrete in certain areas, particularly where the old staging timbers had been, and water pressure in the cavities was likely to displace the blocks.
In summer 1886, the "portion of the breakwater which had sustained the greatest damage from this action was grouted up solid, through sixteen holes bored down through the superstructure" and no further damage was caused. In summer 1887, a further 40 holes were bored and filled with some 215 tonnes of grout, after the joints in the face of the structure had been caulked by divers.
Remedial work undertaken from 1887 to 1892 included breaking out decayed areas of old concrete and refacing the breakwater with an impermeable skin of mortar, filling voids and improving the apron. Iron ties were used to tie the new work to the old. Underwater the repairs consisted of granite chips set in Roman cement, while above water level granite ashlar in Portland cement was used. The total cost of the repair work, 1873-92, was Ł11,000.
In 1937, gale force winds and heavy seas ripped a 30m gap right through the newer South Breakwater. Repair work began in 1938, under assistant harbour engineer Hugh R. Barr. The project was halted during World War II (1939-45), resumed in 1954 and completed in 1965.
The works involved constructing 30.5 tonne precast concrete blocks in a yard (NJ968056) to the south east of the inshore end of the breakwater. These were loaded onto a Sentinel steam wagon by crane, which ran on rails to the inner end of the breakwater. Here the blocks were lifted into place by the 25.4 tonne Titan steam crane Goliath, which was mounted on an overhead gantry. In addition to repairing the breach, the breakwater was widened to 10.7m.
Resident engineer (1812-15): John Gibb
Resident engineer (1869-73): William Dyce Cay
Resident engineer (1938 onwards): Hugh R. Barr
Research: ECPK
bibliography
"The Influence of Sea-Water upon Portland Cement Mortar and Concrete" by William Smith, Proceedings of the ICE, Vol.107, pp.73-97, London, 1892
"Harbours and Docks" by Leveson Francis Vernon-Harcourt, 1885, reprinted by Cambridge University Press, 2014
"House of Commons Papers", Vol.29, H.M. Stationery Office, London, 1835
https://canmore.org.uk
https://doriccolumns.wordpress.com
www.aberdeencity.gov.uk
www.coast-alive.eu
www.ice.org
www.ports.org.uk
www.scotlandsplaces.gov.uk
www.scottish-places.info
reference sources   CEH SHIJSBDCE1
Location

Aberdeen Harbour South Breakwaters