page_title: Forth Bridge
section_title: South Queensferry
hierarchical_section_title: Forth Bridge / Construction / Circular piers / South Queensferry
caption_attribution_description: English: Forth Bridge (1890) Fig. 46, Page 26
context_page_description: The Forth Bridge is a cantilever railway bridge across the Firth of Forth in the east of Scotland, 9 miles west of central Edinburgh. It is considered as a symbol of Scotland, and is a UNESCO World Heritage Site. It was designed by the English engineers Sir John Fowler and Sir Benjamin Baker. It is sometimes referred to as the Forth Rail Bridge, although this has never been its official name.
  Construction of the bridge began in 1882 and it was opened on 4 March 1890 by the Duke of Rothesay, the future Edward VII. The bridge carries the Edinburgh–Aberdeen line across the Forth between the villages of South Queensferry and North Queensferry and has a total length of 8,094 feet. When it opened it had the longest single cantilever bridge span in the world, until 1919 when the Quebec Bridge in Canada was completed. It continues to be the world's second-longest single cantilever span, with a span of 1,709 feet.
  The bridge and its associated railway infrastructure are owned by Network Rail.
context_section_description: The four South Queensferry caissons were all sunk by the pneumatic method, and are identical in design except for differences in height. A T shaped jetty was built at the site of the South Queensferry piers, to allow one caisson to be attached to each corner, and when launched the caissons were attached to the jetty and permitted to rise and fall with the tide. Excavation beneath the caissons was generally only carried out at high tide when the caisson was supported by buoyancy, and then when the tide fell the air pressure was reduced in order to allow the caisson to sink down, and digging would begin anew.
  The north-west caisson was towed into place in December 1884, but an exceptionally low tide on New Year's Day 1885 caused the caisson to sink into the mud of the river bed and adopt a slight tilt. When the tide rose, it flooded over the lower edge, filling the caisson with water, and when the tide fell but the water did not drain from the caisson, its top-heaviness caused to tilt further. Plates were bolted on by divers to raise the edge of the caisson above water level, and the caisson was reinforced with wooden struts as water was pumped out, but pumping took place too quickly and the water pressure tore a hole between 25 and 30 feet (7.6 and 9.1 m) long. It was decided to construct a "barrel" of large timbers inside the caisson to reinforce it, and it was ten months before the caisson could be pumped out and dug free. The caisson was refloated on 19 October 1885, and then moved into position and sunk with suitable modifications.
caption: The tilted caisson
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