Westminster car park
Westminster car park was the most significant deep basement to be built in central London in the 1970s. The five-level underground car park for MPs in New Palace Yard was built at a cost of £2.5M and designed to accommodate 500 cars.
The project called for a combination of advanced research and analytical techniques. EV Zinn Consultants adopted a diaphragm walling design to safeguard the stability of the adjacent Houses of Parliament, with ICOS (Great Britain) installing the 1m thick perimeter diaphragm wall to a depth of 30m using a low headroom trenching rig. Once walling was finished, 43 under-reamed bored piles were installed within the contained area, and the 600mm thick car park roof laid on top. The car park was then excavated top down to form the 400mm thick internal floors.
John Burland of BRE used sophisticated instrumentation to check on areas where settlements could occur, including the Palace of Westminster, the 14th century Westminster Hall, Big Ben and the House of Commons, and also to monitor ground movements near a deep sewer and the London Underground District & Circle Line. Inclinometers installed in walls registered tilt and ground heave in the bottom of the excavation and changes of pore pressure were also monitored.