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Douglas finds itself undisturbed

SHORING FIRM Groundforce supplied the support for a difficult basement excavation on a town centre development in Douglas on the Isle of Man.

Local contractor Dandara Commercial is building the £5M Wellington Street project, which has a night club, fitness centre and shops, for client Vezelay.

The 28m by 21m site is tight up against the street, a Marks & Spencer store and a car park, all of which have shallow foundations on granular marine deposits.

As the 7m deep basement was being formed below all the adjacent footings, it was essential to avoid disturbing the surrounding ground or the tidal groundwater regime.

First, a hard/soft CFA secant pile wall was installed, which also acts as a foundation for the development.

Capping beams were cast and excavation began.

The excavation was to be propped at two levels.

'The original plan was to use shoring specially fabricated from hot rolled sections, ' says Dandara structural engineer Greg Kerwick.

But because of the need for fast installation - 'the main thing was speed' - Dandara decided to use Groundforce's modular hydraulic Mega Brace system.

Installation took only two days.

Mega Beams were installed around the excavation at pile capping beam level, propped across each corner by two knee braces. Corner angles range from 81degrees to 95degrees and were easily accommodated by the pinned end connectors.

Twin large diameter tubular struts spanned the middle of the site between the longest sides.This avoided the need for king piles and gave Dandara an unobstructed space for excavation and foundation construction.

Foundation work is now finished and construction of the four-storey steel framed development above is well under way.

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