Though impressive, Bachy Soletanche's £600,000 retaining walls are primarily temporary works. Their role is solely to hold back the hillside while the three apartment blocks and multi-level underground car park are built into the hillside.
Contiguous CFA piling was chosen over large diameter or secant walling as, says Bachy Soletanche contracts manager Rob Howarth, it is three times quicker to complete and more suited to the site's granular soils.
Although in practice just two walls, at design stage the total 115m length of walls was divided into 20 sections.
The 22m long, 600mm diameter piles are fully reinforced with even the largest 1.3t rebar cage fabricated on site and inserted in one length. A high slump, 35N/mm 2'fluid' concrete mix was needed so reinforcement could be pushed down each pile soon after concreting.
Each of the main wall's 33 ground anchors, drilled in two rows at angles between 30infinity and 45infinity, was also individually designed and is now stressed up to 750kN.
Howarth claims the wall is one of the highest of its type in Britain and represents 'the most complex structure I have yet installed'.