Wagstaff Piling was contracted by Broad to design and build the retention system for a basement car park and foundations for a new Woolworths shopping centre in Inglewood, Perth. The brief at tender stage was a CFA secant retaining wall, however due to the restrictions with space on the site, a high-water table and a strict performance specification from the client, Wagstaff Piling proposed a 400mm thick diaphragm wall for the boundary retention and CFA piles for the foundations. This was proposed and accepted once a number of client consultants were convinced of the benefit of this approach. The diaphragm wall machine used was a Enteco E300 piling rig with diaphragm wall attachment. The project was particularly challenging as a result of the proximity of residential structures on the southern boundary where underpinning was required in order to construct guide walls and to install diaphragm walls within 100mm of the boundary. The CFA piles were installed from the same platform level to a depth of 20m using a Bauer RG25 piling rig. In order to optimise the design Wagstaff piling conducted three in-house PDA tests. Using this method the client was able to excavate below the ground water table and construct the pile caps in a controlled manner. On completion many areas of the diaphragm wall have been left exposed inside the basement due to the quality of the finish.
