Adelaide Central Plaza

This project involved the demolition of the former John Martins Building and site clearing in preparation for the Adelaide Central Plaza development.

The retention system originally proposed in the contract documents was replaced by a retention system put forward by McMahon Services, which ultimately saved the client $500,000.

The alternative system proposed using two MPa sprayed stabilised sand in a batter and a large vertical block to retain the existing basement walls. Two MPa sprayed stabilised sand had never been used before so McMahon Services, along with the supplier and subcontractor, trialled the method until a suitable mix and design was established.

Large pads were excavated in the basement and poured so that the new columns for the next structure could be erected up through the basement floors before the stabilised sand was sprayed. The large pad footing incorporated some of the old footings which had large 250mm holes cored through the concrete up to 2m long to enable the new pads to be constructed.

The works were undertaken in a basement 7m below ground level with no ramp access. The area was extremely tight for small excavators and plant to operate in, as well as the requirement to maintain the atmosphere at a safe level so work could continue without breathing apparatus.