US$70m saving on struts
In another departure from convention, the contractors proposed constructing retaining walls using 1.2m to 1.5m diameter pipe piles instead of the common sheet and soldier pile combination. Pipe piles are far stiffer, making it easier to comply with the LTA’s very tight wall deflection criteria. This meant that two levels of struts were more than adequate, rather than the four to five strut levels specified in the indicative design.
With the first strut level just below ground level, the second was installed at mid-height, 7m down, with deep level restraint provided by the massively strong DCM ground improvement layer. On each contract, the elimination of every strut layer has saved almost US$24 million, yielding a US$70 million combined benefit. Reducing the number of struts from five to two layers has offered a huge time saving and dramatically improved worker safety, with lifting and manual handling operations cut by 60%.