The historic Cathedral and Treasury precinct located in Perth CBD is undergoing a major redevelopment, including:
- Restoration of the existing 135 year old, heritage listed Treasury Building
- Construction of a 35 storey office tower
Mirvac subcontracted geotechnical specialists GFWA to construct the foundations, tunnels and temporary works for the Old Treasury Building (OTB) tower development. Mirvac Design had previously commissioned two geotechnical investigations and permanent retaining wall design. The precinct is one of the most iconic sites in Perth and the $280m tower is enclosed by both the Town Hall and the existing Treasury Buildings.
CMW carried out the detailed geotechnical design under GFWA’s contract. Throughout construction, CMW have provided further geotechnical input to verify, optimise and formalise the already completed designs.
Two boreholes were drilled by CMW to depths of 52m in order to confirm the depth to rock and rock strength parameters for the design of deep foundations. Design components included:
- Underpinning works using permeation grout techniques to create a grout block;
- Retaining walls with grouted anchors, using continuous flight auger techniques;
- Piled foundations encompassing barrette piles and pressure grouted tension piles;
- Construction methodologies for temporary needle beam jacking techniques in order to construct the tunnel from the OTB tower to Cathedral avenue.
Protecting the heritage buildings during construction presented a significant geotechnical challenge.
A lot of uncertainty existed regarding the behaviour of the needle beam’s under jacking. CMW was able to provide a simple, time efficient solution that prevented delay to Mirvac’s schedule.
In addition weekly site visits provided opportunities to suggest alternative construction methods which could better meet the demands of construction schedule and reduce costs.