Design of Working Platforms for Crawler Cranes Over Coode Island Silt

As part of the construction of the City Connections for the West Gate Tunnel Project in Melbourne, temporary platforms were required to support stable lifts for bridge components. The lifts required several large-capacity crawler cranes to be positioned over historical reclaimed lands near the Port of Melbourne comprising variable fill, overlying Holocene-age Coode Island Silt, characterized by soft compressible soils. The combination of the heavy payload of the bridge elements creating significant unbalanced loading under the crane tracks, together with small differential settlement tolerances of the cranes posed unique challenges in the design of temporary platforms that were economical, sustainable, and safe. A combination of bespoke structural crane mats comprising universal column sections over unbound temporary platforms constructed using recycled geomaterial was designed to support the lifts. Presented in this paper is the approach adopted to design the temporary platforms and the structural mats. The approach involved an initial platform design utilizing the bespoke structural mats using limit equilibrium and simplistic structural capacity calculations, followed by finite element assessment of immediate deflections of the platform and structural actions within the mats. The structural capacity of the nominated mats to support and effectively spread the crane loads was checked against the assessed actions and ground response. Real-time monitoring of the deflections against settlement predictions was also undertaken initially during the test loading of a crane lift to validate the design approach.