Temporary working platforms play a crucial role in providing stability and safety for construction activities including piling and crane lifts on transport infrastructure projects. This paper focuses on the design and performance evaluation of steel/geogrid-reinforced working platforms for the operation of crawler cranes utilised for bridge construction as part of the West Gate Tunnel Project over the Maribyrnong River in Melbourne, Australia. Working platform designs conventionally adhere to available codes such as BRE470 and TWF2019. However, these codes may not suit flexible platforms constructed over soft soils like Coode Island Silt (CIS). CIS is a challenging soft soil in Melbourne known for its significant compressibility and nonlinear stress–strain behaviour making it difficult to meet the strict serviceability design criteria for working platforms. This study adopts an innovative approach that deviates from conventional industry standards to provide efficiency, safety and economic viability for working platforms. Settlement monitoring data from field trials was used to back-analyse undrained and partially drained elastic moduli. This helps establish a site-specific correlation between elastic modulus and undrained shear strength, instead of relying on generic published correlations for soft soils. Additionally, a three-dimensional finite element model was developed to accurately simulate the soil structure interaction and to perform sensitivity analyses to optimise the design considering various combinations of platform composition, thickness and reinforcement type and quantity. The outcomes of this study together with the post-construction performance evaluation provide valuable insights into the design of temporary working platforms, particularly on challenging ground conditions.