Performance of a 7.5m high post and panel wall under a 120t piling rig load

Melbourne Metro Rail Infrastructure Alliance (RIA) project is currently under construction as part of the larger Melbourne Metro Rail Tunnel Project in Melbourne. The works at the Eastern entrance to the Metro Tunnel include construction of a cut & cover tunnel and decline structure which will form the entrance to the metro tunnel when completed in 2025. Restricted site access including proximity to residential properties and operational live rail necessitated a purpose built temporary retaining structure as a working platform to support a 120 tonne piling rig for the installation of 18 m long CFA piles for the cut & cover tunnel structure. A post and panel wall comprising 900 diameter CFA piles with 310UC steel sections was considered a feasible solution for constraint site conditions. The maximum height of the wall was 7.5 m including a piling platform to support a piling rig track pressure of 345 kPa operating behind the wall. Ground conditions comprised cemented sandy soils of Brighton Group underlain by Fyansford Formation and high ground water level.

This paper discusses geotechnical characterisation of the site, design development, challenges and site constraints, monitoring of the wall during construction and performance of the retaining wall during the operation of the piling rig from a design and construction perspective.