SMEC is providing specialised engineering and technical services, as well as stakeholder engagement, for the new trunk sewer line being delivered by Rob Carr, which will increase the sewer capacity and provide a safe and reliable wastewater service to the people living and working in Melbourne’s CBD.

The project commenced in late 2019 with the construction of a 20m deep launch shaft near the intersection of Lonsdale and William Streets.This shaft is the starting point for the TBM’s 550m journey to Elizabeth Street. Once it reaches Elizabeth Street, the TBM will be retrieved and returned to the launch shaft, and make the final 350m trip to Spencer Street, where it will connect to the Stage 1 sewer that was completed in 2018.

A 1,500 mm diameter sewer main will be installed via pipe-jacking at depths of between 11 and 23m below street level. Once pipe-jacking is complete, pre-cast glass reinforced plastic (GRP) access chambers will be lowered into the launch and retrieval shafts and connected to the new sewer main.

A major challenge for the project is to ensure that disruption to the busy city traffic is minimised during the 10-month construction period. SMEC has been working with Rob Carr, City West Water and key project stakeholders – City of Melbourne, Department of Transport, Transdev and Yarra Trams – throughout the project to maintain reasonable traffic flow during construction. A testament to the project team’s efforts are the positive reactions from the stakeholders, and the low impacts to traffic disruptions to date.

Planning for success

A detailed 3D model of the access chambers and sewer main was developed by SMEC to illustrate the complex arrangement of the structures, including the various inlet/outlet connections and chase arrangement in the access chambers. The 3D model was also used for clash detection assessments to ensure that the new sewer infrastructure would not interfere with existing buried infrastructure such as the Telstra Tunnel and other adjacent utilities.

During the Investigations and Design phase, more than 50 SMEC specialists in various disciplines contributed to early works investigations, planning of the construction activities, and minimising risks during construction. SMEC, in partnership with City West Water, also maintained extensive and ongoing consultation with transport stakeholders and City of Melbourne throughout the planning, design and construction phases.

SMEC’s contribution to this project includes:

• services proving and non-destructive investigations,
• geotechnical investigations, groundwater monitoring and contaminated soil assessments,
• tree impact assessments,
• cultural heritage investigations,
• detailed design of the new sewer main, access chambers and sewer connections, utilising detailed 3D modelling to illustrate the complex arrangement of the structures and surrounding infrastructure,
• utilities relocation designs,
• community and stakeholder engagement services,
• traffic modelling, impact assessments, planning and diversion strategies,
• road safety audits, and
• dilapidation surveys of buildings and underground structures adjacent to the new sewer main.