trenchless technology
~ ref ereed paper
DESIGN FOR THE REPLACEMENT OF THE MELBOURNE MAIN SEWER M Dixon Abstract The Melbourne Main Sewer Replacement project (MMSR) involves the replacement of a 2.2km, 110 year-old sewer by a new gravity sewer main with six key manhole shafts, known as the Melbourne Main Reliever (MMR). The majority of the MMR sewer tunnel is situated south of the Yarra River and will be constructed using an earth pressure balance (EPB) tun nel boring machine (TBM) and w ill be lined with precast concrete segments. The tunnel will be 2.4m internal diameter and will have a 1 .8m diameter Glass Rei nforced Plastic (GRP) sewer pipe positioned within it. This project represents the first largescale, modern, mechanised tunnel project in Melbourne's Yarra Delta Quaternary sediments. There is little precedent for similar scale tun nelling projects in these particular geological units. The MMSR project has a capital cost of approximately $220 million with the construction of the new MMR sewer tunnel which commenced in mid-2008. The new sewer system commissioning is scheduled for completion by mid-2012.
Introduction Melbourne Water is undertaking the replacement of the existing 2.2 km long, 110 year-old sewer Melbourne Main Sewer (MMS) between the north bank of the Yarra River and the Hobsons Bay Main Sewer (HBMS) in Port Melbourne. The original MMS was constructed in the late 1890's to collect sewage from the City of Melbourne and adjacent residential areas. The existing sewer transfers flows from the city, parallel to the north bank of the Yarra River, t o the downstream side of the Charles Grimes Bridge. It then crosses the Yarra River and flows southwest to join the HBMS in Port Melbourne. This paper is a highly condensed version of the paper presented at 'Trenchless Australasia' - ASTT Conference 2009, September 2009.
58 DECEMBER 2009 water
Figure 1. The Proposed Alignment of the MMR through Port Melbourne.
The MMS was constructed by the Melbou rne Metropolitan Board of Works (MMBW) in the late 1890s using a variety of techniques. One section was constructed using seven different tun nel shields, another section of the tunnel was lined using a cast iron shell with concrete lining whilst other sections were lined using concrete blocks. Compressed air was used only in one section where the tunnel alignment came close to a number of brick houses on the surface. This new infrast ructure wi ll consist of 2,088 m of driven, segmentally lined sewer tunnel, having an internal diamet er of 2.4 m providing the structural support
Boring a sewer in loose sediments close to a 30 story building requires close control of the TBM.
for the new sewer. The new sewer, known as the Melbourne Main Reliever (MMR), has by means of a secondary hydraulic liner w ith an internal diameter of 1 .8 m made from Glass Reinforced Plastic (GRP) will provide increased hydraulic capacity. Difficult ground conditions, crossing of the Yarra River, extensive new surface development s in the area and the risk of settlement damage to buildings have all been major design obstacles to overcome. Simply selecting a horizontal and vertical alignment for the tun nel was very difficult. To find a solution that achieved the best, least cost community solution for the project required considerable effort to inform and liaise with stakeholders, asset owners and the community. The project's design and construction is being delivered under a partnering incentive based arrangement involving GHD as designer, John Holland as
technical features