Tunnelling Triumph

Board of Works Storeyard, 1895
Board of Works storeyard, South Melbourne, Victoria, circa 1895.
Source: Museum Victoria

Just months before work on the construction of the Melbourne Sewerage Scheme started, Victoria was plunged into one of the worst economic recessions in its history as the land boom of the 1880s came to a sudden end and dozens of banks and financial institutions closed. As factories began to close and the economy slowed, the investment in the sewerage project provided a much-needed boost to local industry and employment.

Over 2,000 labourers and tradesmen were employed in the construction of the system while dozens of clerks, draughtsmen, surveyors and engineers were also required. By the end of the 1890s, they had created detailed plans of most of Melbourne and hundreds of construction drawings, built a pumping station and treatment works and constructed 56 kilometres of mains, sub-mains and branch sewers and laid 435 kilometres of pipes for street sewers. Local manufacturers also benefitted supplying over 25,000 tonnes of cement, 13,000 tonnes of cast iron, almost 20 million bricks, tens of thousands of cisterns and toilet bowls, stoneware pipes, hundreds of tonnes of machinery and numerous associated requirements such as 5,000 manhole covers.

One of the most difficult and technically demanding tasks involved in the construction of Melbourne’s Sewerage Scheme was the driving of tunnels for the main sewers under the Yarra River and across the water-logged mud flats of Port Melbourne and Yarraville.

Underground the tunnellers worked in cramped, muddy and poorly lit conditions, facing the constant risks of tunnel collapse, suffocation from noxious gases, drowning by a sudden inrush of water, or the painful and life threatening decompression sickness known as ‘the bends’.

To drive the tunnel under the river a tunnelling shield designed by the British engineer James Henry Greathead was imported. Made of steel plate and cast-iron, the 3.4 metre diameter cylindrical shield was inched forward with hydraulic rams as the working face advanced. Inside the shield miners worked under compressed air at two to three times atmospheric pressure to slow the inflow of groundwater, while a strong bulkhead or diaphragm in the middle of the shield protected the tunnel face from collapsing inwards. As the shield advanced cast-iron segments were erected in rings and bolted together, then lined with 30 centimetres of concrete to form the finished tunnel.

On the night of Good Friday, 12 April 1895, disaster struck below the river when water broke into the tunnel and swamped the workings. A young engineer and five workers were drowned almost instantly with no chance of escape. Three other men waiting in the air lock to enter the tunnel were forced to watch in horror through a small thick glass window in the airlock door, powerless to do anything to help in the few seconds it took to flood the tunnel. After thousands of tons of clay were dumped on the riverbed to seal the hole, the tunnel was pumped out and work was resumed under a different contractor, with the river tunnel finally being completed 12 months later.

Local engineers produced improved shield designs for other contractors and tunnelling techniques were improved by experience. In total 20 tunnelling shields were used to drive 11.3 kilometres of tunnels. In all 16 people lost their lives during the construction of Melbourne’s sewers, which was regarded as a good safety record by the standards of the day.

Image Gallery

Interior of Shaft, Hobson's Bay Main Delivery of Clark's Tunnelling Shield Rear View of Clark's Tunnelling Shield View of Sewer Construction Shafts