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Teacher’s notes

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This clip shows tunnel excavation during construction of the Snowy Mountains Hydro-electric Scheme. It shows how rock spoil blasted from the tunnel face is loaded onto rail trucks by a mechanised loader and how the trucks are shunted into place with the help of a cherry picker. Surveyors then mark out drill holes on the rock face for the next blast and the drilling rig (jumbo) moves into place to commence drilling. The clip includes narration and music.

Educational value points

• Excavation of tunnels in the Snowy Mountains Hydro-electric Scheme, which in this case had an average width of 6 m, often meant tunnelling through solid granite rock. Excavation began simultaneously from both ends of the tunnel and proceeded incrementally. Surveyors marked out the position of drill holes at regular intervals on the rock face. Workers then drilled these holes and packed them with explosives that, when detonated, caused the rock to fracture. The loader, or 'mucker’, then cleared the rock spoil, which was loaded onto train trucks to be transported to the surface.

• The sliding tunnel floor, shown in operation, helped to increase productivity, and world tunnelling records were repeatedly set during construction of the Scheme. The floor was a large steel platform with tracks that enabled rail trucks, the drilling rig (jumbo) and other tunnelling equipment to be moved in and out of the tunnel. The jumbo was a three-tiered platform that allowed workers to drill at various levels of the rock face; it was hinged in the middle so it could be swung back to allow equipment through to clear the rock spoil after blasting.

• The compressed-air drill in the clip was used to cut away rock or to bore holes, which were then packed with explosives. The rock was often so hard that the men had to work in pairs, with one man operating the drill and the other holding it against the rock; water was used to cool the drills. The type of work to be undertaken determined the shape of drill bit that was used. The different drills and drill bits used on the Scheme provided a prototype for the modern masonry drill bit.

• Tunnelling was the most dangerous job on the Scheme. Tunnellers worked hundreds of metres below ground in cold, damp, fetid air and often stood in water for hours. These hazards were compounded by the noise of rock drills, while fumes made it difficult to breathe and dust reduced visibility. Most tunnel injuries were caused by roof falls, premature explosions or by vehicles, such as muckers, navigating the confined space. Thirty-five men were killed during construction of the tunnels.

• In the 1960s the Snowy Mountains Hydro-electric Authority (SMA) made it compulsory for workers to wear safety helmets and safety boots, as shown here; however, workers had no ear or eye protection. During blasting in tunnels, workers blocked their ears with their fingers, and opened their mouths to prevent burst eardrums. Breathing apparatuses were not provided, even though the tunnels were thick with dust. Many tunnel workers experienced significant hearing loss.

• Built between 1949 and 1974, the Scheme was a major post-Second World War construction project and a huge engineering feat. It consisted of 16 large dams, 7 power stations, a pumping station, 145 km of interconnected tunnels and 80 km of aqueducts used to divert water from the Snowy Mountains for use in power generation and irrigation. The scheme cost a total of $820 million.

• As the largest single engineering project undertaken in Australia, the Scheme required a huge stock of heavy plant equipment such as the cherry picker shown. The cherry picker enabled rail trucks to be loaded in a confined space. Once a truck at the front of the train was filled with rock spoil, the cherry picker lifted up the empty truck from the rear of the train. The train was then shunted back underneath the cherry picker and the suspended new truck lowered onto the rails ready for loading. This rotation system was an innovation of the Scheme.

• Workers are shown wearing hard hats bearing the name 'Theiss’. Theiss Brothers is an Australian firm that was awarded several contracts on the Scheme, including construction of the Snowy–Geehi tunnel in 1961, which may be the tunnel shown in this clip. Although the Scheme was a federal government venture run by the SMA, most of the construction was carried out by public works departments and private companies from Australia and overseas who tendered for projects. These included the construction of dams, tunnels, pressure pipelines and power stations.