The Heysen tunnels were completed in 2000, and take the Freeway through a steep-sided hill at a depth of up to 60 metres
This area is geologically complex, consisting of slate and quartzite with strengths ranging from low to very high. The strength, weathering and jointing characteristics of rocks were important considerations in developing a safe method of tunnel excavation.
An SW200 tunnelling machine normally used in heavy-duty mining operations tunnelled through 500 metres of rock for each tunnel at an average rate of 3 metres per day or 21 metres a week.
The support method during construction used the inherent strength in the rock mass to support the tunnel roof during excavation. A permanent concrete lining was installed when the excavation was complete.