KP41 Tunnel

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The alignment of the Sugarloaf pipeline through an area of steep wooded terrain required the construction of a tunnel to avoid slope stability issues arising from excavating benching for trench construction.  Designed by GHD tunnel engineers, the KP41 tunnel (as named after its chainage location) is an 830m tunnel excavated by a pipejacked TBM. The tunnel was excavated upwards on a continuous grade of 0.5% and around an 825m-radius curve.

The tunnel had a geological alignment made up predominately of Sandstone and Siltstone of varying strengths, and some Colluviums with cobbles.  The TBM used was a slurry shield machine with an excavation diameter of a 2.475m.  A hard rock cutting head was used to break the rock, which at times reached strengths of up to 310Mpa.

The drive pit contained a 4 cylinder jacking station that supplied 1400 tonnes of thrust.  Supplementing this, 7 interjack stations were installed along the pipestring, each capable of a further 1000 tonnes of thrust.  

The TBM was jacked in front of the string of 3m long reinforced concrete pipes, each with an outer diameter of 2.4m. 

Tunnelling

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