The tunnel construction was a portion of rehabilitating the Maroondah Aqueduct located in Yarra Glen and Dixons Creek, as the service life was close to an end. A 5.7 kilometer section of the old aqueduct was planned to be substituted with a new 1750 mm diameter concrete lined steel pipe.
As part of the project, John Holland KBR Joint Venture enlisted Geotesta to conduct a geotechnical investigation and carry out tunnel face mapping during excavation. The client needed the geotechnical information to justify the ground model and tunnel support such as rock bolting and shotcreting.
The site-specific geotechnical investigation includes:
- Borehole drilling with SPT and rock coring along the proposed tunnel alignment
- Laboratory testing on the collected samples
- Lugeon Test to determine the permeability of rock mass
- Abrasivity or Cerchar Test on rock samples
Face mapping reports were provided daily during tunnel drive excavations. These reports provided details of major joint sets and the derived Q-value that indicates the quality of the rock mass. From this data, John Holland could determine the ground support type for underground excavations.