Landslide Risk Assessment For Geehi Aqueduct, Snowy Mountains

Geehi River aqueduct diverts waters from left bank tributaries of the Geehi River and conveys these flows into Geehi Reservoir to augment the natural and tunnel inflows.

The aqueduct traverses a section of the steep western flank of the Great Divide with deeply incised valleys and contains numerous inverted syphons.

During the construction of the aqueduct problems were encountered with unstable ground in some areas along the bench. As a result extensive subsoil and surface drainage measures were carried out in the vicinity of the Big Tree Creek siphon, Maria creek siphon and previously burst area.

It was found during the latter stages of construction, that numerous joints between the concrete pipes and fittings had developed excessive gaps due to ground movements. A large proportion of the concrete pipes were found, both before and after laying, to have developed longitudinal internal cracks extending from socket end at the crown. A lap welded stainless steel liner has been installed internally to prevent leaks through the cracks and joints.

The section of the aqueduct passing through the Big tree area was known to be a landslip area. This paper describes the investigation, risk assessment and stabilisation process carried out to mitigate the risks. The construction was completed in March 2001.