2023 – Learnings from Deep Test Pit Investigations into the Filters for the Cardinia Dam Safety Upgrade

Simon Zhong

Filters are a key defensive control incorporated into many embankment dams. Their purpose is to mitigate and/or prevent initiation of internal erosion through defects that may progress through an embankment and lead to breach by gross enlargement or other means (ICOLD 1994, Fell et al. 2014).

For many of these embankment dams, the filters were not designed and constructed to the dam crest level, therefore leaving a residual dam safety risk of piping through the upper embankment. This is the case for the embankments of Cardinia Reservoir, Melbourne’s second largest water supply. The Cardinia Dam Safety Upgrade Project (CDSUP) was commissioned to address these dam safety risks.

Given the importance of the filters and to inform the detailed design of the upgrade works, it was important for the CDSUP to understand the characteristics and as-constructed detail of the filters within the embankment. As such, a range of geotechnical investigations was implemented in stages to investigate the filters including sonic drilling and large-scale deep test pit excavations.

This paper intends to share the lessons learnt from these small to large-scale investigations into the filters of a large dam. Key discussions include the advantages and disadvantages of sonic drilling and test pits, the nature of the information each of these investigative methods provides, and the impact on engineering interpretations, risk assessments, designs, and overall project.

Buy this resource