Cairn Curran Dam is a 44m high zoned earthfill embankment located near Bendigo in central
Victoria. The dam is owned and operated by Goulburn-Murray Water.

A risk assessment had identified that the junction between the embankment and spillway wall was a weakness in regard to the potential for piping. Initial geotechnical investigations indicated a softened zone adjacent to the foundation.
The conceptual upgrade design was to excavate the downstream slope and place filter material and a rockfill weighting berm. A 2-D slope stability analysis gave unacceptably low factors of safety for this excavation. The three dimensional nature of the embankment/spillway interface and excavation geometry was identified as an important factor in the upgrade design.

A detailed geotechnical assessment was undertaken and a geotechnical model developed that
accounted for potential softened zones adjacent to the spillway wall, along the foundation, and within the embankment.

A 3-D limit equilibrium slope stability program was utilised to analyse the 3-D factors of safety. The
program employed an extension of Bishop’s method of slices to a 3-D ‘method of columns’. A 3-D
finite element analysis was also undertaken to estimate likely deformations of the embankment and cut slope during construction.

The development of the geotechnical model and subsequent analysis allowed the upgrade works to be undertaken with confidence.

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