LANCE CREEK RESERVOIR DAM UPGRADE

The Lance Creek Reservoir, located on Lance Creek about 3 km north of Kongwak in Victoria, supplies water to a number of townships in South Gippsland including Wonthaggi, Inverloch and Cape Patterson as well as supplementing Candowie Reservoir. The reservoir has a maximum storage capacity of close to 4600 ML.

The portfolio risk assessment of South Gippsland Water raised the issue of the potential liquefaction of sandy soils in the foundation under the embankment of the Lance Creek Reservoir. The presence of liquefaction susceptible sandy layer was confirmed for both upstream and section of the downstream shoulders by recent investigations. It was also confirmed that the safety factor of the upstream shoulder was far below 1.0 for seismic loading under the MDE (Maximum Design Earthquake), and therefore susceptible to slope stability. Deformation analyses revealed that excessive post earthquake deformations were likely once liquefaction was triggered, leading to a likely catastrophic breach of the embankment.

Concept options for remediation of the embankment against earthquake triggered instability were evaluated. A combination of deep soil treatment and a stabilizing berm provides the optimal solution to bring the embankment up to modern standards.

The Lance Creek Reservoir Dam Upgrade works involved strengthening of the alluvial foundations under portions of the upstream and downstream shoulders, as well as providing additional stabilizing berms to withstand earthquake loading conditions. The reservoir will remain operational during the project at a reduced level, below the temporary upstream platform.

Avopiling was engaged as specialist contractor to carry out the foundation strengthening works with Deep Soil Mixing(DSM). ‘TURBOJET’ technology, was preferred over stone columns and Jet grouting was introduced for the first time in Australia. Extensive laboratory testing and field trial validation tests have been performed to select the optimum parameters for building DSM columns.

SOILMEC R930 – only one available in the country- is being utilised with special DSM tool built by Avopiling Pty Ltd. The rig is equipped with state of the art technology instrumentation developed by the N.D Technology (U.K.) to monitor DSM columns control parameters. Cement – grout with possible bentonite addition will be used to improve the alluvial foundations.

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