Many mapped faults in the south-eastern highlands of New South Wales and Victoria are associated with apparently youthful topography, suggesting that faulting may have played a role in shaping the modern landscape. This has been demonstrated to be the case for the Lake George Fault, and may reasonably be inferred for the poorly characterised Murrumbidgee, Khancoban, Tantangara, Berridale Wrench and Tawonga faults. More than a dozen nearby major faults with similarly youthful topography are uncharacterised. In general, fault locations and extents are inconsistent across different scales of geologic mapping, and rupture lengths, slip rates and other fault behaviours remain largely unquantified. A more comprehensive understanding of these faults is required to support safety assessments for communities and large infrastructure in the region.
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Global climate change will amplify existing risks, as well as create new risks for natural and human systems. Recent climate changes have already had widespread impacts on human and natural systems. Dams provide a range of economic, environmental and social benefits including irrigation, flood control, water supply, hydroelectric power, recreation and wildlife habitat and play an important role in human settlement. Adapting into the effects of climate change is vitally important for future management of dams. This paper uses the recent drought and floods in Victoria to illustrate the importance of considering the effects of climate change in design, operations, maintenance and emergency management of dams.
There are a number of software packages that have been developed to conduct Probabilistic Seismic Hazard Assessments (PSHA’s). Each one has advantages and disadvantages. Two such programs are compared; the licenced subscription-based EZ-FRISK software package developed by Fugro USA Land, Inc. and the open-sourced OpenQuake-engine (OQ) software package by the Global Earthquake Model (GEM) Foundation. Both of these packages use the classical PSHA methodology as described by Cornell (1968) and modified by McGuire (1976). Each of these packages offers different advantages; OQ is freely distributed, code based and provides easy access to a number of tools. EZ-FRISK doesn’t rely on command-line tools and instead provides an easy user interface with quick access to plots to check results. EZ-FRISK is computationally faster than the OQ program.
A simple rectangular source model with four sites was used to investigate the degree of agreement between these two software packages. Results indicate that hazard estimates from the two packages agree to within 4% for the two closest sites. At long return periods for the two furthest sites, the difference is larger.
Many Australian and international dam owners use risk assessments to understand and manage the societal risks posed by their dams. This requires estimates of dam failure consequences, particularly the potential loss of life (PLL). The methods used to assess PLL have become more varied and sophisticated in recent times. This paper summarises the current status of the methods most relevant to the Australian dams industry (i.e. RCEM, HEC-LifeSim, the Life Safety Model), and comments on their applicability for Australian PLL assessments. This commentary is based on material presented by dam owners, regulators, researchers and consultants from the United States, Canada, United Kingdom and the Netherlands, at workshops on estimating dam failure consequences held in Denver in 2016 and Toronto in 2018.
Junction and Clover Dams are central spillway slab-and-buttress dams located in Victoria. Previous safety reviews and assessments of the dams concluded that neither dam met modern dam design standards and remedial works were recommended, including infilling the slab-and-buttress dams with mass concrete to sustain seismic loadings. These conclusions were based largely on the assessed seismic hazard at the site, the results of response spectrum analyses and observed conditions of the dams including alkali-aggregate reaction of the concrete. AECOM used current seismic hazard assessment techniques, conducted concrete investigations and testing, assessed long term surveillance monitoring results and used modern finite element techniques to demonstrate that no upgrade works were required at either dam resulting in a significant saving for AGL.
Investigations into the core material of earth fill dams are undertaken reluctantly due to the potential to cause damage to the embankment. Where investigations are required, Cone Penetration Testing (CPT) is increasingly used to assist with the geotechnical assessment of dam embankments. The risk of hydraulic fracture within embankment core material is well known and procedures are typically adopted to minimise the risk of hydraulic fracture during remediation of the holes. Backfilling is typically done in stages allowing for an initial set of the cement/bentonite grout mixture prior to subsequent lifts.
While the risk of hydraulic fracture is well understood, the lesser known risk of pneumatic fracture is a possibility where certain conditions exist. This paper discusses CPT investigations at Fairbairn Dam, operated by Sunwater in Central Queensland, and the challenges faced in undertaking the remediation of the CPT holes. The potential for pneumatic fracture of the embankment core was highlighted during the investigations and details of alternative techniques adopted for reinstatement of the holes are presented. Recommendations are made to appropriately manage the risk of pneumatic fracture when undertaking CPT’s through embankment core.