Kangaroo Creek Dam is a concrete face rockfill dam (CFRD) located on the Torrens River, approximately 22 km north east of Adelaide. The dam is currently undergoing a major upgrade to align it with updated safety guidelines set by the Australian National Committee on Large Dams (ANCOLD) to better withstand major flood events or earthquakes. As part of this upgrade, external omega-type waterstops have been installed on the vertical and perimetric joints to mitigate the impact of expected joint deformations due to seismic loading. Two profiles were selected for the external waterstops; one capable of extending 200 mm for the perimetric joint and the outer two vertical joints on each side, and one capable of extending 100 mm for the remaining vertical joints and the horizontal joint between the new face slab and the original face slab. Using the external omega-type waterstops as the second waterstop for the extended perimetric joint simplified construction, particularly with respect to reinforcement details adjacent to joints. It is understood that this is the first time in Australia that an omega-type waterstop is being fitted to a CFRD slab. This paper demonstrates the benefits of retrofitting waterstops to existing dam joints when required, provides general installation details, details for providing a continuous barrier with the existing waterstops by overlapping internal and external waterstops, and lessons learnt from the waterstop installation.
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Lessons learned from recent major incidents and related enquiries in Victoria in concert with the adoption
of an all-emergencies all-communities philosophy have informed both the scope and reach of the current
emergency management and dam safety regulatory environment. Victorian dam owners now have a statutory
obligation to implement an all-emergencies all-communities approach to risk assessment at their assets and,
as part of that, to adopt this approach as part of their “business as usual” activities. A major outcome of
this requirement is that for major dams, risk management is now being driven from Board and senior
management level: the implementation of controls and actions is formalised. As a consequence, there is a
better understanding across the organisation of new and emerging risks that require new technologies,
thinking and expertise and an improved appreciation of asset interdependencies and the risk posed to reliant
stakeholders. With other reforms including oversight and audit arrangements in place, the move from “doing
enough” to striving for “good’ industry practice, aided by an improved regulatory regime and statutory
processes, is well established. A brief consideration of the lessons learned from the February 2017 Oroville
dam incident in this context concludes the paper.
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.
In 2018, DNRME released the latest revision of the Failure Impact Assessment (FIA) Guidelines and the first significant change since 2003. An FIA is the instrument for determining if a dam is referable and therefore regulated for dam safety purposes in Queensland.
The guidelines reflect upon changes in legislation and advances in methods and tools for assessing consequences of dam failure. The revised version tends to be less prescriptive and emphasises the responsibility of the engineer completing the assessment to develop appropriate and defensible methods.
The paper provides an overview of the FIA guidelines, key concepts, the steps to follow when preparing an FIA and a comparison to ANCOLD’s latest consequence assessment guideline.
The assessment of the geological foundations of arch dams is required as part of the asset owner’s safety obligations (ANCOLD 2003). The task is often made difficult due to steep topography where arch dams are commonly constructed. Between 2013 and 2017, GHD was engaged by South Australia Water (SA Water) to examine the geological and geotechnical conditions of the Sturt River Flood Attenuation Dam (South Australia) abutment foundations. The dam was constructed between 1964 and 1966 within the Proterozoic “Sturt Tillite”. The foundations of the dam are characterised by a folded and fractured rock mass which creates complex spatial relationships between discontinuities and outcrop expression, difficult to assess in two-dimensional space. In collaboration with Monash University’s School of Earth, Atmosphere and Environment, a high resolution ortho-photogrammetric survey of the downstream dam abutments was undertaken using an Unmanned Aerial Vehicle (UAV) in areas where traditional mapping could only be obtained by rope access methods. Monash also undertook digital geological mapping of inferred discontinuities based on the UAV imagery. The data was then used to construct a three-dimensional (3D) model of the shape and position of high-persistence discontinuities, potentially critical to abutment stability. In addition to digital data, a low cost, high value field investigation to “ground-truth” the digital data and reviewed existing geological information (including rope access scanline data, foundation mapping and rotary cored boreholes) to develop a holistic understanding of the persistent discontinuities in their geological context.
Trustpower’s Mahinerangi Dam in New Zealand’s South Island is a concrete arch and gravity abutment dam built in 1931, subsequently raised in 1946 and strengthened with tie-down anchors in 1961.
This paper discusses a 3D finite element analysis of the dam and the predicted performance of the arch section under Safety Evaluation Earthquake (SEE) loading against identified potential failure modes.
Current guidelines and recent seismic hazard assessments recommend earthquake loadings higher than what was originally accounted for in previous decades. A Comprehensive Safety Review identified stability under SEE loading as a potential deficiency, so a programme of works was commenced to evaluate and better understand the seismic risk by using modern day tools and technology to evaluate the dam against current performance standards.
The final model incorporated the results of extensive laboratory testing, high-resolution LiDAR survey data and dynamic calibration using ambient-vibration monitoring. Motion recordings across the face of the dam during the 2016 Kaikōura earthquake were also used to validate the model. The reservoir has been explicitly modelled together with the opening, closing and sliding of contraction joints and the foundation interface. This allowed the modelling of permanent displacements and the redistribution of loads within the dam under SEE loading, which had been shown to be an important behaviour from the previous stages of analysis.