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Wayne Peck

The SRC operated seismic network is one of the largest privately owned and operated seismic networks in the world. Importantly it bridges the situation awareness gap between the information often provided by national seismic networks, of earthquake magnitude and location, and the emergency response managers questions of “What effects will this event have on my assets?” together with “What should we now be doing to mitigate the event?”

Software development of the Quick Quake app and improved automation of PDF report generation means that detailed, bespoke client specific earthquake response reports that incorporate asset earthquake resistance and failure consequence aspects can be produced by duty seismologists within reduced timeframes.

Preliminary earthquake locations computed by the SRC operated network for the two ML 4.7 Korumburra events in March 2009 and the ML 5.6 Moe earthquake of June 2012 were significantly closer to the final computed locations than those published by any other authority. The network additionally provides bonus outcomes of highly accurate detailed seismic activity maps that reduce uncertainties for Probabilistic Seismic Hazard Assessments (PSHAs) and attenuation data that will be used to develop regional specific ground motion models.

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2016 Papers

2016 – An Earthquake Alarm and Situation Awareness Tool Developed For Areas of Low to Moderate Seismic Hazard: Recent Developments and Past Results
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Wayne Peck

The SRC operated seismic network is one of the largest privately owned and operated seismic networks in the world. Importantly it bridges the situation awareness gap between the information often provided by national seismic networks, of earthquake magnitude and location, and the emergency response managers questions of “What effects will this event have on my assets?” together with “What should we now be doing to mitigate the event?”

Software development of the Quick Quake app and improved automation of PDF report generation means that detailed, bespoke client specific earthquake response reports that incorporate asset earthquake resistance and failure consequence aspects can be produced by duty seismologists within reduced timeframes.

Preliminary earthquake locations computed by the SRC operated network for the two ML 4.7 Korumburra events in March 2009 and the ML 5.6 Moe earthquake of June 2012 were significantly closer to the final computed locations than those published by any other authority. The network additionally provides bonus outcomes of highly accurate detailed seismic activity maps that reduce uncertainties for Probabilistic Seismic Hazard Assessments (PSHAs) and attenuation data that will be used to develop regional specific ground motion models.
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2016 Papers

2016 – Applying Mechanical Thinking to Dam Strategy
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Tom Reed

Asset management and particularly dam safety management at Snowy Hydro is a continually evolving process and at the heart of the program is our desire maintain the legacy of the Snowy dams and to do everything required to meet our obligations and duty of care. There is a significant shift underway from a schedule-based maintenance to a condition-based maintenance plan. The advantage of this is that the right maintenance is delivered at the right time and resources can be efficiently allocated to the right maintenance.

Condition based maintenance is not driven by a desire to cut maintenance or surveillance spend. A key part to this change is determining the condition of an asset or dam. To achieve this, reliability centred maintenance principles have been applied to dam structures through the use of failure mode effects and critically assessment (FMECA) tool, this differs to a traditional failure mode assessment, as it looks at functional failure of individual structures or equipment rather than partial or catastrophic failure of the dam. The outcome of a FMECA is a detailed maintenance and inspection plan that targets the individual functional failure modes.

One of the outputs of this process is a condition assessment methodology which is used as a trigger for corrective and preventative maintenance activities and a tool for the justification of installing performance measuring instrumentation. Condition assessment is therefore the process where asset performance data is assessed against specific criteria to determine its present state. Currently, comparing condition and performance of multiple dams is reliant on a practitioner’s experience and subjective assessment to determine whether an asset’s condition is fit for service. The condition assessment process; reduces subjective data, provides real-time health assessment, highlights performance issues, continuously identifies and updates priorities and provides justification for capital investment.
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2016 Papers

2016 – Assessing Blasting Impacts on Embankment Dams: Limitations with Adopting an Equivalent Earthquake Approach
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Robert Harrington

There is a significant body of knowledge in relation to assessing the impacts of earthquakes on earth and rock fill dams which has led to a number of widely recognised and accepted methodologies for the calculation of potential deformations from an earthquake event. However, limited research has been conducted into the assessment of blasting impacts on earth structures. This has led to an adoption of earthquake analysis methods in the assessment of blasting impacts on earth structures without adequate consideration to the difference between the stresses and displacements imposed on an embankment as a result of a blast as opposed to an earthquake. Adopting earthquake analysis techniques may result in conservative vibration limits being imposed when undertaking blasting near embankment dams which may have negative financial impacts.

This paper explores the risks associated with blasting adjacent to earth fill dams and details the difference between stresses and displacements imposed on an embankment by a blast versus an earthquake.

This paper also discusses previously adopted approaches to assessing potential impacts associated with blasting and the limitations associated with adopting a pseudo-static and simplified permanent deformation analysis for blasts modelled as equivalent earthquakes. Finally, the paper proposes an alternate risk based analysis approach.
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2016 Papers

2016 – Benchmarking 2D Hydraulic Models for Dambreak and Consequence Assessments
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Chriselyn Kavanagh, David Stephens, Peter Hill

Two-dimensional hydraulic models are now widely used to simulate flooding downstream of dams as part of dambreak assessment studies. These models provide high resolution information on velocity distribution across the floodplain, which is of paramount importance to accurate estimation of the depth-velocity product required when undertaking loss of life assessments. In addition, the outputs from these models are much more readily presented as maps and animations, which can be an important tool in the dam safety emergency planning process.

Recently, the United States Army Corps of Engineers released a new version of the popular hydraulic model HEC-RAS which includes the ability to conduct two-dimensional simulations. Other widely used two-dimensional models include DHI’s MIKE suite and TUFLOW. This paper presents a review of the capability, functionality and useability of these models for the specific purpose of dambreak modelling. Key features considered as part of the review include model stability, run times, methods of simulating dam breaches, outputs and the ability to link to loss of life simulation models. A case study comparing the performance of three commonly applied models is presented and discussed, and advice is provided on model selection.
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2016 Papers

2016 – Calculation of the Probability of Failure of Impervious Concrete Lining of Plunge Pools Loaded by High-Velocity Jet Impact
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M. Mahzari

An analytical approach is presented to calculate the pull-out probability of failure of concrete lining of
plunge pools. The concrete lining is aimed to protect the plunge pool against scour where a scour hole may
endanger the stability of the dam foundation. Uplift and pressure loading of the jet are major actions on
the concrete lining. Ground anchors are used to stabilise the lining against these actions and the governing
mode of failure is the pull-out (tensile failure) of these anchors. While the anchoring design for static uplift
is straightforward, dynamic jet action introduces remarkable complexity into the design. The adopted
methodology is based on a stochastic modelling of the high velocity jet action. A bi-linear power spectral
density function is assumed based on the laboratory measurements on the scale physical models done by
the others. This loading mainly reflects the turbulent pressure fluctuations where the jet impacts the plunge
pool floor. Response of the lining, idealised as a single degree of freedom, is calculated by the random
vibration procedures which provides the most realistic structural analysis methodology. It is assumed the
lining is impervious and hence no dynamic under-pressure is developed. The analysis results provide a
probabilistic description of the anchor tensile force which enables the designer to compute the probability
of failure of the anchors knowing their ultimate strength.
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2016 Papers

2016 – Characteristics of Near Fault Ground Motions for Seismic Design
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Paul Somerville

This paper describes the unique characteristics of near-fault ground motions for use in developing ground motions for the design and evaluation of dams that are located close to identified active faults. These characteristics include near-fault rupture directivity effects, permanent ground displacements, and hanging wall effects. In Australia, active faults make a significant contribution to the Maximum Credible Earthquake (MCE) only at near-fault sites when Probabilistic Seismic Hazard Analysis (PSHA) is used. However, some sites may be close enough to nearby or even more distant identified active faults that a Deterministic Seismic Hazard Analysis (DSHA) produces MCE ground motions that are for larger than those obtained using a probabilistic approach even for very long return periods. Knowledge of the unique characteristics of near-fault ground motions should be applied to the development of ground motions for the design and evaluation of dams that are located close to identified active faults.
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2016 Papers

2016 – Comparing CRCFORGE Estimates and the New Rare Design Rainfalls
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J.H.Green, C.Beesley, C.The, S.Podgerand, A.Frost

The ability to estimate design rainfalls for probabilities rarer than 100 years or 1% Annual Exceedance Probability (AEP) is an essential part of dam hydrology. The earliest means of estimating rare events consisted of a pragmatic curve fitting procedure between the 50 and 100 year design rainfalls and the Probable Maximum Precipitation. In the 1990s a more rigorous method of estimating design rainfalls as rare as 2000 years was developed – the Cooperative Research Centre – FOcussed Rainfall Growth Estimation (CRC-FORGE) method. CRC-FORGE estimates were derived for Victoria in 1997 followed progressively by each of the other states. Over the subsequent two decades CRC-FORGE estimates were an integral part of the risk assessment of large dams – being used to determine the AEP of the Dam Crest Flood.

The Bureau of Meteorology will soon release new rare design rainfall estimates for probabilities to 2000 years. The new rare design rainfalls are a significant improvement on the CRC-FORGE estimates as they have been derived using up to date data; contemporary analytical techniques and a method that is consistent across Australia.

However, there are differences between the CRC-FORGE estimates and the new rare design rainfalls. These differences do not constitute a systematic change to the CRC-FORGE estimates but rather vary with location; duration and probability. The results of a detailed comparison between the CRC-FORGE estimates and the new rare design rainfalls are presented together will an assessment of the possible impacts on previous estimates of the AEP of the Dam Crest Flood.
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2016 Papers

2016 – Constructions of a High Capacity Post Tensioned Permanent Carbon Fibre Ground Anchor
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Dr Matthew Sentry, Nabeel Elias

Although permanent ground anchor technology has advanced in leaps and bounds over the past two decades, the focus of anchor technology has been on developing techniques to minimise the risk of component and system failure due to corrosion. The advancements in structural materials available in the market in recent years have enabled research into alternative materials for permanent ground anchor systems.

Carbon fibre has become a significant structural alternative throughout North America for bridge and building construction as well as repair and structural strengthening of deteriorated/corroded structures. These advancements and the necessity to investigate alternative materials for anchor systems have led to research in understanding the long term performance effects of using carbon fibre products as an alternative to steel tendons in permanent ground anchors.
Following on from the advanced research works at Monash University and Geotechnical Engineering which investigated the durability performance of various available CFRP strands when used as an alternative to conventional steel tendons in permanent ground anchor systems, Geotech developed the first post tensioned ground anchor system using CFRP strand.

Following laboratory based trials and small scale bun barrel tests, Geotech was able to successfully design, construct, install and stress the first 27 strand post tensioned CFRP ground anchor installed into Yass Dam. The CFRP strand was stressed and locked off at 4,000kN. Real time monitoring has been installed to monitor the load throughout the anchors service life.

This paper provides the details of the construction, installation and stressing of the first CFRP anchor installed into a dam structure.
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2016 Papers

2016 – Dam Safety Management for Upgrade of an Extreme Consequence Storage
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Mark Arnold, Gavan Hunter and Mark Foster

Following the dam safety risk assessment for Greenvale Dam in 2008, Melbourne Water implemented a 3.0 m reservoir level restriction on the operation of the storage as an interim risk reduction measure. The 3.0 m restriction coincided with the ‘as constructed’ top of the chimney filter in the main embankment. This interim action reduced the dam safety risk to below the ANCOLD limit of tolerability.

Dam safety upgrade works were undertaken in 2014/15 to bring the dam in-line with current risk based guidelines and to enable the removal of the interim reservoir restriction, bringing the storage back to full operating capacity. Greenvale Dam was required to remain operational throughout the works and this required careful consideration of the dam safety risk during construction.

Deep excavations were required within the crest and downstream shoulder of the embankments, that,, without adequate management, had the potential to increase risk to the downstream population. Excavations up to 18 m depth were required into the wing embankments for construction of full height filters from foundation to crest, excavations up to 7 m deep were required in the main embankment to expose and connect into the existing filters and secant filter piles up to 13 m deep were used to connect the new chimney filter of the wing embankments with the original chimney filter of the main embankment.

A key element of the design and construction of the upgrade works was managing dam safety during construction. Dam safety considerations included (i) design based decisions to manage the level of exposure; (ii) implementation of further restrictions on reservoir level by the owner Melbourne Water; (iii) construction methods to manage exposure; (iv) an elevated surveillance regime during the works and (v) emergency preparation measures including emergency stockpiles and 24 hour emergency standby crew. The construction based dam safety requirements were focused on early detection and early intervention, and were managed via the project specific Dam Safety Management Plan.

This paper focuses on dam safety management including the decisions made, actions taken and construction requirements and touches on how these relate to the key project features.
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2016 Papers

2016 – Damage to the Fairbairn Dam Spillway and Subsequent Analyses and Design of the Remedial Works
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Peter Foster, Bob Wark, David Ryan, John Richardson

Fairbairn Dam is a zoned embankment dam completed in 1972 and located in central Queensland near the town of Emerald. The spillway, which is located toward the left abutment, consists of a 168 metres wide concrete ogee crest, converging concrete chute and dissipater basin. The overall length from the ogee to the downstream end of the concrete spillway is approximately 195 m. The chute and dissipater basin are underlain by a matrix of longitudinal and transverse drains for pressure relief of the anchored concrete slabs.

Minor repairs to damaged chute slabs were undertaken following the 2011 flood event. During these rectification works, large voids up to 0.3 metre in depth were found under sections of the concrete chute slabs as well as damage and blockage to the sub-surface drainage system. Discoloured water was also observed discharging from sections of the sub-surface drainage system. Some of the 24 mm diameter bars designed to anchor the slabs to the foundation were found to have corroded at the concrete/foundation interface and subsequent pull-out tests showed that the anchors had minimal or no structural capacity.

These investigations led to a review of the hydraulic design of the spillway, upgrade to the sub-surface drainage system and apron slabs, and installation of replacement anchor bars. An understanding of the transmission of pressures and dynamic pressure coefficients resulting from spillway discharge and the effects of the hydraulic jump was an essential component of the design for the new anchor and drainage system.

This paper provides detail on the investigations undertaken, the hydraulic modelling that is underway including physical hydraulic and computational fluid dynamics (CFD) and the design approach for what is described in this paper as the Stage 1 component of works.
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2016 Papers

2016 – Design Considerations for the Stortemelk Hydropower, South Africa
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BJ Rochecouste Collet, PC Blersch, AL Olivier

The paper shows how multidisciplinary engineering can create future-proofed solutions for dam management and how innovation is bringing those advancements to life. It includes the retrofitting of a small hydropower station to an existing dam structure, enhancing the use of the dam. The paper also reveals design, technical and project finance considerations underpinning the multi-disciplinary services.

Water supply in South Africa’s economic hub of Gauteng journeys from the Lesotho Highlands Water Project (LHWP) through three river systems that converge in to the Vaal Dam from which the water is treated and pumped for domestic usage. One of those systems delivers water originating in Lesotho to discharge into the Ash River. The Ash River was, by origin, a small river with an environmental reserve flow of 50 l/s. However, with the LHWP significantly adding flow, the annual average increased to 24,500 l/s (24.5 m3/s) and is set to increase further with future phases of the scheme. To mitigate significant erosion caused by the greatly increased flow, several structures were erected along the river, including the Botterkloof Dam. Whilst the energy was dissipated in the dam’s spillway, a private developer studied if the water could be used for energy generation. The river also offered some rapids some 1.6 km downstream, which also showed potential for hydropower generation. An option to combine the two sites was also considered.

Aurecon conducted the feasibility study in 2010 for both sites, including the combined option, which concluded that there would be significant benefits in the implementation the projects in two separate schemes. This boasted many advantages including reduced capital investment, reduced social impact (canoeist), reduced geotechnical risks, and lesser land acquisition leading to a better return on investment. Aurecon are currently providing engineering, procurement and construction management (EPCM) services for the entire project. Construction of the 4.4 MW hydropower station commenced construction in September 2014 and was commissioned ahead of time and under budget.

The founding conditions under the proposed hydropower station location, comprising interbedded sandstone and mudstone was fairly poor with the mudstone effectively decomposing in less than two days. The Botterkloof dam was build on a thick layer of sandstone which dips quite steeply towards the right bank. The right bank on the other hand comprises an old paleo channel. The Boston A dam, located on the left bank immediately adjacent to the Botterkloof Dam, is founded on the weather mudstone and the spillway is grass lined. The power station construction was constructed in the narrow space in between the two existing dams – the Botterkloof Dam (owned by the Department of Water and Sanitation (DWS), Government of South Africa) and the adjacent privately-owned Boston A Dam. Permission had to be obtained from the respective owners and all regulatory permits approved before the project could be submitted to the South African Renewable Energy Independent Power Producer Programme (REIPPP) implemented by the Department of Energy (DoE) of the South African Government.

Another significant challenge in the construction itself included the need for deep excavations through the left embankment of the Botterkloof Dam and adjacent to the spillway stilling basin whilst such construction needed to be done without affecting operations and stability of either of the two dams.

The solution was a shallow intake, followed by a cut and cover concrete penstock leading to a compact hydropower station housing a single 4.4 MW vertical “Compact Axial Turbine” Kaplan turbine ending in the tailrace, which was rotated at 90 degrees.
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2016 Papers

2016 – Estimating the Maximum Credible Earthquake (MCE) and its Application in Australia and New Zealand
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Paul Somerville

This paper reviews methods used to estimate the MCE in Australia and New Zealand. In the ICOLD (2016), NZSOLD (2015) and proposed ANCOLD (2016) guidelines, the deterministic approach is applicable only to fault sources, whereas the probabilistic approach is applicable to both fault sources and distributed earthquake sources. Although ICOLD (2016) states that the use of a deterministic approach to develop the SEE “may be more appropriate in locations with relatively frequent earthquakes that occur on well- identified sources, for example near plate boundaries,” the proposed ANCOLD (2016) guidelines retain the use of the deterministic approach for critical active faults which show evidence of movements in Holocene time (i.e. in the last 11,000 years), or large faults which show evidence of movements in Latest Pleistocene time (i.e. between 11,000 and 35,000 years ago). In Australia, active faults make a significant contribution to the probabilistic MCE only at near-fault sites, and even in those cases most of the hazard comes from distributed earthquake sources. However, some sites may be close enough to nearby or even more distant identified active faults that a Deterministic Seismic Hazard Analysis (DSHA) produces MCE ground motions that are far larger than those obtained probabilistically even for very long return periods. Conversely, the deterministically defined MCE may be lower than the probabilistically defined MCE for very long return periods at near fault sites in New Zealand, requiring the probabilistic approach.
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2016 Papers

2016 – Estimating the Probability of Breach for Overtopping of Low to Medium Height Homogenous Earthfill Embankments
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Kelly Maslin, Richard Rodd

As an industry there have been many advances in the assessment of the probability of failure associated with a range of failure modes including embankment piping and stability. However, little work has been done on the development of a meaningful tool to assist in the assessment of probabilities of failure for embankment breach due to overtopping.

In the development of this paper a number of embankment overtopping case studies were reviewed and these were used to anchor the suggested probabilities of failure. The case studies assessed were all low to medium height, homogeneous earthfill embankment dams. Consideration has been given to a range of factors including embankment material and construction, embankment geometry, duration of overtopping and the presence and condition of vegetation on the embankment face.

The results of the analysis of the case studies indicate that the probability of breach due to overtopping, particularly for short duration events, is actually relatively low compared to the typical values being adopted within the industry.

It is the intended purpose of this paper that it provides guidance to the industry on the assignment of the probability of embankment breach due to overtopping to allow more consistent, robust and defensible estimates for dam safety risk assessments.
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2016 Papers

2016 – Extending the Useful Life of Dams in Diverse and Innovative Ways: Three South African case studies
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Peter Blersch

Extending the useful life of a dam to an extent well beyond what was envisaged by the original designer poses diverse challenges. In this paper, three case studies are described, one involving strengthening of two similar dams and two cases involving raising. In all three cases, the dams continue to provide a reliable source of supply in a water scarce country.

The Woodhead and Hely-Hutchinson Dams have substantial historical significance which guided the selection of restressable post-tensioned anchors as the preferred method of strengthening.

The Stettynskloof Dam was almost doubled in height by constructing a clay core rockfill embankment abutting the downstream face of the existing concrete gravity dam. The new structure was well instrumented to cover areas of concern but the dam was found to perform as largely predicted by the designers.

Keerom Dam faced both technical and regulatory challenges that were eventually overcome and the raising of the dam was able to proceed. A further raising will increase the utilisation of this valuable resource still further.
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2016 Papers

2016 – Geotechnical Characterisation of a Tropical Residual Soil in an Embankment Abutment
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James Penman, Terence Jibiki, Len Murray, and Mark Rynhoud

Two earthfill embankments are being constructed to form an impoundment in a mountainous region with a tropical climate. The embankment abutments are underlain by tropical weathered rock/soil including a significant thickness of residual soil. Previous slope failures within the area, including a 150 m wide failure of a construction access road, have been potentially due to weakness of the residual soil. In order to quantify the potential risk to the embankments, a geotechnical characterisation program consisting of in situ and laboratory testing was completed to determine the shear strengths and loading response within the residual soil material. This paper summarises the geotechnical investigation program and characterisation of this tropical residual soil in the context of the embankment stability.

Results of laboratory direct simple shear testing are presented and compared to common empirical methods for estimating the undrained shear strength of both over-consolidated and normally-consolidated materials using index properties and/or over-consolidation ratios. Methods used for comparison include those proposed by Skempton (1952 & 1957), Bjerrum-Simons (1960), Lambe & Whitman (1969) and Wroth & Houlsby (1985) for normally consolidated material and Ladd (1977) and Jamiolkowski et al. (1985) for over-consolidated material.

The results of in situ testing, including pocket penetrometer data and field shear vane data, are also presented.
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2016 Papers

2016 – Hedges Dam – Upstream Face Slip from Rapid Drawdown and Subsequent Remedial Works
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David Laan, Kim Matsen

A slip on the upstream face of Hedges Dam was observed during an annual site inspection in late March 2016. At that stage the slip appeared to be largely contained within the right hand third of the embankment.

By early April, the slip area had developed into a head scarp across the entire central portion of the embankment. Multiple other head scarps were observed, indicating multiple or segmented slips. Several tension cracks were also visible on the face of the dam. The toe of the slips was indicated by a poorly defined bulge.

The most recent drawdown of the reservoir level was identified as a potential driver for the initiation of the slip failure. During the most recent drawdown the maximum drawdown rate was approximately 0.6 m/day whereas in the previous 17 years the maximum drawdown rate was approximately 0.2 m/day.

The remedial works proposed are to place a rockfill weighting zone on the upstream face to stabilise the embankment. The strength of the materials along the sheared surface was back calculated from the mechanics of the failure surface. This data was then used to calculate the shape of the weighting zone required to stabilise the slope.
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