2017 | Product categories |

Search Results: “” — Page 3

Oliver Giudici

A common concern for large spillways is erosion of the receiving plunge pool and potential impacts on the stability of the dam.Devils Gate Dam is an 84m high, double curvature arch concrete dam, located in northern Tasmania and constructed between 1968 and 1970.The full 134m long crest is designed as a free-overflow spillway and spill flows impact the downstream valley sides and plunge pool below, where energy is dissipated to reduce riverbank erosion downstream.To protect foundation rock,the plunge pool and large portions of the valley sides were concrete lined with 450mm thick reinforced and anchored concrete. During spill events the area is inundated by up to 12m of tail-water.In 2016 damage to the plunge pool concrete was discovered by divers during a special inspection of the impact areas, but poor visibility limited the understanding of the extent and severity. Subsequent investigations, including detailed sonar scanning, improved the understanding but it was not until the plunge pool was fully dewatered that the full extent of the damage was quantified.The damage commenced around 35m downstream of the dam arch and consisted of approximately 330 square metres of moderately to severely eroded concrete and exposed, deformed, and in some areas completely removed reinforcing bars. The most significant feature was a penetration through the concrete up to 2.5m into the foundation rock.A number of stressed anchor heads were also damaged or destroyed.A full appreciation of the damage necessitated the decision for immediate repairs given the impending power station refurbishment (commencing January 2018) which will subject the plunge pool to nine months of constant spill.This paper outlines the diving and sonar investigations undertaken in 2016, discusses the challenging tasks of dewatering the plunge pool and gaining access through the narrow canyon, and presents the physical works to strengthen the damaged areas.It discusses the difficulty of identifying and treating such damage, and serves as a cautionary tale for other owners who have fully submerged plunge pools downstream of spillways.

Now showing 25–36 of 47 search results:

$15.00

2017 Papers

2017 – Spillway Concrete Scour Detection and Repair at the Base of an 84m High Arch Dam
Learn more
Learn more

Oliver Giudici

A common concern for large spillways is erosion of the receiving plunge pool and potential impacts on the stability of the dam.Devils Gate Dam is an 84m high, double curvature arch concrete dam, located in northern Tasmania and constructed between 1968 and 1970.The full 134m long crest is designed as a free-overflow spillway and spill flows impact the downstream valley sides and plunge pool below, where energy is dissipated to reduce riverbank erosion downstream.To protect foundation rock,the plunge pool and large portions of the valley sides were concrete lined with 450mm thick reinforced and anchored concrete. During spill events the area is inundated by up to 12m of tail-water.In 2016 damage to the plunge pool concrete was discovered by divers during a special inspection of the impact areas, but poor visibility limited the understanding of the extent and severity. Subsequent investigations, including detailed sonar scanning, improved the understanding but it was not until the plunge pool was fully dewatered that the full extent of the damage was quantified.The damage commenced around 35m downstream of the dam arch and consisted of approximately 330 square metres of moderately to severely eroded concrete and exposed, deformed, and in some areas completely removed reinforcing bars. The most significant feature was a penetration through the concrete up to 2.5m into the foundation rock.A number of stressed anchor heads were also damaged or destroyed.A full appreciation of the damage necessitated the decision for immediate repairs given the impending power station refurbishment (commencing January 2018) which will subject the plunge pool to nine months of constant spill.This paper outlines the diving and sonar investigations undertaken in 2016, discusses the challenging tasks of dewatering the plunge pool and gaining access through the narrow canyon, and presents the physical works to strengthen the damaged areas.It discusses the difficulty of identifying and treating such damage, and serves as a cautionary tale for other owners who have fully submerged plunge pools downstream of spillways.
Learn more
$15.00

2017 Papers

2017 – Steel Fibre Combined with Conventional Reinforcing Joint Free Spillway Chute–Key Elements for Durability and Serviceability
Learn more
Learn more

Tian Sing Ng, David Gardiner

Spillway structures play an important part in regulating the designed reservoir water level and are paramount to protect the structural integrity of the dam structure. Impermeability and tight crack control are prime importance in the design and construction of the spillway lining in order to minimise the potential failure modes of cavitation damage and stagnation pressure related failure. A spillway chute is essentially continuously restrained by the roughness of the rock surface and the ground anchors. The provision of control joints, i.e. expansion, contraction and movement joints,are therefore of little benefit due to the restraint as open cracks will still occur. Steel fibre reinforced concrete has been used for resisting erosion of the surface due to abrasion and/or cavitation. Steel fibres combined with conventional reinforcement also provide an amazing synergy to effectively reinforce concrete due to their ability to provide an effective restraining tensile force across open cracks. For the spillway chute,this means any concrete panel size or shape can be considered, even when the chute is fully restrained. Most importantly, this cost effective solution can be constructed joint free while maintaining watertightness. This paper presents some basic principles governing the design of joint free dam spillways employing steel fibre combined with conventional reinforcement. The focus of this paper describes the design and construction of the 400 m long Happy Valley Dam Outfall Channel together with overseas project examples.
Learn more
$15.00

2017 Papers

2017 – Tailing Dams – How Do We Make Them Safer?
Learn more
Learn more

Dr Andy Hughes

Tailings dams continue to undergo failures at an unacceptable rate compared to water storage dams, including failures at operations owned by high profile mining companies.Tailings dams have often a different form and method of construction than water storage dams in that tailings dams continue to be raised over time as part of the mine operations and rise to considerable heights. These failures are often the result of a combination of design, construction and operations actions that are controlled by humans and must be better coordinated and managed in the future. The consequence of failure can be widespread flows of tailings and water over the landscape and water courses. This can have extreme consequences in terms of life loss, environmental damage, social license to operate, company value, and mining industry sustainability. Therefore,it is necessary that the mining industry strive for zero failures of tailings facilities. Any additional technology and information that enables an owner of a tailings dam to be more certain of its condition and thereby reduce the risk of failure is of tremendous value to reliable tailings and mine water management.The Willowstick method uses low voltage, low amperage, and alternating electrical current to directly energise the groundwater by way of electrodes placed in wells or in contact with seepage or leaks. This approach has been successfully used to identify water flow paths through, under and around tailings dam in plan and elevation.The Willowstick technology provides additional information to supplement the geological, geotechnical and hydrological, evaluations analyses and designs, and to further improve tailings dam safety by more robust designs if necessary. This paper, using several tailings dam case studies, illustrates the procedure, findings, and the benefits of the Willowstick methodology. The findings of many Willowstick surveys range from tailings dams where the methodology has confirmed the design evaluations, to tailings dams where new groundwater and leakage flow paths were identified. In the latter case, the dam designers were able to update the designs, based on the new information,to mitigate the identified risks and to improve the overall safety of the tailings dams in accordance with the goal of zero failure.
Learn more
$15.00

2017 Papers

2017 – Tailings Dam Failures – Lessons Learned and Some Recommendations
Learn more
Learn more

Hongyu Li

Although the total tailings dam failure frequency peaked in 1960s through 1980s, the failure rate of significant tailings dams has not dropped. The significant tailings dam failures the mining industry experienced in the recent history include: Merriespruit, South Africa, 1994; Los Frails, Spain, 1998; Kolontár, Hungry, 2010; Mount Polley, Canada, 2014; and Samarco, Brazil, 2015. The dam failures may be due to inadequate design, poor construction and inappropriate operations.This paper discusses the lessons learned and some recommendations and good practices to reduce the tailings dam failure risks. It addresses existing issues and provides some recommendations in risk based design, water management-integrity of facilities and water balance modelling, loading rates, tailings farming, adequate governance and roles and responsibilities of designers and nominated engineer.
Learn more
$15.00

2017 Papers

2017 – Tailoring Consequence Assessments for Retarding Basins
Learn more
Learn more

Andrew Northfield, Simon Lang, Peter Hill

Melbourne Water currently manages more than230retarding basins (RBs). A large portion of these are less than 4 metres high, and traditionally structures of this size have not been subject to intermediate or detailed ANCOLD Consequence Assessments. However, the need to understand the failure consequences for smaller structures has increased over time, as risk based approaches to managing safety have expanded from large dams to other water retaining assets.

Undertaking detailed consequence assessments for all Melbourne Water’s RBs would not be practical, given the costs and time involved. Therefore, this paper describes a method for assessing the level of ANCOLD Consequence Assessment that is justified, based on the structure’s attributes. It also presents an equation that was used to estimate peak outflows from RB failure. The peak outflow estimates can be used to model approximate failure inundation extents downstream of small dams and RBs.

The paper draws on work that HARC have recently undertaken for Melbourne Water to assess the failure consequences for 88 RBs. The outcomes are relevant to other organisations that own or manage significant numbers of small water dams or RBs.
Learn more
$15.00

2017 Papers

2017 – The Design Flood Frequencies for My Dam Have Changed – Why?
Learn more
Learn more

Mark Pearse, Peter Hill

Risk assessments for large dams and the design of upgrades are often dependent on estimates of peak inflows and outflows well beyond those observed in the historic record. The flood frequencies are therefore simulated using rainfall-runoff models and design rainfalls. The recent update of Australian Rainfall and Runoff (ARR) has revised the design rainfalls used to model floods that are of interest to dam owners. This will change the best estimate of flood frequencies for some dams. However, for most dams the impact of revised design rainfalls on flood frequencies is small compared to other factors that can change (independent of dam upgrades). These include model re-calibrations to larger floods, changes to operating procedures that affect the drawdown distribution and improvements in how the joint probabilities of flood causing factors are simulated. In this paper, we look at how the design flood frequencies for some of Australia’s large dams have changed, the reasons for this and then identify five key questions for dam owners to ask to aid assessment of whether the hydrology for a dam should be reviewed
Learn more
$15.00

2017 Papers

2017 – The Hamata Tailings Dam Design and Construction at the Hidden Valley Mine in Papua New Guinea
Learn more
Learn more

Mark Stephen Rynhoud, David Johns and Len Murray

The Hamata tailings storage facility at the Hidden Valley mine is being constructed in a remote, high rainfall, tropical environment in a mountainous region of Papua New Guinea. Implementation of the design hasrequired adapting the design in response to various challenges encountered on the site during the ongoing construction period, based on observations by the designers and site monitoring data which is continuously collected and compared against design assumptions. This paper describes some of the design and construction modifications which have been implemented since construction of the tailings facility started and provides a case history of some of the challenges facing designers and construction crews when mining in remote, tropical conditions.
Learn more
$15.00

2017 Papers

2017 – The Hampstead Heath Scheme in Central London: a Headache!
Learn more
Learn more

Dr Andy Hughes

On Hampstead Heath in Central London, just 3 kilometres from the centre of the city, there are more than 20 dams and reservoirs set within the landscape setting of Hampstead Heath. A number of dams were built in the 16th century and formed the original water supply to the City of London. They are set in a landscape laid out by the world renowned Humphrey Repton.Three of the embankments which are laid out in two chains of reservoirs across the Heath are subject to safety legislation in the UK. As such they were identified as being deficient in spillway capacity and thus fairly significant works were required to be carried out in this sensitive setting.The Heath is protected by the Hampstead Heath Act of 1870 which seeks to prevent significant changes to the Heath and thus it was quite clear that there would be opposition to any works on the Heath, even though they were required by law to protect persons and property downstream. In fact a significant lobby group formed which challenged the need for the works and also the legislation of the UK via a judicial review. This paper will describe the process by which significant stakeholder consultation was undertaken (costing more than £2M), the judicial review that took place in the Royal Courts of Justice, the option study and the major engineered elements carried out on the Heath.
Learn more
$15.00

2017 Papers

2017 – The Legacy and Potential of the Junction Reefs Dam
Learn more
Learn more

Steven E Pells, Philip J N Pells

Junction reefs dam was designed in 1895 and constructed by 1897 as a multiple arch brick structure which was the first of its kind in Australia, and one of the earliest in the world. The dam was envisioned to provide mechanical and electrical power for gold mining. This paper provides an historical overview of the unique structure, and reassesses some of its engineering characteristics, such as the stress conditions in its unusual arches and reverse concrete gravity wing walls. The hydrology of the dam is re-assessed from the viewpoint of evaluating its potential as a mini hydro scheme. Commentary is also provided on the performance of its unlined spillway, which has been subject to regular spills for 120 years.
Learn more
$15.00

2017 Papers

2017 – Tropical Cyclone Debbie – A SunWater Experience
Learn more
Learn more
Michael Hughes, James Stuart

Tropical Cyclone Debbie (TC Debbie) formed in the Coral Sea on Saturday 25th March, 2017 and developed into a category 4 system that crossed the coast near Proserpine, Queensland with the eye passing very close to Peter Faust Dam. TC Debbie, later becoming Ex-TC Debbie embarked on a tour of SunWater infrastructure (See Figure 1). Of 23 referable dams managed or owned by SunWater in Queensland, only 3 had no inflows with spills resulting at twelve locations. The paper describes the varied experiences of SunWater with relation to preparation for, and operations during TC Debbie. Some key areas of interest to other dam owners include;
- Uncertainty around forecasts;
- Flash flood destruction of key hydrographic equipment;
- A review into dam operation;
- Returning a spillway construction site touse;
- A ‘direct hit’ by the eye of TC Debbie over Peter Faust Dam catchment;
- Successful prediction of Cyclone rainfall temporal patterns; and
- A record flood influenced by land use with learnings for flood risk assessments.
Learn more
$15.00

2017 Papers

2017 – Tullaroop Dam: Ongoing Cracking and Unusual Pore Water Pressure Response in a 60 Year Old Earth Embankment
Learn more
Learn more

Gavan Hunter, David Jeffery and Stephen Chia

The Main Embankment at Tullaroop Dam in central Victoria is a 43 m high earthfill embankment with a very broad earthfill zone and rockfill zones at the outer toe regions. There has been an extensive history of cracking within the Main Embankment since formalisation of visual inspections in 1987.Widespread cracking has been observed on the crest and downstream shoulder. Cracking on the crest has mainly been longitudinal, but transverse cracks have also been observed. Cracking on the downstream shoulder has comprised longitudinal, diagonal and transverse cracking. In April 2004, a 60 mm wide diagonal crack opened on the downstream shoulder of the left abutment (from crest to toe) and Goulburn-Murray Water constructed a local filter buttress in 2005/06 on the left abutment. In 2011/12 a longitudinal crack opened up on the upper downstream berm toward the right abutment. The crack was initially 15m long and 10 to 215 mm wide, then propagated several months later to 70 m in length, 40 to 50 mm width and greater than 3 m in depth.In May 2011 three piezometers within the earth fill core recorded a very rapid rise in pore water pressure equivalent to 12 to 13 m pressure head above their previous readings. The piezometers were located on the same alignment (upstream to downstream) and were located below the crest and downstream shoulder, and the rise was to levels close to and above the embankment surface. The piezometers then showed a steady fall with time returning to the pre rise levels after 4 to 6 weeks.In 2015/16 Goulburn-Murray Water undertook dam safety upgrade works to reduce the risk of piping through the Main Embankment by extension of the filter buttress across the full width of the embankment. During these upgrade works, very deep (greater than 5 m) and extensive transverse cracks were observed in the embankment over relatively subtle slope changes on the right abutment.Thecracking and pore water pressure behaviour in the Main Embankment at Tullaroop Reservoir present an important case study. The paper provides details on the cracking and postulated crack mechanisms, and the rapid pore water pressure rise and postulated mechanisms. A summary of the upgrade works is also provided.
Learn more
$15.00

2017 Papers

2017 – Understanding Victorian Local Government Authority Dams and Retarding Basins
Learn more
Learn more

Monique Eggenhuizen, Peter Buchanan, Reena Ram, Tusitha Karunaratne

The Department of Environment, Land, Water and Planning (DELWP) has a regulatory role for the safety of dams under the Water Act 1989 (Act) and is the control agency for dam related emergencies. Local Government in Victoria is divided up between 79 LocalGovernment Authorities (LGAs), each responsible for administering local infrastructure and community services such as roads, drainage, parks etc. Current records indicate that 42 of the 79 LGAs own or manage up to 435 dams and retarding basins.Many of these assets, which include a mix of old water supply dams, ornamental lakes and retarding basins, have been accumulated by LGAs over many years as a result of asset transfers and conversions, land development projects, flood mitigation programs and opportunistic acquisitions by the transfer of land. DELWP engaged GHD to assist and provide advice to the LGAs to significantly improve and update knowledge on LGA dams and retarding basins. The objective of this project is to ascertain where the State’s LGA dams and retarding basins are located, what risks they might pose to communities and infrastructure, what to consider during emergency management planning and response, and to provide owners with the essential management tools and procedures to effectively manage these assets, if these are not in place already.The outcome of this project was to support LGAs to improve management of their dams and retarding basins. It aimed to do this by assisting LGAs with the development of basic dam safety programs that will enable LGAs to more effectively manage their portfolios of dams and retarding basins in terms of ongoing maintenance, dam surveillance and emergency planning and response, and demonstrate due care.This project had a number of key challenges. These included the requirement to process and assess a large number of sites within a small timeframe whilst achieving good value for money,without compromising DELWP’s objectives. A number of efficient methods were adopted during this project particularly during the initial data gathering process, identifying those dams which needed to be inspected based on embankment heights, reservoir capacity and consequences, rapid preliminary assessment of consequences, the development of effective templates for the site inspections, and a method of applying qualitative risk assessments, applicable to the majority of the dams, allowing a consistent assessment of the status of each dam and damsafety documentation.The methods discussed(although developed specifically for the Victorian LGA dams portfolio)provide a sound basis for a screening tool to assess a large number of smaller dams in an efficient manner and quickly identify higher consequence category dams requiring attention. This method could easily be modified and adapted to be applied to similar portfolios of dams.
Learn more
$15.00

2017 Papers

2017 – Underwater Rehabilitation of Dams with Geomembranes
Learn more
Learn more

Alberto Scuero, Gabriella Vaschetti, John Cowland

Waterproofing geomembranes have been used for new construction and rehabilitation of dams since 1959. Research for underwater rehabilitation with geomembranes started at the beginning of the 1990s. The first installation was made in 1997 at Lost Creek arch dam in USA, where a SIBELON PVC geomembrane system was installed partly underwater, to restore watertightness to the upstream face. Techniques for underwater cracks/joints repair, and for staged repair, were developed and first adopted in 2002 and 2010 respectively. The paper presents through some significant case histories the range of underwater applications available today. The paper also presents a new underwater technology, the Sibelonmat®mattress, that allows water-tightening canals without reducing water flow.The Sibelonmat®can be used in embankment dams, to waterproof the upstream. face or as upstream blanket
Learn more
$15.00

2017 Papers

2017 – Variability between Rainfall Runoff Methods and Observed Floods: Implications for Risk, Design, Dam Operation and Communities in Australia
Learn more
Learn more

James Stuart, Michael Hughes

Several recent rain events in Australia have resulted in impoundment flood levels where there was a surprising variability between the Annual Exceedance Probability (AEP) of the flood level and that of the rainfall. The issue was highlighted during the Queensland Flood Commission of Inquiry (QFCI, 2011) by the Queensland Dam Safety Regulator who suggested there may be a problem with design hydrology after a dam safety event that saw impoundment levels of around 1:9000 AEP with a 1:200 AEP catchment rainfall at North Pine Dam, north of Brisbane in 2011. Wide disparities have occurred at Wivenhoe Dam west of Brisbane, at Callide Dam, west of Gladstone and at other locations.

This paper examines the Generalised Short Duration Method (GSDM) (BoM, 2003) and the Revised Generalised Tropical Storm Method (GTSMR) (BoM, 2003) typically used for dam flood capacity assessments in an attempt to explain the variability outlined above and whether it is, in part, exacerbated by the methods themselves.

It finds that processes of generalising rainfall depth, intensity, temporal and spatial characteristics are working together with adopted hydrological methods to contribute to such variability, that in the worst case could lead to PMF levels in dams with much less rainfall than the associated PMP would infer.

Moreover, two key assumptions; that of AEP neutrality (AEP of rainfall is equal to that of the flood) and frequency of PMP based on catchment area, which are the foundations stones of our understanding of flood frequency for large structures, are found to be untested or simply interim advice. This leads to the conclusion that the likelihood of floods in the range 2000 year AEP to PMF may continue to show surprising variability, potentially of an order of magnitude or more, compared to the rainfall AEP.

There is a need for a review of these methods and potentially provision of interim guidance as these methods are currently being used in dam upgrade programs throughout Australia and are also the basis for emergency planning. The identification of these issues concerns current methods and are independent to any discussion on climate change.Prior to commencing, it is worth defining two terms that re-occur throughout the document:
Annual Exceedance Probability (AEP): The probability that a given rainfall total accumulated over a given duration will be exceeded in any one year. AEP Neutrality is the theory that assumes the probability of the rainfall can be transferred to the resulting flood.

Average Variability Method (AVM): Technique for estimating design temporal pattern of average variability to ensure AEP Neutrality in transition from PMP to PMP design flood
Learn more
$15.00

2017 Papers

2017 -Tenterfield Creek Dam Upgrade, Post-tensioning or Mass Concrete Buttress? Let the Market Decide
Learn more
Learn more

David Guest, George Samios, Richard Rodd

Tenterfield Creek Dam is a 15m high concrete gravity structure that was constructed in 1930 and raised by 1.83m and stabilised using 97 post-tensioned ground anchors in 1974.Recent stability assessments concluded that the dam does not satisfy the ANCOLD Guidelines for Stability of Gravity Dams and that the situation is likely to deteriorate given the questionable performance of the post-tensioning cables and on the grounds of continuing corrosion and demonstrated loss of load.Tenterfield Shire Council is committed to improving the stability of the dam to meet the requirements of the NSW Dam sSafety Committee and engaged Public Works Advisory to assist them achieve this outcome.

Public Works Advisory prepared a dam upgrade options study which selected two options for further consideration. The estimated costs of the two preferred options were found to be potentially close;therefore Tenterfield Shire Council requested that both options be taken to detail design and tender stage to allow the market to indicate which option was in-fact better value.Factors other than construction costs were also considered in the options evaluation process and these factors influenced the selection outcome. The two upgrade options of lowest cost were the conventional gravity dam strengthen solutions i.e. installation of new post-tensioned ground anchors and downstream mass concrete buttressing. The decision to proceed to tender with two options was supported by the other key funding stakeholder, DPI Water.

This paper provides some unique insight on the comparison of conventional upgrade options for concrete gravity dams and also examines some interesting design aspects encounter edduring the design development process
Learn more

All Products

Search Results: “” — Page 3