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J.P. Giroud, Neil Jacka, Christopher Dann and Jeremy Eldridge
The remediation of a large hydropower canal included the lining of selected reaches of the canal with a geomembrane to extend the life of the canal and enhance seismic resilience. This paper presents a summary of innovative analyses performed to select and design the geomembrane liner system. Two mechanisms that induce tensile stress and strain in the geomembrane following the development of cracks in the supporting subgrade resulting in the deflection of the geomembrane over the cracks under the applied water pressure were analysed. The analysis uses the concept of ‘co-energy’, a geomembrane property that evaluates its ability to withstand stresses and strains together. A range of ballast configurations undertaken to assess the tension, strain and deflection of the geomembrane while evaluating the resistance to hydrodynamic forces and other loads were analysed. Stability analyses showed that geosynthetic reinforcement of the ballast over the upper canal slopes was required.
Keywords: Canal, Lining, Geomembrane, Design, Seismic resilience.
Now showing 1–12 of 36 search results:
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2013 Papers
2013 – Hydropower canal geomembrane liner analytical techniques
Learn moreJ.P. Giroud, Neil Jacka, Christopher Dann and Jeremy Eldridge
The remediation of a large hydropower canal included the lining of selected reaches of the canal with a geomembrane to extend the life of the canal and enhance seismic resilience. This paper presents a summary of innovative analyses performed to select and design the geomembrane liner system. Two mechanisms that induce tensile stress and strain in the geomembrane following the development of cracks in the supporting subgrade resulting in the deflection of the geomembrane over the cracks under the applied water pressure were analysed. The analysis uses the concept of ‘co-energy’, a geomembrane property that evaluates its ability to withstand stresses and strains together. A range of ballast configurations undertaken to assess the tension, strain and deflection of the geomembrane while evaluating the resistance to hydrodynamic forces and other loads were analysed. Stability analyses showed that geosynthetic reinforcement of the ballast over the upper canal slopes was required.
Keywords: Canal, Lining, Geomembrane, Design, Seismic resilience.
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2013 Papers
2013 – Remediation of the Tekapo canal with a geomembrane liner
Learn moreNeil Jacka, Christopher Dann, Jeremy Eldridge
The Tekapo Canal Remediation Works were undertaken to extend the life of the canal and enhance its seismic and environmental resilience. The deterioration of the canal lining in specific reaches has been the consequence of internal erosion of the lining under operating conditions.
The remedial works comprised installation of a supplementary geomembrane liner over selected sections of the canal, reconstruction of a culvert where the embankment had suffered piping, installation of filters in the Maryburn Fill, strengthening of the bridges across the canal and replacement of irrigation off-takes.
This paper presents a summary of key issues resolved during the design of the remediation works, in particularly the design of the geomembrane ballast system, the cofferdams and the management of side slope stability during drawdown for the works. A number of construction trials were carried out to confirm design assumptions and test construction techniques. The trials were a significant factor in the successful completion of the first season of work ahead of programme.
Keywords: Canal, Lining, Geomembrane, Cofferdam, Design, Seismic resilience
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2013 Papers
2013 – Past and present usage of the Chelsea Estate dams
Learn moreTim Gillon and Grant Murray
Chelsea Estate is located on the edge of the Waitemata Harbour, and is only ten minutes drive from Auckland central business district. Within Chelsea Estate are four ‘low’ potential impact classification (PIC) dams, which cascade along Duck Creek. Three of the dams are over 100 years old and all dams were built from 1884 to 1917. The dams and the reservoirs have served, and continue to serve, several purposes including stormwater retention, recreational use and water supply for the adjacent sugar factory. In 2008 Auckland Council (AC) purchased the Chelsea Estate from the New Zealand Sugar Company (NZSC) and in 2009 the Estate was registered in the New Zealand Historic Places Trust (NZHPT). This paper discusses the history and functionality of the multi-function Chelsea Estate dams, the development of the site and how it impacts our understanding of the dams today.
Keywords: Chelsea Estate, multi-function dams, heritage dams.
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2013 Papers
2013 – Ashton Dam – meeting the challenge of reconstructing history
Learn moreRichard Davidson, Jennifer Williams, Roger Raeburn and Jason Boomer
Ashton Dam is a 20-m high embankment dam located on the Henry’s Fork River in Eastern Idaho. It is a high hazard structure licensed with the FERC. The dam was completed in 1916 as a zoned earth and rockfill dam utilizing a low plasticity silt core. Ashton Dam is located approximately 13 km north of Teton Dam and is the sole remaining structure of four similarly designed dams. Over the years, the dam’s condition deteriorated, evidenced by periodic recurrence of sinkholes, sediment plumes and settlement.
PacifiCorp initiated a major 3-year rehabilitation project for the structure. Based on a risk-based design process, a new zoned embankment was reconstructed. Significant structural upgrades were also required for the powerhouse, training walls and gated spillway. To facilitate this construction, a new diversion tunnel and gated outlet structure were built to divert the river and manage flood flows. Cofferdams were required for both the upstream and downstream construction works.
Several challenges were encountered during construction, which were managed with a risk-based process. These included addressing the uncertainties that were known during design and the unknowns that were discovered during construction. Some of the construction challenges covered in the paper include utilization and processing of low plasticity silty material for embankment reconstruction, tunnel construction through fractured basalt with a major shear zone, a lake tap excavation in the wet, dewatering of the embankment excavation, left abutment treatment, real-time redesign of structural features, and fill placement in a constrained excavation.
This paper provides a synopsis of how these design and construction challenges were addressed and overcome on a “blue ribbon” trout stream with high public visibility and interest. Of particular concern was the need for cold weather concrete work, managing flood flows, lake tap and embankment excavation during the very limited construction seasons, and maintaining environmental river controls for the sensitive downstream ecosystem.
Keywords: Risk-based design, Embankment Reconstruction, Piping, Aged Concrete Repair
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2013 Papers
2013 – Design considerations in the continuous concrete buttressing of existing concrete gravity dams
Learn moreNicole Anderson and Nihal Vitharana
A large number of aging concrete dams in Australia may not meet the requirements of modern dam safety practices. In addition, there is an ever-increasing demand for the supply of water. Continuous concrete buttressing is a method of strengthening existing dams which allows the dam to be raised to augment the storage capacity at an incremental cost.
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This paper explores the key design considerations involved in concrete-buttressing existing concrete gravity dams. Critical aspects considered include storage level during construction, interface drainage, interface shear transfer, the relative strength of existing and new concrete and the behaviour during the heating and cooling phases of the heat-of-hydration. The discussions will be of relevance to asset owners and water authorities faced with upgrading existing dams in a time where there is an increasing demand for security of supply of water resources. -
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2013 Papers
2013 – Challenges and lessons learnt from high-risk dam construction projects
Learn moreMatthew Sentry and Darren Loidl
To triple Yass’ water storage capacity, Yass Valley Council was required to increase the height of their existing concrete weir by 3.0 m. The 100 m wide weir was originally constructed back in the 1920’s. Upgrade works to the weir included raising the height of the existing concrete weir by 3.0 m with reinforced concrete; install 33 number 27 strand post-tensioned ground anchors vertically into the crest; construct a new outlet structure; upgrade existing mechanical pipe works; and replace the existing pedestrian bridge with a concrete bridge capable of vehicle traffic.
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The key project constraints during construction were to maintain constant water to the town’s water treatment plant and maintain minimum 70% reservoir storage.
The original weir had no auxiliary means of flow diversion and the construction constraints meant that the water storage could only be reduced by 1.0 m from the existing crest during construction, resulting in the construction work being carried out in an active water course with minimal means of flow diversion. These key project constraints meant that there was a high risk of flooding during construction work.
Geotechnical Engineering was engaged by Yass Valley Council to carry out the required upgrade work at Yass Dam. Prior to construction work commencing, risk workshops with client and designers clarified the flood risks during construction. To minimise the impact of flood events during construction, Geotech implemented several flood mitigation measures which were controlled by a detailed construction flood management plan. These control measures included construction of two temporary diversion slots cut into the existing concrete weir capable of supporting a 1 in 2 year rain event whilst allowing construction work to continue; re-design of concrete works to minimise the volume of concrete which was to be cut from the existing wall’s downstream face; detailed construction sequencing to minimise impact to existing and new wall during construction work; and the early installation and stressing of anchors.
Although a detailed construction flood management plan was developed and implemented, the Yass Dam site was impacted by 13 floods during the 20 month construction period. Several floods recorded water levels between 1.5 m and 1.9 m above the existing crest, resulting in work ceasing for weeks if not months at a time. As a result of the consistent flooding, Geotech was able to develop stronger and more resilient methods to be able to effectively work within an active watercourse on dam structures where minimal flow diversions are available. This paper presents the unique techniques implemented through the Yass Dam Upgrade project and discusses the effectiveness of these techniques and lessons learnt through the 13 flood events experienced. -
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2013 Papers
2013 – Application of modern dam safety management practices to older farm dams
Learn moreJohn Duder, David Bouma and Paul McCallum
The authors have been involved in the safety inspection and remediation of many older (pre-dating the 2004 Building Act) farm dams over the past decade coupled with considerable corporate knowledge from dams inspected by Tonkin & Taylor Ltd in its 50+ year history. This paper presents a summary of the varied benefits and risks of these older dams and the difficulties encountered in bringing them into alignment with current practice.
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The many farm dams around New Zealand provide considerable benefit to the owners and often to the environment and wider community including the obvious stock water and irrigation, but also micro hydro, recreation, flood detention, release of environmental flows and flows for downstream users, and wetland habitat.
However, when applying current dam safety practice, and looking forward to the implementation of the Dam Safety Regulations, some of the older farm dams have significant dam safety issues that are often challenging to address. Although there is a high degree of variability, typical issues include:
Little or no documentation of geotechnical investigations, design or construction,
Design standards, particularly for spillway capacity have generally increased,
Little or no formal surveillance or maintenance carried out or recorded since commissioning,
Many farm dam owners have a poor understanding of their obligations under the Building Act and the Conditions of their Resource consents,
Consent conditions may not require dam safety related monitoring and maintenance, and/or the conditions may not have been historically enforced.
Many of these farm dams have been constructed by small contractors at the request of the farmers, often with only “standardised” engineering design and little specific geotechnical investigation. Typically there are no as-built records and the dam owners have been left with a general lack of understanding of owner’s responsibilities to monitor and maintain the dam.
Given that there are often very limited funds available for upgrade work, it has proved important to apply sound engineering judgement and a high degree of pragmatism to realise the greatest possible reduction in dam safety related risk for the available funds. Good cooperation between the Regional Authority, the Building Consent Authority for dams (often they are different organisations), the dam owner, and the dam engineer, together with a pragmatic approach is vital in moving toward current best practice for management of these dams.
Case studies are presented for the Northland Region, where the farm dams are typically homogenous earth fill dams in the order of 8 to 12 m high, fulfilling functions as irrigation, stock water supply, recreation and flood detention structures. The findings are considered relevant to earth fill farm dams across the country. -
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2013 Papers
2013 – Development and application of a risk based approach to managing floods during construction
Learn moreSimon Lang, David Stephens, Peter Hill, Mark Arnold and Tommie Conway
Considerable thought has been given in recent years to managing the risks associated with floods during the construction of new dams and dam upgrades. Both ANCOLD and the NSW DSC provide some limited advice on how this risk should be managed, with many dam owners aiming for societal risk during construction to be no higher than pre-construction. One approach to do this is to draw down the reservoir such that sufficient airspace is created to reduce the probability of overtopping the construction works to be equal to that of overtopping the dam crest pre-construction. However, this frequently leads to very large releases of valuable water resource being required. This approach also fails to consider that the conditional probabilities of failure may be quite different during construction than during normal operation. A risk-based approach was applied for the recent upgrade of Tarago Reservoir. Existing event trees from a failure modes analysis were adjusted to reflect the construction conditions. In some cases, the event probabilities increased (for example as a result of excavation of the dam embankment), however some also decreased (for example as a result of more rapid means of detecting and intervening in breach formation during construction). The conditional probabilities of failure during construction were then used to estimate the overall seasonal probability of failure, and it was found that a limited draw down of the reservoir would be sufficient to ensure that risks were no higher during construction than pre-construction. To reinforce this, the cost-to-save-a-statistical life was estimated for further drawdown of the reservoir and used to demonstrate that the risks were as low as reasonably practicable.
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2013 Papers
2013 – Case study of risk assessment for dam safety management decision-making in Korea
Learn moreJeong Yeul, Lim
For various historical reasons and some technical reasons, the safety of dams has been evaluated using an engineering standards-based approach, which was developed over many years. It was used initially for the design of new dams, but increasingly has been applied over the past few decades to assess the safety of existing dams. Some countries have carried out risk assessments of existing dams that included both the structural and hydraulic safety of the dam and social risk. These methods developed by other countries could be adapted to assist in decision-making for dam safety management. Unfortunately, methods for risk assessment of dams were not established in Korea. This study outlines a beginning risk analysis for structural safety management. The first stage consisted of research on the present domestic dam safety guidelines and reviewing operations for management systems of dam safety abroad. Also, dam risk analysis requires reliable data on dam failure, past construction history and management records of existing dams. A suitable risk analysis method of dams for structural safety management in Korea is use of event tree, fault tree and conditioning indexes methods. A pilot risk assessment was carried out for two dams. The dam risk assessment process was thus established, and we learned the importance of risk assessment. The future includes additional research and risk analysis to develop the system.
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2013 Papers
2013 – Managing the risk of under-designed spillway training walls: an owner’s guide
Learn moreChris Topham, Eoin Nicholson and David Tanner
A number of Australian dams have spillways with reinforced concrete training walls designed in the 1950/60s to the standards of the day, but which could be considered under-designed according to modern criteria. Such walls commonly retain significant depths of earth and rockfill embankment materials, where structural failure of the wall could seriously compromise the safety of the dam. This paper presents the journey to mitigate the risk of such training walls, drawing primarily on experience in managing structurally deficient spillway training walls for a High Consequence Category dam in northern Tasmania. Reflections from each step of the risk management process are presented, including how the portfolio risk assessment contributed to a focus on the dam as a whole, and how that led to more detailed analysis and evaluation of the training wall risk. The use of instrumentation and enhanced surveillance for risk monitoring is discussed, including how real-time deformation data ultimately led to installation of temporary wall bracing works and enhanced contingency planning. The long-term risk treatment for the walls is presented, comprising a $6m structural upgrade to the training walls completed in 2013. The paper concludes with the learnings from the risk management journey and highlights the range of interventions available to owners with similar spillway training walls.
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2013 Papers
2013 – Maroon Dam: A multi-analytical approach for a multi-purpose dam
Learn moreIain Lonie, Malcolm Barker and Colin Thompson
Consideration of flood mitigation benefits, water supply, irrigation and recreational usage played an instrumental role in developing the proposed upgrade for Maroon Dam to meet dam safety and flood capacity requirements. Maroon Dam is a 47.4 m high zoned earthfill dam completed in 1974. The dam is a multi-purpose reservoir which is now owned and operated by Seqwater and plays an important role in the local community. Key drivers for the proposed upgrade design included embankment stability, foundation concerns, piping, spillway capacity and erosion of the embankment toe.
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Six options were reduced to three through a high level screening exercise. A more detailed assessment of the remaining options was undertaken using a Multi Criteria Analysis and a detailed risk assessment. Consideration of the competing uses of the reservoir was critical in the development and assessment of the preferred option. This paper will present the details of the analytical methods used as input for the Multi Criteria Analysis and the detailed risk assessment for the final proposed design option that will meet the requirements of dam safety and flood capacity without impacting on water supply, irrigation and recreational usage. -
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2013 Papers
2013 – Case studies of foundation grouting using the GIN method at the enlarged Cotter Dam
Learn moreSean Ladiges, James Willey, Matthew Norbert and Andrew Barclay
The Enlarged Cotter Dam (ECD) Project, located in ACT, consisted of the construction of a new 87 m high roller-compacted concrete (RCC) dam and two central core zoned earth and rockfill saddle dams up to 23 m high on the low points of a ridge to the south-west of the Main Dam. The Main Dam is the highest RCC dam constructed in Australia.
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A continuous single-line grout curtain with a total length of 1.2 km was constructed across the full extent of the Main Dam and the two saddle dams with the aim of reducing future seepage losses through the dam foundations. The grouting processes were similar for the main and saddle dams respectively, however the grouting of the Main Dam and saddle dams was carried out as two separate contract packages by different subcontractors. As such, the project provides a unique opportunity to undertake a comparison of the foundation conditions and control equipment and outcomes from the two packages of work. The foundation conditions were different at each of the three dams, with varying geology across the site.
The saddle dam grouting was completed in 2010, with the grouting carried out at the base of the core trench prior to construction of the embankments, while the grouting of the Main Dam was conducted in 2012-13, with most of the grouting works executed from the drainage gallery within the constructed dam.
Consistent throughout construction of the ECD grout curtain was a similar philosophy of real-time computer control, the use of Grout Intensity Number (GIN) parameters, water pressure testing, desirable grout mix properties and the avoidance of damage to the foundations. There were a number of key differences in the grouting process for the saddle dams and Main Dam; these include the ground conditions, the pumping control systems used, the GIN parameters adopted and the grout materials and mixes selected.
This paper provides a critical evaluation of the two grouting programmes, an assessment of the effectiveness of the grouting, comments on tools and methods used, and proposes a set of recommendations for curtain grouting over a range of ground conditions based on lessons learnt during the project. -
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2013 Papers
2013 – Falls Dam hydropower retrofit – integrating generation with existing irrigation assets
Learn morePeter Mulvihill and Ian Walsh
The Falls Dam was constructed in the 1930’s to provide storage for several irrigation schemes in the Manuherikia Valley situated in New Zealand’s South Island region of Central Otago.
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The opportunity to retrofit a small hydropower plant to the concrete faced rock fill dam was taken in 2003, utilising existing tunnels complemented by an innovative syphonic penstock system. The key design and construction features of this integrated scheme are described, along with experience from the first 10 years of the generation performance.
Looking ahead, there may be further integration challenges as current investigation of irrigation storage requirements leads to major redevelopment at this dam site and substantial changes to generation parameters. -
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2013 Papers
2013 – Flooded cars: estimating the consequences to itinerants exposed to dam break floods on roads
Learn moreJamie Campbell, Gregg Barker, Paul Southcott and Michael Wallis
The assessment of consequences of dambreak is used as input to the design parameters of dams, dam safety requirements and dam risk assessments. For many low consequence category dams, the consequences of failure can be dominated by itinerants, in particular vehicles on roads within the dambreak inundation area. Estimating the population at risk (PAR) and potential loss of life (PLL) rigorously is mathematically complex, requires significant user judgment and can be very sensitive to input assumptions. This paper presents a simple, practical tool that has been developed to assist engineers and analysts in assessing the PLL of itinerant road users within a dambreak inundation zone. The tool allows for a logical and defensible analysis based on an event tree approach and provides guidance on appropriate factors to be used in calculating the overall fatality rate of people exposed to the dambreak hazard. This paper details the tool and how to apply it to typical dambreak problems, providing the reader with the information required to estimate the consequences on itinerant road users; the paper also details how the concepts discussed can be applied to other itinerants.
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2013 Papers
2013 – Pukaki Canal Inlet Structure (Gate 18) – definition of safe limits of operation for a modified structure
Learn moreM.G. Webby and N.D. Sutherland
Repairs to the floor slab of the outlet transition section of the Pukaki Canal Inlet Structure in November 2009 were likely to have adversely affected the hydraulic jump behaviour in the transition section of the structure and therefore necessitated revision of the safe operating limits for the structure. Three separate series of flow trials were carried out at different lake levels over a period of about a year to carefully observe the behaviour of the hydraulic jump under a variety of gate operating configurations and discharges. New safe limits of operation for the structure were defined for the structure using the flow observations from the flow trials and the framework of analytical models for different types of hydraulic jump. The revised limits of safe operation were successfully implemented in 2013.
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2013 Papers
2013 – A case study: how to minimise risks associated with a portfolio of non-revenue generating dams
Learn moreMonique de Moel and Gamini Adikari
Parks Victoria manages over 4 million hectares of parkland and a portfolio of over $1.9 billion worth of infrastructure assets. Within this portfolio, Parks Victoria is responsible for a large number of dams and their associated structures. Consequence category of these dams varies from Extreme to Very Low. Parks Victoria recognised that these assets required a dam safety management and monitoring program. The development of a program commenced with a portfolio risk assessment in 1998 which progressed to detailed design reviews of a selected number of dams and the initiation of an ongoing dam safety and surveillance program. This initial work identified the need for dam safety upgrade works within this asset portfolio which Parks Victoria has been progressively addressing. In 2012 Parks Victoria identified that a review of the risk profile of the dams was warranted. The review included consideration of alternative options such as staging of works, reducing storage volume and decommissioning, as well as non-technical considerations such as increasing the recreational use and the environmental value of these assets. This paper outlines the approach adopted by Parks Victoria in developing and improving its dam safety program and how it has assisted in minimising dam safety risks. Specifically, Parks Victoria’s approach of adopting measures that recognize the purpose and benefits of the individual storages, whilst being sympathetic to the requirements of the other infrastructure within its diverse portfolio of assets is highlighted. Since this work commenced in 1998, Parks Victoria have been successful in the development of an effective dam safety and management program which has resulted in the reduction of risks associated with this portfolio of assets.
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