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Ahmad Shayan, Robert J. Wark and John Waters

The Canning Dam concrete gravity structure located in Western Australia has shown an upward movement of 18.3 mm and lateral upstream movement of 14.2 mm over the past 15 years of monitoring. These movements have been associated with considerable cracking of the upper parts of the dam and the upper gallery. Investigations have shown that the cause of the cracking was a strong alkali-aggregate reaction (AAR) in the concrete, brought about by a deformed granitic rock. Extensive horizontal and vertical cracking in the upper part of the dam wall has necessitated the removal of the section above the floor of the upper gallery level, and construction of a new reinforced concrete section to act as head beam for post-tensioning of the rest of the dam wall.

A set of small diameter cores were taken from the various parts for diagnostic purposes, and a vertical core of 100 mm diameter was taken through the whole thickness of the wall for the determination of the strength properties, alkali content and residual expansion potential. Based on these, a post-tensioning stress of 1.5-2.0 MPa has been calculated for restraining the residual expansion of the concrete. The spillway bridge structure which is part of the dam wall has also shown mild signs of deterioration. The piers and abutment walls and the deck were surveyed for corrosion activity and extent of AAR. This work showed that the spillway bridge structure was sound and only needed maintenance. The performance of a triple blend concrete mix containing a high volume of fly ash (45%) and silica fume (5%) developed for the replacement of the old concrete is also discussed.

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1999 Papers

1999 – Investigations on Canning Dam Concrete Gravity Structure and it’s Rehabilitation
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Ahmad Shayan, Robert J. Wark and John Waters

The Canning Dam concrete gravity structure located in Western Australia has shown an upward movement of 18.3 mm and lateral upstream movement of 14.2 mm over the past 15 years of monitoring. These movements have been associated with considerable cracking of the upper parts of the dam and the upper gallery. Investigations have shown that the cause of the cracking was a strong alkali-aggregate reaction (AAR) in the concrete, brought about by a deformed granitic rock. Extensive horizontal and vertical cracking in the upper part of the dam wall has necessitated the removal of the section above the floor of the upper gallery level, and construction of a new reinforced concrete section to act as head beam for post-tensioning of the rest of the dam wall.

A set of small diameter cores were taken from the various parts for diagnostic purposes, and a vertical core of 100 mm diameter was taken through the whole thickness of the wall for the determination of the strength properties, alkali content and residual expansion potential. Based on these, a post-tensioning stress of 1.5-2.0 MPa has been calculated for restraining the residual expansion of the concrete. The spillway bridge structure which is part of the dam wall has also shown mild signs of deterioration. The piers and abutment walls and the deck were surveyed for corrosion activity and extent of AAR. This work showed that the spillway bridge structure was sound and only needed maintenance. The performance of a triple blend concrete mix containing a high volume of fly ash (45%) and silica fume (5%) developed for the replacement of the old concrete is also discussed.
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2000 Papers

2000 – Hume Dam Rehabilitation – An Owner’s Perspective
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David Dole and Brian Haisman

The $75 million remedial works at Hume Dam on the Murray River near Albury have been of national significance. The rehabilitation program associated with the structure itself and with its appurtenant works is now in the final steps of construction. The authors summarise this program with an emphasis not on technical details, but on decision processes. Equity in this dam is, in effect, held in equal parts by three State governments and by the Commonwealth government. At the same time, in response to the national water reform agenda, the governments have agreed upon new cost sharing arrangements that more nearly reflect the value of services to each government. The particular problems of decision-making within this evolving inter-State environment are discussed.

Lessons from experiments with application of risk analysis are discussed. Finally, the matter of adequacy of the structure for extreme floods is still under consideration. Hume Dam will presently pass the Design Flood developed in accord with Book VI (1999) of Australian Rainfall and Runoff, and the Dam Crest Flood has been estimated to have an annual exceedance probability of 1:110,000. _ Retrofitting a spillway to pass the estimated Probable Maximum Flood will double the cost of remedial works and is estimated at 10 times the cost of similar capacity built into original construction. The authors discuss the public policy elements of this pending decision.
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2001 Papers

2001 – Restoration of Storage Capacity at Lyell Dam
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Bill Hakin, Phillip Solomon, Geoff Hughes, Peter Siers

Lyell Dam is located on the Coxs River near Lithgow NSW Australia. It was constructed in 1982 to supply cooling water to Delta Electricity’s Mt. Piper and Wallerawang power stations.

In 1994 the storage capacity of the dam was increased by 7,500 MI by raising the embankment height and installing two 3.5m high inflatable rubber dams on an enlarged and slightly raised spillway sill.

Two significant failures of the rubber dams in 1997 and 1999, led the dam owner, Delta Electricity, to seek a more reliable way of maintaining the increased FSL whilst still providing spillway capacity for the design flood.
Following a detailed review of options, Delta Electricity chose to reinstate the storage capacity with the Hydroplus Fusegate System. The Hydroplus System consists of a series of fusible units that progressively tip off the spillway as flood magnitude increases, thereby forming a controlled breach in the spillway and providing for passage of the design flood. At Lyell Dam it has been designed such that no units tip until the 20 000 AEP flood. The System is designed to act as a normal free overflow spillway up until extreme events when it is required to commence operation. Key factors in the selection process were safety, reliability and operation/maintenance.

This is the first installation of the Hydroplus Fusegate System in Australia or New Zealand. There are currently 35 installations throughout the world. The System has wide application with dam owners either seeking to store additional water and/or to increase the capacity of their existing spillways for safety reasons in an economical and efficient manner.

This paper examines the decision and selection process adopted by Delta Electricity. It also presents a case study for the design and construction stages of this unique solution for Lyell Dam.
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2001 Papers

2001 – Sustainable Rehabilitation of Gravity Dams Using Post-Tensioned Anchors
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David Snape

Since the research and development work carried out by the (then) Metropolitan Water Sewerage and Drainage Board for the strengthening of Manly Dam in 1979/80, there has been over twenty years of continuous improvement in the application of advanced post-tensioned anchors for gravity dam rehabilitation.

Up until the Manly Dam remedial works, concerns had been increasing as to the long-term viability of available anchors. Sophisticated monitorable and restressable anchors, with superior corrosion protection afforded by greased and sheathed strands, were developed initially in test-bed conditions. This style of anchor has subsequently been used extensively throughout Australia on dam upgrades.

This paper compares the claims made by the designers with the demonstrated outcomes of installations that have been achieved, with particular emphasis on dams now owned by the Sydney Catchment Authority and Sydney Water Corporation. The original commitments to economy, aesthetics and rapidity of construction have been borne out by experience, with additional environmental advantages also being achieved. With the confidence built up from many successes in the strengthening of older dams, the time appears right to revisit the construction of new dams using the same style of post-tensioned anchors as the primary stabilising force.
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2002 Papers

2002 – Restoration of Storage Capacity at Lyell Dam Using Hydroplus Fusegates and Construction Stages
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Bill Hakin, Phillip Solomon, Peter Siers Bruce Goddard

Lyell Dam is located on the Coxs River near Lithgow NSW Australia. It was constructed in 1982 to supply cooling water to Delta Electricity’s Mt. Piper and Wallerawang power stations.

In 1994 the storage capacity of the dam was increased by 7,500 Ml by raising the embankment height and installing two 3.5m high inflatable rubber dams on an enlarged and slightly raised spillway sill. Two significant failures of the rubber dams in 1997 and 1999, led the dam owner to seek an alternative method of maintaining the increased Full Supply Level (FSL) whilst still providing spillway capacity for the design flood. Although the lost storage has a certain strategic value to Delta Electricity, the main reason for restoring the capacity to its former level was to preserve the environmental and recreational use of the reservoir for the local community.

Following a detailed review of options, Delta Electricity chose to regain the former FSL with the Hydroplus Fusegate System. Because of the freeboard available at Lyell dam it was possible to design the Fusegates such that none tip before the 20 000 AEP flood.

In order to derive accurate as-built levels and dimensions of the existing spillway, new laser scanning methods were utilised to create a digital 3-D model of its complex shape.
The water retaining concrete Fusegates were poured in-situ and designed without anti-crack reinforcement. This innovation was only possible by use of a special design mix and careful temperature control/monitoring during concrete placing.

This is the first installation of the Hydroplus Fusegate System in Australia. The paper examines the philosophy of approach and various unique methods used in the application of the System during the design and construction stages.
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2003 Papers

2003 – Increasing Storafe Capacity at Dartmouth Regulatory Dam with Fusegates: The Construction Stage
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Bill Hakin, Peter Buchanan, Doug Connors, Darren Loidl

To allow greater flexibility in their generation and hence a better response to the peaks in electricity demand, Southern Hydro decided to increase the Full Supply Level of Dartmouth Regulatory Dam by 3.5m using labyrinth Fusegates.

The Regulating Dam is located on the Mitta Mitta River, approximately 8 km downstream of Dartmouth Dam. It is a 23 m high concrete gravity structure with a 60 m long central spillway section. The dam forms the storage required for regulating releases from the Dartmouth Power Station back to the Mitta Mitta River, so as to satisfy environmental requirements.

Although this is the second Fusegate project in Australia it is unique in that difficult access conditions determined that construction in mild steel would be the most appropriate. Initial civil works involved construction of a flat sill to replace the Ogee spillway crest so that it could support the Fusegates. The installation contractor devised an ingenious method for installing the huge structures over the top of the gate-house which blocks direct access to the spillway. Design was very much undertaken with the installation method in mind to ensure a high quality project with minimum contractual risk.

This paper discusses the construction stage of this very interesting spillway modification.
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2003 Papers

2003 – INVESTIGATIONS AND DESIGN OF UPGRADE WORKS AT TANK HILL RESERVOIR IN VICTORIA
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Tank Hill Reservoir is located approximately 25km north-east of Warrnambool and forms part of the fresh water supply for the town. It was built in the 1930’s by the construction of an earthfill dam across the natural breach of the crater of an extinct volcano. The reservoir is an offline storage with a small natural catchment and has a nominal capacity of 770ML at Full Supply Level (FSL). The reservoir is operated by South West Water Authority (SWWA).

Previous investigations had identified instability issues associated with the dam embankment and the necessity for remedial work to increase the stability of the dam embankment. SKM undertook detailed survey and investigations and the proposed upgrade works include the construction of a downstream stabilising berm incorporating graded filters and a drainage system. The condition of the outlet works was investigated as part of the project, with some of these works found to be in poor condition with a risk to the security of supply, necessitating the design of refurbishment of the outlet works. The degree of siltation of the reservoir was also assessed, and some loss of capacity due to siltation was noted.

Detailed investigations were performed to determine the optimum configuration of the stabilising berm and to locate and test suitable construction materials. The embankment interface filters were designed to satisfy modern filter design criteria and were incorporated in the embankment drainage system. The condition of the outlet works, including the intake standpipe, three offtake valves and the outlet conduit beneath the embankment, were assessed via manual and CCTV inspections. An operation review, incorporating the proposed upgrade works within the framework of ongoing operation of the reservoir for supply to downstream customers was also prepared, as was a construction risk assessment.

This paper will present “extremely useful practical information” for dam design engineers, owners and operators where the whole spectrum of dam safety issues is required for the successful completion of remedial works design and construction.
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2018 Papers

2018 – Ash Tailings Dam Rehabilitation – Challenges and Aspirational Targets
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Stafford Griffiths

The rehabilitation of wet tailings storages is likely to become of increasing importance. In a setting of increasing environmental regulation and oversight, the environmental issues inherent in wet tailings storages will increase in visibility. This will translate through to increased regulatory attention, rehabilitation standards and costs. This scenario will necessitate increased engineering ingenuity and approaches to develop cost effective and robust/ defensible outcomes.

This case study of a coal fired power station ash dam rehabilitation compares a conventional (baseline) rehabilitation strategy and the development of a higher land use, with potentially beneficial outcomes for the owner, the community and the environment.

The baseline rehabilitation was a conventional fit-for-purpose rehabilitation approach consistent with the proposed final land use comprising the creation of a stable, open greenspace environment. The higher land use was an aspirational target style rehabilitation, with the assessed highest and best use for the site that was determined to be an industrial land development. While there will be limitations due to the low strength tailings foundation, this higher land use is considered an appropriate stretch target and is a feasible outcome for this site.
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2018 Papers

2018 – Massingir Dam Rehabilitation Project: Construction and Operational Challenges
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Peter Blersch, Charles Nyamariwata, Luis Paulo Mandlate

Following the catastrophic failure of the bottom outlet conduits of the Massingir Dam, a rehabilitation project was launched involving the installation of steel liners and the rehabilitation of the hydromechanical equipment. This paper describes the testing of an emergency gates for possible use as a control gate to maintain supply to downstream water users. It further describes the innovative use of alternative access for concreting and other services, the use and benefits of self-compacting concrete for infill concreting between the steel liner and existing concrete and the programme and cost benefits of pressurising the steel conduit prior to concrete encasement.
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2011 Papers

2011 – Refurbishment of Ambuklao and Binga Hydro Power Dams and Appurtenant Works
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John Grimston, Robin Dawson

The Ambuklao and Binga Hydro-Electric Power Projects are located in Luzon, Philippines and were privatised in early 2008 after public bidding. Ambuklao dam forms an impoundment on the Agno River. The nearest city, Baguio, is approximately 45km or 1.5hrs drive away. The key headworks feature is an embankment central core rockfill dam and reaches a maximum height of some 129 m above the bed of the Agno River. A gated spillway is located at the left abutment, with a steep chute and flip bucket. Binga dam forms an impoundment approximately 20 km downstream of the Ambuklao dam. The rockfill embankment with an inclined clay core reaches a height of about 107 m above the bed of the Agno River. The spillway is located at the left abutment.

Heavy tropical rains and typhoons can cause very high flows in the rivers leading into the Ambuklao and Binga reservoirs. PMF peak flow is 11,600 cumecs. Due to the steep slopes surrounding the reservoir and along the access roads to the Binga Dam, landslides can create a hazard in the reservoir or for emergency access to the dam. There are numerous active faults in the area, including the Abra, Digdig and Philippines Faults (the latter being one of the most active faults around the Philippines). The region around the dams is capable of and has experienced earthquakes with a magnitude of 7.8 on the Richter Scale. This was demonstrated by the 1990 earthquake (7.8 magnitude) and caused minor damage to the dam structures.

The Project owner commenced rehabilitation implementation planning immediately after purchasing the facilities aimed at reactivating the Ambuklao plant’s 75MW capacity (inoperable since 1999 due to reservoir siltation issues triggered by the 1990 earthquake) and increasing it to 105MW. Rehabilitation at the Binga plant will increase capacity from it’s current 100MW to 120MW. The overall rehabilitation works include plant, intakes, associated tunnels, etc. This paper will focus primarily on the dam and spillway related rehabilitation, studies and design including review of the PMF and spillway capacity for both dams, Ambuklao innovative upstream face rehabilitation, Ambuklao spillway studies and rehabilitation and Binga spillway works and reservoir sedimentation studies.

2011 – Refurbishment of Ambuklao and Binga Hydro Power Dams and Appurtenant Works

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Stafford Griffiths

Peter Blersch, Charles Nyamariwata, Luis Paulo Mandlate