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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Buddhima Indraratna, Mark Locke and Gamini Adikari
The main objectives of the filter are to prevent erosion of the dam core, permit controlled passage of seepage flow through the dam and facilitate dissipation of excess pore pressures in the core. In most designs of dam filters, empirical methods based on particle size ratios have been used. These empirical rules are developed through extensive laboratory tests. Although the empirical rules benefit from directly or indirectly incorporating most factors affecting filtration, they cannot be extrapolated for distinctly different soils and do not describe the time dependent changes that occur within the filter medium.
Mathematical models can be formulated to explain the fundamental physics of particle interaction and migration, within a framework of well defined geohydraulic constraints. Considering the mass flow and momentum conservation principles; time dependent changes in particle size distributions, mass flow rates, retention capacity and base soil erosion rates can be simulated.
This paper reviews various empirical and mathematical models, based on the authors experience. A novel approach to large scale filtration is highlighted based on testing actual soil and filter materials from an Australian dam, in a new 500mm diameter apparatus.
Peter Allen, Don Cock, Garry Grant and John Ruffini
The paper examines the performance of the Brisbane River and Pine River real time flood management system for the operation of Somerset Dam, Wivenhoe Dam and North Pine Dam during the 1999 flood event.
The February flood event, which was about 80% of the magnitude of the disastrous 1974 flood event upstream of Wivenhoe Dam, was the first major flood event to be managed by the system and it performed very creditably. The overall flood management system comprises:-
A network of 125 ALERT type rainfall and river height stations throughout the catchment; A data management system to facilitate data collection and data validation;
The paper describes the system and gives details of the performance of the system during the February event. It details the performance of the dams during the event and how this was optimised to maximise the safety of the dams and minimise impacts on those downstream.
Shane McGrath and Michelle Cowan
Goulburn-Murray Water (G-MW) is a Victorian rural water authority with responsibility for management of the major water systems within a 68,000 square kilometre region. Following a detailed business risk assessment undertaken in 1996, Goulburn-Murray Water developed a ten-year program to commence design reviews and address identified deficiencies at thirteen dams for which G-MW has responsibility.
In October 1997, the Victorian Government announced a $450 million regional water reform package, of which $35 million was provided for rural water authorities dam improvements. $18.5 million was allocated to G-MW on a ‘dollar for dollar’ basis. With contributions from G-MW customers, the current total funding amounts to $37 million.
This paper focuses on processes that G-MW has adopted to manage an accelerated program of dam design review and remedial work.
Contracts are usually thought of as documents which set out the respective legal obligations of the contracting parties. If the focus is changed, however, away from closing legal loopholes to the use of contracts to achieving project management objectives, then, among other things, contracts may be drafted as an integral part of the risk management plan for particular infrastructure assets.
In this paper, where the emphasis is on dam projects, the principles of risk management are applied to contracts for construction, maintenance and surveillance and outsourced technical advice, thereby covering issues over the whole life cycle of the asset. The principles are then broader issues of project procurement. Such as selection of contractor, contract packaging, ,clauses within the contract and administration of the contract.
Jim Walker, Murray Gillon and John Grimston
Karapiro Dam is at the end of a cascade of hydropower dams on the Waikato River in New Zealand’s North Island. The 52m high, high hazard, arch dam retains the lake for a 96MW power station at its downstream toe. Safety reviews recommended a re-evaluation of the dam stability under seismic loading.
Dam owner, Electricity Corporation of New Zealand (ECNZ), commissioned consultants Tonkin & Taylor Ltd to carry out a series of studies and investigations which provided better understanding of the dam’s safety status. Investigations located a previously unrecorded continuous low strength thrust fault underlying the left abutment. This provided the potential for movement of the left abutment gravity blocks under earthquake loading, with adverse effects on arch dam and reservoir safety. Investigations showed the abutment cut off walls to be lower than the PMF lake level. High groundwater levels and erodible pumiceous soils were found at the left abutment. These findings prompted ECNZ to implement stability enhancement works.
This paper describes the studies and investigations, peer review process, and design and construction of enhancement works.