Nicole Anderson, M. Tooley, N. Vitharana, D. Moore
There is a significant stock of aging concrete dams in Australia which do not meet the requirements of modern dam safety practices. Where no site-specific information exists, current practice requires unduly simplified, conservative assumptions to be made. In some cases, this results in theoretical dam failure for load conditions which the dam has already experienced and safely withstood.
This paper outlines a range of site-specific field and laboratory investigations undertaken to reduce uncertainties in the assessment of two concrete gravity dams. For one dam, a suite of lab tests was undertaken to determine the residual reactivity so that potential future Alkaline-Aggregate Reaction induced expansion can be incorporated into any upgrade design.
The main purpose of the investigations was to reduce inherent uncertainties surrounding the design assumptions for strength and uplift pressures. This in turn reduced uncertainties relating to the risk profile of the dams.
The findings of this investigation will be of interest to dam designers and owners faced with upgrading concrete dams where a single traditional assumption can result in the difference between no upgrade or an upgrade worth several million dollars.
Keywords: Concrete gravity dams, testing, upgrade, Alkali Aggregate Reaction, dam design guidelines.
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The design of tailings dams under earthquake loading is quite challenging due to the nature of the tailings materials which are generally liquefiable under earthquake shaking. The design will be more complicated when the dam foundation is also liquefiable material. While assessment of liquefaction potentials is well developed in practice, assessment of liquefaction induced deformation varies from the simplest Newmark’s displacement method to the more complex effective stress dynamic analysis approach. It is generally accepted that the simplified method can be used for cases involving non-liquefiable materials. However, the use of this method for cases involving liquefaction may generally result in overly conservative designs to cater for the many simplified
assumptions in the method. With the advance of computer technology, time and cost are no longer obstacles for using the more appropriate method for estimating liquefaction-induced deformations of a tailings dams and achieving an optimum dam design.
This paper attempts to critically discuss issues in seismic design of tailings dams and provide an example of the use of the effective stress dynamic analysis method to estimate the liquefaction-induced deformations of a tailings dam and its importance in optimizing the design. The approach used is capable of estimating pore pressure response of liquefiable materials at any given time during the shaking. The effective stress analysis method used herein is embedded in FLAC software using a specially written FISH routine. Using this method, it can be demonstrated that although liquefaction is an issue, it does not necessarily mean that we must prevent its occurrence. As long as the deformation is acceptable, liquefaction is not necessarily a ‘show stopper’ for the project.
Keywords: liquefaction, seismic deformation, tailings dam design.
Eric Lesleighter, Peyman Andaroodi, Colleen Stratford
In January 2011 major flooding was experienced across a large part of Southern Queensland. The flood discharges through the Wivenhoe Dam spillway caused extensive erosion of the rock in the plunge pool. While not an issue in relation to the spillway structure’s security, the rock erosion experience was dramatic for a number of reasons. The paper presents details of the extent of erosion under head conditions that can be classed as moderate only when compared with many taller dams. The discharges over several days resulted in a pile of huge rock blocks downstream of the plunge pool.
The paper describes the plunge pool design dimensions, the geology, the hydrology of the releases, the hydraulics of the plunge pool, the surveys of the pool and rock mound, and moves on to discuss the mechanism of the fracturing and transport of the rock. Similar relevant experiences will be cross referenced, especially from details of recent experiences at the Kariba Dam and the study of remedies in the context of the dam’s actual safety.
From an actual major experience of erosion, and the sheer volume of rock that was lifted up and out of the plunge pool, the occurrence stands as a timely demonstration of what can happen in similar spillway situations, and suggests the type of awareness that spillway design needs to accommodate for energy dissipation facilities in unlined spillways plunge pool.
Keywords: Spillways, plunge pools, rock erosion, scour, plunging jets, pressure transients.
The Bureau of Meteorology (the Bureau) is revising the current Intensity-Frequency-Duration (IFD) design rainfall estimates which are an essential component in the design of infrastructure. The current IFDs were developed by over 20 years ago using data from the Bureau’s network of rain gauges and adopting techniques for the statistical analysis of the data that were considered appropriate at the time.
The IFD Revision Project, which will provide revised IFD estimates in November 2012, uses a greatly expanded rainfall database in addition to adopting more statistically rigorous methods that are most appropriate to Australian rainfall data. The revised IFD estimates will be provided for durations from 1 minute to 7 days and Annual Exceedance Probabilities (AEPs) from 50% to 1%. The revised IFD information will be blended with the CRCFORGE estimates developed by each state to enable a smooth rainfall frequency curve to be derived from 50% AEP to 0.05% AEP.
Keywords: Design rainfall, Intensity-Frequency-Duration, IFD .
Sofia Vargas, Robert Wark
Logue Brook Dam, 130 km south east of Perth, was completed in 1963 and comprises a 49 m high main embankment with a crest length of approximately 335 m and the reservoir impounds 24.59 GL of storage. The outlet works comprise an inlet tower, an outlet pipe (DN 1100 mm) and a valve house. Water from the dam is released through a clam shell valve and there is a sluice valve upstream of the clam shell which acts as a scour isolation valve.
Previously Logue Brook Dam supplied water into the Harvey irrigation system by releasing water down the river which was then drawn off downstream and pumped into the piped network. The scheme planning had identified that constructing a pipeline from the dam outlet to connect directly into the piped irrigation system would eliminate the need for pumping as the system could then be gravity fed directly from the dam.
The outlet works upgrade comprised the refurbishment of the Inlet Tower, refurbishment of the Valve House, installation of new valves, environmental release and magnetic flow meters, electrical, communications, SCADA, instrumentation and security upgrades.
This paper describes the diving inspection and above water inspections of the inlet tower, refurbishment of the existing installation, challenges of the design, adopted solutions, connection to the Harvey Water pipeline and construction issues. The project represents an interesting case history of improving dam safety standards to current ANCOLD guidelines to provide a modern and safe facility.
Keywords: Outlet works, diving, OH &S Issues, safety, deterioration
Shane McGrath, Andrew Reynolds, Garry Fyfe, Chris Kelly, Steven Fox
Goulburn-Murray Water is a rural water corporation located in Northern Victoria. It has responsibility for 12 State dams and is also the constructing authority for the Murray Darling Basin Authority’s Victorian assets.
Over the past 15 years G-MW has been engaged in a dam improvement program across its portfolio. To date 14 individual projects have been undertaken at 11 dams. The total expenditure is $125 million.
Starting from a base level of data at its inception in 1997, the program has encompassed all facets required for a dam improvement program. From early prioritisation to set the investigation program, through design reviews and risk assessments to develop the upgrading program and subsequent implementation. Some elements of the program were at the leading edge of practice at the time and a range of experiences along the way were character building as dam safety investment challenged other corporate priorities.
This paper sets out the lessons learned in developing the methodology and implementing the program of works, particularly relating to corporate adoption of the program, organisational capability, investigations, risk assessments, design and implementation.