Arthur Yapa, Tom Bowling and Peter Watt
Hydro Tasmania uses an electronic inclinometer to monitor the face deflections of nine of its CFRDs. The inclinometer is lowered down a steel pipe attached to the upstream face of each dam. The inclinometer was designed and constructed by the University of Tasmania and was first used on Cethana Dam when it was completed in 1972.
The success of its use on Cethana Dam lead to its use for the long term monitoring of eight subsequent CFRDs constructed by Hydro Tasmania.
After 25 years of successful operation some irregular readings of face deflection became apparent. This paper describes the investigation of the irregular readings that had been obtained, the assessment of other methods of observing concrete face deflection, and the refurbishment of the inclinometer using modern electronic components.
There are many important dams and other structures on catchments smaller than 1000 km² with response times less than 24 hours, however these catchments have been largely overlooked in previous research into large and extreme floods. This paper is an initial step in “catching up” design practice for short duration rainfall events to the current best practice that is available for estimation of floods from rainfall events with durations of 24 hours and greater.
Two issues are specifically addressed in this paper. Firstly, a regional analysis of short duration rainfall depths is conducted to extend the frequency curve beyond an AEP of 1 in 100. Rainfall frequency curves are estimated for durations between 0.5 and 12 hours, using data from ten pluviograph sites around Australia. Secondly, sets of temporal patterns are derived that could be useful in joint probability analysis of short duration rainfall events. The effects of these new rainfall depths and temporal patterns on flood frequency curves are tested by applying them to rainfall-runoff routing models for three dams with small catchment areas.
John Phillips, Yu Sheng, Jennifer Henderson
The main iron ore body at Cockatoo Island in the West Kimberleys forms a cliff face plunging steeply into the sea. It was mined by BHP down to low tide level, but the tidal range of 10 metres hampered operations. Being a very pure and sought after ore, various investigations were made to determine methods of extracting the ore below the sea. A coffer dam into the sea was investigated with the conclusion that the soft marine sediments and apparent artesian groundwater in the foundation posed a major risk and high costs.
The mine was sold to a smaller company who proceeded to win useful ore from the island. They also eyed off the undersea ore and approached GHD to use soft ground technology developed for the Derby Tidal Power Project. The soft marine sediments and apparent artesian groundwater conditions were investigated.
The paper describes the design processes involved to achieve dam stability in a space limited by lease boundaries and the desire to maximise the amount of ore that could be accessed. A key to the process was the development of construction techniques and core placement procedures that could cope with the tidal range. Timing aspects were crucial and were controlled by observations of an extensive array of instruments installed for control purposes.
N.M. Nielsen and L.Casey
An energy and water company spends $8 million on maintenance each year. This work is defined and scheduled through a maintenance management system, part of an enterprise solution that cost the company over $2 million for licence fees, management consulting and installation.
The company has an ageing asset base and has been spending $18 million annually on capital improvements. The work activities are selected to meet safety requirements, enhance reliability, improve plant and upgrade customer service, and are defined, prioritised and scheduled on Word and Excel, which are standard applications on the desks of the company’s engineers and accountants.
This company is a composite (typical) of many in the energy and water business.
The most significant business decisions that owners usually have to make are capital spending commitments to modernise energy and water assets. To be successful, strategies have to be devised to meet the overall strategic objectives of the business, and processes adopted based on a fully functional and integrated asset planning system.
‘Aptus’ is a web-based planning application built specifically for asset intensive businesses. It enables a consistent analytical framework using engineering knowledge and the dam owner’s financial criteria, to provide new perspectives and support strategic planning and decision making with triple bottom line reporting. Aptus is a proven resource to maximize the value of the asset portfolio and sustain the business into the future.
Churchman Brook Dam is a 26m high earthfill dam with a puddle clay core and impounds a reservoir of 2.2GL. Various remedial works have been undertaken since completion of construction in 1928. In September 2000, a sinkhole in the right abutment was observed during a routine dam inspection. Following this incident, detailed site investigations were carried out. These investigations revealed that there are soft zones and possibly voids formed in the upper part of the clay core.
A comprehensive dam safety study and a risk workshop undertaken in 2002/2003 showed the dam to be deficient in aspects associated with piping, spillway adequacy and outlet works condition. A rational geotechnical model was developed for the foundation utilising triaxial test data from 1980s and recent investigations. The existing spillway chute will be upgraded with a concrete liner attached to the existing chute incorporating no-fine concrete as a free-draining medium. This paper presents the various aspects of the remedial works currently being designed.
In September 2000, pressures being monitored in a geological fracture beneath Arapuni Dam were found to be rising significantly, indicating that a deteriorating condition was developing in the foundation. Two boreholes drilled in 1995 had intersected high water pressures within the fracture in an area close to the downstream face of the dam, posing a risk of major leakage developing from where the fracture day-lighted downstream of the dam. Lumps of clay, bitumen and lake biota, including snails and small fish, were identified discharging from the boreholes, indicating that a significant leakage path had developed. Detailed investigations, the subject of this paper, were carried out from September 2000 to confirm the extent and nature of the deterioration. A range of groundwater investigation techniques and tools were used, while the reservoir remained full, to identify the source of the leak and confirm the path it took. The investigations culminated in development of a groundwater model that described the seepage behaviour in the dam foundation. Based on the investigation information gathered, the foundation fracture bearing the high water pressure was successfully grouted in December 2001 without lowering the reservoir.