The disused Stapylton quarry is located in the suburbs of the Queensland Gold Coast. Gold Coast City Council, as part of the Northern Wastewater Strategy, has included the use of the quarry for storage and re-distribution of reclaimed water from the Beenleigh Water Reclamation Facility (WRF) to the downstream cane farmlands. A comprehensive EIS has been produced, which has strict water quality requirements for the quarry environs as well as the reservoir and outflow. This paper presents the background to the Northern Wastewater Strategy, the requirements for the Stapylton reservoir and the analysis performed for the detailed design of the embankment dam and the inlet bubble plume destratification system. The modelling of the destratification system was undertaken using the programme DYnamic REservoir Simulation Model (DYRESM) coupled with Computational Aquatic Ecosystems DYnamics Model (CAEDYM). The outcomes and implications of the modelling for the design and system operation including environmental monitoring are discussed.
The Diavik Dyke was constructed in 2001/2 in a major sub-Arctic lake in Canada’s Northwest Territories, to permit an open-pit diamond mining operation. The dyke, 3.9km long, was built in water up to 20 metres deep in a period of 17 months. For ten months of this period the lake was frozen. The project was notable for the extreme climate, discontinuous permafrost in the dyke foundations, very difficult logistics and the exceptional environmental constraints.
Project economics dictated a short construction period to permit the early generation of revenue from the mine. To confidently deliver a secure dyke within the time frame, the world’s most technologically advanced cut-off wall equipment was designed and fabricated in Germany.
This paper provides an overview of the dyke and focuses in more detail on the specialty equipment used for the cut-off wall and foundation treatment.
Peter D Amos, Thomas G Newson, Murray D Gillon
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.
In 1998, ANCOLD Guidelines entitled “Guidelines for Design of Dams for Earthquake” was issued. The Guideline mainly deals with the seismic aspects of dams and only a basic reference is made to the seismic assessment of intake towers in Section 8.3. Although the much needed and pioneering step taken to introduce this Guideline is to be appreciated and it has covered the seismic aspects of dams, some confusion does exist amongst dam / structural engineers in assessing the seismic performance of concrete intake towers. This is mainly due to the fact the behaviour of reinforced concrete intakes towers is quite different from that of earth or concrete gravity dams. This confusion could potentially lead to gross overestimate of the inertia loads on concrete intake towers resulting in unnecessary expenditure in investigation and remedial works.
The energy dissipation due to inelastic hysteresis behaviour of concrete members results in a great reduction in the inertia loads compared with those calculated with traditional “elastic” analysis methods. This consequently results in significant reductions in bending moments and shear forces on the tower and its foundation. It is very important to understand the basic behaviour of reinforced concrete, considering the composite action of concrete, longitudinal & hoop reinforcing steel, before embarking in sophisticated dynamic analysis the outputs of which are highly dependent on the input parameters
The authors have developed a methodology in which the hysteresis energy dissipation due to the inelastic behaviour of concrete intake towers is considered. Various criteria were defined for serviceability and ultimate failure modes such as excessive deflection, spalling of concrete, buckling of reinforcing steel. The confinement effect of hoop steel on the core concrete is also considered.
This paper will present the fundamental aspects of seismic behaviour of reinforced concrete structures with practical cases as applied to intake towers. The results showed that the current methods adopted by various Dam Authorities in Australia are cursory and the energy dissipation aspect should be considered, in conjunction with expert advice, before undertaking any remedial works.
There is a widespread perception among dam engineers that tree root invasion occasions a very serious threat to embankment dams by virtue of its potential to initiate piping failure, with appropriate action invariably recommended. Remedial works can, on occasions, be extensive.
While the principle is ostensibly plausible and scarcely challenged, there has never been, to the Author’s knowledge, a satisfactory investigation to establish any credible scientific basis for it. One case that has attracted some attention in literature (by virtue of the extent of the investigation undertaken), viz a piping accident at Yan Yean Dam, is critically reviewed to show that the accepted view on the role of tree roots in this incident is less than satisfactory. In the course of this review, two physical Laws of Piping are proposed, and applied both to this case and to another nearby Melbourne Water dam that also has a history of piping.
Whilst the consequences of piping in a major dam are such that risk from this source must be kept to a very low level, it is concluded here that piping risk arising from tree root invasion has been considerably overstated and that a more balanced assessment is necessary before determining what, if any, action is required.
Stephen Newman, Kelly Maslin
Lake Bellfield is a reserve storage for the Wimmera Mallee Water (WMW) Stock and Domestic System in North Western Victoria, constructed between 1963 and 1967. The dam is located on Fyans Creek approximately 3 km upstream from Halls Gap in an area of high tourist value and is rated in the Extreme category under ANCOLD guidelines. The dam consists of an earth and rockfill embankment 745 m long with a maximum height of 57 metres and retains a reservoir with a storage capacity of 78,500 ML.
Previous studies and a subsequent physical model study confirmed that the existing spillway does not meet the requirements of the current ANCOLD guidelines. The current flood capacity is approximately 40% of the Probable Maximum Flood. A range of potential upgrade options to pass the PMF were evaluated with a 1.9 metre composite earthfill and downstream concrete parapet wall raise in combination with spillway lowering of 3.4 metres selected. Construction of this option was completed in early 2003.
This paper describes the key features of the investigation and design including: