Richard Olive John Wonnacott, Stefan Schwank
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.
J.H. Green, D.J. Walland, N. Nandakumar
The Bureau of Meteorology has recently revised the Probable Maximum Precipitation (PMP) estimates for the Generalised Tropical Storm Method (GTSM) region of Australia. The revision process has involved the application of the more technically rigorous Generalised Southeast Australia Method (GSAM) that was previously developed for the southern part of Australia to a much larger data set of severe tropical storms. This has generally lead to an increase in the total GTSM PMP depths with a resultant increase in the Probable Maximum Precipitation Design Flood (PMPDF) and the Probable Maximum Flood (PMF).
In addition, the revision process has produced significant modifications to the temporal and spatial patterns adopted when applying the PMP depths to a dam’s catchment and these changes have also generally lead to increases in the resultant floods.
This paper discusses the rationale behind the increases in PMP depths and changes in the associated temporal and spatial patterns and presents the justification for the adoption of these more scientifically defensible estimates.
The application of the revised PMP estimates to the Keepit Dam catchment in northern NSW is presented and a comparison between the PMPDF and PMF estimates based on the original GTSM and the revised GTSM (GTSMR) made for this specific case study.
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.
SEQWater is the major supplier of untreated water in bulk to Local Governments and industry in the South East Queensland region of Australia, through ownership of Wivenhoe, Somerset and North Pine Dams. Wivenhoe Dam (Lake Wivenhoe) is located on the Brisbane River in Esk Shire. The storage provides both flood mitigation and water supply storage to Brisbane and Ipswich. The water supply storage capacity at full supply level is 1,160 GL. An additional 1,450 GL of storage above full supply level is used for flood mitigation.
Changes to the estimation of extreme rainfall events has resulted in significant increases in the estimates of the PMF since the original design of Wivenhoe Dam. To upgrade the flood security of Wivenhoe Dam, SEQWater has formed an alliance with Leighton Contractors, Coffey Geosciences, MWH and the NSW Department of Commerce.
This paper details the alliance delivery method, the latest estimates of the PMF based on the GTSMR method and details of the two preferred options being finalised by the Alliance.
A survey of spillway gate systems and operations has recently been completed by dam organisations in Nth America, Australia and New Zealand. The survey sought to identify typical arrangements for spillway gate systems and common features pertaining to reliability such as system redundancy, actuation methods and back-up systems, gate and hoist types, remote and local operation, gate testing programmes, and human factors.
Sixteen organizations responded, covering sixty two dams and nearly four hundred gates. This Paper reports on the preliminary analysis of the data, providing an overview of the industries’ approach to spillway gate operation and control.
M G Webby
Investigations of damaging blowback incidents at the headrace tunnel intake to Rangipo Power Station in the Central North Island of New Zealand are described. The blowback phenomenon is explained theoretically based on evaluation of the evidence available from the incidents and information obtained from the literature. A physical hydraulic model study is described in which this explanation of the blowback phenomenon was verified. The model was also used to devise a solution for the blowback problem.