Cubit T, Swindon A, Tanner D
Catagunya Dam is located on the Derwent River in Tasmania’s south east. During construction of the dam in early 1960’s 412 post-tensioned anchors were installed, however the integrity of the original anchors can no longer be assured. The stability of the dam was restored between 2008 and 2010 using 92 modern, large diameter, load monitorable and corrosion protected post-tensioned anchors. These are the most highly stressed anchors applied to a dam at this time.
Some of the key construction challenges included installing 53 anchors within an operating spillway, utilising a very limited construction window and replacing severed surface reinforcement using carbon fibre rods.
This paper details how these challenges were resolved and presents a number of innovative solutions developed along the way.
Now showing 1-12 of 41 2974:
Thomas Vasconi, Mike Gowan
This paper describes the methodology adopted for the design of a 180 m-high stepped chute spillway to be constructed on a mine tailings storage facility (TSF) in Africa. This TSF dam, constructed using the “downstream method”, will be raised progressively via a series of nine lifts as mining proceeds. The first eight will be equipped with an operational spillway sized for the 1in 10,000 AEP whilst the ninth will house the closure spillway sized for the Probable Maximum Flood. The problem, common to all staged tailings dams, is how to design the spillways for such raising sequence? The very steep ridge declivity favored locating them in a unique configuration rather than the more usual separate hillside spillway on each dam abutment. The design of such spillways was challenging since it had to integrate the TSF interdependency parameters (water balance, dam raise sequence) whilst including flood routing, spillway sizing, stepped spillway design components. Challenging aspects of the design also included optimizing the costs associated with the short service life of these spillways. Furthermore, the design was undertaken in a way that the operating stepped chute could be upgraded and reused at mine closure. The design incorporates an innovative solution which allows reduction in the rock armouring quantity of up to 40% with associated cost benefits, and sustainability in terms of material usage. The lessons learnt in applying this innovative and sustainable design are useful for other sites requiring adaptive construction and short service life spillways.
Keywords: Tailings storage facility, stepped chute spillway, hydrology, hydraulics, mine water management.
Richard Herweynen, Robert Montalvo, John Ager
The choice of materials used in the construction of a dam is one of the most critical decisions in the design process. Our natural behaviour as engineers is to adopt materials which have proven performance, and which conform to Australian or international standards, which sometimes causes us to overlook the specific conditions and demands of the project at hand. In an environment where the majority of concrete produced is for structural purposes, the properties of these concretes is often vastly different to those desired for mass concrete structures such as dams and spillways.
The big question at Wyaralong Dam was could onsite aggregate be used in the Roller Compacted Concrete (RCC)? The Wyaralong Dam is located in the Gatton Sandstone (early Jurassic), predominantly feldspathic to lithic‐feldspathic sandstones with a clay matrix. Early analyses and tests suggested that the Gatton Sandstone was not suitable for RCC aggregate due to a 68% wet/dry strength reduction, high water absorption (5.2 – 7.5%) and petrographic interpretation that clay content was mainly swelling clay, leading to durability concerns.
Due to significant community, safety and cost issues with importing aggregate, Wyaralong Dam Alliance (WDA), during the development of the RCC mix design for Wyaralong Dam, chose to pursue the use of onsite quarried sandstone aggregate instead of importing aggregate. Additional petrographic and XRD analyses and extensive durability tests were undertaken on cores of sandstone and RCC samples, including wet‐dry cycles, soak tests in ethylene glycol, soaks in sodium hydroxide, and heating and cooling cycles. These tests indicated that, if swelling clays are present, they do not impact the durability behavior of the RCC aggregate.
The substantial effort put into testing the sandstone aggregate has paid off for WDA. Not only have the results indicated that the RCC mix performs remarkably well in terms of durability, but the very low modulus of elasticity of the mix has provided exceptional performance in terms of thermal loading; with all the related benefits in reduced restrictions to placement schedule and cooling requirements. Onsite sandstone was not only proven to be a feasible option, it has been demonstrated that it is the best option for the project. Details of the study are provided in this paper.
Keywords: Roller Compacted Concrete (RCC), Sandstone, Aggregate, Clay, Mix, Durability
David Scriven, Errol Beitz, Aaron Elphinstone
The Bowen River Weir is located at AMTD 94.4 km on the Bowen River, some 25 km south of Collinsville in North Queensland. The weir is part of the Bowen/Broken Rivers Water Supply Scheme and it provides a pumping pool for pipelines serving two nearby coal mining developments and a power station, and also acts as a regulator for riparian water users downstream until it meets the Burdekin River.
The weir was constructed in 1982 and incorporated a fishway towards the southern (left) bank, the design of which was based on the old “pool and weir” fish ladder type layout, typical of that era, with 48 separate cells containing partial vertical slots and baffles. This design has since been found to be ineffective for Australian native fish. In addition it was often out of service due to cells becoming filled with river sediment and debris. For these reasons it was decommissioned and made safe in late 2008 on the condition that a new fishway be constructed.
In late 2008 agreement was reached with Fisheries Queensland to install a “fish lock” type fishway at the site. This type of fishway has in recent years proved to be reliable and effective (eg. successful fish locks at Neville Hewitt and Claude Wharton Weirs). The preliminary and then final design was undertaken by SunWater (Infrastructure Development) between September 2008 and March 2009. The construction was undertaken by SunWater direct management, commencing in July 2009 and completed in late 2010.
Bowen River Weir Fishway – Design and Construction
Jim Walker, Jamie Macgregor
The Pukaki Canal Inlet structure is a large gated culvert and stilling basin structure, it is a High PIC appurtenant structure to the Pukaki Dam, located in the Mackenzie Basin area of New Zealand’s South Island.
The 560m3/s capacity inlet structure is founded on glacial moraines. It controls flow from the178 km2 Lake Pukaki storage into the 80m wide, 22km long Pukaki/Ohau canal. It is the owner’s (Meridian Energy) most important valve, as it feeds 1550MW of hydro generation on the Waitaki River.
A risk assessment in late 2009 identified a previously unrecognised trigger for a potential failure mode for the stilling basin. Principally, ongoing erosion of the reinforced concrete base slab could lead to failure of water stops in the slab joints potentially leading to slab uplift, foundation erosion, and ultimately, catastrophic failure of the Pukaki Dam. To better define the risk to the structure, further inspection of the stilling basin was recommended.
A dewatered inspection of the stilling basin was required, as further dive inspections would not improve our understanding of structure condition. Because the stilling basin cannot be isolated from the canal, this requires dewatering the entire Pukaki/Ohau canal, presenting significant risks of damage to the canals from slumping and lining failure. A dewatered outage also has major business revenue impacts.
This paper describes how Meridian were able to take advantage of a transmission network outage, scheduled for just six days after the risk was identified, to plan, safely dewater, inspect, and rewater 22km of hydro canal, and not just to inspect the Pukaki Canal Inlet structure, but also to implement repairs to the stilling basin slab which have successfully mitigated the structure safety and operational risks. This huge undertaking involved mobilising an army of people, plant and materials, and cost over NZ$1.8m. From identifying the risk to the structure, to completing repairs took just 13 (very busy) days.
Lessons learned in the areas of dam safety and asset management are presented. As well as those contributing to the success of the project in seizing an opportunity to mitigate the identified dam safety and operational risks.
Rick W. Schultz P.E.
The Corps of Engineers Risk Management Center is undergoing a nationwide assessment of its navigation and flood control projects. Development of the methodology and tools used to determine probability of failure of mechanical and electrical systems for dams is being presented in this document. Development of the Weibull formulas for specific use in dam will be addressed along with use of fault tree analysis to determine system reliability.
Keywords: Dormant-Weibull Formula, Fault Tree, Characteristic Life of Components, Beta Shape Parameters, Inspection intervals.