Justin Howes, Peter Amos
For many years Mighty River Power has operated an intensive Dam Safety Assurance Programme with respect to our nine large hydro assets, a unique run of river cascade system built between 1927 and 1972. From 2001 to 2007 the Arapuni Foundation Enhancement Project was a high profile activity, but there has also been much dam safety analysis and minor mitigation work that could be classified as “Business As Usual Dam Safety Activity” – this paper seeks to give a high level overview of the work carried out from 2000 to 2010. Items covered include; an overview of the hydraulic structures, their hydrological and geological setting, and the current dam safety regime. Examples of typical issues identified by the Programme are given on a structure by structure basis along the river. Seismic, Flooding, Emergency Planning, Documentation, Monitoring, Control, Electrical and Mechanical type issues are covered.
Paul C. Rizzo, Ph.D., P.E.; Carl Rizzo; John Bowen
The Authors served in key roles for the design and rebuild of the Dam for the Taum Sauk Rebuild Project between 2007 and 2009. Taum Sauk is the largest RCC Dam in the United States and has a symmetrical cross-section with conventional concrete faces upstream and downstream. The curvilinear shape and the cross-section presented a number of placement issues. In addition, a large number of “Lessons” were learned because of the rapid construction schedule, highly variable temperatures, highly confined working space, numerous details related to waterstops, construction joints and crest-to-gallery drains, foundation preparation, lift maturity, bedding mixes, crack repairs and the conventional concrete upstream face. The authors discuss these issues from the perspective of the Designer, Contractor and Construction Manager.
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
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.
Monique de Moel, A/Professor Jayantha Kodikara, Dr Gamini Adikari
All embankment dams have some seepage as the impounded water seeks paths of least resistance through the dam and its foundation. Seepage must, however, be controlled to prevent internal erosion of the embankment or foundation and avoid damage to surrounding structures. Embankment dams are designed to operate under controlled steady state seepage, which over time may change due to movement in the foundation and the dam, chemical actions and other forms of deterioration. Effective monitoring of seepage within embankment dams is therefore essential in regards to management of dam safety and prevention of failure.
Traditional methods of seepage monitoring have involved measurement or visual monitoring on the downstream side of the dam after the seepage has occurred. Effective, early detection of seepage in embankment dams has been difficult as it originates and develops in the subsurface. Infrared Thermal Imaging is such a technique that is non-contact, non-intrusive, simple and flexible. The analysis draws on the temperature behaviour and the heat capacity of materials within the body of the dam and consequently allows the user to identify and isolate temperature variations along the surface of interest. This paper describes the method, application and feasibility of infrared thermal imaging for the detection of seepage in earth and rockfill embankment dams. The value of this technique as an additional tool in the surveillance of dams is discussed.
Infrared thermal imaging has been in use in other fields of engineering for condition monitoring and defect detection of structures. It has shown great potential in identifying variations in surface characteristics, which may not be evident through visual inspection alone. In this paper, reliability of this technique for seepage detection in embankment dams has been analysed using 8 case studies in order to arrive at a fair understanding of the best conditions under which Infrared Thermal Imaging field inspections should be carried out. The results of field investigations undertaken at these dams suggest that Infrared Thermal Imaging is a useful and effective tool for detection of seepage and an aid in identifying seepage behaviour.
Keywords: Seepage Detection, Infrared Thermal Imaging, Dam Surveillance, Monitoring
G.L. Vaschetti, C.A. Verani, J.W. Cowland
Geomembranes are an established technique for long-term waterproofing of hydraulic structures including all types of dams, canals, tunnels and reservoirs.
Three construction projects are presented that feature unique waterproofing solutions leading to faster construction programmes and granting safer and longer service life at lower costs: The 35 m high Paradise Dam (aka Burnett River), Australia’s largest volume Roller Compacted Concrete (RCC) dam waterproofed using a PolyVinylChloride (PVC) geomembrane sandwiched between prefabricated concrete panels and the RCC itself; The 50 m high multipurpose Meander Dam in Tasmania, designed as a RCC dam of the low cementitious content type whose imperviousness is provided by a PVC geomembrane installed in exposed position and mechanically anchored to the upstream face of the dam; And the Eidsvold Weir, a 115 m long 15.45 m high RCC structure used for water supply, waterproofed using an external PVC waterstop installed on the upstream face and able to accommodate the expected movements at the joints.
The paper will outline the technical details, installation and performance of the geomembranes.
Advantages gained from the use of a geomembrane waterproofing system on RCC dams – experiences from Australia