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
David Ryan, Peter Richardson, William Steen
Ibis Creek Dam, a referable dam and classified as a mass concrete gravity structure, was constructed in 1906 to supply water for both tin ore processing and the local township of Irvinebank. Irvinebank is a small township near Atherton in North Queensland and is situated about 3 km downstream of the dam. The mill ceased operation in 1990 but the township of Irvinebank remains reliant on the dam for water supply.
In 1996 the dam was raised about 1 m and strengthened by the addition of mass concrete on the crest and downstream face.
One recommendation of the Safety Review conducted in 2009 was that an investigation be made of the strength of the lift joints and the shear capacity of the connection between the Stage I and Stage II concrete sections. The investigations revealed that the structure was not constructed as had been originally assumed and the overall stability of the structure had been overestimated.
This paper details the investigations and remedial works proposed to strengthen the structure so that it complies with current design standards.
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
Brendan Sheehan, Chris Topham, Alan White, Rowenna Lagden
Darwin Dam is a 21m high embankment dam constructed on a geologically complex foundation that includes karst limestone features. The dam retains the top 15m of Lake Burbury on Tasmania’s west coast, and borders the Tasmanian Wilderness World Heritage Area. Defensive design of the dam addressed the key failure modes of piping through the complex foundations of limestone, sandstone, gravels and silts, and guarding against sinkholes forming in the limestone foundations. During construction, a comprehensive range of instruments were installed in the dam and foundation, as a long term means of monitoring this structure. A range of surveillance data has been collected since lake filling and this data, along with historic geological investigation information, was used to develop a three dimensional (3D) geological model of the dam and
foundation with phreatic profiles. The software used was a commercially available geographical information system. This tool has assisted Hydro Tasmania to better understand and manage the dam. The paper outlines the need for a 3D model, the methodology for development of the model, resources required, limitations and lessons learned. The benefits of the model, such as aiding understanding of foundation behaviour, assisting with interpretation of surveillance data, supporting decision making, and potential use during incident response are also discussed.
Keywords: Three dimensional, computer model, karst foundation, geology, hydrogeology ,dam surveillance
Jared Deible, Richard Herweynen, Gary Dow
The foundation is an important element in the stability of any dam. Understanding the foundation and the potential failure mechanisms associated with the dam foundation is critical to developing the final dam design. This paper will discuss the challenges encountered with the foundation at the Taum Sauk Upper Reservoir Dam and the Wyaralong Dam.
The Upper Reservoir of the Taum Sauk project is a 2.3 million cubic metre roller compacted concrete (RCC) dam located near Ironton, Missouri, USA. The RCC dam was constructed in accordance with United States Federal Energy Regulatory Commission (FERC) guidelines to replace a rockfill dike that failed abruptly on December 14, 2005. Wyaralong Dam is a new RCC dam, for water supply, located on the Teviot Brook near the township of Beaudesert in south-east Queensland.
Wyaralong and Taum Sauk each had challenges associated with identifying potential failure mechanisms in the foundation and with analysing the stability of the dam for these potential failure mechanisms. The geology at the projects was very different, but challenges for each project were quantifying the amount of reliance that was placed on the rock mass at the toe of the dam, developing the shear strength parameters, and developing the associated failure mechanisms that would be analysed.
The design of Wyaralong and the rebuilt Taum Sauk Upper Reservoir, including the geometry of the dam sections, were developed based on the foundation features at each project. Foundation treatments and excavation designs were developed based on the stability analyses conducted during the design phase. These foundation treatments included removal of weak layers or defects where necessary, but features were left in place in the foundation at selected locations at each project. Where features were left in place, stability analyses concluded the dam was stable. The stability analyses at each project considered three dimensional effects along features in the foundation where appropriate.
As the foundation was uncovered during the construction phase of each project, the parameters used in the stability analysis conducted during the design phase were confirmed or adjusted. The excavation and foundation preparation activities were adjusted as necessary based on actual conditions during the construction phase.
Challenges Associated with Identifying and Analysing Potential Failure Mechanisms in Dam Foundations – Taum Sauk Upper Reservoir Dam & Wyaralong Dam Case Studies
Keirnan Fowler, Peter Hill, Phillip Jordan, Rory Nathan, Kristen Sih
Although there are considerable uncertainties in the science of climate change, there is a growing recognition of the importance of the issue. Incorporation of climate change impacts is now required in policy guidance from several government authorities and it is prudent risk management to consider the effects of climate change in planning for water resource infrastructure, including assessment and design of dam upgrades. This paper describes the potential impact of climate change on extreme flood estimates and provides a case study for Dartmouth Dam in south-eastern Australia. Three inputs to flood estimation were considered according to the projected impact of climate change; namely design rainfalls, modelled losses and initial reservoir level. The relative influence of each of these factors is explored. Rainfall and losses had a similar (and opposite) influence on results and for this dam the reservoir level prior to the flood event had the largest influence on results. This case study demonstrates that the insights of climate modellers and hydrologists need to be integrated in order to provide defensible estimates of the impact of climate change in flood hydrology studies. Credible projections of changes in design rainfall intensities are required for the full range of exceedance probabilities across Australia.
Application of Available Climate Science to Assess the Impact of Climate Change on Spillway Adequacy