2010 – Challenges Associated with Identifying and Analysing Potential Failure Mechanisms in Dam Foundations – Taum Sauk Upper Reservoir Dam & Wyaralong Dam Case Studies

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

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