Stability and Failure Mechanisms of Dams A dam safety research project Kjetil Arne Vaskinn

During the latest year there have been a strong focus on dam safety. This has been reflected by: several reassessments of dam safety new dam safety regulations introduction of risk analysis dam-break flood routing etc. Background Reassessment: Uncertainty and discussion about the dam regarding the demand of: Stability Slide or erosion during large throughflow Drainage capacity The cost of rehabilitation is several millions of NOK at each dam Simulation of flood propagation resulting from dam-break Breach development: Size of the breach as a function of time Teton

Increase the knowledge about: Safety of the downstream shell in Norwegian dams during large throughflow. Breach formation in embankment and concrete dams. The results shall be user-friendly, so that it can easily be used in the damowners safety work: Design tool Design criteria Simplified point of view Results are hoped to become a base for new “accept criteria". Aim of the project

Subproject no. 1: Shear strength and permability of rock-fillings Find shear strength and stability of different embankment material Find correct material parameters Find realistic analyse methods Project manager: Kaare Høeg, NGI Literature study Discussions with international experts Summarize experiences from dams Evaluation of earlier tests and calculations Field tests

Subproject no. 2: Stability and failure mechanisms of dams Develop tools/routines for evaluating the stability based on tests and international experiences from similar topics. Project manager: Einar Ødemark, Statkraft Grøner AS Piping Damtoe Support fillingWater tight core Filter Overtopping Subproject status: Field tests, carried out/new are planned Laboratory tests, carried out/new are planned Data reports, nearly finished Analysis, ongoing Parameters that are studied: Particle size Grading of the material Downstream slope Tailwater level Scale effects

Subproject no. 3: Breach formation in embankments Study the failure mechanisms of rockfill dams using tests and data from earlier failures. Develop methods for breach analysis. Design and layers of the dam should be included. Project manager: Einar Ødemark, Statkraft Grøner AS Subproject status: Literature study Field tests Field- and laboratory tests from subproject no. 2 and IMPACT

Subproject no. 4: Breach formation in concrete dams Study the failure mechanisms of different kind of concrete dams using Finite Element Method. Project manager: Per Magnus Johansen, Norconsult Subproject status: Initial phase Literature study planned and started?

Laboratory model – 0.6 m high dam 1:31:1.5 1:1 Water-level measurement 1: meter Q ut Q inn 0.5 m 1.2 m

Laboratory model - scale 1:10 Downstream slope: 1:1.5 Tailwater level: Low Uniformly graded material d 10 = 5 mmd 50 = 11 mm Smallest particle size tested in this flume Downstream slope: 1:1.5 Tailwater level: Low Uniformly graded material d 10 = 78 mmd 50 = 100 mm Largest particle size tested in this flume

s Filter :3 Q max = 600 l/s meter 4.00 Q ut Water-level measurement 1: Laboratory model – 1.2 m high dam

Test-flume scale 1:5 Downstream slope: 1:1.5 Tailwater level: Low Uniformly graded material d 10 = 66 mmd 50 = 88 mm

Project scheme, 2002 Finalise data reports from the tests in 2001 Analysis based on tests and literature Field tests Laboratory tests Literature studies Workshop