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 resultingfrom dam-break

Breach development:

Size of the breach as a function of time

Teton 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

1:1.5

1.8 meter0.40.90.7

QutQinn

0.5 m

0.5 m

1.2 m

Laboratory model - scale 1:10

Downstream slope: 1:1.5Tailwater level: LowUniformly graded materiald10 = 5 mm d50 = 11 mm

Smallest particle size tested in this flume

Downstream slope: 1:1.5Tailwater level: LowUniformly graded materiald10 = 78 mm d50 = 100 mm

Largest particle size tested in this flume

s

Filt

er

1.20

1.20

1.60

1:3

Qm

ax =

60

0 l/s

1.0 3.6 meter

4.00

Qut

Water-level measurement

1:1

1:1

1.8 3.6

Laboratory model – 1.2 m high dam

Test-flume scale 1:5

Downstream slope: 1:1.5Tailwater level: LowUniformly graded materiald10 = 66 mm d50 = 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