Large Scale Embankment Failure IMPACT WP2.1 Breach Formation - Large Scale Embankment Failure Kjetil Arne Vaskinn Statkraft Grøner AS Forskjellige firma sendte inn hvert sitt prosjektforslag man disse hadde så mye til felles at det ble bestemt å slå disse sammen til et stort prosjekt som inkluderer store deler av bransjen. HMK-02

Norwegian national project: IMPACT Norwegian national project: Stability and Breaching of Rockfill dams Forskjellige firma sendte inn hvert sitt prosjektforslag man disse hadde så mye til felles at det ble bestemt å slå disse sammen til et stort prosjekt som inkluderer store deler av bransjen. HMK-02

Large Scale Embankment Failure WP2.1 Breach Formation - Large Scale Embankment Failure The objective of this work package is to undertake controlled failure of large scale embankments in order to monitor and record the failure process and mechanisms in detail. This will provide valuable data to assist in understanding the fundamental failure process, for developing predictive models and for assessing the validity of smaller scale laboratory testing.

Deliverables

Milestones and Expected Results

Large-scale field test Lysaker/Oslo Tromsø Trondheim Large scale test-site Arctic circle

Large-scale field test Damsite

Large Scale Field Test

Large Scale Field Test Test-site

Large Scale Field Test

Test of drainage capacity of the dam toe 2001 Dam-toe

Large Scale Field Test 2001

Large Scale Field Test 2001

Large Scale Field Test 2001

Large Scale Field Test 2001

Large Scale Field Test 2001

Large Scale Field Test 2001

Large Scale Field Test 2001

Large Scale Field Test 2001

Large Scale Field Test 2001

Field tests 1:2002 Homogeneous (maximum cohesive) dam of silty clay (25% clay, >65% silt, <10% sand ) Failure by overtopping Optimal water content ~ 15%, 0.15 m layers, compaction by dozer 2 layers of pore pressure gauges 2 m 2,0 1 H = 6 m

Field tests 2a:2002 Homogeneous (minimum cohesive) dam. Gravel 0-60 mm, fines (0,074mm)<5%, 4 mm<d50<10 mm, dmax<60 mm Optional slope protection test with rockfill (0-500mm). Failure by overtopping – no protective layer. 0.5 m layers, compaction by 4 ton vibrator roller, 2 layer with pore-pressure sensors 2 m 0,9 m 1,7 1 H=5m

Field tests 2b:2002 Homogeneous (minimum cohesive) dam. Gravel 0-60 mm, fines (0,074mm)<5%, 4 mm<d50<10 mm, dmax<60 mm Failure by overtopping – no protective layer. 0.5 m layers, compaction by 4 ton vibrator roller, 2 layer with pore-pressure sensors 2 m 1,7 1 H=5m

Field tests 3:2002 B A Composite rockfill dam. Failure by overtopping. Central moraine core (Fines (0,074 mm)>25%; dmax < 60 mm) Rockfill support: A. 0-500 mm, d10 > 10 mm in downstream fill B. 300-400 mm in upstream fill 1 m layer, 4 ton vibrator roller. 2 layer with 2 pore-pressure sensors in the core, 3 sensors at the foundation in the supporting fill. B = 2,5m B = 1m 1 1,5 H=6m H=5,5m 1 B A 4

Field tests 4:2002 Toe stability. Rockfill support 300-400 mm Construction: 2- 3 layers (2 m) Instrument: 6 pore-pressure sensors at the foundation 2 m 1,5 1 H = 4-6m

THE PLAN FOR THE FIELD TEST OUTLINE 1. Preparing the site for the test dam Building of transport road to the riverbed. Prepare the foundation of the test-dams. Preparing the side-slopes 2. Selection and transport of the of the materials for dam-building. 3. Building of test-dam #1 4. Test #1 5. Cleaning up at dam-site and preparing for test #2. Step 2-5 will be repeated for each test.

Data Requirements Breach formation geometry Water levels Discharge into the reservoir upstream of the test-dam Flow/velocity Sediment movement Material properties

Breach formation geometry 3D surface of breach at any time Photo, Video, Photogrammerty Sonar upstream Some points within the body either through wires or 'balls'.

Breach formation geometry From the Chinese- Finnish research work

Breach formation geometry From the Chinese- Finnish research work

Breach formation geometry Photo/video Paint a grid across whole of embankment - including crest and upstream face to aid video and photography Video to be taken from: Downstream: 3 camera stations (2001-2) Above: 1 camera (?) Upstream: 1 camera Still camera shots Downstream 3 camera or from video footage Quality is high enough.(Morten Strand F&W) Aerial video/photo will require some form of structure to support camera Photogrammetry offers a possible method for identifying movement of embankment material. Requires at least two cameras, firing simultaneously, at a fixed spacing.

Photopoints

Wires

Movement sensors Use of movement sensors - floating balls etc. A possible solution is to bury sensors within the dam that are released as erosion occurs. These sensors need to be uniquely identifiable, unrestricted by cables, traceable or disposable.

”Dambreak” Sensor Sensor contains tilt switch which will trigger when the sensor moves. A number of sensors will be built into the dam. The number of sensors will determine the resolution. Need to position all sensors by survey. Processor with built-in timer will log and store time for movement. Stored data together with the sensor ID will be downloaded to a PC after collecting the sensors downstream. Sensor will be housed in watertight (IP68) enclosure. Floating element will ease location of the sensors after the dambreak. Sensor size approx. 10x10x10 cm. (To be followed up)

Sonar Offers a possible means of monitoring breach growth underwater. Not appropriate for downstream conditions, but will be placed underwater upstream to show growth of breach through upstream face.

Sonar - Example

Water levels in the river and reservoir Water level - automatic recording (pressure sensors) upstream of the test-dam (2) downstream (several along the river to monitor the flood wave)

Pressure sensors in the dam

Inflow Rate to the test-reservoir Discharge through the gates at Røssvassdammen = inflow to the reservoir upstream of the testdam Gate opening every minute Water level in the reservoir

Discharges Stage/waterlevel: Discharge from calibrated stage-discharge relationship automatic sampling of water pressure/water level + manual readings

Discharges from water velocity Water-velocity recordings - automatic recording by use of ADCP: 1) Floating on the surface 2) Mounted at the bottom

Discharge/leakage through the test-dam (before failure) 1. Direct measurement Gauge readings ADCP (EasyQ ) 2. Indirect by simulation/calculation

EasyQ velocity data

Discharge during the faillure 1. Direct measurement ADCP (Aquadopp Profiler - bottom mounted) Gauge readings Problem with gauges downstream due to sediment/debris flow. 2. Indirect by simulation/calculation

Aquadopp Profiler

Sediment movement By survey / calculation of bed surface changes

Sediment movement By survey / calculation of bed surface changes

Material properties Particle size distribution Liquid / plastic limit Type of clay Compaction Rock properties (interlocking effect) Clay will require further tests – chemistry Should we be undertaking pre and post failure tests on samples?