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IMPACT

WP2.1

Breach Formation - Large Scale Embankment Failure

HMK-02

Kjetil Arne Vaskinn Statkraft Grøner AS

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IMPACT

HMK-02

Norwegian national project:Stability and Breaching of

Rockfill dams

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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.

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D Deliverables Date

D2.1.1 Initial Laboratory Modeling anddevelopment of monitoring instruments

Mn5

D2.1.2 Preparation of field test site Mn6

D2.1.3 First failure test program Mn11

D2.1.4 Further laboratory modeling anddevelopment of second test program

Mn16

D2.1.5 Second failure test program Mn 23

Deliverables

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M Milestones and Expected Results Date

M2.1.1 Completion of initial 3 embankmentfailure & provision of field data

Mn13

M2.1.2 Completion of further 2 embankmentfailure & provision of field data

Mn25

Milestones and Expected Results

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Lysaker/Oslo

Tromsø

Trondheim

Large scale test-site

Arctic circle

Large-scale field test

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Large-scale field test

Damsite

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Large Scale Field Test

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Large Scale Field Test

Test-site

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Large Scale Field Test

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Test of drainage capacity of the dam toe 2001

Dam-toe

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Large Scale Field Test 2001

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Large Scale Field Test 2001

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Large Scale Field Test 2001

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Large Scale Field Test 2001

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Large Scale Field Test 2001

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Large Scale Field Test 2001

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Large Scale Field Test 2001

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Large Scale Field Test 2001

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Large Scale Field Test 2001

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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

1H = 6 m

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Field tests 2a:2002

Homogeneous (minimum cohesive) dam. Gravel 0-60 mm, fines (0,074mm)<5%, 4 mm<d50<10 mm, dmax<60 mm

A. Optional slope protection test with rockfill (0-500mm). B. 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

1H=5m

0,9 m

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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

1H=5m

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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 fill1 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.

Field tests 3:2002

H=6m1

1,5

B = 2,5m

1

4

H=5,5m

B = 1m

AB

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Toe stability. Rockfill support 300-400 mm

Construction: 2- 3 layers (2 m)

Instrument: 6 pore-pressure sensors at the foundation

Field tests 4:2002

H = 4-6m

1,5

1

2 m

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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.

THE PLAN FOR THE FIELD TEST OUTLINE

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Data Requirements

• Breach formation geometry

• Water levels

• Discharge into the reservoir upstream of the test-dam

• Flow/velocity

• Sediment movement

• Material properties

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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'.

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Breach formation geometryFrom the Chinese- Finnish research work

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Breach formation geometryFrom the Chinese- Finnish research work

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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.

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 footageQuality is high enough.(Morten Strand F&W)

Breach formation geometryPhoto/video

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Photopoints

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Wires

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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.

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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.

”Dambreak” Sensor

Sensor housing

Floating element

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.

(To be followed up)

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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

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Sonar - Example

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Water level - automatic recording (pressure sensors)

– upstream of the test-dam (2)

– downstream (several along the river to monitor the flood wave)

Water levels in the river and reservoir

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Pressure sensors in the dam

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• Gate opening every minute

• Water level in the reservoir

Discharge through the gates at Røssvassdammen = inflow to the reservoir upstream of the testdam

Inflow Rate to the test-reservoir

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Stage/waterlevel: Discharge from calibrated stage-discharge relationship

automatic sampling of water pressure/water level + manual readings

Discharges

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Water-velocity recordings - automatic recording by use of ADCP:

1) Floating on the surface2) Mounted at the bottom

Discharges from water velocity

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Discharge/leakage through the test-dam(before failure)

1. Direct measurement Gauge readingsADCP (EasyQ )

2. Indirect by simulation/calculation

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EasyQ velocity data

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Discharge during the faillure

1. Direct measurement ADCP (Aquadopp Profiler - bottom

mounted)

Gauge readingsProblem with gauges downstream due to sediment/debris flow.

2. Indirect by simulation/calculation

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Aquadopp Profiler

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By survey / calculation of bed surface changes

Sediment movement

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By survey / calculation of bed surface changes

Sediment movement

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Particle size distributionLiquid / plastic limitType of clayCompactionRock properties (interlocking effect)

Clay will require further tests – chemistry

Should we be undertaking pre and post failure tests on samples?

Material properties