health of ash dyke
TRANSCRIPT
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Presented By
D N Naresh
AGM(PE-Civil)
Effect of Water Logging and Excess pore pressure
in
Dyke Maintenance.
O&M Conference on SUSTAINABLE GROWTH
Theme – Ash Management Technologies
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MOEF stipulates
•
Minimum land• Safe design of dyke – No breach/failure
• No leachates- liner
• Effluent discharge TSS less than 100ppm
•
Control of Fugitive dust
Before any construction activity - MOEF clearance is a must
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TYPE OF SECTION and METHOD of CONSTRUCTION
Sub soil exploration & Geo Hydrological studies
Access suitability
& availability of soil
Type of sectionSub soil characteristics
INVESTIGATIONS are taken up after site selection
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CRITERIA FOR SAFE DESIGN.MATERIAL PROPERTIES for deciding type of DYKE and method of CONSTRUCTION
• FOUNDATION
• FILL
NO OVERTOPPING
• ADEQUATE FREE BOARD --- min 1.5m as per IS 10635• SETTLEMENT OF DYKE/FOUNDATION
FOUNDATION STABILITY
• SHEAR STRESSES should be less than SHEAR STRENGTH
SEEPAGE LINE WITHIN d/s FACE of DYKE
• SEEPAGE ANALYSIS
TO PREVENT PIPING ACTION IN FOUNDATION & EMBANKMENT
• SLOUGHING & TOE SOFTENING
• INTERNAL DRAINAGE like (SAND CHIMNEY, SAND BLANKET, ROCK TOE ,TOE DRAIN) is provided---as per IS:9429
•
SLOPES TO be PROTECTED AGAINST
• WAVE ACTION,WIND ACTION,RAIN WASH ,VELOCITY OF FLOW
---as per IS 8237
STABILITY OF SLOPES
– STABILITY ANALYSIS
– ALLOWABLE FACTORS OF SAFETY (FOS) --- as per IS 7894
– STATIC >= 1.5, DYNAMIC >= 1.0
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Design
• Stable slopes
• Internal drainage
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Provision of internal drainage
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Dyke under construction
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Water logging
Signs of Distress :Water Stagnation
Water logging
Due to water logging
there is softening of base
sloughing
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Effect of water logging
….
Pore Pressure
WATER LOGGING LEADS TO SLOUGHINGWILL WEAKEN THE BASE
LOSS OF SHEAR STRENGTH
REDUCE PASSIVE RESISTANCE
WILL REDUCE FoS
WILL TRIGGER THE SLIDING FAILURE
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Before saturation
During saturation
24 hours of saturation
Cleavages & split seen
on cores
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Effect of water logging
on safety of dyke
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Control Measure
• Do not allow water logging/inundation in and
around the dyke
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Maintaining DRY CONDITIONS D/S
STORAGE LAGOON-I STORAGE LAGOON-I I
SLURRY PIPE LINE
OVERFLOW LAGOON
SPILLWAY
WATERESCAPE
STRUCTURE
ASHPIPE LINE TO PLANT
WATERRECIRCULATION
N AT U R AL W AT E R B O D Y
DISCHARGE CHANNEL
TAPPING FOR
RECIRCULATION
* *
* ASH FILLING SHALL BE CARRIED OUT
NEAR THE WATER ESCAPE IN THEINITIAL PERIODS
XX
DYKE ALIGNMENT
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Effect of Excess pore pressure
exit to Pore pressure
No proper exit to Pore pressure
exit to Pore pressure blocked
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Present Practice of assessing the pore water……Piezometers
• Monitoring dykesreacting quickly to inadequate performance or
to danger signals is a continuing
critical aspect for dyke safety.
• Instrumentationdata will fore tell of any abnormal behavior
quick response to abnormal behavior
can prevent failures in many cases.
i f
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Location of instruments to measure pore water
Location of
Piezometers
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Present Practice of assessing the pore water……Piezometers
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Seepage /piping seen on the d/s slope Slippage of slope due to pore pressure
Need to have data of seepage path along the dyke
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Need for State of art
GPR…..
Based on the forgone discussion there is an urgent needto get pore pressure on the dyke section on continuumbasis for better management of ash disposal
In order to assess the pore water pressure across thedyke on continuum basis can be obtained from GroundPenetrating radar(GPR).
This is a non destructive test which uses electromagneticwaves to image the water table/seepage path in thedyke section.
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Basic Principle………
Photographs: Georadar Inc.
Different Dielectric Constant
Hyperbola – Image Formation
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Field Example- Pipes………
Buried PipeBuried Pipe
Trench
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Field Operation………
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Application of GPR in Ash Dyke
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Conclusions……. Water logging in and around the dyke - not desirable for safety of the dyke
excess pore pressure leads to slippage of slopes/piping
there is need to detect seepage path along the dyke instead of discretelocations
GPR - Quick assessment of seepage path in non-destructive manner
GPR - Helps in prediction of seepage path in ash dyke indicating the behaviorof dyke.
• Highly effective for R&M Projects.
• Recommended as a tool
for dyke inspection, monitoring and maintenance
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Signs of healthy dyke
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SUSTAINING GROWTH
WITHOUT LOSS OF GENERATION THRU SAFE ASH DISPOSAL
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• BACK UP SLIDES
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Dielectric Constants of Various
Materials
• Clay 2.8-3.0
• Sand 5.0-5.5
• Air 1.0
• Glass 5.0
• Quartz 5.0
• Slate 7.0
• Mica 9.0
• Water 88
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Depth Determination………
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Need for continuous profile of pore pressure
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S TORA GE L A GOON- I S TORA GE L AGOON- I I
SLURRY PIPE LINE
OVERFLOWLAGOON
SPILLWAY
WATERESCAPE
STRUCTURE
ASHPIPE LINE TO PLANT
WATERRECIRCULATION
N AT U R ALW AT E R B O D Y
DISCHARGE CHANNEL
TAPPING FOR
RECIRCULATION
* *
* ASHFILLING SHALLBE CARRIEDOUT
NEARTHE WATERESCAPE INTHE
INITIALPERIODS
XX
DYKE ALIGNMENT
Water Recirculation
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Maintaining Zero Discharge
STORAGE LAGOON-I STORAGE LAGOON-II
SLURRY PIPE LINE
OVERFLOWLAGOON
SPILLWAY
WATERESCAPE
STRUCTURE
ASHPIPE LINE TO PLANT
WATERRECIRCULATION
N AT U R AL W AT E R B O D Y
DISCHARGE CHANNEL
TAPPING FOR
RECIRCULATION
* *
* ASH FILLING SHALL BE CARRIED OUT
NEAR THE WATER ESCAPE IN THE
INITIAL PERIODS
XX
DYKE ALIGNMENT
RAMAGUNDAM
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ASH POND MAINTANANCE
PRACTICES
RAMAGUNDAM
ENSURING CLEAR FLOW OF
WATER FROM TOE DRAINS AND
SLOPE DRAINS
ENSURING HEALTHINESS OFDOWNSTREAM AND UPSTREAM
SLOPES OF DYKE
REGULAR MONITORING OF
PIEZOMETER READINGS
MONTHLY ASH DYKE INSPECTION
BY CROSS FUNCTIONAL TEAM
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Typical section of healthy dyke
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MANAGEMENT OF ASH DISPOSALDESIGN,CONSTRUCTION , ROUTINE CHECKS & SAFETY ASPECTS
D.N.NARESHPE-Civil
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ISSUES RAISED IN OPERATING STATIONS
• SEEPAGE FROM BODY OF DYKE
• WATER LOGGING ON d/s SIDE
• SETTLEMENT
• OVER TOPPING/BREACH
• RAT HOLES
• EROSION OF u/s AND d/s SLOPE
• PIPING
• DELAY IN PLACING AWARD/COMPLETION OFCONSTRUCTION LEADING TO OVER LOAD ON THE DYKE
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WATER LOGGING
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T i l ti f h lth d k
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Typical section of healthy dyke
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BASIC FEATURES
•TO BE DESIGNED for MOST CRITICAL CONDITIONS.
•ENSURE FoS AGAINST THE ULTIMATE LOADS WHICH THE STRUCTURE IS LIKELY TO
FAIL