UNDER PRESSURE: AGING OUTLET CONDUITS Jeremy Young, PE Tyson Clouser, PE Dam Safety 2013 – ASDSO National Conference Providence, Rhode Island September 9, 2013
Aug 20, 2015
UNDER PRESSURE: AGING OUTLET CONDUITS
Jeremy Young, PE
Tyson Clouser, PE
Dam Safety 2013 –
ASDSO National Conference
Providence, Rhode Island
September 9, 2013
CONDUITS THROUGH EMBANKMENT DAMS
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AGING, PRESSURIZED CONDUITS
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PRESENTATION OUTLINE
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External Seepage and Earth Pressures
PRESSURIZED CONDUIT/DOWNSTREAM CONTROL
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Ref: FEMA 484
Internal Water Pressure
PFMs ASSOCIATED WITH CONDUITS
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• PFM 1: Erosion of Soils into a Nonpressurized Conduit
• PFM 2: Erosion by Flow from a Pressurized Conduit
• PFM 3: Erosion of Soils Along the Outside of a Conduit
• PFM 4: Erosion in the Earthfill Above/Below/Adjacent to a Conduit
PFM 2: EROSION BY FLOW FROM A PRESSURIZED CONDUIT
7Ref: FEMA 484
CONTRIBUTING FACTORS TO FAILURE
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COMMON PFMs ASSOCIATED WITH IRON PIPES
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Ref: NRCC
COMMON PFMs ASSOCIATED WITH IRON PIPES
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Ref: NRCC
IDENTIFYING CORROSIVE POTENTIAL
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CORROSION RATES
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• As MC increases, so does corrosion rate
• Corrosion rates are slower under saturated conditions (Less Exposure to O2)
MOISTURE CONTENT
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CORROSION RATES AS A FUNCTION OF TIME?
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• Development Has Been Elusive to Researchers
• Generally Decrease with Time
• DIPRA provides average pitting rates for various soils on the 10-pt rating scale
Ref: Bonds et al. 2005
ESTIMATE LIFESPAN OF DUCTILE IRON PIPES
DIPRA Research –
Asphaltic Coated DIP
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16Ref: Spickelmire 2012
DIP vs. CIP
INSPECTION OF PRESSURIZED CONDUITS
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INSPECTION
• Requirements vary widely
Visible portions of outlet system are inspected, detailed internal inspection only required if problems noted.
Require detailed inspections on regular intervals, from 2 to 10 years.
Requirements on how a detailed inspection is defined varies, from only inspecting accessible portions of the outlet conduit to inspecting each and every portion of the outlet works system.
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INSPECTION
• Inspections can be accomplished by manned entry or with push-cameras or ROVs, depending on size.
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INSPECTION
• Visual quality in the wet is typically poor to accurately assess the condition / potential defects in the pipe.
• Recommended to dewater pipe Drain Reservoir? Not typically feasible, especially with water
supply reservoirs. Install Bulkhead on upstream end of pipe Access to downstream end of pipe?
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DIFFICULT ACCESS - MANIFOLD SYSTEM
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Flow
DIFFICULT ACCESS – VERTICAL BENDS
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Flow
BULKHEAD/PLUG TYPES
• Steel Plate
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BULKHEAD/PLUG TYPES
• Inflatable Plug
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WHAT HAPPENS WHEN THE LIMITS ARE PUSHED?!
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TURBERCULATION, PIPE CLEANING AND LINING
• Tuberculation - Friend or Foe? Hydraulic Capacity Concerns
Water Supply
Remove to facilitate effective inspection of pipe interior Tuberculation acts a protective layer
Corrosion begins more quickly, then tapers as pipe is tuberculated
Sliplining or Cured In-Place Pipe
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PIPE CLEANING - JETTING
• Pre-cleaning inspection must be performed
• Based on results of this inspection, jetting pressures and angles, pace of jetting action, etc. can be established
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PIPE CLEANING – PIGGING
• Must have adequate access
• Any fixed obstructions within the pipe prevent this type of cleaning
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PIPE CLEANING - CHAINING
• Risk of damage to pipe
• Should only be used before sliplining
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INSPECTION CASE HISTORY
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NON-DESTRUCTIVE TESTING
• Varying Degrees of Accuracy and Application
• Methods available (from FEMA 484) Voids on outside of a conduit
Self-potential Resistivity Seismic tomography Ground penetrating radar
Pipe thickness Ultrasonic Magnetic Flux Broadband Electromagnetics
New Technologies Sensor passes through pipe to find potential leaks from pressurized pipes
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REDUCING RISK OF FAILURE
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REDUCING RISK OF FAILURE
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EMBANKMENT RAISE/CONDUIT EXTENSION
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RETROFIT CONDUITS WITH UPSTREAM CONTROL
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CONSTRUCTION WITH FULL POOL?
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CASE HISTORY
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• Constructed 1879• Pressurized CIP, No Concrete Encasement, Corroded• Abandoned (Grouted) Conduit In-Place• Constructed New Siphon Intake Structure on Abutment
RECOMMENDATIONS
• Evaluate Each Dam Site Independently
• Plan and Coordinate with Entire Project Team Owner Engineer Regulators Contractors
• Balance Technical, Practical, and Regulatory Constraints
• Develop an Appropriate Investigation/Repair Plan
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RISK INFORMED DECISION MAKING
• Can be Used to Prioritize Investigations and Repairs
• Refer to Procedures Developed by Various Federal Agencies
• Consider Factors that Contribute to Failure and their Consequences:
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Conduit Type, Age, Encasement Wall Thickness and Section Loss
Defect Dimension Pipe Coating
Soil Gradation and Erodibility Soil Resistivity
Hydraulic Fracture pH of Reservoir
Seepage Gradient
QUESTIONS?
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UNDER PRESSURE: AGING OUTLET CONDUITS
Jeremy Young, PE
Tyson Clouser, PE
Dam Safety 2013 –
ASDSO National Conference
Providence, Rhode Island
September 9, 2013