ASDSO Dam Safety 2013 Presentation

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