2023 Webinar: Sliplining Low-Level Conduits

Registration Closed

This webinar will focus on planning, investigation, design, and construction considerations associated with the abandonment of low-level conduits through earthen embankment dams. In addition, the course will include planning, investigation, design, and construction considerations for the sliplining of low-level conduits. Methods for evaluating and diagnosing the condition of existing conduits will be discussed. The course will include a review of technical guidance developed by FEMA, including FEMA 484 – Technical Manual: Conduits through Embankment Dams and FEMA 675 – Technical Manual Plastic Pipe Used in Embankment Dams. Best practices associated with selecting and installing the appropriate carrier pipe and grout, as well as case studies of projects where design guidance has been applied will be presented.

Key Takeaways:

1. A brief review of the design of conduits through embankment dams.
2. Reasons why an existing conduit through an embankment dam may need to be abandoned or sliplined.
3. Procedures for evaluating the condition of an existing conduit through an embankment dam.
4. An introduction to FEMA 484 and FEMA 675 as the basis for developing design documents and construction procedures to address deficiencies with conduits through embankment dams.
5. Selection of carrier pipes to repair deficient conduits through dams, based on loading conditions and other project goals.
6. A discussion on grout mix design and installation.

J. Tyler Coats

Associate

Schnabel Engineering, LLC

Tyler Coats is an associate in Schnabel’s Alpharetta, Georgia office. Mr. Coats has over 15 years of experience as a civil engineer with a significant majority of the time spent in dam engineering. He has been involved in the hydraulic and structural analysis and design of dams throughout the southeast including several NRCS flood control structures. Tyler has served as the assistant design engineer, lead designer, project manager, and technical leader for numerous projects that have included low-level conduit sliplining or abandonment. Tyler is a licensed professional engineer in Georgia, Alabama, Virginia, and Arkansas.

Joseph S. Monroe, P.E.

Principal, Schnabel

Schnabel Engineering, LLC.

Joe Monroe has 25 years of experience in the design and construction of new and rehabilitation of earthfill dams and concrete gravity dams, including the associated spillway systems. His design experience includes subsurface explorations and geotechnical evaluations, hydraulic and structural design of spillways, and preparation of bidding and construction documents. In addition to design-related functions, he has also provided construction administration duties during the implementation of the design for which he had responsible charge. For remediation projects, Mr. Monroe has been involved with the design and construction of dozens of abandoned and sliplined conduits. He has been involved with dam-related projects throughout the United States and numerous countries throughout the world. Mr. Monroe is a licensed professional engineer in Alabama, Georgia, Maine, North Carolina, South Carolina, Texas, and Virginia.

Conduits through Embankment Dam Design Review
1. Dam Failure Modes
  - i. Most can be associated with conduits through embankments
2. Webinar Definitions
3. Low-Level Conduit Failure Example
4. Design Considerations
  - i. Hydraulic Capacity
  - ii. Structural Considerations
    1. Material selection
      1. Environmental conditions
    2. Joint integrity
  - iii. Geotechnical Considerations
    1. Foundation of conduit
    2. Soil compaction adjacent to and above conduit
  - iv. Seepage Control
    1. Internal drain system/filter diaphragm
    2. DO NOT PRESSURIZE YOUR PIPE
  - v. Inlet Protection
    1. Reduces potential for obstructions or damaging debris
  - vi. Energy Dissipation
Conduit Evaluation Procedures
1. FEMA 484 – Chapter 9
2. Inspection Types
  - i. Initial or formal
    1. Established by regulatory agency and/or owner
      1. Dam Safety; Reclamation; FERC; NRCS; USACE
    2. Review of design and construction data, as well as inspection and instrumentation records.
    3. Observations during first filling after construction
    4. Following major modifications (replacement; embankment repair)
  - ii. Periodic or intermediate (quarterly to annually)
    1. Focus on current status of conduit
  - iii. Routine (weekly to quarterly)
    1. Performed by operating personnel during other routine tasks
  - iv. Special or Emergency
    1. During or after unique circumstances or events
      1. Droughts
      2. Floods
      3. Earthquakes
    2. Inspections should be staggered so that components are observed during every season of the year.
3. Safety Procedures
  - i. Lower or drain reservoir or outlet channel
  - ii. Structural adequacy of controlled inlets (gates, valves)
  - iii. Confined space protocols; ventilation
4. Exterior observations
  - i. Whirlpools in reservoir
  - ii. Sinkholes, depressions, slides, sloughs
  - iii. Seepage along exterior of conduit including color
  - iv. Seepage from interior of conduit including color
  - v. Evidence of soil migration at the end of the conduit or accumulating in outlet channel
  - vi. Unusual noises or vibrations
  - vii. Pulsating or unstable flow
  - viii. Inexplicable reductions in discharge capacity
5. Interior observations
  - i. Man-Entry versus remote
    1. Conduits with diameters 36 inches or larger can be inspected by man-entry if proper OSHA precautions are taken
    2. CCTV is most common remote method
  - ii. Ponding water (indicator of settlement)
  - iii. Crack mapping (direction, length, and width)
  - iv. Joint separations between conduit sections and at connections to entrance and terminal structures
  - v. Corrosion to include exposed reinforcement
  - vi. Discoloration or staining
  - vii. Damaged protective coatings
  - viii. Chemical deterioration
  - ix. Leaks into or out of the conduit
  - x. Misalignment of conduit sections
  - xi. Voids behind pipe walls near observed cracks, joint separations, or misalignments
  - xii. Spalled concrete
  - xiii. Drummy or hollow-sounding concrete
  - xiv. Erosion or abrasion damage
  - xv. Cavitation damage
  - xvi. Blockages
6. Kansas State University Conduit Evaluation Tool
  - i. Observations made of watershed dams in Kansas with various principal spillway conduits
    1. CMP and C-76 RCP (lowest rated; shortest expected life)
      1. CMP Issues: Corrosion; joint leakage
      2. C-76 Issues: Cracking
    2. Lined welded steel and C-301 concrete pipe (longest expected life)
    3. Relationships between expected conduit life and environmental conditions
Conduit Deficiencies Requiring Action
1. FEMA 484 Section 9.5.2.2
2. Deterioration
3. Obstructions
4. Joint offsets and separations
5. Defective Joints
6. Cracking
Introduction to FEMA 484 and FEMA 675
1. Best practices for design, construction, problem identification and evaluation, inspection, maintenance, renovation, and repair
2. FEMA 484 – Technical Manual: Conduits through Embankment Dams (September 2005)
3. FEMA 675 – Technical Manual: Plastic Pipe Used in Embankment Dams (November 2007)
Carrier Pipe Selection Considerations
1. Advantages and Disadvantages of Sliplining
2. Available exterior diameter
3. Structural considerations
  - i. Loads and stress imposed by embankment and grouting
4. Hydraulic considerations
  - i. Spillway capacity during design storm event(s)
  - ii. Drawdown requirements
5. Material types
  - i. HDPE, DIP
  - ii. Jack & Bore (Steel Casing with Concrete Carrier)
Grout Mix Design & Installation
1. Grout Mix
  - i. Cementitious Grout
    1. Water, Portland cement, fly ash, plasticizer
    2. Fluidifying and expansive agent
  - ii. Cellular Grout
    1. Foam, high porosity
    2. Not recommended for use in embankment dams per FEMA 675
2. Installation
  - i. Grout ports and vent configuration; staging consideration
  - ii. Centralizers and spacers
  - iii. Bulkheads
  - iv. Pumping considerations
    1. Grout pump pressure
    2. Hydrostatic pressure
3. Quality Control
  - i. Bleeding
  - ii. Mud balance
  - iii. Compressive strength