Geotechnical Dam Investigation and Analysis in the PNW: Agenda
  • John France, P.E., D.GE, D.WRE, M. ASCE, JWF Consulting
  • Mike Beaty, Ph.D., P.E. GE, Beaty Engineering
  • Doug Johnson, P.E., Federal Energy Regulatory Commission, Portland
  • Brent Black, PG, CEG, Cornforth Consultants
  • Silas Sanderson, P.E., USACE Portland District
  • Chris Carpenter, P.E., GE, Cornforth Consultants
  • Keith Mills, P.E., GE, OWRD
MARCH 3, 2020
8:00 am – 5:00 pm
Geotechnical mechanisms of dam failure
  • Internal erosion
  • Seismic deformation
  • Spillway failure
  • Landslide
What you need to know about PNW geology
  • PNW geology for dam engineers
  • Sub regions – Coast, Interior Valleys, Cascades, Intermountain, Northern glaciated
  • Rock units and general emplacement
  • Discontinuities
  • Landslides briefly (will cover later as well)
  • How the site is the way it is
Other PNW geologic issues Differences between glaciated and non-glaciated sites
  • Drilling into existing dams
  • Verification of geologic interpretation data
9:50 am -10:10 am BREAK
Dam types and where they are most effective
  • Dam types (earthfill, rockfill, RCC, gravity, arch)
  • Embankment dam details and zoning
  • General considerations for drainage of dams
Important Soil Properties
  • Moisture content, compaction, and potential for future defects
  • Differences in material treatment from road embankments (hydraulic fractures)
  • Strength – problem soil/material – those that fail and lose strength at low strain (Brazil tailings), materials that liquefy, strain softening materials
Seismic issues
  • Earthquakes in the PNW
    • Cascadia earthquakes – subduction and intraslab
    • Crustal earthquakes
  • Effects on dams
  • Seismic site characterization
  • Differences between deterministic and probabilistic analysis
12:20 pm- 1:30 pm LUNCH ON OWN
Seismic Behavior and Analysis of Dams
  • Deformation analysis methods
  • Information needed for most reliable analysis
  • Strength loss – liquefaction and strain softening
  • Limitations
  • Implications for dams not founded on rock
Flow through dams
  • Considerations for dam drainage
  • Reliability of seepage volume estimates
  • Flow through a low permeability core
  • Presence of a confined layer in the foundation
3:05 pm - 3:25 pm BREAK
Geologic Conditions and subsurface flow affecting dams
  • Abutments
  • Reservoir floor
Internal erosion factors
  • General causes of internal erosion
  • Penetrating conduits through embankments
    • Compaction and movement issues
    • Conduits under pressure
  • Filters and filter diaphragms
5:00 pm End of Day
MARCH 4, 2020
8:00 am - 12:00 pm
Internal Erosion evaluation
  • How prone are PNW typical embankment materials
  • Concrete structures adjacent to embankments (problems at transitions)
  • Case study at Hills Creek dam
Stability of rock spillways
  • Spillways on “rock”
  • Effects of joints and fractures
Concrete spillway issues
  • Concrete channels
  • Historical designs and review
  • Investigating what is under the concrete
9:40 am - 10:00 am BREAK
  • LiDAR observations
  • Steepness, size, and approximate age
  • Old slide reactivation versus new slide in sensitive material
  • Is it big and fast enough to move the dam or put a wave over the reservoir
  • What are the typical modes of failure
  • Historical risk
  • Other ways to evaluate risk
  • What is different in the Pacific Northwest
  • Approaches to assessment and analysis of risk (each speaker that has an example)
    • Internal erosion
    • Seismic
    • Spillway stability
    • Landslide
12:00 pm End of Workshop
12:15 pm - 4:00 pm - Field Trip : Optional half day field trip to Scoggins Creek dam 
Tour to Scoggins Creek Dam 
  • Dam History
  • Geologic setting
  • Seismic evaluation
  • Internal erosion evaluation
Special thanks to our sustaining members