Cornforth Consultants
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      • Bull Run No. 2 Seismic Stability Analysis
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      • Port Westward Power Plant Seismic Design
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      • Montana Rockfall Hazard Rating System
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      • Fern Hill Water Treatment Plant
      • Tualatin Valley North Transmission Line
      • Evaluation of 28 Water Storage Facilities
      • City of Sandy Water Treatment Plant
      • Mt. Tabor Reservoir No. 5 Cap Study
      • Oakridge Water System Improvements
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Fern Hill Water Treatment Plant Liquefaction Study

Forest Grove, Oregon
The Fern Hill Water Treatment Plant provides drinking water to the cities of Hillsboro, Beaverton, Forest Grove, and the Tualatin Valley Water District (Joint Water Commission). Due to increased demand, the Commission planned to increase the capacity of the plant by 20 million gallons per day. Cornforth Consultants (CCI) were retained as part of a multi-disciplinary design team for the expansion study.

The plant expansion consisted of an additional surge basin, a new filter building, and an additional sedimentation basin. The new facilities would be founded on loose, cohesionless silt near the Tualatin River - material that could potentially liquefy during an earthquake.

Cornforth's investigation included drilling and sampling, assessing maximum credible earthquake magnitude and potential ground acceleration, cyclic triaxial tests of undisturbed silt samples and engineering analyses to estimate potential ground movement (lateral spread and settlement). Cyclic shear strengths were compared with estimated seismic shear stresses to calculate the factor of safety against liquefaction. Post-liquefaction slope stability analyses, lateral spreading evaluation, and estimation of settlement due to liquefaction were also performed.

​Stone columns installed through the granular soil were the most cost-effective measure for improving the foundation conditions. The columns increase the strength of the foundation and create a path for groundwater to flow out of liquefied soil. CCI also provided construction inspection services during the installation of over 1,700 stone columns, as well as QA/QC during construction of other structure foundations.
Investigation at the First of Three Sites
Fern Hill Water treatment Plant

​Services Provided:

  • Regional and Site Specific Seismic Evaluation
  • Deformation Analyses
  • Soil Response
  • Liquefaction Susceptibility​
  • Home
  • Services
    • Earth & Rockfill Dams
    • Reservoirs, Canals, and Levees
    • Spillway Safety Inspections
    • Landslides and Rockfall
    • Earthquake Engineering
    • Geologic Hazards
    • Geotechnical Site Characterization
    • Hydrogeology
    • Expert Witness
    • Concrete Dams and Locks
    • Geotechnical Instrumentation
    • Deep and Shallow Foundations
    • Geotechnical Manuals
  • Industries
    • Water Resources
    • Energy
    • Natural Resources
    • Industrial
    • Transportation
    • Ports and Airports
    • Expert Witness
  • Projects
    • Earth and Rockfill Dams >
      • Barney Reservoir
      • Frog Lake Reservoir
      • Iron Gate Dam Raise
      • McGuire Dam Raise
      • Bonneville Cofferdam
      • Bull Run No. 2 Seismic Stability Analysis
    • Levees and Canals >
      • Libby Dike Rehab.
      • St. Johns Dike Stabilization
      • Cowlitz River Levees
      • Swift Canal Failure
    • Earthquake Engineering >
      • Barney Dam Seismic Analysis
      • Fern Hill WTP Liquefacation Study
      • Bull Run No. 2 Seismic Stability Analysis
      • Mt. Tabor Seismic Stability Analysis
      • Port Westward Power Plant Seismic Design
    • Rock Slopes and Tunnels >
      • Libby Rockfall Mitigation
      • Sandy River Pipeline Tunnels
      • Ketchikan Third Avenue Extension
      • Sain Creek Water Supply Tunnel
      • Montana Rockfall Hazard Rating System
    • Foundations >
      • Port Westward Power Plant
      • Cascade Locks Casino
      • Air National Guard Hangar
      • Biglow Canyon Windfarm
      • Oakridge Water System Improvements
    • Concrete Dams and Locks >
      • John Day Lock & Dam
      • Marmot Dam Removal
      • The Dalles Dam
      • Willamette Falls Dam
      • Bonneville Dam
    • Transportation >
      • OTIA Cracked Bridge Geotechnical Baselines
      • Newburg Dundee Bypass Design DEIS
      • I-84 Sandy River Bridge Investigation
      • Tanana River Bridge Foundation, Tok, Alaska
      • Montana RHRS Implementation
      • Ketchikan Third Avenue Extension
    • Ports and Airports >
      • Navy CVN Drydock
      • Depoe Bay Seawall Distress
      • Willamette Falls Flow Control Structure
      • Air National Guard Hangar
    • Water and Wastewater >
      • Fern Hill Water Treatment Plant
      • Tualatin Valley North Transmission Line
      • Evaluation of 28 Water Storage Facilities
      • City of Sandy Water Treatment Plant
      • Mt. Tabor Reservoir No. 5 Cap Study
      • Oakridge Water System Improvements
  • Staff
  • Resources
  • Careers
    • Geotechnical Engineer
  • Contact Us