Cornforth Consultants
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    • 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
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Water Supply Tunnels Crossing Sandy River

Sandy, Oregon
The primary water supply for 800,000 people in the Portland metropolitan comes from the Bull Run Watershed through three large-diameter pipelines. Sandy River, a natural barrier to the three conduits, is crossed with two bridges, which expose the supply to natural hazards including earthquakes, volcanic debris flows, landslides, forest fires and wind and ice storms. Cornforth Consultants was retained by the City of Portland Bureau of Water Works to determine the feasibility of relocating the existing and future conduits into underground crossings at the river.

The site geology and natural hazards were mapped and evaluated, and geotechnical explorations were performed with vertical and angled borings drilled deep into rock. Rock samples were collected and tested to determine the rock mass characteristics, and permeability tests were performed to estimate the flow of groundwater through the fractured rock. Environmentally sensitive exploration methods were used to protect the wild and scenic Sandy River and included helicopter access and pontoon-barges, and low-impact mobile drilling rigs. Cornforth Consultants and the design team conceptualized cut-and-cover and bored tunnel options for the City of Portland Water Bureau to identify an environmentally sensitive and cost effective tunneling technique. After a tunneling option was identified, Cornforth performed preliminary geotechnical engineering.

Preliminary engineering phase included site specific subsurface explorations, geophysical testing, laboratory testing and rock mass classification and seismic considerations. Geophysical testing included ground penetrating radar, acoustic sub bottom profiling and electrical resistivity imaging to supplement drill hole data. Laboratory testing of rock conditions was conducted along with the rock core sampling to develop Rock Quality Designation (RQD), Rock Mass Rating (RMR), and Rock Mass Quality (Q) characterization. Seismic hazards were evaluated to include regional fault sources and the Sandy River Fault Zone. Ground motion parameters of peak horizontal (particle) velocity and shear wave velocity were also assessed. Foundation design consisted of evaluating potential seepage into the tunnels, and constructability of large concrete shafts at each end of the tunnel crossings.

Selecting Rock Bolt Locations
Overwater Drilling and Sampling

​Services Provided:

  • Site geologic reconnaissance
  • Review of geomorphic conditions
  • Plan of explorations
  • Field explorations
  • Over-water drilling
  • Geophysical testing
  • Geologic hazards evaluation
  • Sampling and laboratory testing
  • Geotechnical instrumentation
  • Volcanic hazards
  • Regional and local seismicity
  • Seismic ground response
  • Rock mass classification
  • Tunnel feasibility
  • Seepage evaluation
  • Constructability evaluation
  • 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