Cornforth Consultants
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The Dalles Dam Bay 8/9 Spillway

The Dalles, Oregon
The Portland District Corps of Engineers evaluated several design concepts to improve juvenile fish survivability at The Dalles Dam, including a Behavioral Guidance Structure (BGS) and two training wall alignments below the spillway. The BGS was proposed to be constructed in the forebay to direct migrating fish away from turbine intakes and toward bays 1-6 of the spillway. The conceptual design of the BGS consisted of a floating guidewall anchored to the floor of the reservoir by large-diameter drilled shafts. The two training walls evaluated consisted of 10-foot-wide walls anchored to the bedrock at the base of the channel with high capacity rock anchors. To further develop the designs, the Portland District retained Cornforth Consultants to complete over-water explorations, laboratory testing, engineering geology, and foundation design studies.

Cornforth Consultants (CCI) and their subcontract driller completed a total of 42 borings at the project under challenging conditions including water depths up to 110 feet and currents up to 15 feet/second. All exploration work was completed within permitted in-water work period without a spill or injury. To utilize exploration funds efficiently, crews used survey-grade GPS tools with real-time data correction to locate the floating plant. The GPS tools saved the cost of mobilizing a survey crew and enabled the floating plant to be positioned more quickly. In situ testing was performed in borings using single- and double-packer setups to measure permeability of bedrock. Selected zones of borings were tested with a Goodman Jack to measure the in situ deformation modulus of the rock. Borehole imagery was completed in all borings to measure the strike, dip, and aperture of fractures and the size of voids.

​Laboratory testing was completed on samples of rock core collected during subsurface explorations. The testing primarily focused on determining the compressive strength and laboratory deformation modulus of intact rock. The results of laboratory and in situ rock engineering parameters were used to characterize the rock mass for different basalt flows underlying the proposed structures. Once the Spillway Bay 8/9 design concept was selected by the Portland District, CCI assisted the design team by completing foundation design for the spillwall. Foundation design included allowable bearing capacity for the spillwall, estimated total and differential settlements, and calculating stability of bedrock subjected to high uplift loads. Cornforth assisted the structural designers with evaluating potential construction issues including feasibility of underwater rock excavation, benefits of foundation grouting, and several aspects of high-capacity anchors with 40-strand tendons. CCI assisted Corps structural design teams with preparation of plans and specifications.
Type 2 RHRS Slope on Highway 26
Spillway Anchors and Capping

​Services Provided:

  • Fish Passage Geotechnical Design
  • Laboratory Testing
  • Instrumentation
  • Anchorage Design
  • Uplift Pressure Investigation
  • 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