- A 275-foot long, 20-foot diameter tunnel replaced a failing culvert under an active railroad, restoring fish activity in the stream.
- The original culvert was classified as a complete fish-barrier using a Washington Dept. of Fish and Wildlife assessment protocol.
- GeoEngineers kept the railroad open during construction using innovative geotechnical analysis for trenchless design.
- The unique trenchless design concept, created by GeoEngineers, was a reinforced grout arch allowing safe tunneling and liner plate installation followed by shotcrete finishing.
- Large wood was used upstream and downstream to stabilize the channel and banks as well as increase habitat complexity.
US Navy Culvert Replacement and Fish Passage Design
Trenchless design was used to restore fish passage at a failing culvert along the Shelton-Bangor-Bremerton railroad.
GeoEngineers developed the civil design concept and geotechnical details for constructing a 275-foot long, 20-foot diameter tunnel to replace a failing 48-inch diameter culvert under the Shelton-Bangor-Bremerton railroad near Belfair, WA. The railroad, owned by the US Navy and maintained by Puget Sound and Pacific Railroad, is used to transport various goods, supplies, building materials, waste and equipment to and from Puget Sound naval facilities on the Kitsap peninsula in Washington State. Final plans and specifications were completed by Reid Middleton to comply with US Navy requirements.
The original culvert was failing and classified as a complete fish-passage barrier following an assessment protocol developed by the Washington Department of Fish and Wildlife. To fix the culvert and reactivate 1.2 miles of fish habitat for steelhead and salmon, GeoEngineers provided the Navy with a trenchless design concept that allowed construction without disrupting railroad operations.
From assessment and design concepts through construction, the entire project took two years to complete. GeoEngineers provided both geotechnical engineering and river and stream management services, including:
- Geomorphic assessment
- Stream habitat assessment
- Hydrologic and hydraulic analyses
- Geotechnical explorations and tunneling design
- Construction and permitting support
GeoEngineers designed a fish passage solution using trenchless construction methods to replace the failing culvert while keeping the railroad open. The steps involved included:
- Installing a thickened section of pre-grouted arch from both ends of the new tunnel using high-pressure injection methods prior to excavation
- Incrementally excavating the tunnel while simultaneously installing tunnel liner plates
- Reinforcing the tunnel wetted perimeter with shotcrete
- Placing streambed material within the culvert and realigning and grading the stream bed channel
- Constructing wingwalls and large woody debris revetments to stabilize the river bank, provide increased habitat and prevent cut channels and erosion
Large wood was used upstream and downstream of the tunnel to stabilize the stream channel and banks as well as increase habitat complexity. Fish use was immediate throughout the tunnel and into upstream areas as soon as the channel was flowing.