| Construction Method | Auger Boring |
|---|---|
| Project | Lewis & Clark Riverfront Trail Tunnel |
| Location | The Dalles, Oregon |
The Lewis & Clark Riverfront Trail Tunnel stands as a remarkable example of innovative trenchless construction and engineering excellence. Constructed beneath an active railroad corridor in The Dalles Oregon, the project created a safe pedestrian and bicycle connection while maintaining uninterrupted railroad operations throughout construction.
The project required the installation of an approximately 12-foot-diameter steel tunnel casing beneath the active rail embankment. Due to challenging subsurface conditions consisting of loose sands and unstable soils, conventional tunneling methods alone would not provide the level of ground stability necessary to safely complete the crossing.
To overcome this challenge, the contractor, implemented an innovative ground stabilization method known as soil freezing. Prior to tunneling operations, a series of freeze pipes were installed through the railroad embankment. Refrigerated brine circulated through the pipes, freezing the surrounding soil and creating a temporary frozen arch around the tunnel alignment. This process transformed unstable sandy soils into a solid, ice-bound mass while leaving a controlled unfrozen core at the center for excavation.
The frozen soil arch provided exceptional ground support, preventing settlement beneath the railroad tracks and allowing crews to safely advance the tunnel. Once the tunnel excavation was completed, the large-diameter steel casing was installed through the stabilized ground using specialized tunneling and jacking equipment.
One of the project’s greatest achievements was completing the tunnel without disrupting railroad service above. The innovative soil-freezing method eliminated the need for track closures, extensive excavation, or surface impacts while maintaining the structural integrity of the rail embankment throughout construction.
The completed tunnel now serves as a permanent pedestrian and bicycle passage beneath the railroad corridor, safely connecting users of the Lewis & Clark Riverfront Trail while preserving the vital transportation infrastructure above.