Project Name: Pioneer Tunnel
Client: BNSF Railway
Location: King County, WA
Prior to the construction of the current Cascade Tunnel, an 8-mile tunnel completed in 1929, engineers first excavated a small auxiliary tunnel known as the Pioneer Tunnel. This access tunnel was 8 ft by 9 ft and was driven from both the west portal and a vertical shaft at Mill Creek. The Pioneer tunnel functions included:
- Draining water from the main tunnel
- Providing ventilation
- Allowing installation of compressed-air pipes, power lines, and lighting
- Transporting men, supplies, and excavated rock via light rail
The Pioneer Tunnel dramatically accelerated construction, enabling work from multiple faces simultaneously. Work began in December 1925, and the fully completed Cascade Tunnel was dedicated on January 12, 1929. Construction volumes were impressive—nearly 935,000 cubic yards of rock and earth moved, and 262,562 cubic yards of concrete placed. LRL Construction has been working in this tunnel since May 2025 and will continue operations into October. LRL has a contract to return for the next two years until all the passageways have been opened. We have performed ground support and rehabilitation work within the tunnel to stabilize conditions and restore safe access. The scope of work includes installation of rock bolts, mine straps, split bolts, and shotcrete, as well as removal of timber sets and scaling loose material. In addition, we have provided mucking operations to clear collapsed sections of the tunnel. These activities are carried out to reinforce the ground, improve structural integrity, and ensure safe working conditions for ongoing operations.
