Nine tunnels varying in length from 480 to 4,200 feet (146 to 1,280 m) extend along the Coos Bay Rail Line for approximately 134 miles (216 km) from Eugene to Coquille, Oregon. The rail line and tunnels were built between 1911 and 1916. The tunnels were excavated through predominantly sandstone and mudstone, characteristic of the Coast Range mountains. Because of the weathered rock of the Coast Range mountains, the harsh climate near the Pacific Coast, and lack of maintenance, the timber-lined portions of the tunnels fell into disrepair, causing the line to shut down in 2007.
In 2009, the Oregon International Port of Coos Bay received $2.5 million in American Recovery and Reinvestment Act of 2009 stimulus funds to repair the tunnels as a first step in reopening the line.
Delve Underground performed extensive condition assessments of each tunnel, supporting the owner’s funding applications with recommendations, conceptual designs, cost estimates, and construction schedules for structural and drainage rehabilitation. Delve Underground then led a multidisciplinary team to complete the planning, design, permitting, and construction management for the tunnel rehabilitation program.
The tunnels had experienced localized collapses before the project began. Delve Underground’s top priority during the design and construction monitoring process was to prevent further collapse from occurring during the repair process. To that end, Delve Underground recommended two methods of timber set replacement: (1) placement of steel jump sets for ground support before timber set removal and pre-support with steel channel spiling immediately ahead of timber set removal; and (2) replacement with a shotcrete lining and rock bolts. Both methods proved successful.