Cascade Tunnel Investigation and Stabilization

DESCRIPTION

BCE provided engineering and environmental services to address structural instability and hydrologic concerns at the historic Cascade Tunnel, originally constructed in 1900 by the Great Northern Railway and decommissioned in 1929. Following a partial roof collapse in the winter of 2006–2007, public access through the tunnel was impeded, and accumulated debris began impounding significant water on the east side. The resulting buildup periodically released through the west portal in hazardous flash flooding events. A comprehensive geotechnical investigation was performed, and a 9-month hydrologic assessment was conducted to evaluate the failure zone and understand water dynamics within the tunnel. A mineral rights survey was also conducted. Based on the findings, actionable recommendations were developed for stabilizing the tunnel, mitigating future flooding risks, and implementing secure closures at both portals to prevent unauthorized access.