Emergency Response to a Rockslide on BNSF Snowshed #4, Stampede Pass, WA

摘要

One of BNSF's primary freight lines cross the Cascade Range in Washington State at Stampede Pass. On November 27, 2015, a large rockslide occurred above the east portal of Tunnel #4, at MP49.4 within the Stampede Subdivision. Approximately 50 cubic yards of rock debris hit and penetrated the snowshed roof, breaking some of the timber set members, and fouled the track. Rock debris was spotted by the BNSF track inspector and traffic was stopped, averting a derailment. BNSF requested that McMillen Jacobs Associates mobilize to the site to evaluate the damaged snowshed and rockslope conditions. We inspected the structural integrity of the snowshed and worked closely with BNSF maintenance-of-way personnel to safely remove a large boulder lodged in the roof over the tracks. We oversaw rock scaling above the snowshed to establish safe working conditions for BNSF staff and rail traffic. After completion of the initial rock scaling, BNSF constructed a temporary roof cover over the open holes. Rail traffic was restored within 72 hours of the incident. When conditions improved in 2016, authors directed additional rock scaling during live track windows. Once scaling was completed, we characterized the existing rockslope conditions using rope access techniques to evaluate geologic kinematic stability and rockfall characteristics. Based on the results, results, we produced conceptual designs for mitigation measures, including rock anchors and wire mesh, and then provided construction management during final repair of the snowshed. Presently, we are designing a rockfall deflection shed above the Snowshed #4 (snowshed) based on the rockfall characteristics.