Union Pacific Railroad’s Moffat Tunnel Subdivision, west of Denver, Colorado, was significantly impacted by an approximately 500 to 1,000 year storm event that occurred between September 9, 2013 and September 13, 2013. As a result of this historic event, washouts, earth slides, and debris flows severely impacted track infrastructure by eroding track embankments, destabilizing surrounding native slopes, and overwhelming stormwater infrastructure. Emergency response activities performed to restore track operations at Milepost (MP) 25.65 and MP 22.86 required the integration of civil, hydraulic, environmental and geotechnical engineering disciplines into emergency response and construction management efforts. Additionally, support from UPRR’s Real Estate Division was required when addressing private ownership and site access issues. The following text summarizes how coordinated efforts between various groups worked together in a pressure setting to restore rail service.
The most significant damage occurred at MP 25.65 in a mountainous slot canyon between two tunnels accessible only by rail and consisted of a washout, approximately 200 feet (61 m) in length with a depth of 100 feet (30 m). MP 22.86 experienced slides on both sides of the track resulting in an unstable and near vertical track embankment which required significant fill and rock armoring. In addition to the embankment failures at MP 22.86, flood flows scoured around the underlying creek culvert, further threatening the geotechnical stability of the track embankment. The storm event highlighted the vulnerability of fill sections, where original construction used trestles.
The repair plan engineered for MP 25.65 was developed to restore the lost embankment fill to near pre-flood conditions while limiting environmental impacts in order to minimize regulatory permitting requirements. Fill replacement performed during the initial emergency response was completed within 22 days, notwithstanding site remoteness and difficult access. Repair of the embankment required the placement of approximately 90,000 cubic yards (68,800 cubic meters) of fill and installation of four 48-inch (122-cm) culverts.
Repair of embankment sloughing and scour damage at MP 22.86 was accomplished without the need for environmental permits by working from above the ordinary high water mark, using a “one track in – one track out” approach while restoring infrastructure to pre-flood conditions. A new headwall to address flow around the culvert inlet received expedited permit authorization from the U.S. Army Corps of Engineers by limiting the construction footprint through implementation of best management practices and minimizing placement of fill below the ordinary high water mark.
Service interruptions, such as those at MP 22.86 and MP 25.65, require sound engineering practices that can be quickly and efficiently implemented during emergency response situations that often occur in less than ideal working environments. Track outages not only impact the efficiency of a railroad’s operating network, but also impact interstate and global commerce as transportation of goods are hindered. The need to have a team of experienced engineering and construction professionals responding to natural disasters was demonstrated by this storm event.
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