Fossil Creek Pedestrian Tunnel

摘要

The Fossil Creek Pedestrian Underpass was constructed through a 30-foot high Burlington Northern Santa Fe (BNSF) railroad embankment to serve pedestrian traffic in southern Fort Collins. The tunnel, located immediately south of Fossil Creek, was constructed by the installation of a hydraulically jacked, 14-foot diameter, steel casing pipe. Excavated materials encountered during construction included primarily lean clay embankment fill and a smaller percentage of underlying coarse alluvium. Tunnel excavation was performed with a mini-excavator within a shield, custom made for the project. Unique, arch walls approximately 20 feet in height constructed on a 25-foot radius supported railroad embankment and allowed for an approximately 40 percent decrease in tunnel length. Arch walls were constructed top down within the BNSF designated 'A-zone' requiring shored excavations. Temporary shoring was provided by flat sheet piles installed prior to arch wall construction. The 'arch' shape of embankment support portal walls economized quantities of steel and concrete and provided efficient construction. Laterally loaded, reinforced drilled shafts connected to each arch wall corner were designed to resisting horizontal earth and railroad live loads.