Many railroad tunnels in the United States and Canada are close to 100 years old and are showing their age-concrete deterioration and seepage through liners causing icing problems in winter and drainage problems the rest of the year. These tunnels are located on vital transportation routes carrying freight and passenger trains daily; therefore, any repair work must be performed under live-track conditions with work windows as short as 4 hours. The constraints of limited site access, track time, and staging areas must be considered during project planning, design, and construction. A recent example of an aged tunnel requiring rehabilitation is the BNSF Windham Tunnel (near Great Falls, Montana), which is a concrete-lined tunnel suffering from liner deterioration due to freeze-thaw effects of icing and ice buildup, and fouled ballast from poor drainage. On this project, McMillen Jacobs Associates performed the design, prepared the bid documents, and provided design services during construction. Rehabilitation plans included grouting behind the liner to improve structure/soil interaction and minimize seepage through the lining, installing rock bolts and dowels to tie back concrete liners and footings, and improving drainage in and through the tunnels by reestablishing existing ditches and adding lower sidewall drain holes. In the Windham Tunnel, a shotcrete overliner with a water barrier was placed to reduce seepage and improve liner strength.
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