Filling a 1.2-mile gap to connect the Fossil Creek Trail

Fossil Creek BNSF Pedestrian Tunnel

The City of Fort Collins has an extensive bicycle and pedestrian trail system of over 35 miles. Approximately 10 years ago, the city annexed a significant amount of residential and commercial properties along its southern border. Since that time, trails have been extended into this area, including the popular Fossil Creek Trail.

Fossil Creek Trail is a set of two separate paved pathways, totaling 5.3 miles, running through neighborhoods and local parks that the city is working on connecting. Complicating this effort is an existing Burlington Northern Santa Fe (BNSF) Railroad system—a main freight corridor along Colorado’s Front Range.

We worked with the city on a solution that maintained the daily train traffic by using a below grade tunnel rather than a more traditional crossing. The tunnel consists of a 14-foot diameter, 1.25-inch thick pipe extended for 75 feet constructed using an open-face shield with personnel and equipment to excavate the soil face. A creative curvilinear shotcrete headwall was constructed at each portal and relies on 36-inch drilled caissons to laterally support the walls.

The tunnel is a critical part of filling the 1.2-mile gap in the trail and connecting it to Shields Street and the Cathy Fromme Prairie Natural Area. Our team prepared construction drawings and specifications for the tunnel, headwalls, a retaining wall, trail pavement, and stormwater improvements. We also provided construction administration.