The City of Fort Collins (Colorado) recently completed construction of a tunnel underneath BNSF Railway tracks to connect more than 30 miles of trails. The prospect of tunneling under an active rail line is a pretty big deal, and the railroad had strict requirements. The original concept of the tunnel was modified by the contractor and their engineer to utilize secant pile retaining walls to allow the construction of the portals closer to the rail line and decreasing the overall tunnel length. The tunnel was constructed by BT Construction and Lithos Engineering was their design engineer. Yenter construction was responsible for the retaining walls, including segments of sheet pile wall used to start things off. Anderson Drilling constructed the shafts for the secant pile wall and for the thrust wall. Read more about the project at TBM.
In keeping with our theme of rising costs on tunnel projects, the Brightwater sewage-treatment plant and treated waste pipeline project in King County Washington (Seattle area) is now up to at least $1.84 billion according to the lead consultant on the project. The treated waste pipeline is 13 to 14-miles long and at depths of 40 to 440-ft! It is being constructed nearly entirely by TBM. One source of delay was due to a tunneling subcontractor not being able to get parts (ball bearings?) because they were all being requisitioned by the US War Department for use in military equipment in Iraq and Afghanistan. Click through for information sources and links.