Underground Infrastructure Technologies, Lakewood, Colo.
Project: 20-in. Main Installation at 40th and Blake Street
Underground Infrastructure Technologies’ (UIT) project consisted of an approximate 400-ft undercrossing of the Union Pacific Railroad (UPRR) and Regional Transportation District (RTD) train tracks for the purpose of constructing a new 20-in. PVC water main encased in a 32-in. minimum steel casing pipe. Portions of the water main alignment approaching the tracks were open cut. The tunnel location is at a junction where several main line tracks branch off into 13 separate siding tracks. The train corridor is heavily traveled with UPRR diesel freight trains and an RTD commuter rail line currently under construction. UIT reviewed the benefits and risks associated with each of the three proposed methodologies: microtunneling, open-face TBM and hand mining with consideration of the site location, proposed alignment and subsurface conditions. Following initial evaluations, UIT planned to lower the proposed casing invert alignment 6 ft into the fine alluvium and utilize slurry microtunneling with an armored cutting shield as the methodology to advance and complete installation of the tunnel casing pipe. They selected a 36-in. MTBM so the machine could handle the maximum size boulders (typically 1/3 of the shield diameter) anticipated in the geotechnical baseline report (12 in.). Additionally, the 36-in. casing is a standard pipe size that was readily available from local suppliers. In the end, UIT completed a project that was previously attempted without success due to the complexity of the subsurface conditions.