Dulles East/West Automated People Mover
Atkinson/Clark/Shea, a joint venture of Clark Construction Group, LLC, Atkinson Construction, and J.F. Shea Co., Inc., performed excavation and support work for the Dulles East/West Automated People Mover (APM) project. Encompassing more than 6,775 linear feet of rock excavation and averaging a depth of 50 feet, this project is one of the largest and most challenging, the team has ever completed.
The joint venture team performed the support of excavation and cast-in-place concrete for the cut-and-cover tunnels and stations. In addition to the tunnels, the Dulles Airport East/West APM Tunnel's scope of work included the construction of a Tier One Station, a Tier Three Station Shell, an inner Spur Track using the cut-and-cover method, and a tunnel portal at the Vehicle Maintenance Facility. Further, Clark performed the MEP fit-out of the tunnel stations as well as the installation of the Emergency Radio Supplemental Radiating System for handling emergency communications with the Metropolitan Washington Airport Authority, Loudoun County, and Fairfax County.
Two 21-foot diameter Robbins Single Shield Tunnel Boring Machines (TBM) excavated of over 3,600 linear feet of the tunnels. The machines were fitted with 15-inch disc cutters for excavation through relatively soft rock (UCS < 7,000 psi). Precast concrete segments were erected, concurrent with the excavation, within the tail shield to form the final tunnel lining. Both TBMs moved through a 600-foot long station, as well as negotiated radii as shallow as 410 feet to complete each run.
On the northern end of the East Automated People Mover project, the joint venture team excavated two 400-foot-long, 22-foot diameter tunnels utilizing NATM techniques. This system used roadheaders for excavation, robotic shotcrete application machines, and complex convergence and settlement monitoring technology to determine the state of relaxation of the ground around the tunnel. NATM tunnels were excavated in one-meter advances of the 14-foot-high top heading, followed by immediate and occasionally concurrent application of up to 12-inch thick shotcrete.
On the West Automated People Mover, two 1,200-foot-long tunnels, and two 210-foot-long tail tunnels were excavated using NATM techniques. Throughout the excavation sequence, the shotcrete delivery system was kept continually active to be able to apply shotcrete at any time during the excavation cycle.