CONSTRUCTION OF THE DULLES CORRIDOR METRORAIL PROJECT NATM TUNNELS AT TYSONS CORNER, VIRGINIA: A CASE HISTORY

摘要

The Metropolitan Washington Airports Authority (owner) and Dulles TransitrnPartners, LLC (Bechtel Infrastructure, Inc., the contractor) are constructing 1,700 ft longrntwin tunnels in Tysons Corner, Virginia. An integral part of the Washington MetropolitanrnTransit Authority’s new $3.1-billion Phase I Silver Line passenger rail service to DullesrnInternational Airport, the twin tunnels are being constructed beneath the major trafficrnarteries of Routes 7 and 123. Tysons Corner is one of the most congested retail, commercialrnand residential centers in the Washington D.C. region. This paper describes thernNATM, or Sequential Excavation method, used to construct the tunnels in soft groundrnconditions with shallow heading cover. Employing this method the tunnel drive is presupportedrnwith a continuous overlapping pipe arch canopy and excavated in 42 ft ‘sawrntooth’ increments. The initial ground support consists of a 10 inch thick layer of steelrnfiber reinforced shotcrete which is furnished by a state of the art on-site batch plant.rnThe final liner includes PVC waterproofing and a 12" thick cast-in-place final liner.