Drilling of a half-mile (approx. 0.8km) tunnel in Tysons Corner, Washington D.C. experienced a breakthrough last week.
The tunnel, which was under construction for 13 months and cost USD 85 million, is the most expensive section of the 23 mile (37km) Dulles Corridor Metrorail Extension. It is 29 feet (8.8m) in diameter and lies 40 feet (12m) below a heavily congested section of road.
It is intended to connect future passengers to two of the four planned rail stations in Tysons Corner. Bechtel was the contractor chosen to handle tunnelling works, which were the preferred solution to the 515-foot (157m) Slope in Tysons.
Progress was difficult as the subterranean environs of Tysons Corner are littered with gas and water pipes. However, Dominic Cerulli, an engineer working for Bechtel, announced that they are still weeks ahead of schedule.
