Hong Kong, December 1, 2011 – GZ has been elected Finalist in the “International Tunnelling Project of the Year 2011” category with the Dulles Corridor Metrorail Project – Extension of Silver Line Metro to Dulles International Airport.

The twin NATM (New Austrian Tunneling Method) tunnels at Tysons Corner, as part of the Dulles Corridor Metrorail Project, serve as a good example of how close integration of tunnel design and construction management can accelerate a project and achieve a consistently high level of quality throughout all phases. This complex infrastructure project with the goal of making Dulles International Airport accessible to public transportation and connecting it directly to the heart of the District of Columbia posed a number of unique challenges: a dense urban setting, complex ground conditions (soft ground, groundwater table in tunnel cross-section, multiple settlement sensitive utilities directly above the tunnel), twin tunnels, shallow overburden with a busy six-lane highway crossing over the top of the tunnels, deep parking garage and multi story building next to alignment.

GZ developed a tunneling method to meet this unique combination of challenges and minimize any impacts at the surface and sub-surface levels, optimize safety during construction, and cost in relation to effort and risk. The construction of the twin tunnels at Tysons Corner was scheduled on the critical path of the overall project program. Any delays in the construction of the tunnel segment would have had a major impact on the timely completion of Phase 1 of the project, thus making overall efficiency the primary goal. To reach this goal, a comprehensive risk mitigation strategy was put in place, and the GZ design team was integrated in the overall project.

This integration and GZ’s hands-on involvement during the construction phase ensured optimal, time efficient solutions for the design, delivery, and approval processes. Ultimately, the initial tunnel design as well as the diligent management of the construction process resulted in the completion of this part of the project ahead of schedule and under budget, thus rendering any initial concerns regarding the tunneling segment as “stumbling block” for the whole project invalid. Another main factor in the overall success of the tunneling project was overall technical excellence. The integration of the latest technology in the design, such as the systematic installation of the steel pipe pre-support, using high precision drilling equipment and automatic pipe feeding ensured that the construction would be completed in as short of a timeframe as possible.

The NATM tunnels at Tysons Corner earned an Excellence in Automation Award by the American Society of Civil Engineers (ASCE). The honor is awarded for processes, techniques, and actual cases that represent creative use of automation tools for civil engineers, lending further credibility to the superior design methods and meticulous execution of the Dulles Corridor Metrorail Project’s tunnel segment.