Congress Heights Station & Tunnel

Clark performed excavation, support, concrete, finishes and restoration work for the 1,100 linear-foot, 90-foot-deep, below-grade Congress Heights Metro Station and two 1,500 linear foot tunnels in an urban environment. During construction, over 200,000 cubic yards of soil were excavated to make way for the new station and tunnels. The excavation of up to 100 feet was supported by the contractor-designed and installed retention system.

Construction began with support of excavation design submittals. Station bracing consisted of soldier beams and lagging with five tiers of cross-lot struts. The station was partially open cut from north of Alabama Avenue to the southern limits of the Dogwood Drive and Cherry Street decking. This laid back cut resembled a large bowl extending from existing grade down to an elevation above the top of the lower vault wall.

The Congress Heights Station Tunnel's design called for an alternate, less expensive tunneling procedure during excavation, called the New Austrian Tunneling Method (NATM). NATM is a means of tunnel excavation and support used under conditions in which there are multiple excavation phases that must be executed because the exposed surface of a single excavation phase is too large to be supported at one time.