When almost 20 in. of rain fell on Washington, D.C., this past May, the Anacostia River Tunnel proved to be the solution that owner DC Water needed. The tunnel along the Anacostia River captured 650 million gallons of combined sewage overflow that would have gone into the river before the tunnel’s completion in March. The joint venture contractor built the 7-mile-long tunnel over the past five years. The soft-ground tunnel, created with a 26-ft-dia tunnel-boring machine, was entirely lined in prefabricated concrete segments. The team had several challenges, including not affecting an aquifer under the tunnel and not disturbing fragile, older water utilities or the regional underground line as the TBM progressed. Use of compensation grouting resulted in settlements of less than ¼ in.

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