WMATA Blue Line Extension to Largo
Location
Largo, Maryland
Client
LGS (Lane Construction Corp., Granite Construction Inc., Slattery Skanska)/Jacobs Civil, Inc.
Services Provided
Project Overview
Schnabel was geotechnical engineering subconsultant for the LGS/Jacobs Civil design-build team performing the subsurface exploration and geotechnical engineering analysis for the final design of the WMATA Blue Line Extension to Largo design-build project. The extension ran from the existing Addison Road Station on the Metro Blue Line to the proposed Largo Town Center in Largo, Maryland and consisted of approximately three miles of new Metro track. The tracks were constructed predominately below grade using cut and cover techniques, with aerial structures and transition structures over prominent drainage swales, at the two planned stations, and over Interstate I-95. The cut and cover and near-grade covered portions of the work comprised approximately 80 percent of the line.
In addition to the cut and cover, covered, and aerial structures, the other predominant features of the project included a pile-supported Multi-Cell Box Structure over a low-lying drainage area, and the Operations Building at the eastern end of the line. The remaining portions of the track were constructed near existing grades with retaining wall structures providing the necessary transitions to below-grade portions.
Schnabel performed a subsurface exploration consisting of soil test borings, cone penetrometer testing, and pressuremeter testing to evaluate the subsurface conditions. Schnabel provided recommendations for spread footings, mat foundations, pile foundations, lateral earth pressures, earthwork, temporary excavation support, and dewatering in accordance with WMATA design criteria.
Schnabel was retained by LGS, the contractor of the design-build project, to provide construction phase services during construction. Our services included observations of the box tunnel structure subgrades, temporary excavation support system, and monitoring of dynamic and static load testing of pile foundations.
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