Dulles Corridor Metrorail Project (DCMP) is an extension of the existing 106-mile Washington, D.C. Metrorail system from the current Orange Line in Fairfax County, Virginia through Tysons Corner to the Washington Dulles International Airport and beyond the airport into Loudoun County. Phase I of the Project consists of approximately 11.7 miles of rapid rail transit that includes about 3 miles of aerial guideway structures supported by 725 drilled shafts. A total of 14 load tests, including ten (10) Osterberg Cell (O-Cell) Tests and four (4) Statnamic Tests, were performed to verify the axial load carrying capacity of drilled shafts at selected locations along the alignment. The capacity results of skin friction (side resistance) and end bearing (base resistance) measured by load tests are compared with values computed in accordance with the AASHTO 1999 â- Method (Beta) and the FHWA-1999 Method for cohesionless soils and Intermediate Geo-Materials (IGM), respectively. Comparisons for skin friction were made for the fill/low strength soils, high strength native soils, and for the decomposed rock of the Piedmont formation. Comparisons of end bearing were made for the decomposed rock only. According to results of these comparisons, the approach used by DTP can be considered somewhat conservative overall, which proved to be prudent later to accommodate construction conditions at some shafts.
Subjects: drilled shaft, O-Cell, side shear and end bearing
Author: Sujan K. Bhattacharya, Senior Geotechnical Engineer, Lloyd W. Young, Senior Principal Geotechnical Engineer and Jeongbok Seo, Project Tunnel Engineer
Publisher: DFI, EFFC