Foundation Optimization and Design for Replacement of the Woodrow Wilson Bridge

The new Woodrow Wilson Bridge (WWB) will replace the existing bridge over the Potomac River to connect Alexandria, Virginia to Prince Georges County, Maryland. The new WWB will extend approximately 1.1 miles across the river, with a 367-ft long bascule span in the main river channel where the water depth is about 36 ft. The subsurface soil profile consists of up to 50 ft of a soft organic silty clay layer that is very vulnerable to scour, underlain by a deep deposit of hard sandy clay. This paper will present results from a Pile Demonstration Program (PDP) that was conducted as part of the bridge replacement project, discuss the various aspects of the seismic design and analysis, and describe how those data were applied to optimize foundation design. The PDP included dynamic monitoring, static load tests and Statnamic load tests at several locations, to evaluate: (i) the pile driveability and associated parameters necessary for dynamic analysis; and (ii) the ultimate skin friction and end bearing values for design. The PDP provided a basis for eliminating static load tests during construction and construction quality control, and for evaluating potential settlement of the existing bridge. Although the seismicity of the region is low, considering the importance of this bridge and the consequences of potential damage during an earthquake, seismic issues were addressed thoroughly in the design of the new structure, including: (i) development of design spectra based on site-specific seismic hazard and ground motion analyses; (ii) implications of the complex soil profile and potential scour on the dynamic response of the foundations; (iii) Soil-Structure Interaction (SSI) analyses for the various foundation alternatives; and (iv) evaluation of the significance of the kinematic SSI effect on the piles. The presented case study proves how results of a pile demonstration program and extensive seismic studies can enable significant optimization of the foundation design and cost savings, and provide significant quality control during construction

New I-95 Woodrow Wilson Bridge Foundations

The new Woodrow Wilson Bridge (WWB) will replace the existing bridge over the Potomac River to connect Alexandria, Virginia to Prince Georges County, Maryland. The new WWB will extend approximately 1.1 miles across the river, with a 367-ft long bascule span in the main river channel where the water depth is about 36 ft. The bridge is primarily comprised of fixed spans in relatively shallow water and a bascule span over the navigation channel. The subsurface soil profile was quite variable along the bridge alignment. In Virginia there was fill over soft Alluvial deposits underlain by dense Terrace deposits, as well as remnant foundations from a former ship yard. At the bascule span there was up to 50 ft of a soft organic silty clay layer underlain by a deep deposit of stiff Cretaceous clay. Along the Maryland approach there were Alluvial deposits over dense Terrace deposits over stiff Cretaceous clays and dense Cretaceous sands. The variation in subsurface conditions lead to the selection of alternative deep foundations that suited the specific conditions and were based on the design phase testing program, from which ultimate design capacities were determined. During construction there were instances of unexpected pile performance, notably different than that experienced during the design phase testing, requiring changes to the contract installation criteria and re-design. This paper will present the types of deep foundations used for the project, the performance criteria assumed during the design, the measured performance and difficulties encountered during construction, and the resulting remedial actions, i.e., changes to contract installation criteria and/or re-design due to the unanticipated field conditions