Abstract:
VDOT awarded the $3.8 billion Hampton Roads Bridge-Tunnel Expansion Project to Hampton Roads Connector Partners (HRCP) as a design-build project, with HDR as the lead geotechnical and structural designer for all of the bridges on the project. HDR was responsible for the design of the five marine trestles, crossing nearly 3 miles of the James River on both sides of the Tunnel Approach Islands.
Heightened risk and complexity of the foundation design of the marine trestles were recognized early in the design phase due to the use of large diameter piles (54-inch precast concrete cylinder piles and 24-inch square precast concrete piles) and the relatively soft Atlantic Coastal Plain soils. Most bridge foundations in Tidewater Virginia are driven into the Yorktown formation, an overconsolidated marine deposit that generally consists of loose to medium dense silty and clayey sands, and generates significant excess pore pressures during pile driving that could take days to weeks todissipate and allow for sufficient setup of axial resistance to occur.
HDR utilized Leapfrog Works 3D modeling software to more effectively characterize and visualize the subsurface conditions. The model was updated as new data became available during the subsurface exploration program of over 200 SPT borings and CPT soundings and was shared to Leapfrog Viewer within the design-build team on a periodic basis. CPT tip resistance, sleeve friction, and excess pore water pressure were visualized and used as communication tools to better inform target pile bearing elevations and relative setup periods for pile restrikes.
The 3-D visualizations depict local features like the recent history of scour around the existing South Island in the James River. 3-D Viewer files produced greatly reduced time and effort spent on understanding the large amount of data collected and communicating subsurface conditions within the design-build team and to VDOT.