- Geometric constraints for subsurface investigation
- Multiple foundation designs
- Drilled shaft design
- Spread footing design
- Micropile design
- Driven pile design
- Thermal integrity profile testing
- Construction observation and documentation
Challenge
This project involved replacing the Madawaska International Bridge over the St. John River between Madawaska, Maine and Edmundston, New Brunswick. The original bridge was opened in 1920 and had become fatigued enough to warrant load limits threatening this vital international link. MaineDOT and their bridge designer, HNTB, opted for a replacement bridge on a new alignment in association with a new U.S. Land Port of Entry (LPOE). The new structure consists of an 1,850-foot-long, six-span, steel girder, concrete deck bridge crossing from the U.S. LPOE, the Maine Northern Railroad, the St. John River, and the CN Railroad, ending at the Canadian LPOE.
The foundation alternative evaluations relied heavily on a variable top of bedrock profile. Because access to the river was restrictive, GZA preliminarily implemented an in-water seismic refraction survey paired with land borings, and subsequent heavily coordinated over-water borings with transportation aid via helicopter and a raised drill platform during final design.
Solution
GZA conducted geotechnical engineering evaluations and provided foundation design criteria for multiple foundation types that were selected for bridge support, considering subsurface conditions, access and topographic challenges, and proximity to infrastructure. Specifically, due to geometric constraints and to avoid issues with the Canadian railroad, a narrow abutment footprint supported by drilled micropiles with insulation details was chosen for Abutment 2, while a conventional gravity abutment with footing bearing on soil was chosen for Abutment 1. The river piers included drilled shafts over water, and driven H-piles were chosen for the riverbank pier. GZA recommended and included Thermal Integrity Profiling (TIP) in the specifications to be used as the primary concrete quality assurance method. This would be the first bridge in Maine to use TIP testing as the primary drilled shaft concrete quality assurance tool.
GZA’s foundation criteria included nominal and factored bearing resistance values for the spread footings for both soil and rock, nominal and factored side friction values for the drilled shafts, lateral earth pressures and sliding resistance for the abutment and wingwall designs, and nominal and factored axial resistance values for driven piles and drilled micropiles. GZA also provided geotechnical seismic design criteria, evaluated the appropriate Seismic Site Class, and provided recommendations for temporary access roads and permanent embankment slopes. GZA prepared the Geotechnical Design Report and developed special provisions for bidding the drilled shafts.
GZA recommended and included TIP in the specifications to be used as the primary concrete quality assurance method. This is the first bridge in Maine to use TIP testing as the primary drilled shaft concrete quality assurance tool.
Benefit
During construction, GZA provided full-time monitoring of the drilled shaft installation, including confirmation borings, drilled shaft excavation, reinforcing steel and concrete placement, and performed TIP testing to assess the quality of the constructed shafts. GZA made perioding visits to assess the progress of subgrade preparation for the spread footing foundations, reviewed logging and load testing of drilled micropiles, conducted wave equation analysis, and performed high-strain dynamic (PDA) testing and CAPWAP analysis for driven piles.