DESCRIPTION

The New NY Bridge will mean less congestion for motorists, with eight traffic lanes, four breakdown/emergency lanes, and state-of-the-art traffic monitoring systems, as well as a dedicated commuter bus lane from the day it opens. Designed and constructed to be mass-transit-ready, the new crossing will be able to accommodate bus rapid transit, light rail or commuter rail. The bridge will also include a bike and pedestrian path. The first span of the new twin-span bridge is scheduled to open in 2016, and the new bridge should be complete in 2018. The design-build project will mark the single largest bridge construction project in New York’s history and is designed to last 100 years without major structural maintenance.

CHALLENGES

GeoStructures, Inc. was contacted to support the west abutment of the new Tappan Zee Bridge. The West abutment was originally to be supported on spread footings. However, due to a liquefiable layer discovered underneath the abutment an alternative approach was necessary. Initially, drilled shafts were recommended. Though, due to their high cost another option was desired by the owner and general contractor.

Soil conditions generally consist of sand and silty sand extending down to partially weathered rock and rock, encountered at depths of 20 to 30 feet below grade.

SOLUTION

A ground improvement option was found to the most cost effective option to support the abutments and provide liquefaction control. A total of 338, 20-inch Impact Pier elements were put in at a depth of 25 ft. With, 84 to support the abutment, 52 for a generator facility, and 202 to mitigate liquefaction risk and settlement control of the abutments.