CDTA/Amtrak

RENSSELEAR, NEW YORK

The Capital District Transportation Authority planned construction of a new passenger rail station, parking garage and fly over access roadway in the City of Rensselaer, NY. The 4-5 story station and contiguous two level garage are sited at the eastern edge of the historic Hudson River flood plain and the toe of the Hudson Upland slope. The site had been used as a rail yard for well over 100 years. Shallow fills mantle the natural soils in the area, a stiff grading rapidly to a soft deposit of varved silt and clay within the flood plain and desiccated, overconsolidated hard silt and clay soils forming the upland slopes. These cohesive soils extend to shale bedrock at depths ranging between 40 and 60 feet across the site. The new station is a steel framed and masonry clad structure. The new garage is a precast concrete structure with its lowest level set beneath the fills within the soft silt and clay soils with its eastern edge extending into the slope where a 32' high cast in place retaining wall was planned. The approach road fly over connecting to the garage and station ramps up upon a filled embankment with segmental wall faces extending some 34' above the existing site grades before crossing the four active CP/Amtrak rail tracks upon a precast concrete bridge. Because the overburden soils at the site were incapable of supporting the concentrated structure loads at tolerable settlements, driven H-piles were selected for support of the building and garage. H-piles driven to end bearing within the thin bedded shales of the area usually experience capacity relaxation effects as great as 20% as the shales rebound and fracture after pile driving. A program of dynamic pile testing documented the relaxation effects and allowed the pile capacities to be verified. The retaining wall planned along the eastern side of the garage was designed with GEOFOAM backfill to minimize the lateral loads it is to support. The existing desiccated clay soils were excavated and the slopes modified several times to create a stable condition as the overconsolidated clays heaved and sloughed during the period when they were relieved. A soldier pile and lagging wall was designed and installed along a historic fire station to assure its stability during the construction period. The bridge abutments and piers were supported upon H piles with the approach road embankment fills constructed of lightweight fill materials. The light weight materials were necessary to assure stability above the soft silt and clay soils and limit embankment settlements to less than two (2) inches.