US Highway 17 Hutchinson Island interchange: Low-density cellular concrete embankments over soft soils in Savannah, Georgia

Terracon Consultants, Inc., Savannah, Georgia, USA

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Abstract

Low-density cellular concrete (LDCC) is increasingly used as a lightweight embankment fill to reduce dead load and control settlement over soft soils. This case history documents the Georgia Department of Transportation’s first LDCC application on highway ramps founded on deep marsh deposits at the US 17 Hutchinson Island Interchange in Savannah, Georgia. Hutchinson Island is underlain by 30 to 35 feet (9–11 meters) of very soft, highly compressible marsh clay overlying sand and marl. Two loop ramps were reconstructed: the East Ramp (1999) and West Ramp (2001), both founded on geofabric-reinforced platforms and wick drain improved soft clay topped with LDCC placed in one to two-foot (0.3–0.6 m) thick lifts. The LDCC has a unit weight of 27 pcf (432 kg/m³) and a minimum compressive strength of 40 psi (276 kPa). Long-term performance diverged. The East Ramp remained stable for more than 25 years. The West Ramp developed longitudinal pavement cracking within three years, linked to localized differential settlement where new embankment abutted a 1954 embankment, shortened consolidation waiting periods, missing reinforcement layers, and local LDCC fracturing. The project highlights LDCC’s potential and limitations: success requires completing primary consolidation, integrating transitions with the previous embankments, and reinforcing LDCC to bridge differential settlements.