Instrumented Geofoam and Sheet Pile Wall for a Roadway Lane Addition in a Peat Marsh

This paper describes a 10-ft high steel sheet-pile wall backfilled with geogrid-reinforced geofoam (expanded polystyrene-EPS) within a peat marsh. The wall and reinforced lightweight fill were used to reduce global stability concerns, reduce long term settlement of the new roadway lane, and to reduce impact to adjacent wetlands. The wall backfill settlement and two inclinometers attached to the full length of the steel sheeting in the critical wall section were monitored during construction. Using simple beam theory and inclinometer data, the moments in the sheeting associated with the deflection profiles are calculated. Pressure diagrams for each inclinometer location are back-calculated based on the observed moment diagrams. Design implications inferred by the back-calculated pressure diagrams are discussed. Wall backfill settlements up to about 6 inches were measured during construction. Lateral displacements at the top of sheeting reached about 2 inches to 3 inches with a 2.5-ft thick aggregate pre-load surcharge in place. Back-calculated pressure diagrams indicate the otherwise highly compressible peat marsh deposits behaved for a short period like a high viscosity fluid supporting the weight of the existing and new fill. Comparison of two adjacent inclinometers gives insight into some three-dimensional behavior in the wall.