Backfill‐Stiffened Foundation Wall Design

Foundation walls have been formed by assembling lightweight sandwich panels without a crane, then pouring lightweight concrete fill between the panels and surrounding excavation. The wet fill exerts low pressure on the panels because it weighs less than 50 lb/cu ft and is poured in two lifts. The first lift is hardened with an accelerator before the second lift is poured. The hardened fill stiffens the panels against subsequent earth pressure. The method is useful for soils cohesive enough to support a vertical cut until the fill is placed. Construction is illustrated using mesh‐reinforced mortar‐faced polystyrene foam‐core sandwich panels and backfill containing fly ash and recycled polystyrene foam aggregate. Design examples use laboratory test values and illustrate the calculation of minimum‐cost thicknesses of sandwich panel and fill for required bending stiffness.