Consolidation integrated buoyancy equation for soft ground improved with lightweight polyurethane foam

Abstract

Consolidation settlement occurs when a saturated soil is subjected to an increase in overburden pressure that causes a volume change in the soil. When a lightweight material is used as a ground improvement, the stress is reduced as the soft soil is partially removed and replaced by the lightweight material. In addition, the improved ground with lightweight material has a potential to uplift due to the buoyancy of lightweight material. The uplift force reduces the stress imposed on the underlying soil as it acts in the upward direction, thus further reducing the consolidation settlement. This study is executed to produce an alternative equation for consolidation settlement incorporating the buoyancy effect for lightweight polyurethane (PU) foam as a ground improvement method. A Rowe Cell consolidation laboratory test was conducted on untreated marine clay soil as well as on improved marine clay with different thicknesses of lightweight PU foam. Validation of the laboratory test results was done by finite element analysis, PLAXIS 2D. The thickness of PU foam governs the buoyancy and the hydrostatic pressure of water displaced by PU foam, which is incorporated in the alternative equation. The alternative consolidation settlement equation is applicable for ground improved with lightweight polyurethane foam and found to be more economical and practical as the buoyancy is taken into account in the equation.