Buoyancy Ground improvement Clay Nanostructured materials Partial replacement Polyurethane Foam Polyurethane foams Polyurethanes Soft clay layer ASH Buoyant forces COEFFICIENT Compressibility index Consolidation settlement Different thickness Different water contents Lightweight Polyurethane Rigid foamed plastics SOIL Settlement of structures Strain rate Undrained conditions compaction compressive strength geopolymer laterite soil palm oil boiler ash