While designing a hydraulic structure, the piezometric head at bottom of the floor is computed as 10m. The datum is 3m below floor bottom. The assured standing water depth above the floor is 2m. The specific gravity of the floor is computed as 10m. The datum is 3m below floor bottom. The assured standing water depth above the floor is 2m. The specific gravity of the floor material is 2.5. The floor thickness should be