At a depth of 5 m underneath the surface of a swimming pool, the total and effective stresses respectively measure__________________?
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Answer: B. 0.5 kg/cm2 and zero
Explanation
At a five meter depth in water total stress equals hydrostatic pressure which is zero point five kg/cm2. Effective stress in a pure fluid medium equals total stress minus pore water pressure. Since pore water pressure equals total stress in water the resulting effective stress is zero. Hydrostatic pressure increases linearly with depth in water due to fluid density and gravity. Effective stress represents intergranular contact forces which cannot exist in a fluid medium. Swimming pools contain pure water without solid soil skeleton interparticle contact points.
Divers experience hydrostatic pressure increases with depth while floating in swimming pools or oceans. Geotechnical engineers distinguish between total stresses, pore pressures, and effective stresses in soils. Submerged structures experience uplift pressures equal to hydrostatic head pressures at depth. Zero total stress ignores the actual hydrostatic pressure exerted by five meters of water depth. Zero effective stress is correct, but total stress is not zero point five with zero pore pressure. One point zero kg/cm2 overestimates hydrostatic pressure which equals zero point five at five meters.
- Subject
- Engineering
- Category
- Civil Engineering
- Topic
- —
- Difficulty
- medium
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