In: Civil Engineering
What is liquefaction of sand? how can it prevented
Loose saturated sand deposits can lose a part or whole of their Shear strength when subjected to a sudden shock or other dynamic loading.Shear strength of Sand is given by
where
= effective stress at depth z
If the Sand deposit is shaken by an earthquake or other dynamic loads. extra pore pressure(u) is developed and shear strength equation becomes
If
Therefore the phenomenon when the shear strength of sand becomes zero or negligible due to dynamic loads is called liquefaction of sand.Sand flows like a liquid and structures resting on such sands sink or excessively settle.
Liquefaction can be prevented by
1. Vibroflotation of Sand : Compacting loose sand deposit by inserting probes deep into soil to reduce air voids
2. Stabilizing materials injected into the soil
3 Electro - osmosis: Electrodes placed beneath structures to reduce pore pressure during earthquake.
4. Compaction piles
5. Replacing the sandy soil with a cohesive soil which does not liquefy during earthquake
6. Placing Sand or gravel drains in the soil to help dissipate extra pore pressure quickly during earthquakes.