The following phenomenon a saturated sandy or silty soil beh

The following phenomenon (a saturated sandy or silty soil behave like liquid) is called? . How much is the effective stress (> 0, = 0, or < 0) in this soil? . Will the soil recover to its original state after a certain time period? What are the total stress, effective stress, and pore water pressure change (i.e. increasing, decreasing, or stay the same) during this time period?

Solution

LIQUEFACTION :- It is the phenomenon in which loose saturated sandy soil losses it\'s shear strength. As the shear strength is reducing the pore water pressure increases and effective stress reduces. Liquefaction occurs when effective stress becomes zero. At this stage soil start to behave like a liquid.

The soil contains lots of voids and these voids are filled with the water. Soil will take the load whenever a load is applied and start compressing but it will be prevented by the all round pressure of water present in the voids. Thus pore water pressure increases and soil losses it\'s effective stress. Water will move from high preesure area to low pressure area ie, from bottom to up since pressure at top is atmospheric.

The soil can be recovered by drainage only. It may be possible after a certain period of time. It depends on the type of soil,surrounding soil,time,type of loading,void ratio etc.

TOTAL STRESS = EFFECTIVE STRESS + PORE WATER PRESSURE

EFFECTIVE STRESS is the stress exerted by the soil grains only it is reducing as the PORE WATER PRESSURE is increasing. TOTAL STRESS remains unchanged. When load is applying initially, load is taken by soil solids only. But it reaches a state that soil cannot compress more due to the influence of water in the voids at that stage water will start to take load and soil will start to withdraw from taking load. LIQUEFACTION occurs at this stage.