Liquefaction is a process that leads to soil suddenly losing strength, As a result of ground shaking during an earthquake. However, not all the soils liquefy during an earthquake.
It is a phenomenon in which the strength and stiffness of soil are reduced by earthquakes. It occurs in saturated soils in which the space between individual soils is completely filled with water. This water exerts pressure on the soil particles. The water pressure is however relatively low before the occurrence of an earthquake. Earthquake shaking can increase the water pressure to the point at which the soil particles can readily move with respect to each other.
Although earthquakes often trigger this increase in water pressure, activities such as blasting can also cause an increase in water pressure. When liquefaction occurs, it decreases the strength and ability of the soil to support the construction above it.
To understand liquefaction, it is important to recognize the conditions that exist in a soil deposit before an earthquake. A soil deposit consists of an assemblage of individual soil particles. Each particle will be in contact with the number of neighboring particles.
Causes of liquefaction:
Liquefaction occurs when the structure of saturated and breaks due to applied loading. As the structure breaks down, the loose soil particles move into a denser medium.
In an earthquake yet, there is not enough time for the water in the pores of the soil to come out. Instead, the water trapped and prevents the soil particles from moving closer together. This is an increased water pressure which reduces the contact forces between particles. It also softens and weakens the individual soil particles.
Liquefaction mitigation methods:
Methods to mitigate the effects of soil liquefaction are:
1. Vibro compaction:
Loose soil or granular backfill can be compacted in depth by the penetration of vibrating probes. The main purpose of vibro compaction is to densify the in-situ soils by vibration.
2. Dynamic compaction:
This process involves dropping heavy weights repeatedly on the ground at regular intervals. The weight and height determine the amount of compaction that would occur. The weight used varies from 8 to 36 tons. The height is usually from 1m to 30m.
3. Vibro stone column:
Vibro replacement stone columns are a ground improvement technique to improve the load bearing capacity and reduce the settlement of the soil. On many occasions, it is noted that the local soil is by nature not able to bear loads of proposed structure. The stone column consists of crushed coarse aggregates of various sizes.
The detailed study of liquefaction must be undertaken by the Indian earthquake regions. The preventive measures must be taken against failures and improve the techniques of compaction.
Liquefaction is a process that leads to soil losing strength. Most commonly, as a result of ground shaking during large earthquakes. Not all soils yet, will liquefy during an earthquake.
Kit required to develop Soil liquefaction: