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What Is Soil Liquefaction?
Soil liquefaction is a phenomenon of soil losing its’ strength due to externally applied stress. Partially saturated or saturated soil under seismic events loses firmness and strength.Why Does Soil Liquify?
The soil mass consists of soil particles and voids. Under normal conditions, the soil particles are packed together. The compact soil structure distributes the load among particles.
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Which Type Of Soil Is Prone To Liquefaction?
Sandy soil is more susceptible to liquefaction than clay. The sandy soil has less or no inter-particle cohesion. Also, sand has a bigger particle size that offers a lesser degree of compaction when compared to fine-grained soil. Thus, they liquefy easily.Types of soil liquefaction
1. Flow Liquefaction
Flow liquefaction is a phenomenon of static equilibrium disturbance caused by the external load. The initial trigger is relatively small but, it converts to a stronger event that overtakes the inter-particle bonding. After the start of the phenomenon, the soil has no shear strength and behaves like a thick liquid. The flow liquefaction is identifiable by large and rapid movements. The ground movement leads to the failure of bearing capacity. The structure under the influence of flow liquefaction may tilt or overturn. Historically, it has been observed that a large flow of soil liquefaction takes place with rapid movement.2. Cyclic Liquefaction
The cyclic loading causes soil liquefaction. This phenomenon is triggered in soils having lesser shear stress than the soil’s shear strength. The deformations in cyclic liquefaction are in the lateral direction. The lateral deformations are commonly observed in roads, rivers, and lakes.Estimation For Soil Liquefaction Possibility
The estimation takes the following factors into account.- Soil type.
- Soil particle size.
- Water saturation level.
- Degree of soil compaction.
- Seismic activity in the region.
- Historical data of the region for liquefaction.
- FSL = CRR/CSR
Effects Of Soil Liquefaction
The soil liquefaction has disastrous effects on the buildings and facilities. The structure built on liquefiable soil may face foundation settlement, cracks, tilt, and overturning. Some of the major effects of soil liquefaction are as follows.1. Building Failure
The building foundation is designed as per the bearing capacity of the soil. In soil liquefaction, the bearing capacity of soil reduces to nil. As a result, the building settles into the ground. It may also tilt or overturn. The differential foundation settlement can also cause cracks in the structure.2. Foundation Crack
The uneven settlement of a raft foundation may damage it. The cracks in the foundation are dangerous for the structure’s safety. A cracked foundation fails to distribute the load evenly on the ground.3. Slope Erosion
The liquefaction destroys the soil slopes. The soil flows down and settles at the flat ground. The sliding soil causes a large fissure formation on the slopes. The slope failure is a potential threat to the structures in the vicinity and utilities.4. Retaining Wall Failure
A retaining wall fails by sliding, tilting, or overturning. The liquified soil exerts an additional force on the retaining wall, and hence it may cause the failure of the wall.5. Damage To Pile Foundation
The pile foundation acts as a column that transfers the structural load to the deeper strata. The liquified soil exerts lateral stress to the pile that causes buckling. The pile may distort, and its’ load- carrying capacity decreases.6. Damage To Utilities
The utilities like water lines, sewers, gas lines, etc., are disturbed due to liquefaction. The sewer manholes vertically uplift in the liquefaction phenomenon.Mitigation Methods
It is suggested to avoid the construction on liquifiable soil. If unavoidable, soil condition improvement methods, reduce the soil liquefaction potential. The liquefaction mitigation methods make the ground safer to carry the structural load. The cost of the mitigation method is 5-10% of the building cost.1. Vibro-Compaction
The deep vibrators compact the liquefaction susceptible soil. The loosely packed strata are compacted up to the required depth.2. Dynamic Compaction
The dynamic compaction method involves the dropping of weight from a height. A crane drops the weight at every point of the ground, thus compacting the entire area.3. Drainage Columns
The drainage columns are the boreholes in the ground at suitable spacing. The permeable material (gravel) fills the boreholes which helps dissipate the pore water pressure quickly.Soil Liquefaction Cases Around The World
Soil liquefaction has been observed in several countries around the world. The damages due to the soil liquefaction have been devastating. Some of the earthquakes that triggered the liquefaction are as follows-- Shillong (India) Earthquake, 1897. An earthquake of 8.1 (on the Richter scale) liquified the Brahmaputra plain. Massive floods destroyed the plains and plateau.
- The Great Alaska Earthquake (magnitude of 9.2 on Richter Scale), 1964.
- Christ Church (New Zealand) Earthquake, 2011.
- Palu (Indonesia) Earthquake (magnitude 7.1 on Richter Scale), 2018. More than 800 people died in building collapse due to liquefaction.
Consolidation Of Soil
Methods Of Soil Stabilization
Ground Improvement Techniques
How To Build Earthquake-Resistant Building
Current Environmental Problems For Construction
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