what is soil liquefaction, types, effects and remedies
What is soil liquefaction:
Liquefaction is the process where the soil will losses its strength in saturation and cohesive less soil, because of increased pore water pressure and hence the effective stress will reduce due to dynamic loading.
=> The soil particles move freely with respect to each other. due to this the strength of the soil decreases and the ability of a soil deposit to support foundations for the buildings and bridge is reduce.
Types of liquefaction:
=> Flow liquefaction: The Flow liquefaction is the process in which the static equilibrium will destroyed by the static or dynamic loads in the soil deposits with low residual strength. It mainly occurs when the static shear stress in these soil increases the shear strength of the liquefied soil.
i) Deformation due to cyclic mobility develop incrementally because of static and dynamic stresses that exists during an earthquake.
Effects of liquefaction:
=> Loss of bearing strength: The ground can liquefy and loose its ability to support structure.
=> Lateral spreading: The ground can slide down very gentle slopes.it is mainly caused by cyclic mobility. lateral spreading causes damage to foundation of the buildings pipelines, railway lines and also cause the shaking at pile, due to increased lateral loads.
=> Sand boils: The sand water that can come out from the buried liquefied layer and blow up at the surface that to form the sand volcanoes. Then the surrounding ground often the fractures and settles there.
=> Flow failure: Flow failures are the most catastrophic ground failures caused by the liquefaction. These failures commonly displace large masses of the soil laterally. Flows develop in the loose saturated sands or silts on relatively steep slopes.
=> Ground oscillaion: When the ground is flat or the slope is too gentle to allow the displacement, the liquefaction at the depth may decouple and overlying the soil layers from the underlying ground, allowing the upper soil to oscillate back and the forth and up and down in the form of the ground waves. These oscillations are usually accompanied by the opening and closing of the fissures fracture of a rigid structures such as pavements and pipelines.
=> Flotation: Light structure that are buried in the ground {like pipe lines, sewers and empty fuel tanks}that can float to the surface when they are surrounded by the liquefied soil.
=> Settlement of soil: Liquefied ground reconsolidates during an earthquake the ground surface may settle and the underlying liquefied soil become more dense.
Remedial measures to reduce liquefaction:
=> Avoid liquefaction susceptible soil: The first possibility is to avoid the construction on the liquefaction susceptible soil.
=> => Build liquefaction safe structures: It might be conceivable to make the structure liquefaction safe by planning the establishment components to oppose the effects of liquefaction.
=> Shallow foundations: It is very important that all foundations elements in a shallow foundations are tied together to make the foundation move or settle uniformly, thus decreases the amount of shear force induced in the structure elements resisting upon the foundation.
i)A stiff foundation mat is a good type of shallow foundation. Which can transfer loads from locally liquefied zone to adjacent stronger ground.
=> Deep foundation: Liquefaction can cause large lateral loads on pile foundations. Pile driven through a weak, potentially. The soil layer to a stronger layer not only have to carry the vertical loads from the supers structures, but must also be able to resist the horizontal loads and the bending moments that induced by the lateral movements and if the weak layer liquifies the piles of larger dimensions and more reinforcement that can achieve the sufficient resistance.
=> The soil improvements techniques aganist soil
liquefaction: The main important of the soil improvement techniques used for reducing the soil liquefaction which hazards to a large increasing in the pore water pressure during the earthquake shaking by the enhancing the strength, density, and drainage characteristics of the soil.
=> Vibro compaction: Vibro compaction is the process that involves the use of a vibrating prone that can be penetrate granular soil to deposit to a depth of over 100 feet. The vibration of the probe will cause the grain structure to collapse, there by the densifying soil to surroundings the probe.
=> Dynamic compaction: The dynamic compaction is the process in which it is done by the dropping of a heavy weight steel or concrete in a grid pattern form the heights of 30 to 100 feet's.
=> Compaction grouting: The compaction grouting's is one of the technique where by a slow flowing water/sand/cement mix is injected into the loose sand under the high pressure. Grout does not enter the soil but forms a bulb that compact and densify the forcing then it occupy less space.
=> Stone columns: Stone columns are columns of gravel constructed in the ground. Stone columns can be constructed by the vibro compaction methods. In this approach the steel casing is driven into the soil and gravel is filled in from the top and tampered with a drop hammer as the steel is successively withdrawn.
Watch the below video to get clear understanding on this topic.
Conclusion:
=> Liquefaction is one of the important where problems arises time to time, so we have to be careful before constructing any of the construction in these types of soil.
=> We have to test the liquified soil first and then after we have to analyze the problem and then we have to find the accurate solution of the problem.
=> Liquefaction of soils damages a lot and damages the building foundations and in some cases it can damage whole building.
=> Liquefaction of soils damages a lot and damages the building foundations and in some cases it can damage whole building.
