Soil liquefaction is the phenomenon in which the stiffness and the strength of the soil are lost under the action of earthquake force or due to rapid loading conditions. Soil liquefaction occurs in a fully saturated soil.
Soil liquefaction, also called earthquake liquefaction, ground failure or loss of strength that causes otherwise solid soil to behave temporarily as a viscous liquid. The phenomenon occurs in water-saturated unconsolidated soils affected by seismic S waves (secondary waves), which cause ground vibrations during earthquakes. Although earthquake shock is the best-known cause of liquefaction, certain construction practices, including blasting and soil compaction and vibroflotation (which uses a vibrating probe to change the grain structure of the surrounding soil), produce this phenomenon intentionally. Poorly drained fine-grained soils such as sandy, silty, and gravelly soils are the most susceptible to liquefaction
Granular soils are made up of a mix of soil and pore spaces. When earthquake shock occurs in waterlogged soils, the water-filled pore spaces collapse, which decreases the overall volume of the soil. This process increases the water pressure between individual soil grains, and the grains can then move freely in the watery matrix. This substantially lowers the soil’s resistance to shear stress and causes the mass of soil to take on the characteristics of a liquid. In its liquefied state, soil deforms easily, and heavy objects such as structures can be damaged from the sudden loss of support from below.
Effects of Liquefaction:
  • Sand Boiling: When liquefaction occurs below the surface that is fully compacted, the water pressure below the surface makes the water to break out like a bubble. These come out as boiling water. This is called as sand boiling.
  • Damage to offshore structures: Liquefaction is common in soil that is submerged. These conditions cause huge damage for the bridge construction, structures supporting submerged soil deposits.
  • Failure of Dams and Retaining Walls: The soils supporting Dams and Retaining walls undergoes liquefaction, which results in the collapse of these structures. As the structures lose the ability to control the huge water it further results in floods that are uncontrollable.
  • Surface Landslides: The failure of water carrying bodies can result in surface landslides.
  • Failure of Structures under Earthquake: Liquefaction followed by earthquake forces make the structures to lose its stability. They can either split or lean bringing complete collapse of the structure. Past earthquake records have shown a huge failure of building structures due to liquefaction. These hazards do not provide enough time for evacuation that it results in a huge loss of life and property.
Importance of soil Liquefaction:
After Liquefaction, the soil no longer behaves as an inactive grid of particles. The strength and stiffness of the liquefied soil are significantly decreased, often resulting in a variety of structural failures. Hence, a liquefied ground is no longer considered stable and fit for construction of structures. It has no ability to take even its self-weight nor weight of structures above. Hence it is very necessary to know the importance of the study of liquefaction so that adequate precaution is taken before construction. Understanding the liquefaction chances of the soil helps to decide what treatment method is to be chosen to make the soil liquefaction free. This hence helps to have stronger and safer construction of the structure.
​
Methods of Reducing soil liquefaction hazards:
  • By Avoiding Liquefaction Susceptible Soils: Construction on liquefaction susceptible soils is to be avoided. It is required to characterize the soil at a particular building site according to the various criteria available to determine the liquefaction potential of the soil in a site.
  • Build Liquefaction Resistant Structures: In certain situations, the construction over a land which shows the chances of liquefaction are not avoidable. Hence, foundation structures constructed must be designed such a way to resist the effects of liquefaction. The major reasons for constructing structures over liquefiable soil are space restrictions, favourable conditions, and other reasons.
  • Improve the Soil: This involves mitigation of the liquefaction hazards by improving the strength, density and drainage characteristics of the soil. This can be done using a variety of soil improvement techniques.
​Liquefy Pro (Liquefaction and settlement analysis):
LiquefyPro is software that evaluates liquefaction potential and calculates the settlement of soil deposits due to seismic loads. The program is based on the most recent publications of the NCEER Workshop and SP117 Implementation. The user can choose between several different methods for liquefaction evaluation: one method for SPT and BPT, and four methods for CPT data. Each method has different options that can be changed by the user. The options include Fines Correction, Hammer Type for SPT test, and Average Grain Size (D50) for CPT. The settlement analysis can be performed with two different methods. LiquefyPro has a user-friendly graphical interface making the program easy to use and learn. Input data is entered in boxes and spreadsheet type tables. CPT data files can be imported to reduce the amount of time spent on entering and editing data. The results of the liquefaction evaluation and settlement calculation can be displayed graphically and/or sent to a text file. The graphic report can be printed to be included in engineering reports, if desired. The image of the graphic can be saved as a Windows metafile, which can be inserted into Windows applications such as MS-Word, PowerPoint, Excel, and AutoCAD. The image also can be copied and pasted to other Windows applications. The text file with result data can be imported and used in other software programs such as spreadsheets and word processors.