Criteria, Level 2

     The compositional and state criteria are important for a complete understanding of the liquefaction phenomena and are therefore explained in more detail below.

Compositional Criteria

     As described in Level 1, a uniformly graded soil is more susceptible to soil liquefaction than a well-graded soil because the reduced tendency for volumetric strain of a well-graded soil decreases the amount of excess pore pressure that can develop under undrained conditions.
     Historically, sands were considered to be the only type of soil susceptible to liquefaction, but liquefaction has also been observed in gravel and silt. Strain-softening of fine grained soils can produce effects similar to those of liquefaction. Fine-grained soils are susceptible to this type of behavior if they satisfy the criteria (Wang, 1979) shown in the table below.
  •  Fraction finer than 0.005 mm< 15%
  •  Liquid Limit, LL < 35%
  •  Natural water content > 0.9 LL
  •  Liquidity Index < 0.75
  •      Liquefaction susceptibility also depends on particle shape. Soil deposits with rounded particles, usually found in the types of deposits described in geological criteria, are more susceptible to liquefaction than soils with angular particles.

    State Criteria

         There are many factors that can be incorporated in the state of soil deposit. Here are some described that are of importance to the liquefaction susceptibility. At constant confining pressure, the liquefaction resistance increases with the relative density, Dr, and, at constant relative density, the liquefaction resistance increases with increasing confining pressure. Various investigations (Castro, 1969; Geotechnical Engineers, Inc.,1982; and Kramer and Seed,1988;) have shown that pre-existing shear static stress in a soil deposit is critical to a soil's susceptibility to static liquefaction. The higher the initial shear stresses, the greater is the liquefaction potential and the smaller disturbance is needed to liquefy the soil.

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