Consistency or Liquidity Index of Soil

Consistency or Liquidity Index of Soil (LI)

It is defined as the natural moisture content of the soil in excess of the FL expressed as a percentage of the PL,
i.e.,

{ (Natural moisture content—PL )/(Liquid limit—Plastic limit) }x 100 Percent

and is a measure of the consistency of the soil. It merely describes the moisture condition of a soil with respect to its index limits. It shows in what part of its plastic range a given sample of soil lies. A cohesive soil with a natural water content of the same order as its Liquid Limit will, in general, be a very soft material, while with a natural water content of the same order as its plastic limit will, in general, be a stiff material. Soft clays have a LI approximating to 100 per cent, while stiff clays have a LI which approximates to zero and may be even negative.

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