• Consistency
  of soil means ease with which a soil paste can be deformed.
• It is
  denoted the degree of firmness of soil which may be referred as soft, stiff
  or hard soil depending upon its water content.
• This behavior
  of phase change with the amount of water is known as consistency.

Stage of Consistency.

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There are
three stage of consistency liquid, plastic and solid. Increase the water content
in soil. Soil passes from solid to plastic & plastic to liquid stage. Similarly If we heat a liquid paste of soil to reduce its water and decrease in
volume. It’s called shrinkage of soil.

Shrinkage
of soil up to a certain point after that soil volume mass will be remains
constant. These are the different stage of consistency.  [ what is brick ]

Consistency Limit.

It can also
be defined as the water content at which soil passes from liquid stage of
consistency to plastic stage of consistency and vice-versa.

Liquid
stage of consistency determined by any standard experimental method.

All the
soil at liquid limit are found to have negligible shear strengths of 2.7 KN/m3. Which
can be just measure.

Determination of Liquid Limit. ( IS – 2720, Part 5-1985 )

• This test is
  performed in a laboratory; Standard apparatus is used known as casagrande’s
  apparatus.
• In casagrande
  apparatus brass Cup mounted on a hard rubber pad. This brass Cup can be raised
  and made to fall on the hard rubber pad.
• By the
  screws distance of the fall can be regulated.

Cassagrande Apparatus

• This test
  is performed for the soil particle passing through 425µ (micron).
• From the
  point of view of a determination of liquid limit, which may also be defined as
  the minimum water content at which a part of soil cut by a Standard tool
  flow together by a distance of 1/2 inch in exactly 25 number of blows. [chain surveying]
• In order to
  find the liquid limit, this test is performed at different water content and
  gross cross ponding number of blows required to flow the soil together by a
  distance of 1/2 inch is noted and the result is expressed in the form of curve, called as flow curve.

Flow Curve

Plastic Limit (WP) :-

Plastic
limit is defined as the minimum water content at which soil remains plastic
stage of consistency.

It may also
be defined as the water content at which soil passes from plastic stage of
consistency to semi-solid stage of consistency and vice-versa.

Determination of Liquid Limit. ( IS – 2720 )

• About 15 gm of air dried soil and passing through 425µ (micron) sieve is taken for plastic
  limit determination. [ concrete compaction ]
• Make paste of soil passing through 425µ (micron) sieve and
  lift it for some times.
• Take about 8 gm of soil and the rolled it with
  finger on a glass plate.
• Rate of
  Rolling should be about 80 to 90 times per minute to from thread of 3 mm diameter.

Liquid limit

• Plastic
  limit is defined as the minimum water content at which soil begin to crumble
  when rod into a thread of 3 mm diameter.

Shrinkage Limit (WP) :-

It is define as the maximum water content below which any reduction in the water content on the soil has no effect over the volume of soil as below shrinkage limit water is being replaced by air of equal volume.

It may also be define as the minimum water content at which soil is completely  saturated.

It may also be define as the water content at which soil passage from solid stage of consistency to semi-solid stage of consistency or vice-versa.

• Passing 425 micron sieve is taken 30 gm of soil sample in an
  evaporating dish.
• The soil sample is mixed with sufficient quantity of water
  to bring the soil to a consistency that it may flow. [ type of brick bond ]
• Mixed soil sample is placed in shrinkage dish in 3 equal quantities
  and fill the dish and excess soil sample is removed and weighed the dish with
  the soil.
• Allowed to dry till the colour changes from dark to light.
• Consider a sample of soil having W greater than shrinkage
  limit and having mass and volume M1 and V1.
• The sample is subjected to drying in oven at 110℃ and at particular stage of drying where the W
  is equal to shrinkage limit it’s mass and volume is M2 and V2 and at completely
  drying let it’s mass and volume be Md and Vd.

Determination of shrinkage limit

FAQ’s

1. What is consistency of soil.
Consistency of soil means ease with which a soil paste can be deformed.