ATTERBERG LIMITS
The
Atterberg limits are water contents which define the limits of various stages
of consistency for fine-grained soils. The liquid limit (LL) and the plastic limit
(PL) define the upper and lower limits, respectively, of the plastic range of a
soil; the numerical difference between these two limits expresses the
plasticity of a soil and is termed the plasticity index (PI).
Liquid Limit
The
liquid limit of a soil is the water content, expressed as a percentage of the
weight of oven-dried soil at which two halves of a soil pat separated by a groove
of standard dimensions will close at the bottom of the groove along a distance
of 1/2 in. under the impact of 25 blows in a standard liquid limit device.
Plastic Limit
The
plastic limit of a soil is the water content, expressed as a percentage of the
weight of oven dried soil at which the soil just begins to crumble into short pieces
when rolled into a thread 1/8 in. in
diameter.
PI= LL-PL
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