Determining the Liquid Limit of Soil - Soil Properties: Testing, Measurement, and Evaluation - page 73

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CHAPTER SEVEN

CHAPTER SEVEN

Determining
the Liquid
Limit of Soil

Determining
the Liquid
Limit of Soil

(Referenced Document: ASTM D 4318)

Atterberg [1, 2] established four states of consistency—i.e., degree of
firmness—for fine-grained soils: liquid, plastic, semisolid , and solid
(Figure 7-1). The dividing line between liquid and plastic states is the
liquid limit , the dividing line between plastic and semisolid states is the
plastic limit , and the dividing line between semisolid and solid states is
the shrinkage limit . If a soil in the liquid state is gradually dried out, it
will pass through the liquid limit, plastic state, plastic limit, semisolid
state, and shrinkage limit, and reach the solid state. The liquid, plastic,
and shrinkage limits are therefore quantified in terms of water content.
For example, the liquid limit is reported in terms of the water content at
which a soil changes from the liquid to the plastic state. The difference
between the liquid limit and plastic limit is the plasticity index .
The three limits and the index just defined are useful numbers in
classifying soils and making judgments in regard to their applications.
This chapter gives the laboratory procedure for determining liquid
limit, whereas Chapters 8 and 9 give the procedures for determining
(1) plastic limit and plasticity index and (2) shrinkage limit, respectively.
As explained, the liquid limit is the dividing line between the liq-
uid and plastic states. It is quantified for a given soil as a specific water
content; from a physical standpoint, it is the water content at which
the shear strength of the soil becomes so small that the soil “flows” to
close a standard groove cut in a sample of soil when it is jarred in a

INTRODUCTION

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