1 Fine-Grained Soils: Water content is a major factor, especially when the soil contains so-called active clays.

2 Each soil type will generally have different water contents at which it behaves like a solid, semi-solid, plastic, and liquid. For a given soil, the water contents that mark the boundaries between these soil consistencies are the so-called Atterberg Limits.

3 Consistency The physical state of a fine-grained soil at a particular water content is known as its consistency. Depending on its water content a soil may exist in: The liquid, Plastic Semi-solid or Solid state. The water contents at which the transitions between states occur vary from soil to soil.

4 Atterberg (Consistency) Limits: liquid limit, LL plastic limit, PL and shrinkage limit, SL

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6 The dividing line between the liquid and plastic states is the liquid limit (LL). The dividing line between the plastic and semisolid states is the plastic limit (PL). And the dividing line between the semisolid and solid state is the shrinkage limit (SL). The plasticity index (PI) defines the complete range of plastic state.

7 Liquid Limit (LL) The liquid limit defines the boundary between plastic and viscous fluid states. It is determined using a standard "Liquid Limit Device," which drops a shallow cup full of soil 1 cm consistently. When a groove cut through the sample closes 1.2 cm, the number of drops is recorded and a moisture content sample processed. Repeating the procedure for a total of four drop-count ranges provides enough data to plot on a semi-log scale. From the plot, the moisture content at 25 drops defines the Liquid Limit.

8 Liquid Limit Device (Cassagrande’s Device)

9 Determination of Liquid Limit:

10 Plastic Limit (PL) The plastic limit is that moisture content of a soil at which it becomes too dry to be plastic. The plastic limit defines the boundary between non-plastic and plastic states. It is determined simply by rolling a thread of soil and adjusting the moisture content until it breaks at 3 mm diameter.

11 Determination of Plastic Limit:

12 Plastic Limit:

13 Determination of Plasticity Index Plasticity Index, PI = LL - PL The plasticity index (PI) is the range of the plastic region. These limits are expressed as a percent of moisture content.

14 5- Liquidity Index: Significant values of LI indicating the consistency of the soil are: LI < 0 semi-plastic solid or solid 0 < LI < 1 plastic LI >1 liquid

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