311 GEOTECHNICAL ENGINEERING

1. FCE 311 GEOTECHNICAL ENGINEERING
6. CONSISTENCY AND PLASTICITY
Department of Civil & Construction Engineering
University of Nairobi

2. 6.1 State of Consistency
• The term consistency refers to the
relative ease with which a soil mass can
be deformed and is used to describe the
degree of firmness of fine-grained soils
for which consistency relates to a large
extent to water content.

3. 6.1 State of Consistency –
cont’d
• The four states of consistency suggested
by Atterberg are ;
18
Liquid Limit, LL
Liquid State
Plastic Limit, PL
Plastic State
Shrinkage Limit, SL
Semisolid State
Solid State
Dry Soil
Fluid soil-water
mixture
Increasingwatercontent

4. 6.1 State of Consistency –
cont’d
• The four states of consistency in a chart
form;

5. 6.1 State of Consistency –
cont’d
• The water contents, which arbitrarily
define the boundary between the four
states of consistency, are referred to as
consistency limits or Atterbag limits.
• The three consistency limits are Liquid
Limit, Plastic Limit and Shrinkage Limit.
• Liquid limit is denoted by WL and is the
boundary between plastic and liquid
states of consistency. It is the minimum
water content at which the soil mass still
flows like a liquid.

6. 6.1 State of Consistency –
cont’d
• Liquid limit is defined as the water
context at which a groove, cut with a
standard grooving tool, in soil pattaken
in the cup of a standard liquid limit
device closes for a distance of 13mm
when the cup is imparted 25 blows.

7. 6.1 State of Consistency –
cont’d
• The standard liquid limit device

8. 6.1 State of Consistency –
cont’d
• Plastic limit is denoted by WP and is the
boundary between semi-solid and plastic
states of consistency. It is the minimum
water content at which the soil mass can
still be deformed without cracking.
• Plastic limit is defined as the water
content at which the soil mass can be
rolled into a threat of 3mm diameter and
the thread first shows signs of cracking.

9. 6.1 State of Consistency –
cont’d
• Shrinkage limit is denoted by WS and is
the boundary between solid and semi-
solid state of consistency. It is defined as
the maximum water content at which
there is no reduction in volume of soil
mass accompanying reduction in water
content.
• The laboratory determination of these
states is discussed in Chapter 7.

10. 6.1 State of Consistency –
cont’d
• Shrinkage limit is denoted by WS and is
the boundary between solid and semi-
solid state of consistency. It is defined as
the maximum water content at which
there is no reduction in volume of soil
mass accompanying reduction in water
content.
• The laboratory determination of these
states is discussed in Chapter 7.