4. ATTERBERG LIMITS
When a cohesive soil is mixed with an excessive amount of water, it will be in a somewhat
liquid state and flow like a viscous liquid. However, when this viscous liquid is gradually
dried, with the loss of moisture it will pass into a plastic state. With further reduction of
moisture, the soil will pass into a semisolid and then into a solid state. This is shown in Figure
below The moisture content (in percent) at which the cohesive soil will pass from a liquid
state to a plastic state is called the liquid limit of the soil. Similarly, the moisture contents (in
percent) at which the soil changes from a plastic to a semisolid state and from a semisolid
state to a solid state are referred to as the plastic limit and the shrinkage limit, respectively.
These limits are referred to as the Atterberg limits.
Figure 4-1. Atterberg limits
PART ONE: DETERMINATION OF LIQUID LIMIT
OBJECTIVE:
1. Prepare soil specimen as per specification.
2. Find the relationship between water content and number of blows.
3. Draw flow curve.
4. Find out liquid limit.
NEED AND SCOPE:
Liquid limit is significant to know the stress history and general properties of the soil met with
construction. From the results of liquid limit the compression index may be estimated. The
compression index value will help us in settlement analysis. If the natural moisture content of
soil is closer to liquid limit, the soil can be considered as soft if the moisture content is lesser
than liquids limit, the soil can be considered as soft if the moisture content is lesser than liquid
limit. The soil is brittle and stiffer.
, THEORY:
The liquid limit is the moisture content at which the groove, formed by a standard tool into the
sample of soil taken in the standard cup, closes for 10 mm on being given 25 blows in a
standard manner. At this limit the soil possess low shear strength.
APPARATUS REQUIRED:
1. Balance
2. Liquid limit device (Casagrende)
3. Grooving tool
4. Mixing dishes
5. Spatula
6. Electrical Oven
PROCEDURE:
I. Determine the mass of three moisture cans (WI).
2. Put about 250 g of air "dry soil, passed through No. 40 sieve, into an evaporating dish.
Add water from the plastic squeeze bottle and mix the soil to the form of a uniform
paste.
3. Place a portion of the paste in the brass cup of the liquid limit device. Using the spatula,
smooths the surface of the soil in the cup such that the maximum depth of the soil is
about 8 mm.
4. Using the grooving tool, cut a groove along the center line of the soil pat in the cup (Fig.
4-2 a).
5. Turn the crank of the liquid limit device at the rate of about 2 revolutions per second.
By this, the liquid limit cup will rise and drop through a vertical distance of 10 mm once
for each revolution. The soil from two sides of the cup will begin to flow toward the
center. Count the number of blows, N, for the groove in the soil to close through a
distance of 1/2 in. (12.7 mm) as shown in (Fig. 4-2b).
If N = about 25 to 35, collect a moisture sample from the soil in the cup in a moisture can and
determine the mass of the can plus the moist soil (W2).
Remove the rest of the soil paste from the cup to the evaporating dish. Use paper towels to
clean the cup.
If the soil is too dry, N will be more than about 35. In that case, remove the soil with the
spatula to the evaporating dish. Clean the liquid limit cup with paper towels. Mix the soil in
the evaporating dish with more water, and try again.
If the soil is too wet, N will be less than about 15. In that case, remove the soil in the cup to
the evaporating dish. , Clean the liquid limit cup carefully with paper towels.
When a cohesive soil is mixed with an excessive amount of water, it will be in a somewhat
liquid state and flow like a viscous liquid. However, when this viscous liquid is gradually
dried, with the loss of moisture it will pass into a plastic state. With further reduction of
moisture, the soil will pass into a semisolid and then into a solid state. This is shown in Figure
below The moisture content (in percent) at which the cohesive soil will pass from a liquid
state to a plastic state is called the liquid limit of the soil. Similarly, the moisture contents (in
percent) at which the soil changes from a plastic to a semisolid state and from a semisolid
state to a solid state are referred to as the plastic limit and the shrinkage limit, respectively.
These limits are referred to as the Atterberg limits.
Figure 4-1. Atterberg limits
PART ONE: DETERMINATION OF LIQUID LIMIT
OBJECTIVE:
1. Prepare soil specimen as per specification.
2. Find the relationship between water content and number of blows.
3. Draw flow curve.
4. Find out liquid limit.
NEED AND SCOPE:
Liquid limit is significant to know the stress history and general properties of the soil met with
construction. From the results of liquid limit the compression index may be estimated. The
compression index value will help us in settlement analysis. If the natural moisture content of
soil is closer to liquid limit, the soil can be considered as soft if the moisture content is lesser
than liquids limit, the soil can be considered as soft if the moisture content is lesser than liquid
limit. The soil is brittle and stiffer.
, THEORY:
The liquid limit is the moisture content at which the groove, formed by a standard tool into the
sample of soil taken in the standard cup, closes for 10 mm on being given 25 blows in a
standard manner. At this limit the soil possess low shear strength.
APPARATUS REQUIRED:
1. Balance
2. Liquid limit device (Casagrende)
3. Grooving tool
4. Mixing dishes
5. Spatula
6. Electrical Oven
PROCEDURE:
I. Determine the mass of three moisture cans (WI).
2. Put about 250 g of air "dry soil, passed through No. 40 sieve, into an evaporating dish.
Add water from the plastic squeeze bottle and mix the soil to the form of a uniform
paste.
3. Place a portion of the paste in the brass cup of the liquid limit device. Using the spatula,
smooths the surface of the soil in the cup such that the maximum depth of the soil is
about 8 mm.
4. Using the grooving tool, cut a groove along the center line of the soil pat in the cup (Fig.
4-2 a).
5. Turn the crank of the liquid limit device at the rate of about 2 revolutions per second.
By this, the liquid limit cup will rise and drop through a vertical distance of 10 mm once
for each revolution. The soil from two sides of the cup will begin to flow toward the
center. Count the number of blows, N, for the groove in the soil to close through a
distance of 1/2 in. (12.7 mm) as shown in (Fig. 4-2b).
If N = about 25 to 35, collect a moisture sample from the soil in the cup in a moisture can and
determine the mass of the can plus the moist soil (W2).
Remove the rest of the soil paste from the cup to the evaporating dish. Use paper towels to
clean the cup.
If the soil is too dry, N will be more than about 35. In that case, remove the soil with the
spatula to the evaporating dish. Clean the liquid limit cup with paper towels. Mix the soil in
the evaporating dish with more water, and try again.
If the soil is too wet, N will be less than about 15. In that case, remove the soil in the cup to
the evaporating dish. , Clean the liquid limit cup carefully with paper towels.
