Determination of liquid limit.
Aim:
To determine the liquid limit of soil by using Casagrande Apparatus.
Specification:
This test is done to determine liquid limit of soil as per IS: 2720(Part 5)-1985. After receiving the soil sample it is dried in air or in oven (maintained at a temperature of 60oC). If clods are there in soil sample then it is broken with the help of wooden mallet. The soil passing 425 micron sieve is used in this test.
Equipments Required:
- A mechanical liquid limit apparatus (casagrande type) with grooving tools.
- Evaporating dishes, wash bottle etc.
- Balance accurate to 0.01 g.
- Airtight container to determine water content.
- Oven to maintain temperature at 105oC to 110oC.
- Sieve (425 micron).
- Spatula
- Desiccator and other accessories.
Theory:
When water is added to dry soil, it changes its state of consistency from hard to soft. We can define liquid limit as the minimum water content at which the soil is still in the liquid state, but has a small shearing strength against flow. From test point of view we can define liquid limit as the minimum water content at which a pat of soil cut by a groove of standard dimension will flow together for a distance of 12 mm (1/2 inch) under an impact of 25 blows in the device.
Consistency of fine-grained soils may be defined as the relative ease with which a soil can be remoulded. Consistency limits may be categorized into three limits called Atterberg limits. They are 1) Liquid limit 2) Plastic limit and 3) Shrinkage limit Liquid limit is the moisture content that defines where the soil changes from a plastic to a viscous fluid state. Other limits will be discussed during corresponding experiments.
Precautions:
- Soil used for liquid limit determination should not be oven dried prior to testing.
- In LL test the groove should be closed by the flow of soil and not by slippage between the soil and the cup
- After mixing the water to the soil sample , sufficient time should be given to permeate the water throughout out the soil mass
- Wet soil taken in the container for moisture content determination should not be left open in the air, the container with soil sample should either be placed in desiccators or immediately be weighed.
- After performing each test the cup and grooving tool must be cleaned.
- The number of blows should be just enough to close the groove.
- The number of blows should be between 10 and 40.
Procedure:
- A representative sample of mass of about 120 gm passing through 425 micron IS sieve is taken for the test. Mix the soil in an evaporating dish with distilled water to form a uniform paste.
- Adjust the cup of the device so that the fall of the cup on to the hard rubber base is 10 mm.
- Transfer the portion of the paste to the cup of liquid limit device. Allow some time for the soil to have uniform distribution of water.
- Level the soil topsoil so that the maximum depth of soil is 12 mm. A channel of 11 mm wide at the top, 2 mm at the bottom and 8 mm deep is cut by the grooving tool. The grooving tool is held normal to the cup and the groove is cut through the sample along the symmetrical axis of the top.
- The handle of the device is turned at a rate of about 2 revolutions per second and the number of blows necessary to close the groove along the bottom distance of 12 mm is counted. A sample of soil which closes the groove is collected.
- Another soil sample of same weight has to be taken and above procedure is repeated by taking increaments of percentage of water(2% for gravels and sand, 4% for silt)
- At least 4 tests should be conducted by adjusting the water contents of the soil in the cup in such a way that the number of blows required to close the groove may fall within the range of 5 to 40 blows. A plot of water content against the log of blows is made as shown in figure. The water content at 25 blows gives the liquid limit.
Table:
| Trials No. | Test No.1 | Test No.2 | Test No.3 | Test No.4 |
|---|---|---|---|---|
| Moisture can and lid number | ||||
| Weight of container (W1), gm | ||||
| Weight of container + wet soil (W2), gm | ||||
| Weight of container + dry soil (W3), gm | ||||
| Water content, ω=(W2-W3)/(W3-W1) | ||||
| No of blows (N) | ||||
| Liquid limit, LL = | ||||
Verification/ Validation:
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 is brittle and stiffer. Hence if the points on the graph are obtained scattered, we need to draw the linear curve at the mean.
Table:
| Soil Type. | Liquid limit |
|---|---|
| Sand | - |
| Silt | 30-40 |
| Clay | 40-150 |
Conclusion:
As per the procedure the experiment is carried out. Water content for 25 blows, w = _____%.
Viva Questions:
- Define consistency of the soil. How is it measured ?
- What is liquid limit of soil ?
- What is the apparatus used to determine the liquid limit ?
- When a soil sample is given, what is the procedure to determine the liquid limit of the sample ?
- In a liquid limit test, the moisture content at 10 blows was 70% and that at 100 blows was 20%. The liquid limit of the soil, is ?
- What is the purpose of computing liquid limit of the soil ?
- With the organic matter in the soil, will the liquid limit increase or decrease ?
Aim:
To determine the liquid limit of fine soil by using Casagrande Apparatus.
Specification:
This test is done to determine liquid limit of soil as per IS: 2720(Part 5)-1985. After receiving the soil sample it is dried in air or in oven (maintained at a temperature of 60oC). If clods are there in soil sample then it is broken with the help of wooden mallet. The soil passing 425 micron sieve is used in this test.
Equipments Required:
- A mechanical liquid limit apparatus (casagrande type) with grooving tools.
- Evaporating dishes, wash bottle etc.
- Balance accurate to 0.01 g.
- Airtight container to determine water content.
- Oven to maintain temperature at 105oC to 110oC.
- Sieve (425 micron).
- Spatula
- Desiccator and other accessories.
Theory:
When water is added to dry soil, it changes its state of consistency from hard to soft. We can define liquid limit as the minimum water content at which the soil is still in the liquid state, but has a small shearing strength against flow. From test point of view we can define liquid limit as the minimum water content at which a pat of soil cut by a groove of standard dimension will flow together for a distance of 12 mm (1/2 inch) under an impact of 25 blows in the device.
Consistency of fine-grained soils may be defined as the relative ease with which a soil can be remoulded. Consistency limits may be categorized into three limits called Atterberg limits. They are 1) Liquid limit 2) Plastic limit and 3) Shrinkage limit Liquid limit is the moisture content that defines where the soil changes from a plastic to a viscous fluid state. Other limits will be discussed during corresponding experiments.
Precautions:
- Soil used for liquid limit determination should not be oven dried prior to testing.
- In LL test the groove should be closed by the flow of soil and not by slippage between the soil and the cup
- After mixing the water to the soil sample , sufficient time should be given to permeate the water throughout out the soil mass
- Wet soil taken in the container for moisture content determination should not be left open in the air, the container with soil sample should either be placed in desiccators or immediately be weighed.
- After performing each test the cup and grooving tool must be cleaned.
- The number of blows should be just enough to close the groove.
- The number of blows should be between 10 and 40.
Procedure:
- A representative sample of mass of about 120 gm passing through 425 micron IS sieve is taken for the test. Mix the soil in an evaporating dish with distilled water to form a uniform paste.
- Adjust the cup of the device so that the fall of the cup on to the hard rubber base is 10 mm.
- Transfer the portion of the paste to the cup of liquid limit device. Allow some time for the soil to have uniform distribution of water.
- Level the soil topsoil so that the maximum depth of soil is 12 mm. A channel of 11 mm wide at the top, 2 mm at the bottom and 8 mm deep is cut by the grooving tool. The grooving tool is held normal to the cup and the groove is cut through the sample along the symmetrical axis of the top.
- The handle of the device is turned at a rate of about 2 revolutions per second and the number of blows necessary to close the groove along the bottom distance of 12 mm is counted. A sample of soil which closes the groove is collected.
- Another soil sample of same weight has to be taken and above procedure is repeated by taking increaments of percentage of water(2% for gravels and sand, 4% for silt)
- At least 4 tests should be conducted by adjusting the water contents of the soil in the cup in such a way that the number of blows required to close the groove may fall within the range of 5 to 40 blows. A plot of water content against the log of blows is made as shown in figure. The water content at 25 blows gives the liquid limit.
Table:
| Trials No. | Test No.1 | Test No.2 | Test No.3 | Test No.4 |
|---|---|---|---|---|
| Moisture can and lid number | 1 | 4 | 2 | 6 |
| Weight of container (W1), gm | 22.23 | 23.31 | 21.87 | 22.58 |
| Weight of container + wet soil (W2), gm | 28.56 | 29.27 | 25.73 | 25.22 |
| Weight of container + dry soil (W3), gm | 27.40 | 28.10 | 24.90 | 24.60 |
| Water content, ω=(W2-W3)/(W3-W1) | ||||
| No of blows (N) | 31 | 29 | 20 | 14 |
| Liquid limit, LL = | ||||
Verification/ Validation:
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 is brittle and stiffer. Hence if the points on the graph are obtained scattered, we need to draw the linear curve at the mean.
Table:
| Soil Type. | Liquid limit |
|---|---|
| Sand | - |
| Silt | 30-40 |
| Clay | 40-150 |
Conclusion:
As per the procedure the experiment is carried out. Water content for 25 blows, ω = %.
1. First video
2. Second video
3. Third video
Websites and blog
Click on the link below to study about standard proctor test.
1. First blog
2. Second blog
3. Third blog
Refrence
1. Venkataramaiah, C. (2018). Geotechnical Engineering (6th ed.). New Age International Publishers Pvt Ltd.
2. Punmia, B.C( 2017)Soil mechanics and foundations(17th ed.).Laxmi publications Pvt Ltd.
3. Gopal R, Rao, A, S, R( 2016)Basic and applied Soil mechanics(3rd ed.).New Age International Publishers Pvt Ltd.
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