Determination of plastic limit of given sample

Determination of plastic limit of the soil

Aim:

To determine plastic limit of the soil. The plastic limit of fine-grained soil is the water content of the soil below which it ceases to be plastic. It begins to crumble when rolled into threads of 3mm dia. Specifications: This test is done to determine the plastic limit of soil as per IS: 2720 (Part 5)-1985. Take out 30g of air-dried soil from a thoroughly mixed sample of the soil passing through 425µm IS Sieve. Mix the soil with distilled water in an evaporating dish and leave the soil mass for 24hrs.

Specification:

This test is done to determine the plastic limit of soil as per IS: 2720 (Part 5)-1985. Take out 30g of air-dried soil from a thoroughly mixed sample of the soil passing through 425µm IS Sieve. Mix the soil with distilled water in an evaporating dish and leave the soil mass for 24hrs.

Equipments Required:

• Porcelain evaporating dish.
• Flat glass plate.
• Balance accurate to 0.01g.
• Drying oven, maintained at 110 ± 5°C (230 ± 9°F).
• Weighing dishes, non-absorbent, with lids.
• Flexible spatula, blade approximately 102 mm (4 in.) long x 19mm (0.75 in.) wide.

Theory:

The plastic limit is the moisture content that defines where the soil changes from a semi-solid to a plastic state. It may also be defined as that water content at which soil starts crumbling when rolled into threads of 3mm diameter. Use the paste from liquid limit test and begin drying. May add dry soil or spread on plate and air dry.

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 limit to a viscous fluid state.

Precautions:

• Soil used for plastic limit determination should not be oven dried prior to testing.
• 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. The container with soil sample should either be placed in desiccators or immediately be weighed.

Procedure:

1. Select a representative sample of fine-grained soil of about 20 g or more passing through 420 micron IS sieve. Mix it with distilled water thoroughly on a glass plate such that the palm of the soil can be rolled into a thread of 3 mm diameter. Allow some time for the proper distribution mixed with water.
2. Take about 10 g of this wet sail and roll it into a thread on a glass plate with the palm of the hand. The rolling must be such that it forms a uniform thread of 3 mm diameter. If the thread cracks before attaining 3 mm diameter, and add little more water, knead it and roll again.
3. the rolling can be done to diameter less than 3mm, mix some dry soil, knead it to remove same extra moisture in the soil. This process has to continue till the sample crumbles just at about 3 mm diameter. Collect the crumbled soil (at least 6 g) and measure its water content.
4. Repeat the process to get at least three water content determination (after they have been in the oven at least 16 hours).
5. The average of water content so obtained is the plastic limit of the soil.

Table: water content of 3mm soil

Trials No.	Test No.1	Test No.2	Test No.3	Test No.4
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)
Average ω = (ω1+ω2+ω3+ω4)/4
Liquid limit, LL =

Result:

The Plastic limit of soil (average water content) is, PL_______________.

Plasticity index = LL - PL = ______________%

Verification/ Validation:

Determine the plasticity index Ip, which is the difference between liquid limit and plastic limit. Following table list the standard values:

Table:

Soil Type.	Wl	Wp	Ip
Sand	-	-	Non-plastic
Silt	30-40	20-25	10-15
Clay	40-150	25-50	15-100

Conclusion:

The plastic limit of the soil = ____

plasticity index = ____.

The type of soil is _____.

Viva Questions:

1. How is plastic limit computed in laboratory ?
2. What is the practical significance of determining plastic limit of the soil ?
3. What is plasticity index ?
4. What is toughness index ?
5. What is meant by unified soil classification ?
6. What is liquidity index and consistency index ?
7. What is A-line and U-line ?

Aim:

To determine plastic limit of the soil. The plastic limit of fine-grained soil is the water content of the soil below which it ceases to be plastic. It begins to crumble when rolled into threads of 3mm dia. Specifications: This test is done to determine the plastic limit of soil as per IS: 2720 (Part 5)-1985. Take out 30g of air-dried soil from a thoroughly mixed sample of the soil passing through 425µm IS Sieve. Mix the soil with distilled water in an evaporating dish and leave the soil mass for 24hrs.

Specification:

This test is done to determine the plastic limit of soil as per IS: 2720 (Part 5)-1985. Take out 30g of air-dried soil from a thoroughly mixed sample of the soil passing through 425µm IS Sieve. Mix the soil with distilled water in an evaporating dish and leave the soil mass for 24hrs.

Equipments Required:

• Porcelain evaporating dish.
• Flat glass plate.
• Balance accurate to 0.01g.
• Drying oven, maintained at 110 ± 5°C (230 ± 9°F).
• Weighing dishes, non-absorbent, with lids.
• Flexible spatula, blade approximately 102 mm (4 in.) long x 19mm (0.75 in.) wide.

Theory:

The plastic limit is the moisture content that defines where the soil changes from a semi-solid to a plastic state. It may also be defined as that water content at which soil starts crumbling when rolled into threads of 3mm diameter. Use the paste from liquid limit test and begin drying. May add dry soil or spread on plate and air dry.

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 limit to a viscous fluid state.

Precautions:

• Soil used for plastic limit determination should not be oven dried prior to testing.
• 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. The container with soil sample should either be placed in desiccators or immediately be weighed.

Procedure:

1. Select a representative sample of fine-grained soil of about 20 g or more passing through 420 micron IS sieve. Mix it with distilled water thoroughly on a glass plate such that the palm of the soil can be rolled into a thread of 3 mm diameter. Allow some time for the proper distribution mixed with water.
2. Take about 10 g of this wet sail and roll it into a thread on a glass plate with the palm of the hand. The rolling must be such that it forms a uniform thread of 3 mm diameter. If the thread cracks before attaining 3 mm diameter, and add little more water, knead it and roll again.
3. the rolling can be done to diameter less than 3mm, mix some dry soil, knead it to remove same extra moisture in the soil. This process has to continue till the sample crumbles just at about 3 mm diameter. Collect the crumbled soil (at least 6 g) and measure its water content.
4. Repeat the process to get at least three water content determination (after they have been in the oven at least 16 hours).
5. The average of water content so obtained is the plastic limit of the soil.

Table: water content of 3mm soil

Trials No.	Test No.1	Test No.2	Test No.3	Test No.4
Weight of container (W1), gm	7.78	7.83	15.16	7.83
Weight of container + wet soil (W2), gm	16.39	13.43	21.23	13.43
Weight of container + dry soil (W3), gm	15.28	12.69	20.43	12.69
Water content, ω=(W2-W3)/(W3-W1)
Average ω = (ω1+ω2+ω3+ω4)/4
Liquid limit, LL =	26

Result:

The Plastic limit of soil (average water content), PL is =

Plasticity index = LL - PL =%

Verification/ Validation:

Determine the plasticity index Ip, which is the difference between liquid limit and plastic limit. Following table list the standard values:

Table:

Soil Type.	Wl	Wp	Ip
Sand	-	-	Non-plastic
Silt	30-40	20-25	10-15
Clay	40-150	25-50	15-100

Conclusion:

The plastic limit of the soil =

plasticity index = .

The type of soil is = .

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.