Monday, 2 January 2017

Liquid Limit test for soil - To Determine soil behaviour related to Water

Liquid Limit Test For Soil :

Introduction :

When dealing with density,void ration,settlement and strength characteristics of both disturbed and undisturbed soils will depend on water content of soil. Atterberg limits called as Liquid limit,Plastic Limit and Shrinkage limits will define the water content present in the soil. 

When water is added to dry soil,the individual particle is covered with absorbed water forming a thin film around it.If the addition of water is continued the thickeness of the water film will continue to increase,thereby facilitating the sliding effect between adjoining ostriches.

This is the fact that the behaviour of the soil is relate to the amount of water in the system.

Atterberg defined the boundaries of the four states of soils in terms in limits

  • Liquid limit: The boundary between liquid and plastic states
  • Plastic Limit: The boundary between Plastic and Semi Solid States.
  • Shrinkage Limit: The boundary between semi solid and solid states.
In this article I am going to Discuss in detail about Liquid Limit. Further we will deal with Plastic limit and Shrinkage Limit.


  1. Once we know about Liquid Limit along with Plastic Limit it will be easy for us to classify fine grained cohesive soils according to Indian Standard of Soil Classification.

Once the soil is classified it helps us a lot 
  • Understanding soil behaviour
  • Selecting suitable methods for construction
  • It also Helps us to Maintain the structures
2. With the help of Liquid Limit and Plastic Limit We can caluclate the flow index,toughness index and relatively plasticity index which will be useful for us to understand about soil's Plasticity,cohesiveness,compressibility,shear strength,Permeability etc.,

3. By knowing Liquid Limit and Plastic Limit we can determine Plasticty index using Plasticity chart.

Let's not go so deep about Plasticity chart as it may divert us from pile to well.

Apparatus :

  • Casagrande Apparatus
  • Grooving tool
  • 425 Micron Sieve
  • Rod of Diameter 3mm
  • Drying Oven
  • Balance with Sensitivity 0.01 mm
  • Spatula and Basin
  • Water Content Containers
  • Glass Plate

Fig: Liquid Limit Casagrande's Appartus

Fig: Details of Casagrande's Appartus and Tools

Test Procedure :

  1. Before Starting the Experiment we have to adjust the cup of liquid limit apparatus with the help of grooving tool gauge and the adjustment plate. The cup must be adjusted so that plate have to give a drop of 1 cm on the point of the contact on the base.
  2. Take about 120 gm of an oven dried sample passing through 425 micron sieve.
  3. Now we have to add distilled water to the sample and mix it thoroughly so that it forms a uniform paste.
  4. Now place a portion of the paste prepared from above step into the cup of Casagrande's apparatus,Now smooth the surface with the help of spatula to a depth of 1 cm.
  5. Now with the help of Grooving tool,holding it perpendicular to the cup make a groove through the sample.
  6. Now we have to work with handle. Turn the handle at the rate of 2 revolutions per second and count blows. This part of the experiment continues till the soil sample come into contact at the bottom of the groove along a distance of 10 mm.
  7. Transferring of 15 gm of the soil forming the edges of the groove that flowed together to a water content container and determine the water content by oven drying.
  8. Transfer the remaining soil in the cup to the main soil sample in the basin and mix thoroughly after adding a small amount of water.
  9. Repeat the steps 4,5,6 and 7 . It is advisable to obtain at least four sets of reading in the range of 10 to 40 blows.
  10. Draw the flow curve between Number of blows (log N) and Water Content where N=Number of blows generally 25 blows are considered to calculate Liquid Limit
It is found convenient to start with soil drier than the liquid limit and obtain values by increasing the water content.

Table: Liquid Limit Determination
Deremination No
1.Number of Blows
Container No.
2.Mass of Container + Wet Soil, gm
3.Mass of container + Dry Soil , gm
4.Mass of Container
6.Mass of Dry Soil , (4-5)
Mass of Water, (3-4)
Moisture Container,w- (7/6)%
Draw a Graph taking Log N on X-axis and Water Content on Y-asxis to determine Liquid Limit of Soil

Fig: Liquid Limit Flow Curve

Thus We Got the Liquid Limit from the Graph


  • Use Distilled water in order to minimize the possibility of ion exchange between the soil and any impurities in the water
  • Soil used for test must not be over dried
  • No slippage of Grooving tool while making groove
  • As test is repeated,for each test cup and grooving tool should be clean
Hope You got to know now How to Determine Liquid Limit.if You have any queries Comment below and I will be glad to share knowledge with you.

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