Methods of test for soils, Part 40: Determination of free swell index of soils
1977 Edition

IS 2720 Part 40 - Introduction & Key Equation

Scope: This segment of IS 2720 defines the method for measuring the free swell index of soil, which reflects the extent to which soil expands when submerged in water.

Fundamental Formula for Free Swell Index (FSI)

[ \text{FSI (%)} = \frac{V_w - V_k}{V_k} \times 100 ]

Where:

• ( V_w ) = Soil volume when immersed in distilled water (swollen volume)
• ( V_k ) = Soil volume in kerosene (baseline volume)

Note: Kerosene is employed as a non-polar liquid that does not cause swelling.

Equipment Details:

• Graduated cylinders are used for volume measurements.
• Separate cylinders filled with kerosene and distilled water are utilized.
• Volume readings are taken directly from the cylinders.

Summary Table

flowchart LR
  SoilSample --> MeasureVolume{Measure Volume}
  MeasureVolume -->|In Kerosene| V_k[Volume in Kerosene]
  MeasureVolume -->|In Distilled Water| V_w[Volume in Distilled Water]
  V_k & V_w --> Calculate[Compute Free Swell Index]
  Calculate --> Result[FSI = ((V_w - V_k)/V_k) * 100%]

Refer to IS 2720 Part 40 (1977) for comprehensive procedural details.

IS 2720 Part 40 (1977) — Essential Formula and Equipment Specifications for Free Swell Index

Free Swell Index Computation

The free swell index quantifies the relative increase in soil volume upon immersion in water compared to a non-swelling liquid like kerosene.

[ \boxed{\text{FSI (%)} = \frac{V_w - V_k}{V_k} \times 100} ]

• ( V_w ): Volume of soil in distilled water (swelled volume)
• ( V_k ): Volume of soil in kerosene (original volume)

Important Considerations:

• Kerosene is used as it does not induce swelling.
• Graduated cylinders must be accurately calibrated.
• This test is instrumental in evaluating the swelling potential of soils.

Reference Details:

• IS 2720 (Part XL) - 1977 specifies apparatus and test methods.
• Use graduated cylinders with precise volume graduations.

Summary Table

flowchart LR
  SoilSample --> PlaceInCylinder{Place in Graduated Cylinder}
  PlaceInCylinder --> KeroseneCylinder[Soil + Kerosene]
  PlaceInCylinder --> WaterCylinder[Soil + Distilled Water]
  KeroseneCylinder --> ReadV_k[Read Volume V_k]
  WaterCylinder --> ReadV_w[Read Volume V_w]
  ReadV_k & ReadV_w --> CalculateFSI[Calculate Free Swell Index]

For full apparatus specifications and test procedures, consult the original IS 2720 Part 40 (1977) documentation.

IS 2720 Part 40 — Details of Equipment and Core Formula

Equipment:

• Two glass graduated cylinders with a capacity of 100 ml each, conforming to IS: 878-1956.
• One cylinder filled with kerosene (a non-polar fluid preventing swelling).
• The other filled with distilled water.

Core Formula:

Calculate the Free Swell Index (FSI) using:

[ \text{FSI (%)} = \frac{V_w - V_k}{V_k} \times 100 ]

Where:

• ( V_w ) = Soil volume in distilled water (post-swelling)
• ( V_k ) = Soil volume in kerosene (initial volume)

Notes:

• Kerosene maintains the original soil volume as it does not cause swelling.
• Distilled water induces swelling, enabling measurement of expanded volume.

Equipment Summary Table:

This apparatus setup ensures precise assessment of soil swelling characteristics in line with IS 2720 Part 40 (1977).

IS 2720 Part 40 (1977) outlines guidelines for sampling and preparing soils for the free swell index test. Although the full text isn't included, the general procedure involves:

Sampling:

• Collect representative soil samples from various points to capture soil variability.
• Typical sample weights range from 2 to 5 kilograms depending on the test.
• Ensure tools and containers are clean to prevent contamination.

Sample Preparation:

• Air-dry the soil by spreading it thinly at ambient temperature.
• Pass the dried soil through a 4.75 mm sieve to remove coarse fragments.
• Gently crush lumps to maintain particle size but ensure uniformity.
• Thoroughly mix the soil to achieve homogeneity before testing.

Sample Preparation Summary Table:

flowchart LR
  SampleCollection[Collect Soil Sample] --> AirDry[Air Dry Sample]
  AirDry --> Sieving[Pass through 4.75 mm Sieve]
  Sieving --> Crushing[Crush Lumps if Necessary]
  Crushing --> Mixing[Thoroughly Mix Sample]
  Mixing --> Ready[Sample Ready for Testing]

This procedure guarantees reliable and reproducible test outcomes conforming to IS 2720 Part 40.

IS 2720 Part 40 (1977) — Procedure for Free Swell Index Determination

Overview:

This standard describes the laboratory test to evaluate the free swell index of soil samples.

Procedure Highlights:

• Use oven-dried soil passing a 425-micron sieve.
• Place the soil sample in graduated cylinders filled separately with distilled water and kerosene.
• Measure the initial soil volume ( V_0 ) and the volume after 24 hours immersion ( V_1 ).

Calculation Formula:

[ \text{FSI} = \frac{V_1 - V_0}{V_0} \times 100 ]

Where:

• ( V_0 ): Initial soil volume (ml)
• ( V_1 ): Soil volume after 24 hours immersion (ml)

Data Rounding:

• Final results should be rounded according to IS 2:1960 standards.

Interpretation Table:

flowchart TD
  PrepareSample[Prepare Soil Sample] --> PlaceInCylinder[Place in Cylinder with Liquid]
  PlaceInCylinder --> RecordInitial[Record Initial Volume V_0]
  RecordInitial --> Wait[Wait 24 Hours]
  Wait --> RecordFinal[Record Final Volume V_1]
  RecordFinal --> ComputeFSI[Calculate Free Swell Index]
  ComputeFSI --> Interpret[Interpret Swelling Potential]

This test aids in assessing soil expansiveness crucial for foundation design.

IS 2720 Part 40 — Method to Calculate Free Swell Index

The Free Swell Index (FSI) is computed as:

[ \text{FSI (%)} = \frac{V_w - V_k}{V_k} \times 100 ]

Where:

• ( V_w ): Soil volume after immersion in distilled water (swollen volume)
• ( V_k ): Soil volume in kerosene (initial volume)

Notes:

• Kerosene, being non-polar, prevents swelling and represents the original soil volume.
• Distilled water induces swelling, indicating the expanded volume.
• Measurements must be taken with calibrated graduated cylinders as per IS 2720 Part 40.

Summary Table:

flowchart LR
  SoilSample --> Kerosene[Place in Kerosene]
  SoilSample --> Water[Place in Distilled Water]
  Kerosene --> MeasureV_k[Measure Volume V_k]
  Water --> MeasureV_w[Measure Volume V_w]
  MeasureV_k & MeasureV_w --> CalculateFSI[Calculate Free Swell Index]
  CalculateFSI --> Result[FSI = ((V_w - V_k)/V_k) * 100]

This calculation helps evaluate soil swelling characteristics vital for foundation and earthwork designs.

IS 2720 Part 40 (1977) — Reporting Guidelines for Free Swell Index

Free Swell Index Formula (Clause 4.1)

[ \text{FSI (%)} = \frac{V_w - V_k}{V_k} \times 100 ]

• ( V_w ): Soil volume in distilled water (swollen volume)
• ( V_k ): Soil volume in kerosene (original volume)

Note: Kerosene is selected due to its non-swelling nature (non-polar liquid).

Specifications:

• Volume measurements must be done using graduated cylinders.
• Readings are taken directly from the apparatus.
• Results should be rounded following IS 2:1960 guidelines.

Result Reporting:

• Document the Free Swell Index as a percentage.
• Specify the test procedure used and any rounding applied.

Summary Table:

flowchart LR
  SoilSample --> KeroseneCylinder[Place in Kerosene]
  SoilSample --> WaterCylinder[Place in Distilled Water]
  KeroseneCylinder --> ReadV_k[Read Volume V_k]
  WaterCylinder --> ReadV_w[Read Volume V_w]
  ReadV_k & ReadV_w --> CalculateFSI[Calculate Free Swell Index]
  CalculateFSI --> Report[Report Result]

Refer to IS 2720 (Part 40) - 1977 for detailed procedures and equipment specifications.

IS 2720 Part 40 — Essential Notes and Precautions

Core Formula:

The Free Swell Index (FSI) is determined by:

[ \text{FSI (%)} = \frac{V_w - V_k}{V_k} \times 100 ]

Where:

• ( V_w ): Soil volume in distilled water (swollen volume)
• ( V_k ): Soil volume in kerosene (original volume)

Vital Notes:

• Kerosene is chosen as a non-polar liquid to prevent swelling, reflecting the original volume.
• Distilled water induces swelling; thus, volume measurements here represent swollen soil.
• Graduated cylinders must be calibrated and compatible with kerosene and distilled water as per IS 2720 Part XL - 1977.
• Round off results conforming to IS 2-1960 standards.
• This test is crucial in assessing soil expansiveness for foundation engineering.

Precautions:

• Avoid air bubbles in the soil sample during measurement.
• Use clean, properly calibrated graduated cylinders.
• Take volume readings at the bottom of the meniscus.
• Conduct tests at stable temperatures to avoid volume fluctuations.

flowchart LR
  SoilSample --> KeroseneCylinder[Place in Kerosene]
  KeroseneCylinder --> ReadV_k[Read Volume V_k]
  SoilSample --> WaterCylinder[Place in Distilled Water]
  WaterCylinder --> ReadV_w[Read Volume V_w]
  ReadV_k & ReadV_w --> Calculate[Compute FSI]

This ensures precise and reliable free swell index determination as defined in IS 2720 Part 40.