Calculate soil expansion-index arithmetic from laboratory height measurements, or separately calculate fractional volume change and constant-coefficient thermal expansion.

Use measurements from the standardized confined wetting test.

Soil EI is a qualitative laboratory swelling indicator, not a field-heave prediction. Thermal results assume a constant coefficient over the temperature range; ฮณ โ‰ˆ 3ฮฑ applies to isotropic solids.

Related Calculators

Expansion Index Formula

Soil-test expansion index uses EI = 1000 ร— (Hf โˆ’ Hi) / Hi, with initial and final specimen heights measured under the standardized wetting-test conditions. The separate general-volume mode uses the fractional change below.

e = (Vf - Vi) / Vi

Variables:

  • e is the fractional volume change, separate from laboratory soil EI
  • Vf is the final volume (mยณ)
  • Vi is the initial volume (mยณ)

For general fractional volume change, subtract initial volume from final volume and divide by the positive initial volume. Percent change is 100e and the volume ratio is 1 + e. For soil EI, use standardized specimen-height measurements instead; arbitrary volume changes do not establish an ASTM D4829 result.

What is an Expansion Index?

Soil expansion index indicates the qualitative swelling potential of a compacted specimen under standardized laboratory preparation, confinement and wetting. It does not predict actual field heave or establish site-specific structural safety. Reference bands are 0โ€“20 very low, 21โ€“50 low, 51โ€“90 medium, 91โ€“130 high and above 130 very high; use the laboratory reported EI for formal classification. General fractional volume change has a different meaning and scale.

How to Calculate Expansion Index?

The following steps demonstrate general fractional volume change. Thermal mode separately uses V = Vโ‚€(1 + ฮณฮ”T), assuming a constant coefficient and small expansion; ฮณ โ‰ˆ 3ฮฑ is an isotropic-solid approximation.

  1. First, determine the final volume (Vf) in cubic meters (mยณ).
  2. Next, determine the initial volume (Vi) in cubic meters (mยณ).
  3. Next, gather the formula from above: e = (Vf - Vi) / Vi.
  4. Finally, calculate the fractional volume change e.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

final volume (Vf) = 50 mยณ

initial volume (Vi) = 30 mยณ. In general-volume mode, e = (50 โˆ’ 30) / 30 = 0.666667, or 66.6667% volume increase. This is not a laboratory soil EI.