"Linear extensibility percent" is the linear expression of the volume difference of natural soil fabric at 1/3-bar or 1/10-bar water content and oven dryness. The volume change is reported as percent change for the whole soil.
Shrink-swell classes are based on the change in length of an unconfined clod as moisture content is decreased from a moist to a dry state. If this change is expressed as a percent, the value used is LEP, linear extensibility percent. If it is expressed as a fraction, the value used is COLE, coefficient of linear extensibility. The shrink-swell classes are defined as follows:
| Shrink-Swell Class | LEP | COLE |
|---|---|---|
| Low | <3 | <0.03 |
| Moderate | 3 - 6 | 0.03 - 0.06 |
| High | 6 - 9 | 0.06 - 0.09 |
| Very High | ≥9 | ≥0.09 |
If the shrink-swell potential is rated moderate to very high, shrinking and swelling can damage buildings, roads, and other structures. The high degree of shrinkage associated with high and very high shrink-swell potentials can damage plant roots.
Source: U.S. Department of Agriculture, Natural Resources Conservation Service. National soil survey handbook, title 430-VI. Available online. Accessed 9/13/2012.