GE 441 Advanced Engineering Geology & Geotechnics Spring 2004
VARIOUS ASPECTS OF EXPANSIVE SOILS
RELEVENT TO GEOENGINEERING PRACTICE
Simple Correlations Between Soil Plasticity and Expansion Potential
Soil Expansion Potential (ASTM D-4829)
This test was developed in Orange County, California in the mid-1960s and introduced in
the 1973 Uniform Building Code as UBC Test Standard 29-2. It was re-designated as
UBC Test Standard 18-1 in the 1994 code. This standard was adopted by ASTM in 1988.
Soil material is disaggregated and passed through the #4 sieve and then brought to
approximately the optimum moisture content (as determined by ASTM D-1557). The
optimum moisture content equates to approximately 80 to 85% of saturation. After
setting for 6 to 30 hours, the moisture-conditioned soil is compacted into a 4-in diameter
mold. The moisture content is then adjusted, if necessary, to bring the sample to 50%
saturation. A 144 psf surcharge is applied and the sample is wetted and monitored for 24
hours, measuring the volumetric swell. The Expansion Index is calculated as follows:
EI = 100 x ∆h x F
Where ∆h = percent swell and F = fraction passing No. 4 sieve
Section 1803.2 of the 1994 Uniform Building Code directs expansive soil tendency be
graded by this method. The UBC mandates that “special [foundation] design
consideration” be employed if the Expansion Index is 20, or greater (UBC Table 18-1-B).
UBC Table 18-1-C may be applied to gain a “weighted index”, allowing for a lessening
of expansion with increasing depth (confinement).
EI Expansion Potential
0 to 20 Very Low
21 to 50 Low
51 to 90 Medium
91 to 130 High
>130 Very High
According to ASTM, “The expansion index has been determined to have a greater range
and better sensitivity of expansion potential than other indices” (such as Atterberg limits).