CSLB General Building (B)Site Work, Foundations and ConcreteMedium
A geotechnical report indicates that a soil sample from a building site has an Expansion Index (EI) of 75, determined using standard laboratory testing. According to typical classification tables used in California soils reports, this soil would be categorized as having:
- AHigh expansion potential
- BVery low expansion potential
- CLow expansion potential
- DMedium expansion potential
Show answer & explanationAnswer & explanation
Correct answer: D. Medium expansion potential
Standard Expansion Index classification tables categorize EI values of 0-20 as very low, 21-50 as low, 51-90 as medium, 91-130 as high, and above 130 as very high. An EI of 75 falls within the 51-90 range, placing the soil in the medium expansion category, which typically requires moderate mitigation measures for foundation design.
Why the other options are wrong
- A. High expansion corresponds to EI values of 91-130, above the given value.
- B. Very low expansion corresponds to an EI of 0-20, well below 75.
- C. Low expansion corresponds to an EI of 21-50, below the given value.
Expansion Index (EI) Classification
A standardized soil test result (ASTM D4829) used to classify soil expansion potential, ranging from very low to very high based on defined EI value ranges.
- 0-20 = very low, 21-50 = low, 51-90 = medium
- 91-130 = high, above 130 = very high
- Higher EI requires more foundation mitigation measures
Memory trick: '75 sits in the middle' — medium expansion soils fall between 51 and 90.