R403.1.8 Foundations on Expansive Soils
Exception: Slab-on-ground and other foundation systems that have performed adequately in soil conditions similar to those encountered at the building site are permitted subject to the approval of the building official.
Soils meeting all of the following provisions shall be considered to be expansive, except that tests to show compliance with Items 1, 2 and 3 shall not be required if the test prescribed in Item 4 is conducted:
- Plasticity Index (PI) of 15 or greater, determined in accordance with ASTM D4318.
- More than 10 percent of the soil particles pass a No. 200 sieve (75 μm), determined in accordance with ASTM D422.
- More than 10 percent of the soil particles are less than 5 micrometers in size, determined in accordance with ASTM D422.
- Expansion Index greater than 20, determined in accordance with ASTM D4829.