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Code Update: Significant Code Changes

Excerpted from the Significant Changes to the 2006 International Codes series.

The Significant Changes to the 2006 International Codes series has been developed by the International Code Council and published by Thomson-Delmar Learning to accommodate the transition from the 2003 to the 2006 editions of the International Codes. To purchase books in the series, visit the Code Council website.

International Residential Code

SUBJECT:Compressive or Shifting Soil
CHANGE TYPE: Modification

~~R401.5~~ R401.4.2 Compressible or shifting soil. Instead of a complete geotechnical evaluation, Wwhen top or subsoils are compressible or shifting, such soils shall be removed to a depth and width sufficient to assue stable moisture content in each active zone and shall not be used as fill or stabilized within each active zone by chemical, dewatering or presaturation.

CHANGE SIGNIFICANCE: Within the format of the 2003 International Residential Code (IRC), the requirements for compressible or shifting soils are found in Section 401.5, which is a distinct and separate section from that of soil tests, found in Section R401.4. By application of 2003 IRC Section R401.4, the building official must determine whether to require a soil test “in areas likely to have expansive, compressible shifting or other unknown soil characteristics.” These two separate and distinct requirements created a situation where the geotechnical investigation and the soils report could provide analysis and recommendations for compressible and shifting soils that possibly could not be used because Section R401.5 required the removal of such soils regardless of the geotechnical report recommendations.

The 2006 IRC resolves this problem by relocating the criteria for compressible and shifting soils as a subsection of the soil tests section. The revision further clarifies that the removal of compressible or shifting soils is mandated only when there is no geotechnical evaluation. When there is a geotechnical evaluation, the resulting recommendations are to be used. Further reasons for this revision are that many soil investigation reports classify bearing soils as compressible and that design procedures exist for designing foundations on compressible soils (e.g., Post-Tensioning Institute Design of Post-Tensioned Slabs-on-Ground). Thus, it is not necessary for all compressible soils to be removed; rather, the geotechnical engineer must decide the best course of action.