U.S. Department of Transportation

Geotechnical Engineering Notebook: Geotechnical Differing Site Conditions (Geotechnical Guideline No.15) U.S. Department of Transportation

The 23 Federal Code of Regulations (CFR 635.109) contains policies, requirements, and procedures for standardized "changed conditions" clauses for Federal aid highway projects. In summary, unless prohibited by State law, Part 635 requires that a "differing site condition" clause shall be made part of and incorporated into each highway project approved under Title 23. This guideline provides information on geotechnical aspects of differing site conditions, adequate site investigation, disclosure and presentation of subsurface information by highway agencies, and the use of such information in mitigating or resolving contractor claims of differing site conditions. Recommendations are provided for disclosure of factual, qualified and interpretive geotechnical information. The uses of geotechnical design summary reports are described and a typical report outline provided in the appendices.