I did the geotechnical work for many industrial slabs on grade. I’ve also served as an expert witness on failed slabs. Usually, the earthwork testing was out of control (i.e., wrong proctor and inadequate compaction).To the best of my knowledge, they all performed just fine. Here was my basic approach:
- Field exploration
- Lab work (classification, percent sand, Proctors and CBRs).
- Determine if there were any soils that just weren’t any good for earthwork. If all that existed happened to be fat clay, then I had little choice but to expect cut to fill with fat clay. I’d certainly have natural moisture contents, classification, proctor and CBR data on that material though.
- Correlate CBR to subgrade modulus. Use the ACI “bump” factor on subgrade modulus depending on the thickness of the subbase (we always recommended dense-graded aggregate for industrial floor slabs rather than open-graded aggregate).
- Tell the owner if natural moisture content would be a problem during earthwork (i.e., too wet or too dry).
- Anticipate soil modification (e.g., lime) if that would be a cost-effective way to address soil properties or natural moisture content issue).
- Use settlement plates if the thickest fills were much more than 10 ft or so.
- Be involved during the construction phase of the project.
I hope these tips help you in your work.