How to determine if soil is expansive? 1

Hire a soils engineer.

1) Limits/values- no clue. In our area (southern US), the geotechnical engineer will normally calculate a standardized quantity, "potential vertical rise" and if that's less than 1", then it's usually a non-issue for tank foundations. I assume other kinds of construction might vary, and that same geotechnical engineer should have a pretty good idea of what to use for different cases.
2) In our work, it's usually a matter of overexcavating and backfilling with non-expansive material. In some cases, lime-injection. If things are bad enough, drilled piers.
3) Common practice is that those bore logs don't just get plopped on the paper, the company that does the bore log also has a geotechnical engineer evaluating that log and making recommendations based on what they found. If for some reason, you're only furnished the log, you may need to hire a geotechnical engineer for additional work. If a geotechnical report was furnished for some type of work, and you're doing something different, you may need additional recommendations. If the log is "old", you may need updated info.

Occasionally, I see only the logs furnished for contractor's use, where the only question is "Will I hit rock", but those logs are not intended for design use.

We do have a soil consultant who has prepared the attached bore log (soil report) based on testing. But this report doesn't say anything about expansiveness of soil, I am concerned since it is clay. Before going to the soil engineer I wanted to do my homework. From UBC-97 I found the criteria that expansion index should be greater than 20 for a soil to be expansive. but this report doesn't give any such value. I was worried if I could figure it out using some other values.


Thank you very much

On the soils reports that I see, if expansive soils are an issue, they will automatically bring that up as a major issue and address what to do about it. If it's not an issue, they'll normally mention that also. Anyway, just run that question by the geotech.
I assume you're not in the US, and I don't know what the practice is elsewhere.

I have never experienced expansive soils before so don't have any idea about how do they mention it in report. I am not in US. Thank you very much for you valuable time.

The value PI listed under the Atterberg Limits is the plasticity index. It can be related to the expansive quality of the clay.

Did they determine the liquid limit or plasticity index?

Yes, have a look at the attached bore log. It is the same soil I am concerned about.

The plasticity index (PI) is the difference between the liquid limit and the plastic limit (PI = LL-PL).
Soils with a high PI tend to be clay, those with a lower PI tend to be silt, and those with a PI of 0 (non-plastic) tend to have little or no silt or clay.

Some years ago a south Texas geotech taught me another "rough" (very rough) test for expansiveness of clays. He said to get some wet samples of the clay and form small cubes (1" x 1" x 1") out of them. Then set them out to dry for a day or two. Once dry, take a cube between forefinger and thumb and try to crush the cube.
If you have trouble crushing it - or can't crush it at all, then it is most likely an expansive clay.
If it crushes fairly easily then not.

Oops, should have looked at the attachment. The upper zone is a CL clay. I would not be too concerned, but you should reach out to the geotech on the telephone to have a quick chat if any measures are needed.

The boring log shows one sample with a PI of about 10, which is not considered very high; not a red flag for being expansive.
And per IBC definition, it's not expansive since PI<15.

Thank you very much everyone. You people have been of great help like always. It really means a lot. Keep helping young engineers.