Regarding soil classification 2

[Nayan67]

Hello all,
I need to conduct a lateral load analysis of the drilled shaft, and for that, I must classify soil as either clay or sand. According to the geotechnical report, there are few soil layers which are desginated as GC and SC based on Unified soil classification system. I am unsure whether I should categorize this soil as clay or sand.

Your comments would be greatly appreciated.

Thank you.

 

[dik]

I'm not a geotechnical, but I've generally treated the soil based on the percentage of clay. If the clay content is greater than about 15%, I treat it as a clay. I don't have a reference for this. It's better that a geotechnical fellow will comment. I don't know what the lower limit is; I've just used 15% based on info from an earlier engineer.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Nayan67]

Thank you dik for your input.
I will wait geotechnical fellow for their comments.

 

[GeoEnvGuy]

I would expect clay behaviour if the soil was classified as a SC or GC, that means that the fine grained fraction dominates the sample and it had plasticity which plots above the A-line.

 

[Nayan67]

Thank you GeoEnvGuy for your response.

 

[dik]

Do you know of an approximate percent of clay that causes the matrix to behave like a clay. I've arbitrarily used 15%... is this a realistic number or should it be lower or higher?

Thanks, Dik

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[EireChch]

Dik in the UK we use 15% as when the material will perform like a cohesive material during compaction. anything above 15% fines is classed as a Class 2 fill, either dry or wet depending on its moisture content relative to OMC.

For engineering performance, i.e. will it have an undrained shear strength, will it consolidate, about 30-35% is more appropriate. Not this applies to run of the mill Clay minerals. If you get 15% of a highly sensitive, highly plastic Montmorillinite then the % of this material that makes the entire unit perform as a cohesive material will be lower. See extract below of BS5930 which is the British Standard for soil classification.

 

[GeoEnvGuy]

Do you know of an approximate percent of clay that causes the matrix to behave like a clay. I've arbitrarily used 15%... is this a realistic number or should it be lower or higher?

I don't believe there is a minimum clay fraction (below 0.002) that determines the behaviour. This depends on the clay minerology, I just look at if the atterberg test plots above the A line. For example if you mix wyoming bentonite (a super plastic clay) with pure silt you won't need much to get clay behaviour.

 

[MTNClimber]

Nayan - While everyone sharing their experience in this thread is nice, talk to the project's geotechnical engineer. The GC/SC soils in your area may act differently than the GC/SC soils in the areas of those who reply in this thread.

 

[dik]

Thanks...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[MTNClimber]

No offense dik. Just pointing out why there are geotechnical engineers on projects. It’s their job to help out the design team with questions like this.

 

[dik]

...don't have to convince me. It may be my lack of experience with geotechnical, but I think their work can be far more difficult than mine... and I often deal with 'tricky' stuff.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Nayan67]

Thanks everyone for the input.

 

[dik]

I still remember the cartoon on the company bulletinboard from over 40 years back. A contractor is holding up an elevation sketch of the Tower of Pisa with the caption, "...and we can save another 700 lira if we don't get a soils test."

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[emmgjld]

Dik
Engineers Testing Laboratories, Phoenix, Ar. 19

60

 

[dik]

Great... thanks very much... My recollection of the 'toon' was pretty good after all these years. I even had the right amount. Ihave now got it on file. again thanks...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[emmgjld]

and another, for your pleasure