Sampling while performing field vanes

[grouterup]

Hello all:

I am planning a field exploration program in an area with v. soft - soft clay. I would like to do field vanes as well as take undisturbed tube samples. I do not have much experience with field vanes, and was wondering how people generally sequence vane tests and tube samples as they go down a borehole.

My current plan is to take split spoons until I am in the material of interest, then take vane - tube - vane. Is this an acceptable practice? Is there need for that many tube samples?

I am looking forward to any input that you could give.

Thanks!

John

 

[jdonville]

grouterup,

You do not want to disturb the soils that you will be sampling with the Shelby tubes - otherwise it's wasted effort.

For a recent project we specified (for example) SPT from 8.5-10, Shelby from 10-12, Vane from 12.5-13.5, SPT from 13.5-15,... over the area of interest.

This strategy provides opportunity to "preview" the su and sensitivity of the Shelby tube sample at the most "undisturbed" end prior to assigning specialty tests on the tube samples.

If the samples are very soft and silty, you may want to look at using a piston sampler, if you get no recovery in the Shelby tubes.

Hope this helps,

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

 

[BigH]

jdonville - I would second your intervals although each job would be slightly different. On my job here, we used 100 mm dia shelbys - so I took the shelby first, then put the split spoon (SPT) through the shelby hole - keeps having to "drill" out from 8.5 to 10 to get the tube. So - it would be tube from 8 to 10; SPT from 10 to 11.5 and then vane from 12 to 13.5 or so. Of course, one can argue that the SPT might be affected but as all say, SPTs in soft clays are for getting some sample not for design!

 

[eric1037]

It may be good to do a continous split-spoon (SPT) all the way down to get an idea of where the soft layers are located, then do another boring in close proximity with shelby tubes and vane shear.

This technique may save you a vane. I have seen them get destroyed by trying to test soil that was too stiff.

It will also give you an idea of what size vane to use. In very soft soils you may need a vane device with larger vanes.