Field and Laboratory Tests on "GC"

[cmorgh]

Comments on the most suitable and practical tests (both field and laboratory) to investigate the mechanical properties of clayey gravels is appreciated.
It is usually very hard to trim the samples for triaxial (if suitable shellby or corebarrel sample could be collected),for many cases also the trx tests have not shown suitable results due to the existance of carse-grained gravel,....
The main purpose of the question is the consolidation settlement of the layer.
I do not mean the large scale insitu direct shear test or the long term large scale plate bearing test ( say, on RC pads).

Regards
cmorgh

 

[davecooper]

cmorgh:

Gravel always complicates things in the lab. What we do is run a gradation to find out how big and how much of the big stuff we have. We then batch the sample and remold. What I mean by batching is to fabricate the sample to the exact gradation of the as received material. If we run 6" diameter samples we will batch each two inch lift. We fabricate each lift to the exact gradation needed, add the exact amount of water needed and put it in a bag to cure. We put together 6 bags then remold the sample in two inch lifts. Some labs would use smaller lifts but remember we are working with a 12" tall sample that is going to weigh about 30 pounds. Gravel doesn't really have a structure so I think remolding a large sample to the same gradation and M&D is OK. We get very good results with the large scale samples. As far as consolidation you could run Ko on a triaxial size sample and the gravel would not affect the results nearly as much as a typical 1x3" sample in an incremental or CRS consol. When ever we get a request for a direct shear test and it turns out to be a gravel everything stops and the client is called and it always turns out to be an expensive and time consuming testing program. Another approach is to scalp on the #4 sieve and test the matrix. It is a very conservative approach and saves allot of time and money. It is not the preferred method.

Good Luck,

Dirtdoc1

 

[davecooper]

cmorgh:

I forgot to mention that there are 6" diameter shelby or pither tubes if you have to have undisturbed samples. We have those come in the door but usually just on litigation testing jobs with lawyers from both sides watching every move we make. I finally figured out how to get rid of them. Charge $100 per hour per person and they run for the hills.

Best Regards,

Dirtdoc1

 

[Focht3]

Give us some specifics on the samples: in situ UDW, percent gravel by weight, PL, WC, LL, G_S of the clay.

 

[cmorgh]

Dear dirtdoc1,
Thank you very much for your comments. Remoulding samples for investigating such a texture is also performed by me, but the point is that not very suitable answers are usually got, i.e. rather scattered ones which are not always due to the remoulding process.
Let me know please, the way you usually judge about the suitability of the results, being compared with the actual undisturbed characteristics of such a soil, being located underground?
However I myself (and usually) have to use this method, aswell.
Thank you again for your care
Regards (and apologize for delay- Busy with site work)
cmorgh

 

[cmorgh]

Dear Focht 3,
I will send the parameters requested, as soon as possible. I hereby apologize for delay.

Regards
cmorgh

 

[davecooper]

cmorgh:

Remolding samples are never the best or representative approach. If you are working with granular materials that don't really have a structure then remolding to the same moisture and density may be usefull. You have to be sure to make the diameter of your remolded sample at least 6 times the largest particle size. You will need to run a gradation and fabricate your sample to that same gradation. If there is a structure to the material then undisturbed samples are your best bet. I'm sorry but I can't give you any more than that.

Best Regards,

Dirtdoc1

 

[cmorgh]

Dear Dirtdoc1

Thank you very much for your valuable comments. You have been very helpful to me.

Regards
Cmorgh

 

[Focht3]

Dirtdoc1 is right on target rregarding the testing. But keep in mind that you may not be able to perform consolidation tests on gravelly clays that give you any meaningful results. You may be forced to use correlations oc C_C with the clay's liquid limit, then reduce the settlement estimate based on the volume occupied by the gravel. It's crude, but it may be your only viable option.

Two other possible options: hand carve "gravel free" samples for consolidation testing, then apply the "gravel correction." Or use SHANSEP to evaluate the clay fraction, then reduce settlement based on the gravel content.

Let us know what you decide to do -