Reconstituted clay Triaxial testing

[jojo200]

I am trying to perform CD Triaxial tests on Kaolin clay. I assume the clay powder is to be mixed with water more than the liquid limit and sand can be added to make the saturation process faster. Can any one provide any information about the procedure to prepare an intact cylinder from a the clay slurry?

 

[EireChch]

I worked with Kaolin clay for some lab testing. I mixed the powder to 1.5 times its liquid limit. The material, as you can expect, was like water. I dont think you will be able to perform a triaxial test on it it that state.

I think you will need to consolidate the mixture in a mould using a consolidation plate with drainage at top and bottom.

 

[fattdad]

I guess it depends on the end game. Firstly, is there some reason to use triaxial shear testing? In Drained direct shear testing, you have a better option to place the sample at its liquid limit into the shear box and apply a normal load to consolidate and shear.

In the triaxial cell, it's more likely that you'd have to place the LL sample into a static load machine to get the target density, then extrude to a triaxial cell.

I guess your end game is fully-softened strength and/or residual strength? In that regard, I'd just go to the DDS.

f-d

ípapß gordo ainÆt no madre flaca!

 

[jojo200]

@FireChch : Did you have to mix it with sand to speed up the consolidation ?
@fattdad : I am looking at the effects of temperature on the pore pressure and volumetric changes so I need to perform CD tests on Kaolin and maybe with some sand to make the consolidation faster.

 

[EireChch]

Jojo200 - No didnt mix it with sand to speed up the process. The purpose of my use of Kaolin was to create a homogenious clay bed to use in the physical modelling of stone columns. This was mixing to 1.5LL then consolidating it using a consolidation plate. Consolidation load started at 20kPa and maintained for 24hours, then increased by 20kPa and maintained for another 24hours. This process was repeated up until 120kPa. Drainage pipes on both top and bottom and filter paper used to ensure only water escapes. This resulted in Kaolin clay bed with a undrained shear strength of 10-20kPa. I reviewed a lot of literature regarding this and never seen anyone using sand to speed it up. Thats not to say that its not possible. The literature i reviewed specially needed a pure clay so hence they may not have considered sand.

 

[LRJ]

Rowe cells are often used for testing of reconstituted clays. They can be quite hard to come by, however.

If you have to start above the liquid limit for some reason then you'll need to do your sample preparation in a mould mounted on the triaxial apparatus, as EireChch suggests, because the slurry would be too fragile to transport.

The shearing stage of a CID on clay needs to be slow enough to ensure excess pore-water pressures don't develop. Adding sand will help the excess pore-water pressure dissipate more quickly, so you can shear the sample more quickly. It is this shearing stage of a clay CID which takes a long time; the consolidation stage is comparatively short. Also as EireChch suggests, two-way drainage will help speed things up a bit, though I wouldn't recommend doing it during the consolidation stage since you want to make sure your initial PWP reading at the start of shearing (i.e. end of consolidation) accurately reflects the PWP throughout the sample.

 

[jojo200]

@EireChch: Did you use a consolidometer and a mold the same size of your soil cylindrical sample and then you extrude it and wrap it by the membrane ?
@LRJ :I think also the saturation stage of the triaxial test will take a very long time

 

[LRJ]

Saturation for a reconstituted, normally consolidated clay should be relatively quick. Especially if you have some sand content.

 

[EireChch]

I didnt use a consolidometer. I think its too small for what you are intention. We literally used a perspex mould 200 x 200 x 500mm high. We mixed the slurry and filled it to 400mm height and then applied pressure through a plate connected to a pneumatic pump. After approx 5-7 days of applying pressure, the sample reduces in height to approx 200mm.

See my previous thread before where i was having problems with a steel mould.

http://www.eng-tips.com/viewthread.cfm?qid=426956