Saturation of Clay in Triaxial

[ekincia]

hi everyone
I am working on a phd project where we \re using Lambeth group clay (LL 60% PL 26% OMC 19% particle density 2.7)I have collected disturbed samples from site and remolded them into 100mm dia 200mm length mould applying specific compaction effort. I am trying to saturate the sample in triaxial equipment aplaying 50kpa cell and 30 kpa back presure. I have been waiting for few days and there is no hope. Anyone has any saggestions for making saturation process faster or possible .Concern is that during compaction samples from the site chopped into 10 to 15mm small pads and brought to OMC inorder to simulate site condition. I think this is causing some discontinuitys within the sample and not allow full saturation. Any comments, new ideas can help.
Thankyou

 

[fattdad]

Is the end game strength of permeability?

I'd recommend that you take the bulk sample and prepare it at 90 percent saturation to the relative compaction you are interested in (this will likely be a point on the wet side of the standard Proctor curve). I'd add the water, seal the sample in a bag and let it sit for 24 hours (i.e., moisture condition the sample).

I'd compact the sample, trim it and put it into the triaxial cell.

I'd expect you'd need somewhere around 70 to 90 psi of back pressure to get all the air into solution (480 to 620 kPa). So, you're nowhere close to what you'll need.

f-d

¡papá gordo ain’t no madre flaca!

 

[GeoPaveTraffic]

I agree with fattdad.

 

[ekincia]

Aim is to Characterise and understand the behaviour of compacted clay pads.
Drained and undrained laboratory element tests will be performed on saturated samples to characterise the behaviour(Critical state soil mechanics).
We will test laboratory compacted and insitu compacted (obtained by block sampling method (undisturbed)samples. Therefore they should carry same properties. If I increase the moisture content and compact the sample the formation will not be similar to the insitu sample.

 

[ekincia]

Image of sample compacted at its optimum moisture content. So you can see that there is empty gaps within the soil.

 

[fattdad]

Just a note: As a researcher, the strength of clay depends not only on the degree of compaction but also on the compaction moisture content. When you say, "compacted at its optimum moisture content," I'm not "really" sure what you are talking about. There is an optimum moisture content to acheive 100 percent relative compaction and there is an optimum moisture content to acheive 95 percent relative compaction. These are not the same. Moisture density relations have a "line of optimums," which parallel the zero air-voids curve.

You should include research into the behavoir of compaction clays as strength corelations that don't account for compaction moisture content would be remiss.

f-d

¡papá gordo ain’t no madre flaca!

 

[ekincia]

I will try to explain the compaction procedure I am following

Soils that was extracted from the site and sealed in plastic bags was chopped in to small pieces from 10mm to 15mm.

This was done because in-situ ped size will be too large to avoid scale effects within the triaxial apparatus.

From same bag another compaction test was carried out to obtain Optimum moisture content and Maximum dry density
(Please See attached Image for Compaction curve. please avoide the teriminology such as classic compaction and 24ht compaction they are for my use compaction curve is red one)

Once the optimum moisture content was obtained the soil in the barrel should either let to dry or moisture should be added to achieve optimum moisture content

To achieve the desired moisture content, distilled water was sprayed at intervals onto the soil over a period of several hours

This will enable the water to penetrate the granules and achieve equilibrium

Clay was moistened to 1-2% wet of their respective optimum values and sealed back into the barrel and stored in a controlled humidity room for several days

100 x 200mm compaction mould was used with specific compaction effort to prepare sample ( 5 layers 25 blows) BS 1377-4:1990

Immediately after the compaction, compacted samples were placed in highly sealed begs and stored for Triaxial tests

Then saturation problem as I mentioned above.

 

[ekincia]

fattdad I would like to thank you for your contributions.

 

[Erdbau]

Fattdad is right, your backpressure is not high enough. When you recompact a specimen, you will inevitably trap air in the soil. Compact the soil at your target moisture content, put in the cell, increase the cell and back pressure periodically until the specimen is saturated. This may take a while, but if you get the pressures up high enough, you will push the air into solution. I've gone as high as 115 psi cell and 110 psi back on some frustrating soils.

You can also try presaturating under vacuum. When the sample is in the membrane, apply a vacuum to the sample. Then run water through the sample using elevation head (<3 feet) to drive the water though.

The key is patience and high pressure.

 

[ekincia]

For better understanding I am uploading the set-up image. And readings. There was a variation in readings from 6pm last night to 10 am this morning. (There is no temperature control where the equipment is and last night oven was working. Tech told me that air-conditioning goes of at night. Therefore if you look at the first graph you can see that after 1130 pm volume starts to decrease) However if you look at the second graph which is since this morning volume gauge is showing very slow increase.
Any idea on what was the cause of decrease last night and what do you think will this specimen saturate with current set-up?

 

[ekincia]

Set Up

 

[ekincia]

Fig-1 Readings from last night

 

[Erdbau]

Is the drain line draining into the flask at the top? It looks like it is open to atmosphere. On another note, the 0.15 cc or so is not that much water for that size specimen. Is that the total amount of water that has gone into the sample?

 

[ekincia]

Fig-1 Readings from last night

http://files.engineering.com/getfile.aspx?folder=8877ab8a-381a-4a53-b339-b1

Please ignore this attachment its wrong figure.

Yes drain line is draining to the flask which is open to the atmosphere. Yes thats the total amount of water gone into the sample in 24 hours. Seems to me that it will take ages to saturate.

 

[Erdbau]

If the drain line is open to atmosphere, you are pushing water straight through the sample, but you will not be able to raise the back pressure (the water will just flow through the sample faster). You will need to close the drain line to increase the backpressure (and cell pressure at the same time).