Over 100% saturation for clays

[Cristina Cavero]

Dear all,

I would like your comments about clays with over 100% saturation calculations. What could be the reason for this escenario?, if the specific gravity has been determinated, water content and dry density. What could be wrong for this. The results from the measurements have been double checked. This sample does not contain salts.

Please if you had experienced something similar o do you have some explanations about it, I will appreciate you answer.
Best regards,

Cristina

 

[Ron]

I'm not sure what you are asking. While the moisture content of soil can exceed 100%, the degree of saturation ranges from 0 to 100%. Is your moisture content greater than 100%? If so, it is not uncommon for clayey soils to have a moisture content that exceeds 100%.

 

[oldestguy]

Ron: I think the volume calculations of water and soil together exceed the measured volume of the saturated sample. Could be some determination is in error, such as the specific gravity number.

 

[Ron]

OG...if that's the case, I agree....probably an error in specific gravity. Sometimes better to guess the specific gravity than try to measure it!

Christina....what was the specific gravity of the material and what type of material is it?

 

[dik]

Can it be a bentonite type of material? Can pick up 10 times its weight in water... and swell by more?

Dik

 

[fattdad]

the short answer is, "No!" Reported values over 100% are therefore in error. Maybe precision error? Maybe calculation error? Doesn't matter, it's wrong.

f-d

ípapß gordo ainÆt no madre flaca!

 

[Cristina Cavero]

Hi,

Thanks for your comments, these are the values that we had from the specimen.

Initial mass: 1019.8g
Dry mass: 825.48g
MC:29.33%
Gs:2.6

I know that a saturation result more than 100% can not be, but I am trying to understand and find the error, and maybe could be the measure content, because it seems very high, but these values were measured and double checked.

All the 3 specimens have the same result in water saturation.

Another additional information is that while the triaxial was performed for these specimens, the parameter B started with 0.74 -0.8

Thanks for your replies,
Cristina

 

[fattdad]

Hi Cristina,

For the data you provide, what was the volume?

For the triaxial you cite, I'd reject the findings. B value at the start of the test should be at least 0.95! So, how do you interpret the pore pressures when the sample didn't start out saturated?

f-d

ípapß gordo ainÆt no madre flaca!

 

[Ron]

f-d...you beat me to it!

 

[BigH]

This is always an issue especially in compaction control. ALWAYS check your field compaction point against the Zero Air Voids line. I know of a reputable firm that was sued and this was a topic. It might have had any real effect on whatever the suit was about - but it was an error that, of course, is brought into the discussion.

 

[Cristina Cavero]

Hi all,
Thanks for your answers!

When i mean that the B parameter was 0.75, it means that we started to saturate and we had 0.74 for one specimen and 0.8 for other specimen, but we increased the pressures and we got 0.97 for B parameter.

So it strange that initial saturation is so high, and also with wrong values (more than 100%).

The sample is SC and IP=11

Specimen volume:532.7cm3

Thanks for your feedback,
Cheers,
Cristina

 

[Ron]

Your saturation is 90% based on the info you provided.
Your void ratio is 0.67

The volume of soil is 825.48/2.6 = 317.49 cm³
The volume of water is 1019.8-825.48 = 194.32 cm³

Your void volume is 532.7 - 317.49 = 215.21 cm³

Therefore your saturation percentage is 194.32/215.21 = 0.90 = 90%

 

[Cristina Cavero]

Hi,

Thanks for your reply, but i need to clarify: Gs is the specific gravity=2.6 and the Total volume of the specimen is 532.7cm3

Regards,

Cristina

 

[Ron]

Yes. That is what I used for the calculation.

Google "weight-volume relationship"....you should find numerous references. This is basic geotechnical stuff. Almost all geotechnical texts cover it.

 

[Cristina Cavero]

Oh thanks Ron, but i had a my mistake when i wrote it here. the intial specimen weight for this specimen is 1067.6g with all the values i said before.. dry mass:825.48g, Gs:2.6 and total volume:532.70cm3.

And with this initial weight, i do the calculation: saturation percentage is 242.12/215.21 = wrong result.


Thanks

 

[Ron]

You have a bust somewhere in your measurements. In order for you to achieve 100 percent saturation with the weights and volume you have shown, the specific gravity of the soil would have to be 2.84. While some clays have specific gravities of 2.7 to 2.75, the 2.84 value is out of common range unless there is a chemical constituent in the clay that is causing this. Is there a chance that there is magnesium hydroxide or similar in the clay? That would run the specific gravity up.

Otherwise, you have one of your measured values off. What is the diameter of your triaxial specimen?

 

[LRJ]

Your particle density (specific gravity) seems a little low to me for clays. Or, rather, lower than what I'm used to seeing: I'd expect something in the range 2.7-2.75 instead. If particle density increased then you'd be closer to a sensible answer.

Your water content measurement could also be off by a little - these can vary even locally. As could your measurement of specimen mass if the scales were out a little (e.g. you need to make sure the scale are level).

In essence, there are a lot of little things which can come together to create strange results like this. I think it's safe to assume you have a fully-saturated specimen. I'd just cap your results at 100% in these instances.