Consolidation test on silt

[pelelo]

Hello experts,

I started running a consolidation test on a silt (MH).

It's qu = 400 kpa (8000 psf).

This sample is 40' deep. It's overburden pressure is approximately 190 kPa.

As per ASTM D2435, when running the consolidation test, you are supposed to start with small load increments (5 kpa, 10 kpa, etc), keeping a delta P/P = 1.

In my case, i started with 5 kpa increment load and noticed the dial indicator hasn't moved during the first 6 readings (0.25 mins, 0.5 mins, 1 min, 2 mins, etc).

Then I doubled up the applied load (10 kpa) and noticed the same behavior.

The question I have is:

Is this behavior due to such small load (5 kpa - 10 kpa compared to a qu = 400 kpa) or because it;s overburden pressure is way greater than the first load increments??

If this continues happening, I will continue increasing the load until some deformation behavior can be read. The problem is I don;t want to add such high load ad once that could damage the soil sample.

Please let me know,

Thanks in advance.

 

[BigH]

Well if you have Su of about 200 kPa, that is quite a stiff clay and I'd say that your overconsolidation ration would be in the order of 4 or so. So you have a long way to go to get to it . . . I know that you say you have a MH soil - what are the Atterberg limits?

 

[BigH]

Check this paper out - overconsolidated silt

http://www.deepseadrilling.org/93/volume/dsdp93_04.pdf

 

[pelelo]

Big H,

Thanks for your reply. This are the atterberg limits:

LL = 60%, PL = 20%, IP = 40%.


What do you think?

 

[fattdad]

I'm agreeing with BigH - very stiff silt! What's the natural moisture content?

f-d

¡papá gordo ain’t no madre flaca!

 

[pelelo]

thanks for your reply.

The moisture Content is 43%.

 

[geoman110]

I agree with BigH and fattdad. The moisture content is almost halfway between PL and LL. Considering this and the Su of 200 kPa, you are definitely dealing with overconsolidated soil. My estimate is OCR between 3.5 to 5.5; therefore, what BigH noted above is spot on. However, this all assumes that your sample was saturated (or close to saturation) when conducting the shear strength test. If the soil is not saturated, all of these discussions are not applicable. With the natural moisture content of 43%, I believe this sample is below groundwater table and therefore, saturated.

In respect to readings, you are not going to get much movement on the small loads, particularly in silt. I expect the Cr to be lower in silt than a clay with similar LL

 

[pelelo]

Guys,

Thanks for your imputs.

So far, I have added the 5th load increment (around 272 kpa), and yet I haven't experienced any deformation.

FYI,

I am using an arm ratio of 11:1. So far, I have added 8 kilograms. This consolidometer can support a max weight of 88 kgs. By keeping a delta P/P =1, probably I will be able to add 3 additional load increments. Other than that, I will try to run the test on a higher capacity consolidometer.