I have done some Oedometer tests on my fine soil which is normally consolidated clayey silt (It was a slurry and I consolidated it using bottom-perforated mold and a 1.25kPa surcharge). I got an initial curved portion of the best fit line for e-log sigma curve. Do you know what the reason(s) could have been? any suggestions?
Yazeeed,
You are analyzing the preconsolidation pressure of the clay silty soil?
If it is, for the compressibility model, in my study, I used five water levels; the first 0.05 kg kg-1 and the last = saturated soil and three intermediate levels varied according to the limits of contraction and plasticity. For each point of the curve I used three replications in a total of five points and three replicates per point. I used the sigma plot software for models of compressibility.
How did prepare the tested soil samples? Are you using the initial water content close to the liquid limit of the tested soil?
Thank you Oswaldo for your response. I did not understand your point by testing the specimens below saturation, how did you measure the saturation of your specimens and what was your interest from that.
Kátia
Thank you for your response. They were slurry of water content of 62% and I consolidated them in a perforated mold for one day at 1.25kPa. Then, I mix them slurry of reduced water content in the mold and poured that in the consolidometer ring. Water content at that time was above the LL; therefore, fully saturation is something warranted.
Yazeed,
compression curves obtained by odometer tests on remolded clays differ considerably for clay remolded at different liquidity índex.
best regards, Katia
Compressibility of clays and silts is detailed and needs the understanding of the fundamentals of soil behaviour.
Hello Yazeed Alsharedah: The explanation for your observation is quite simple. From what depth did you extract your sample, 1.0m 2.0m? Assume that the soil has an effective unit weight of 8 KN/m2 then the initial consolidation pressure of a sample extracted from a depth of 1.0m is about 8.0 KN/m2 depending on the value of Ko, the lateral earth pressure at rest. Thus, the sample you consolidated in the lab to a pressure of only 1.25 KN/m2 has become overconsolidated. Hence, the e-logp will be curved for pressures up to 8 KN/m2. The plot will become straight when the pressure exceeds the initial consolidation pressure. My explanation can be found in any standard textbook on soil mechanics. I hope you will find my answer useful.
Hi Nagaraj
I really understand the concept but for N.C clay I expect a linear e-log sigma curve and that is way I am enquiring about it. It could be that this slightly curved e-log sigma is ok for N.C clays and one can take the best fit "linear" line of it.
Hello Amaechi
The material I am testing is N.C as it was slurry before I consolidated it. And you are right for your explanation if the material has been taken from the field. Thank you very much for your comment.
Assuming that you have liquid limit different from the measured value, your material is not NC. The quality of the prepared tested samples may be the reason for the obtained curves. Katia
Yazeed Alsharedah
I did oedometric test.
I used a consolidômetro to evaluate soil preconsolidation pressure (Are different tests). What is the maximum deformation that the soil may suffer able to return to its original condition, that is, to evaluate the load bearing capacity thereof. This test is used to verify that the tension support and that the soil water content to prevent compression thereof.
Dear Yazeed,
The curve in the initial portion can be a possibility for normally consolidated soil started at high water, being near to liquid limit water content or slightly more. Even I have obtained for many NC clays and silts.
Nagaraj
Dear Yazeed,
You should read some publications by Nagarat about it
and the paper from Burland. The curves depend on the preparation and mineralogy of the samples. Katia
Nagaraj's papers present several tests results on different clays.
Katia
Dear Nagaraj,
Thank you for your valuable comments. I really appreciate them.
Yazeed
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