estimating consolidation curve from basic soil data

[soildynamics]

I have the sieve analysis results, specific gravity, density for naturally consolidated soil... is there anyway where i can estimate the Consolidation curve of this soil.

 

[TDAA]

Perhaps if you have data from the same formation, at about the same depth, and have the data from that to compare to. Then you might get close. There are also some calculations based on limit properties that may get you some of the numbers you are looking for. I guess if you can estimate the initial void ratio, calculate C sub c and C sub s, and know if you have a normally or over consolidated soil, you could sketch something – but, I am guessing you wanted the curve to get the numbers for C sub c and C sub s to do settlement calcs.

 

[fattdad]

Not sure what "naturally consolidated soil means". I'd say the answer to your basic question is, "no". You can gleen some idea of consolidation characteristics from Atterberg limits and natural moisture content. You can also use the data that you've suggested to calculate the void ratio. There's a correlation between LL and Cc, which if you had the void ratio you could then use to calculate the expected degree of consolidation if (big IF) you are on the virgin consolidation portion of the curve.

If the natural moisture content is at (near) the liquid limit, you'd be safe anticipating that the soil is normally consolidated.

If you had undrained shear strength, you could relate that to the overburden pressure and then see whether the shear-strength v. effective overburden pressure was within the "norms" for normally consolidated soil. If not then you would have some degree of overconsolidation.

All this stuff is like reaching around your back to scratch your elbow. For several hundred bucks and the cost for shelby tube sampling, you can just get a consolidation test.

Good luck - others may have different opinions.

f-d

¡papá gordo ain’t no madre flaca!

 

[soildynamics]

I am just working on a academic problem.Analyzing the consolidation of Fully saturated Tailings (S=100%) whose specific gravity ,grain analysis and inital void ratio at deposition are known. These materials usually start to consolidate from a normally conslidation state.
I do not have Atterberg's limits that would lead to Consolidation characteristics (WOOD,1991).
By the way I do not know if any of you uses Soil Vision (Knowledge Based program) .. if yes.. can this program help in this situation

 

[fattdad]

What is the grain size distribution (D10, D20)? Do you have any basis to determine permeability? One thing for sure, it's normally consolidated!

Interesting problem.

f-d

¡papá gordo ain’t no madre flaca!

 

[soildynamics]

Sure it is normally consolidated .All the materials I have are finner than 0.063 mm. If there is no way to do so from the grain size distribution, void ratio and other physical properties.
Now let us assume that we can get the permebility function
k(e) from the grain size distribution (say using Hazen's function). Can permeability function k(e) lead to the consolidation curve p'(e).

 

[fattdad]

Permeability can get you to Mv, which controls the rate of consolidation. You'd have to guess how the void ratio would vary over time - like maybe Cec equal to 0.2 or 0.3. You really need a consolidation test!

f-d

¡papá gordo ain’t no madre flaca!

 

[BigH]

To be perfectly honest soildynamics, Hazen's estimation of permeability was not developed for silt and clay sized particles - it was developed for medium filter sands where the D10 size (not the D50 size or so) was in the order of 0.03mm or larger - so using it would be a crap shoot too. Have you do a search of fine grained tailings deposits. There has been some extensive work in this area and "matching" your materials to similar tailings will likely lead you to a reasonable estimation of the consolidation characteristics. But, as has been pointed out earlier, a consolidation test would be the most appropriate means.

 

[soildynamics]

thanks .. we cannot perform any tests.. I have the data from literature. But any way .. I have given it deep thought and concluded that , because of the low permeability of the materials at the considered zone (order of 10E-08 m/s), I will assume that the materials respond with undrained shear strength (Cu). So we will not need isotropic (hardening) consolidation curve in this case. However , I still have to estimate Cu based on the initial void ratio, give grain size distribution and specific gravity. .. Any Ideas ..?
If I cannot predict it from the above data , I will assume it based on the available literature.
Best regards

 

[fattdad]

I would not do that. It would be better to consider a consolidation ratio of 0.2 and run the numbers rather than assume elastic behavoir. Guessing the time for 90 percent dissipation of excess pore pressure will be another problem. I'd take the saturated moisture content and let that be the Liquid limit and then do correlation (I think there's one out there for LL to Cv).

Good Luck.

f-d

¡papá gordo ain’t no madre flaca!

 

[soildynamics]

Thanks
-Please note that the normally consolidated soil has a moisture content that is close to its plastic limit PL and not to its liqid limit
-Your point is smart. However, by considering the soil responding with its Cu we are not considering it as elastic, instead we assume it as elastoplastic (just like Mohr coloumb but with zero friction). The coupled analysis ( deformation of soil due to dissipation of water) is still there. But the soil will be considered failing when the shear stress = Cu. In the case of assuming that the soil behaves according to Odemetric curve P'(e) then the soil will harden upon reaching the yield (plastic strain) and not fail instantly. When encountering low permeability (e.g embankment of fine grained soils being raised) it is justified to consider the behaviour observed in UU triaxial test

 

[fattdad]

So, now I'm confused. Are you trying to determine failure strength (i.e., slope/bearing failure) or are you trying to determine the change in vertical height as a response to loading?

What information do you have on the Atterberg limits and the natural moisture content? Can you provide natural density and specific gravity? Do you have any undrained shear strength (either via UU or pocket penetrometer)? What is your end game objective for this. . . . ?

f-d

¡papá gordo ain’t no madre flaca!

 

[soildynamics]

q.Are you trying to determine failure strength (i.e., slope/bearing failure) or are you trying to determine the change in vertical height as a response to loading?
a:Both
q.What information do you have on the Atterberg limits and the natural moisture content? Can you provide natural density and specific gravity?
a.No Atterberg limits are given. Void ratio, moisture content, specific gravity are known
q. Do you have any undrained shear strength (either via UU or pocket penetrometer)?
a.No
q.What is your end game objective for this. . . . ?
a.Stability analysis considering transient/coupled behavior of the system

 

[fattdad]

Just for the record, I have nothing further to add to this other then wonder what "transient/coupled behavior of the system" means.

f-d

¡papá gordo ain’t no madre flaca!

 

[soildynamics]

It is hard to explain in an answer what transient coupled analysis means because it is not classic geotechnical subject. However, if interested , please read for example the following words concerning a software that indicates what Coupled transient analysis means
"SIGMA/W can be used together with SEEP/W to perform a fully-coupled consolidation analysis. When these two integrated products are run simultaneously,
SIGMA/W calculates the deformations resulting from pore-water pressure changes while SEEP/W calculates transient pore-water pressure changes. This procedure is
used to simulate the consolidation process in both saturated and unsaturated soils. A fully-coupled analysis is required to correctly model the pore-water pressure
response to an applied load. In certain cases, the pore-water pressure increase under an applied load can be greater than the applied load. This phenomenon is
known as the Mendel-Cryer effect. Figure 1-8 shows a SIGMA/W analysis of a saturated triaxial sample with an applied lateral load of 100 kPa. The initial pore-
water pressure before loading is zero. Figure 1-9 shows the pore-water pressure response with time at the center of the sample. The pore-water pressure rises to
about 110 kPa, (110% of the applied load), before it gradually decreases".

 

[fattdad]

Well, that's interesting, but what's the end game? I guess to me, you are developing a seemingly complicated model of behavior for some practical problem - just not sure what the problem is. . . .

One way to approach this (perhaps) is to just do a parametric evaluation (once the model is set up) as a sensitivity study using input parameters that are "typical" for the material.

I wish you well and hope you fill us in on the details as they develop.

f-d

¡papá gordo ain’t no madre flaca!