Preconsolidation pressure against moisture content / dry density?

[ot110]

Hi,

I've recently run a few experiments to investigate the impact on changes in moisture content and dry density on the saturated preconsolidation pressure, and am a little confused on to how to conclude.

The test run were on a clayey silt, first compacted using the standard proctor method, then saturated and consolidated in a triaxial cell using an isotropic pressure ramp up to 1500kPa. Several problems came up during testing which meant I could only test 4 samples of moisture contents between 15.8% and 16.8% (optimum = 16.4%) and dry densities between 1.74 and 1.77 g/cm³. The resulting graphs plotted against preconsolidation pressure show a scatter of points, but i havent found any real way of going about forming any relationship between them, if one even exists.

Does anyone have any tips on what i should be looking for, or what theoretical existence should exist? I was under the impression that with lower moisture contents, and higher dry density, the preconsolidation pressure should increase.

Please reply a.s.a.p, I need to submit my findings tomorrow at midday.

Many thanks

 

[paganel]

You should know something about consolidation.
In the normal consolidation test,with the rise of load pressure the void ratio will decrease, thus the moisture content will decreas also.

I am a little confused about your post.

 

[AussieGeoEng]

Determination of preconsolidation pressure on a natural specimen specimen is difficult at the best of times. Preconsolidation pressure seems a little misleading for a compacted specimen - I would prefer to use yield pressure - i.e. change from elastic to elasto-plastic behaviour.

Compaction in a mould is one dimensional therefore you have an anisotropic material (Ko).

Compacted specimens can have different structure depending on moisture content at the time of compaction.

 

[ot110]

The testing is an addition to the Barcelona Basic Model for partially saturated soils, which changes to a critical state model in saturated conditions. The idea of the tests was to investigate the possible existence of a relationship between the preconsolidation pressure (or yield pressure) and the initial moisture content, and the preconsolidation pressure against the initial dry density.

The final measurements (after consolidation) did show a change in moisture content, as you said paganel, but it is the initial conditions which are being plotted against the final Po value.

The idea was to (eventually) aid in further predictions of the saturated preconsolidation stress of a soil given its moisture content and dry density without need for testing, but at this stage just to see whether a relationship might exist at all. I was just wondering whether any similar testing has been done previously or whether anybody could point me towards some useful theory which would suggest how the results should turn out.

Thanks again

 

[AussieGeoEng]

Are you trying to determine yield pressure for saturated or partially saturated?

Can you post the results?

 

[aeoliantexan]

The range of initial conditions is probably insufficient to show the relationships you want. One would expect considerable scatter, and with the initial conditions so tightly grouped, scatter is all you see.