Remoulding sample procedure

[pietro82]

Hi all,

I have to carry out a direct shear test on remoulding samples. Is there any standard procedure for remoulding a soil sample in order to achieve similar moisture content and load history to it have in the field.

Thanks

Regards

Pietro

 

[Ron]

The best you can do is replicate the density and moisture content.

 

[pietro82]

Hi Ron,

but how may I pratically do it? Dry the soil, add a specific quantity of water to reproduce the moisture content, right? What about the density? I read that it is also necessary to consolidate the soil specimen in order to reproduce the same load-history, but whith which load? The vertical stress it had the specimen in the field before sampling?

 

[Ron]

It is better not to dry the soil then rehydrate. The soil as sampled will be at the moisture content you want. Compact to achieve the density replication of the in-situ density, then apply the overburden pressure to replicate the history.

 

[oldestguy]

Explaining something regarding the use for test as well as what type of soil is it, may assist in getting more comments that may help.

 

[pietro82]

Hi,

@Ron: How to compact it to achieve the same density?
@Oldestguy:well, I want to remould some sample to carry out the direct shear test and the triaxial test. The type of soil is 40% clay, 40% silt and 20% sand.

 

[fattdad]

Compacted fill: Obtain the moisture-density relations and remold to the desired level of compaction within the specified band of cmopaction moisture content. Please pay attention to how soil with 95 percent relative compaction can have different properties if compacted wet or dry of optimum. Please understand that the line of optimums is (essentially) parallel to the zero air voids curve and IS NOT a vertical line from the opimum moisture content for 100 percent compaction. (i.e., what is the optimum moisture content for 95 percent compaction?)

What's the intent of the strenght value? So, if you have a plastic clay or silt and you are building earthworks for long-term performance, there could be a chance of softening. To mold a sample for fully-softened shear strength, take the soil and hydrate it to the liquid limit, place the, "Mud" into the DDS machine and add incremental normal load to form a normally-consolidated sample in the DDS machine that's under the target effective stress for your design ranges.

If youa re looking to design for residual strength, just shear to failure or shear to failure over and over again. For residual strength, the normal load is a factor, but the compaction effort is unlikely to affect strength.

It's hard to add much more, because I'm not sure of your project and I'm not even sure, I'd be using a DDS for your data objectives.

f-d

ípapß gordo ainÆt no madre flaca!

 

[pietro82]

Thanks Fattdad. The intent is to get soil friction angle. I do not have the DDS machine and I got soill samples 30cm below the topsoil.

 

[Ron]

Guess the friction angle from the soil classification! You won't be any further off than for a remolded sample. You're not building a watch.

 

[pietro82]

Thanks Ron. Which standard may I refer for getting the friction angle? Using the soil classification, is it also possible to get the Young's modulus, Poisson's coefficient, too?

 

[Ron]

All of those are correlated to classification. You won't be that far off. As for citation, use the classification standard and then refer to the numerous geotechnical papers written on such correlations. Do a little research...you'll find them

 

[pietro82]

Thanks Ron. May I find the Young's Modulus and the Poisson's ration in the same way, as well?

 

[pietro82]

By the way, just for curiosity I haven't understood how to reconstruct a sample! As far as I have understood: the soild should be saturated, than consolidated with the same load it had on the field but how may I control the soil density and moisture content? Thanks

 

[BigH]

How to remould? Can you prepare batter for a cake? Put in your clayey/silty sample, get a spoon or pestle and start pounding and stirring it until the sample becomes like a batter. This assumes you are in the plastic range. Add water if you want. That's how I'd do it. Then the question is how do you reconstitute the sample into a mould - a bit at a time, work it in . . . like one would do with a mortar sample into a small cube. Unless someone else has a better idea . . .

 

[pietro82]

Thanks BigH, but my doubt is how to reproduce the same density and water content in the same time.

 

[L0k]

I think it is better to carry out in the CBR mold and you may reproduce the samples based on the water content, the density and the hammer blow count.
The hammer blows may represent the same soil history.

 

[pietro82]

Thanks L0K. Is there any ASTM standard for the reproduce it?