Correlation of Atterberg limits to shear strength 1

[jicker23]

I am about to embark on some research into the relationship between PI and shear strength.

As I understand at present, there is a vast amount of work already undertaken in this field, however this is largely based on overconsolidated clays (London, Gault etc). Can anyone tell me if the work extends into all soil types or if it was soley undertaken on the overconsolidated clays?

Many thanks

 

[geonet]

Ladd, et al in 1977 has a correlation between PI and effective friction angle of normally consolidated clay. I believe this is widely published (Holtz & Kovaks - Inro to geotech Engineering).

 

[CIVGEOT]

Check the following:

Stark, 2005, 1997 and 1994 - all published in ASCE Geoetch Journal

Mesri, 2003 - published in ASCE Geotech Journal.

These publications provide specific discussions on the use of Atterberg limits and CLay Fractions as itr relates to residual strengths ...

 

[jicker23]

Thank you for your valuable comments.

Any more suggestions always welcome.

 

[drobi]

Jicker 23

As you are uk based, you may want to look up an old CIRIA publication which gives a correlation between liquidity index and undrained shear strength. The publication is CIRIA Special Publication 25, dated 1983, 'Site Investigation Manual'.

Hope this is of assistance.

 

[BigH]

I believe that Leonards (1961) book on Foundations has correlations - like the one noted by drobi. Then there is the classic Su/p' = 0.11 + 0.0037Ip; Su/p' = 0.45(Ip)^0.45 (Bjerrum and Simons); Su/p'= 0.005LL for LL>20; etc. Sangrey wrote a nice note back in 1975 or so (plus or minus a couple of years) in ASCE JSMFE on use of Atterbergs in estimating undrained shear strength.

 

[jicker23]

Thanks BigH and Drobi.

Specifically, do you know of any work in this field which relates to more complex glacial till (boulder clays) deposits as oppose to relatively homogenous cohesive deposits? I would like to possibly develop/prove empirical relationships by incorporating a local geological model to these deposits. My aim is to provide a more accurate way of predicting undrained shear strength by looking at the geological history of the site.

An Ambitious Post Grad!

 

[drobi]

There is a bit more info in CIRIA Report PG5, 'Piling in Boulder Clay'. This is quite an old publication (1978)and there is a large scatter when looking at a relationship between liquidity index and shear strength of a Till which by its very nature has variable proportions of granular and cohesive material.

To get a better relationship you are probably going to have to look at a way of taking into account the proportion of coarse/fine material. This could perhaps be done by determining the liquidity index on the basis of the 'modified' natural moisture content, ie, the moisture being held only in the proportion finer than 425microns and not the coarser fractions.

Good luck with your research

 

[jicker23]

What do you think to "modifying" the PI through the BS 5930 description or by a PSD test? Just throwing these ideas around at the moment but my thinking is that this would be the ideal way of relating the two as it would involve little further testing.

 

[drobi]

Using a modified PI is a standard procedure for assessing, for example, the heave potential of a mixed soil.

I think it is better to have an actual number to work with rather than an assessment based on a description. If you are determining the PI according to BS1377, the test is undertaken on material finer than 425microns, so any lab doing the test will determine the amount of such material as part of the test. You are then in a position to modify the PI or moisture content.

Over to you, jicker23

 

[jicker23]

Drobi,

Sorry, being a bit slow - my initial thinking was that the gravel and cobble content would effect the undrained shear strength during the lab test and therefore effect the correlation. However this of course is not a function of the shear strength and the test result would not be valid anyway.

Thanks for your advice to date - its appreciated. This is the first time i've used this site properly and I am impressed by the prompt number of replies.