Relationship between LL, PL and PI with Swell Potential for Clays

[garrettk]

I recall seeing a formula that utilized Plasticity information for predicting swell potential in clays. The problem is I no longer have access to those books and my smallish library doesn't have information about this.

Does any one know of the equations that provide information on this relationship? Or helpful charts that provide similar information?

Thanks in advance,

Garrett K.

 

[BigH]

There are a number of ways - I put in a Table from Terzaghi, Peck and Mesri (1995)

_________________________________________________________
Table 48.1 Approximate Relation Between Plasticity Index and Inherent Swelling Capacity

PI = 0 to 10; Low Inherent Swelling Capacity
PI = 10 to 20; Medium
PI = 20 to 35; High
PI > 35 ; Very High
_________________________________________________________

There is also, same reference, Figure 16.2 - Swelling Strain of soils as function of clay fraction and liquid limit (CF x LL) - would have to scan this and send to you.

There are some more relationships - I'll try to look up for you but Focht3 and others might have them at hand.

 

[ashjun]

Hi,
You could also take a lead by doing a net search on the activity of clays.

Activity = (plasticity Index)/ (percent clay content)

I do not recall clearly, but if activity is less than 0.75, the clay is termed as having "low activity" and anything above 1.25 is termed as of having high activity.

Regards

 

[BigH]

Two more I found - likely to make life more confusing:

1. US Army Waterways Experimental Station (as compiled by O'Neill and Poormoayed):

LL < 50; PI < 25; potential swell <0.5; Low
50<LL<60; 25<PI<35; pot swell 0.5 to 1.0; Marginal
LL>60; PI>35; pot swell >1.5; High

2. USBR (uses CF size as 0.001mm)

CF>28; PI>35; SL<11 Prob Expansion >30%; Very High
CF: 20-30; PI 25-41; SL 7-12; Prob Exps'n 20-30%; High
CF: 13-23; PI 15-28; SL 10-16; Prob Exps'n 10-20% Medium
CF<15; PI>10; SL>15; Prob exps'n <10%; Low

SL stands for shrinkage limit.

Above from text by Dr. Nitin Som of Jadavpur University of Calcutta - a very good engineer and one of the best in soft ground geotechnical in India. (Ph.D. at Imperial in mid-60s).

 

[emmgjld]

Please note that in-place density of the clays and the beginning vs. final moisture contents have an enormous influence on the actual swell/heave which is experienced. The above references indicate relative severity and give virtually no indication of what amount of swell/heave will actually occur. Actual testing is required.

 

[BigH]

emmgjld - you are quite right - testing is the best - but original post asked for relationships of various index testing and potential for swell.

 

[garrettk]

Thanks for all of the tips. I have a good idea of where to start my work now.

 

[genomty]

garrettk:

Although the U.S. Army Corps of Engineers refers to it as an conservative method. There is an helpfully empirical method based on the encountered subsurface soil conditions(Atterberg Limits), a surcharge load and an active zone. This method for estimating soil related movements is widely used in Texas and is known as “Tex-124-E, Method for Determining the Potential Vertical Rise (PVR)” of the Manual of Testing Procedures of the Texas Department of Transportation (TxDOT).

This is an empirical method and should be used applying criteria for local conditions.

You can try a manual published by “Department of the Army USA, Technical Manual TM 5-818-7, Foundations
in Expansive Soils, 1 September 1983.” wich is available for dowloading at

http://www.usace.army.mil.

It contains helpful tables, for instance table 6-1

 

[Focht3]

If you decide to try using TEX-124-E (PVR method), then we need to discuss it a good bit. A lot of judgment is needed to use it...



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[genomty]

I agree with Focht3. There was a company working around the city which apparently was a &quot;fanatic&quot; of the PVR method. However they were not very familiar with the soils at this region. I can not remmember very well, but I believe they determine a PVR around 4 inches and they recommended improve at least 3 feet of these soils with hydrated lime and accomadate certain surcharge which was equivalent to 4 or 5 feet of engineered fill, in a pad of about 300,000 square feet. There were previous studies from other firms around the area, some of them included tests made using a consolidometer by saturation after load application and free swell. These tests instead of swell demonstrated settlement after moisture increase. So it is totally true that lot of judgements should be applied in order to apply this method specially when you are not familiar with the method or the soils.

 

[Focht3]

Where are you, [blue]genomty[/blue]?



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[genomty]

I'm in northern Mexico

 

[Focht3]

I'll bet they are headquartered in San Antonio - big (regional) firm (Texas/New Mexico/Mexico.) Their recommendation sounds typical, assuming you don't have a good borrow source of crushed rock nearby.

If it's the same firm, that isn't the most ridiculous recommendation they have ever made. How about removing and replacing (with crushed limestone base) 12 feet of soil?!



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[genomty]

Focht3:

I do not know if we are talking about the same guys. However you look very familiar with the Texian Engineering firms and their procedures, where are you based?

It could be pretty helpful dicusse this method and other methods to estimate soil movements. Most of the firms here in town frecuently do not review this issue due to the cost and time that a test take them or because some of them simply ignore the swell effect of some soils.

There was a PE in the company that I used to work who said me, after I skip the PVR calculations because of the subsurface conditions and proposed structure were not the typical conditions for swelling effect, when he was training me. Geno, I believe you know well when and where use the PVR method, many engineers around apply this method just following the method as a cookies recipe. They do not stop to judge where or when it should applied, and there are others that know but wrongly prefer stay at the &quot;safety&quot; side in order to avoid lawsuits.

I have seen some firms that consider the moisture conditions as &quot;dry&quot; and skip grading corrections when apply the TxDot 124 just for protection. I wonder if this is an standard ethic and professional procedure around the Lone Star State or just for the companies that I have known.

 

[BigH]

More general - back to providing added info, check out the work Vijayvergiya, V.N. and O.I. Ghazzali (1973) &quot;Prediction of Swelling Potential of Natural Clays&quot;, Proceedings 3rd International Research and Engineering Conference on Expansive Clays, pp. 227-234. I'll send chart to you Foch3 through our typical channel.

 

[VAD]

Hello garrettk

In general while the Atterberg limits were used by many to derive simple relationships, the governing factor regarding swelling is related to the soil mineralogy. In my experience despite clays may be classified as very heavy, they do not necessarily exhibit high swell characteristics.

Clays with a high percentage of montmorillonite for example
would have a higer propensity for swelling than on that is composed of predominantly kaolinite and illite minerals.

To quote an example, in one jurisdiction (Guyana) the clays have liquid limits ranging from 60 to 90 and PI's from 30 to 60 The composition of the clay fraction is as follows Kaolinite 20-25 %, illite 30-35%%, chlorite 10-15 % and montmorillonite 0 to 5 %. Hence the importance of understanding the clay mineralogy.

This clay does not exhibit swelling characteristics and this jurisdiction does not undertake swell tests as part of thier evaluation. Based on the Atterberg limits this clay would be potentially high swelling.

Generally, the observations made through the performance of structures indicate wheteher or not swelling clays are present and are of concern. This is often why some jurisdictions decide to use the Atterberg limits as an indicator.

If one is uncertain then the swell test should be undertaken. The free swell test is often sufficient. Jennings et al from South Africa undertook much research in this area. His work is often quoted in publications on swelling soils.

One should review the text &quot;Clay Mineralogy&quot; by Grimm to understand how complex the cay particulate structure is and to appreciate that the geological composition is very important to clay behaviour.

Unfortunately, we do not traditinally undertake x-ray diffraction tests and as such we should only utilize the general correlations unless we have knowledge that the clay soils in a particular area are swelling etc. Even then, I would always undertake a swell test in designing of a remedial measure.

There are a number of technical papers on the subject. I refer you to one that incorporates the empirical approach using the Atterberg Limits and as well as swell tests. This paper is by Diyaljee and Forbes and was published in the Proceedings of the 5th International Conference on Swelling Soils, Adelaide, Australia in 1983. This was based on a case study of heaving of side walk slabs of a shopping centre in Edmonton, Alberta, Canada, which I undertook in 1981.

Please excuse the length

Regards

 

[BigH]

Good post VAD!!

 

[Focht3]

The Grimm reference is a good one; just be aware that he produced more than one book - and that reading any of them can be a little tedious...



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