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# Correlation friction angle/grain size for stone material for embankments

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## Correlation friction angle/grain size for stone material for embankments

(OP)
Hello,
I have a embankment of stone material whis is stabile with friction angle fi=42 and cohesion c=0. Are there any connections/correlations between the friction angle and cohesion of my stone material and grain size of the stone of the materials. Does exists dependence of grain size due to the friction angle and cohesion? Which granulation of stone material I must to select for my parameter?

### RE: Correlation friction angle/grain size for stone material for embankments

I assume your 42 degree measurement is of the slope angle above horizontal. I'd not attribute that angle to a specific grain size distribution, but more likely on shape of particles. Let's say the material was a series of building bricks laid horizontally. Their relative size would be less important than their shapes.

Cohesion is usually unrelated to friction angle but mineral type.

### RE: Correlation friction angle/grain size for stone material for embankments

Friction angle of stone material is related to the shape of the particles, the density of the material and the strength/hardness of the intact particles. For relatively small embankments the strength/hardness of the intact particles is unimportant since it only matters if the stresses are high enough to crush the particles.

A lower bound phi can be determined by measuring the angle of repose of the material.

As oldestguy indicates, no cohesion is generally present in granular/stone material.

Mike Lambert

### RE: Correlation friction angle/grain size for stone material for embankments

The angle of repose does not represent a lower-bound for saturated friction angle. (I do agree that it represents a safety factor of unity for the infinite slope condition and for that moment it does depict the unsaturated friction angle for the temporary state of stresses.) Pseudo-cohesion can develop by tension in the unsaturated soil, which shows up on the angle of repose. If you want to know the friction angle, run a lab test under the normal conditions of the lab standard.

Irrespsective of measured values for cohesion, don't rely on that strength for your long-term performance.

f-d

ípapß gordo ainÆt no madre flaca!

### RE: Correlation friction angle/grain size for stone material for embankments

(OP)
This is embankment of reservoirs for irrigation. I agree with you that it is a very important shape of particles. How would you put granulation of stone material for the embankment fi = 42 and c = 0, and taking into account the shape of the particle course. I must say to investor exact granulation stone material to the mound.

http://files.engineering.com/getfile.aspx?folder=f...
http://files.engineering.com/getfile.aspx?folder=3...

### RE: Correlation friction angle/grain size for stone material for embankments

Generally when designing a dam you work the other direction. First you determine what the dam will be constructed of, stone type and expected gradation that you can produce. Then you determine the strength properties of the material. The size of the dam also has an impact on the material strength.

Have you ever designed a dam before?

Mike Lambert

### RE: Correlation friction angle/grain size for stone material for embankments

There is the Duncan 2004 presentation on rock material for dams. It needs a few parameters and you can come out with phi-c pairs.

It's no more online, apparently, hopefully I can retrieve it from my chaotic jumble of material...

### RE: Correlation friction angle/grain size for stone material for embankments

Guys, I'm happy to announce that, notwithstanding approaching old age, apparently I still can manage to keep a semblance of order in my technical material, having been able to find with but ignorable delay Duncan's lecture amidst an overwhelming and ever growing quantity of articles, presentations and so on.

Mike Duncan's lecture 'Friction Angles for Sand, Gravel and Rockfill' is pretty good and authoritative I reckon.
Results should still be evaluated with technical commonsense.

If interested you may click on the www.mccoy.it site, get my e-mail there, I'll answer to your email with Duncan's paper attached.

www.mccoy.it

### RE: Correlation friction angle/grain size for stone material for embankments

eh this question resembles one that a woman asked me , she wanted friction angle from sieve analysis.
Shear strength of soils especially Phi rely on many parameters including
the effective normal stress
the existence of water or not .
The confining pressure .

### RE: Correlation friction angle/grain size for stone material for embankments

Killswitchengage - the original question was about c and phi; not shear strength.

### RE: Correlation friction angle/grain size for stone material for embankments

BigH : No its highly dependent , the more confining and normal pressure you have the greater the phi value will be especially if there is no water. Using identification analyses destroys the initial stress state the sample had and therefore it losses all meaning when it comes to this correlation he seeks. Nevertheless , i believe there are correlation that helps equates the two parameters he seek to use , but it just gives you a lower boundary for me

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