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qwedsa (Civil/Environmental) (OP)
22 Oct 03 14:11
Has anybody got information about effect of grain size of sand or gravel on internal angle of friction or angle of repose?

Helpful Member!  jdonville (Geotechnical)
22 Oct 03 17:38

Bowles and others have produced tables that present empirical correlations between the particle/grain sizes and other engineering properties.

Generally, the correlations suggest that the friction angle for a coarse sand is greater than that of a fine sand with similar relative densities.

For example, Bowles (1988) Table 3-4 says that for a very loose sand, a very loose coarse-grained sand typically has a friction angle of about 28-30 degrees, while a fine-grained sand has a friction angle typically about 26-28 degrees. The effect becomes somewhat more pronounced as the relative density of the sand increases.

Jeffrey T. Donville, PE
Wang Engineering, Inc.

Focht3 (Geotechnical)
24 Oct 03 12:08
Generally, the correlations suggest that the friction angle for a coarse sand is greater than that of a fine sand with similar relative densities.

That's the problem (at times) with using correlations.  You can get into real trouble if you aren't careful.  Frequently, the biggest difference between a uniform coarse sand and a uniform fine sand (of the same material) is the particle shape.  The smaller particles tend to be less angular as a result of more weathering.  But this isn't always the case -

The major factors that affect the soil angle of internal friction are particle shape, density, grain size distribution, composition, particle strength, and stress history.  And not necessarily in that order.

The angle of repose is affected by the particle shape and grain size distribution.  But the angle of repose is not the angle of internal friction.  In fact, there is no such thing as the angle of internal friction...

Please see FAQ731-376  by VPL for tips on how to make the best use of Eng-Tips Fora.

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