hand vane/ effective angle of internal friction 3

[domdem]

Hi Guys and girls

Does anyone know if there is a loose correlation for a sand and gravel(structural backfill)by using a hand vane to get a indication of the shearbox angle???, i have to wait two weeks for the result of the shearbox but time is of the essence. or any other ideas????

thanks guys

 

[GeoPaveTraffic]

In short no. Shear vanes do not give give drained results.

 

[domdem]

geopavetraffic

is there nothing that could give an indication say to the nearest 5 degrees???

 

[casimmons]

If you only need the accuracy to within 5 degrees it is probably not even worth running the test. One should be able to make an estimate based on the particle size, degree of compaction, and previous experience with similar soils in the area.

 

[GeoPaveTraffic]

domdem, no you could estimate a value as recommended by casimmons, but the shear vane is not going to help. It is a test developed for undrained strength in clay and that is what it is good at.

You could drive a split spoon sampler or other type of penetrating tester to get an idea.

 

[dgillette]

If all you need is 5-degree precision, you can get a "typical" number from a chart, considering grain size and density. For example, depending on density, particle shape, fines content, etc., the drained friction angle of a sand-gravel mixture could be anywhere from 33 to 40. (See Roy Hunt's book on investigations, USBR's Design of Small Dams, or almost any intro soils text.) If much compactive effort is put into it at all, it's unlikely to be weaker than 35 deg. In my experience, the acceptability of a designed or existing structure is not often very sensitive to the friction angle within the plausible range.

That said, make sure the drained friction angle is really what you need for the type of loading involved. It probably is for that material, unless it is loose and saturated.

Also, if (as I think I read between the lines) you are interested in pressure on a basement wall or something, remember that the pressure near the top of the fill is going to be larger than what you get from the oft-cited Ko = [1-sin (phi')] or 0.9*[1-sin (phi')] because of the effect of compaction and "locked-in" horizontal stress.

 

[domdem]

many thanks fella's i am confident i'll get the 35 degrees now