Angle of Repose versus internal friction angle
Angle of Repose versus internal friction angle
(OP)
I am in the process of designing storage buildings for road salt. The hiring firm is a DOT and has set the properties of the salt as follows:
density = 100pcf
internal fricition angle = 34 degrees
angle of repose = 34 degrees
AS I am sure you have already concluded, using the same angle of repose as the internal friction angle in Rankine's equation yeilds a very high Ka. A reduction to and angle of repose to just 33.4 degrees yields a Ka almost 20% smaller.
I have (2) questions:
1. Is it possible for the angle of repose to match the internal friction angle of a non-compacted granular material?
2. Are there any references out there that either correlate angle of repose and internal angle of friction that would carry enough clout to challenge a DOT? If not, are there any industry standards out there that carry enough clout to challenge a DOT?
Thanks for any help you can provide.
density = 100pcf
internal fricition angle = 34 degrees
angle of repose = 34 degrees
AS I am sure you have already concluded, using the same angle of repose as the internal friction angle in Rankine's equation yeilds a very high Ka. A reduction to and angle of repose to just 33.4 degrees yields a Ka almost 20% smaller.
I have (2) questions:
1. Is it possible for the angle of repose to match the internal friction angle of a non-compacted granular material?
2. Are there any references out there that either correlate angle of repose and internal angle of friction that would carry enough clout to challenge a DOT? If not, are there any industry standards out there that carry enough clout to challenge a DOT?
Thanks for any help you can provide.





RE: Angle of Repose versus internal friction angle
RE: Angle of Repose versus internal friction angle
Why do you want to fight the DOT on this, unless they are doing something obviously wrong? You're taking on liability for using different material properties without having testing to back you up, for no additional profit? If you think you could save them a pile of money, then propose a testing program.
RE: Angle of Repose versus internal friction angle
Since it is likely that there are storage buildings for salt in your area also, I'd visit a few sites and ask about experiences with salt storage. For one, those guys unloading the last parts of the pile are likely to put imp[act pressure against the walls with the buckets of the equipment.
A community I was with decided to go for some concrete blocks as the base parts of the wall due to this possibility, but with treated timber walls above. Most of the salt storage buildings I have seen are glorified pole buildings with creosote treated poles set in the ground. Also our DNR requires the salt to be on a concrete slab with a curb all the way around.
RE: Angle of Repose versus internal friction angle
RE: Angle of Repose versus internal friction angle
RE: Angle of Repose versus internal friction angle
RE: Angle of Repose versus internal friction angle
*
*
*
* <-Slope@repose
*
|
|
| <- Wall
|
|_______________
This is the only way I can think of right away for the active pressure to be sensitive to both repose AND phi' as separate variables.
It's not this:
| * * * * *
| Level or slope flatter than repose
|
| <- Wall
|___________________
RE: Angle of Repose versus internal friction angle
This can be illustrated by watching a dump truck dump a load of granular material. The slope of the resulting stable pile is the "Angle of Repose" for that specific granular material.
This angle is very important in determining the maximum slope of excavated material stored near the excavation as well as the slope of the sides of the excavation itself for safety reasons, and determining if excavation supports are required by design in absence of specific codes or regulations.
RE: Angle of Repose versus internal friction angle
The number you gave for Phi is very close to the value I, and many of my associated assume for granular materials (30 - 33) in the absence of a geotechnical report. As both a structural and geotechnical engineer with laboratory experience, I am often required to generate my own geotechnical information by performing all required geotechnical manual calculations, which I prefer to do using a program called Mathcad, so I can see the effect my assumed value of Phi has on other related variables being calculated to be sure they make sense and are reasonable. That way, I don't have to keep redoing calculations in a manual iterative process, which is too time consuming for most project budgets.
My approach allows me to change variables in a function or equation and see the effect it has on subsequent operations as I make the change, as well as the final result in real time, automatically. I get a better overall perspective on the calculation than I do on paper.
RE: Angle of Repose versus internal friction angle
RE: Angle of Repose versus internal friction angle
RE: Angle of Repose versus internal friction angle
In parts of volume 2 discussing backfills at angle of repose, they do use alpha quite a bit, in order to avoid having to include both alpha and phi (which they repeatedly say are approximately equal).
RE: Angle of Repose versus internal friction angle
I only have the 1974 Volume 1. On page 148 "Charts for Determining Thrust" it uses the angle of repose. I have over 15 retaining wall books and Reimbert is the only one that uses angle of repose. Nonetheless its a great book.
RE: Angle of Repose versus internal friction angle
The City wanted the foundation walls to extend 8'-0" above finish grade, and act as retaining walls as well as the framed building foundation. As a result, I designed the foundation as a two sided retaining wall, which was required to retain both soil from the exterior grade, and the salt pile (actually a sand / salt mix) on the inside.
As I recall, the the internal friction angle, Phi, was obviously different for the outside retained soil, the sand / salt mixture, and the in situ soil at the base of the retaining wall / foundation. Phi for the soil at the base of the retaining wall footing was used in determining the summation of resistance against sliding, and was unrelated to either retained material in my case. Phi for the outside retained material was also different from the sand / salt mixture retained from the inside of the building. In my case, the angle of repose, which is not necessarily the same as the angle "Alpha", which denotes the slope of material being retained (and is illustrated by the "Slope@Repose" diagram above by dgillette, only it isn't necessarily equal to the Angle of Repose in most cases), was never used, and neither was Alpha due to the construction and final conditions. Since all the soil I was dealing with, except the sand / salt material, was permanently compacted and level, neither Alpha or the Angle of Repose was ever used on the wall / foundation I designed to calculate lateral force coefficients to determine the design moments on the walls, footings, or the overturning moments and sliding force / resistance. But Phi certainly was.
In the absence of ground water in my design for the below grade and outside compacted retained material, I elected to assume a value of PHI which gave me a value of ka=0.33, which past experience has shown to be conservative for many designs in my area of the country, and is confirmed by both peer review and tabulated values in a soils text I use frequently, as well as by my associates.
With all that said, if you have been provided with values for Phi and other required design values by "others", then by all means, use them without question, and you will not assume any liability for no apparent reason, as dgillette points out. That is probably the best advice if it applies to your situation.
RE: Angle of Repose versus internal friction angle
www.PeirceEngineering.com
RE: Angle of Repose versus internal friction angle
Geostability - As used in the Reimbert book brought up by CAP4000, alpha is the angle of repose. The fill slope is designated as alpha', which seems like odd notation to use, but that's how they did it. (This is not the alpha in tan(alpha= sin(phi) from CSSM.)
RE: Angle of Repose versus internal friction angle
Can you verify that the Reimbert book indicates a much lower Ka than Rankine. He does not use salt but he uses wheat, rice, river sand and plastic granules to dispute both Rankine and Coulomb.
RE: Angle of Repose versus internal friction angle
To tell you the truth, I bought it in 1986 or earlier from Publishers Central Bureau or one of those places that sell excess stock of books. I have barely looked at it, in part because I have not done much work on retaining walls (except recently, with seismic loads), and when I have, I've used Coulomb, and just once, Sokolovski for passive load in an unusual case.
Won't have time to study up on it any time in the near future, because of the work they pay me to do and a research report I agreed to review.
RE: Angle of Repose versus internal friction angle