Angle of Repose = Lateral Pressure 2

[DYork]

I am designing a retainig wall that will utilize only piers for lateral support (horrible soil an need for considerable movement). It is a material storage facility for a brick manufacturer, and I need information on transfering the materials angle of repose to an effective lateral pressure (wt=93pcf, angle=35). It would great if could give me some suggestions or where I could get some idea on how to approach the project. Thanks in advance, from a new EIT.

 

[SlideRuleEra]

The geotech's can tell you the best way. But I like to use Rankine theory that uses the soil unit weight and the angle of repose (I believe they call it "angle of internal friction" these days) to "convert" the soil into an equivalent hydrostatic fluid. It's not "right" but it is usually consevative enough to keep you out of trouble.
Here is a decent explanation:

http://www.pdhengineer.com/Course F...h Pressure for Non-Geotechnical Engineers.pdf

 

[Focht3]

You are courting disaster.

Placement of the material within the containment area will have a huge impact on the "equivalent fluid pressure." Rankine may make you feel right, but will seriously mislead you.

The piers will have to move in order to achieve an "active" state within the material stockpile. Move every time that material is added; and the deflections don't fully return as the material is consumed, so you will get permanent "set."

Better to assume a minimum equivalent fluid pressure of 100 to 150 pcf.

And check with your client. What has worked in the past?



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[SlideRuleEra]

DYork - Focht3 brings up a good point, in rather dramatic fashion, the total load on the stucture you descibed will be higher that just the static lateral pressure from the material. You certainly have to consider factors such as the "impact" of both placing (by falling from a conveyor belt?) and later removing the material (maybe with a front end loader?). However your question about how to find the lateral pressure from (static) material is nicely handled (for us structurals) by Rankine Theory.

Other factors to consider would be the shape of the pile (flat, sloping, conical, etc). and environmental conditions (does the material get wet from rain, dust control, etc.) while in storage. As usual, there are many ways to look at a problem.

There is also a nice side benefit to you for learning Rankine Therory. At this time (may change later of course) the Geotechnical portion of the Civil (Structrual) PE exam is based on Rankine. Geotech makes up 20% of the morning session. This may be helful (in a few years) when you take the Principals & Practice Exam.

Best Wishes