Retaining Wall with downward sloping backfill?

[scotthicks99]

How do I calculate the passive and active coefficients for a retaining wall with a downward sloping backfill. If you know, can you point me to a good reference?

Essentially, what I want to calculate is the resisting force of a "wedge" of rock or soil up against a vertical face. The "wedge" would have a defined height and slope.

All I can find is theory for straight and inclined backslopes and short of deriving my own theories, I haven't been able to come up with a solution. It seems simple enough though...unfortunately, I don't feel confident enough in my knowledge of the theory to develop it myself.

 

[DRC1]

Try DM 7.2 Foundations (Navy Document) at:

http://www.vulcanhammer.net/download/dm7_02.pdf

Chapte 3 page 7.2-64 Figure 3

 

[BigH]

Almost any respectable text will give ka and kp tables which includes +B and -B where B is the slope angle behind the wall. You could, if the bug hit you right, do a Culmann graphical method on it!

 

[scotthicks99]

So, in a general application a negative angle (-B) can be used to denote a declined backfill?

Thanks for the tip on the vulcanhammer design manual. It does have a nice concise table for Ka/Kp respective to phi for granular soils. Unfortunately, my case is cohesive....which means I need to get into a trial wedge analysis (I think).

Regarding respectable texts...while I don't have an exhaustive collection, my Das text and other design manuals (COE) do not list have any negative angles in their tables....

 

[fndn]

The active would be same as level backfill-conservative but practical. The passsive fluid pressures, you may take the inverse of the active multiplied by the moist unit weight at 85% compaction and then divide that by 1.5 to get a passive for a horizontal backfill. Since you've sloping downward, you may reduce that value by multiplying it with 0.67. This is due to surficial sliding potential, creep and worms loosening the outer downward slope.

You may also search online for the california shoring manual-a link is found in one of my previous posts.

 

[BigH]

scottshick99 - sorry about "respectable" texts. I don't have Das, myself, so . . . but if I remember right, Bowles has the data all in tables Fang (or Winterkorn and Fang), does as well and several other texts I have. The Navy manual (downloaded from VulcanHammer) is a good one but in graphical format.