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# Coulomb Failure Plane Angle

## Coulomb Failure Plane Angle

(OP)
Does anyone have a reference showing the equation for this angle? The only reference I have is NCMA Segmental Retaining Wall Design Manual. But I would like to see this derived in a different text.

### RE: Coulomb Failure Plane Angle

(OP)
Forgot to add the equation includes:
-Backslope, wall batter and wall friction.

### RE: Coulomb Failure Plane Angle

It is on pages 4-14 through 4-17 of the 2011 Caltrans Trenching & Shoring Manual. Careful with the wall friction angle value.

(OP)
Thanks!

### RE: Coulomb Failure Plane Angle

(OP)
So I finally got around to checking this out and I realized they don't include a coulomb failure plane or a failure plane equation that includes wall friction. Not a huge deal, but I just can't seem to find this equation anywhere.

### RE: Coulomb Failure Plane Angle

I think the reason there's no stancdard equation for all cases of soil strength is because Coulomb is a trial and error method. At least that's what I recall from grad school oh so many years ago. . .

f-d

¡papá gordo ain’t no madre flaca!

### RE: Coulomb Failure Plane Angle

fattdad - I think I remember setting it up with the force on the wall as a fn. of the base angle, taking the first derivative w.r.t. the angle, setting that to zero, and solving for the angle that gives the highest active pressure. As you know, however, that was a few years back.

Cheers!
DRG

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