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# Coulomb Passive pressure on soldier pile walls.2

## Coulomb Passive pressure on soldier pile walls.

(OP)
I've recently designed some soldier pile/ concrete sleeper retaining walls using Brom's method.

Using Coulombs equation for passive pressure and allowing for a wall friction angle of 0.5*Phi gives a much higher kp value than Rankine's.
Based on a previous topic Here
I gathered allowing for wall friction is okay as long as it is done in moderation.

Using above method gives a kp of around 4.2 for a phi = 30. These parameters give a pier depth of around 2.1m for a wall height of 2.0m with 1.6m pier spacing.
I was hoping to get some advice on the depth of the footing from those experienced in soldier pile walls.

Any advice/ recommended resources is greatly appreciated.

### RE: Coulomb Passive pressure on soldier pile walls.

I got a Kp of 9 (didn't account for wall friction). If the piles are spaced more than 3d, you get to use a value of Cp=phi/10 (approximation). Cp accounts for arching in that the horizontal load is not plane strain. Refer to Brinch-Hanson.

f-d

ípapß gordo ainÆt no madre flaca!

### RE: Coulomb Passive pressure on soldier pile walls.

Rule of thumb used on many thousands of wall designs: Unless the soldier beams are toed into very competent bedrock (not hard gravel), it is good practice to have at least 5' embedment for braced or anchored, non-gravity, retaining walls and at least as much embedment as the exposed wall height for cantilevered walls, despite what the calcs may say.

### RE: Coulomb Passive pressure on soldier pile walls.

I have done a lot of soldier pile design, anchored and cantilevered. For cantilevered walls the calculated embedment depth is usually between 90% and 110% of the exposed wall height, in really poor soils it can be as high as 130%. For supported piles a rule of thumb is much harder, as the required embedment will depend on the number of supports and how low the bottom support is. For walls with 1 support, embedment should be around 50% of wall height. With 2 supports 30% of wall height, and with more supports 20-25% of wall height. If my calculations/output are giving me results that vary a lot from these percentages I would look to see why.

### RE: Coulomb Passive pressure on soldier pile walls.

Very useful posts !

### RE: Coulomb Passive pressure on soldier pile walls.

(OP)
Hi All; sorry for the late reply to this. Notifications for it were diverted to spam automatically. So I did not realise.
To quickly respond;

F-D
Does Cp just stand for arching in pile?
I do allow for this but I use 0.08*phi and limit it to 3. I dont normally apply arching to kp though, rather as an effective width when balancing moments

@DanMcGrew
these sizes are pretty inline with what I get. Generally the only time I start to get very small footings in in soils with large friction angles (35-40)
Which may be because Brom's theory is not appropriate for design on in rock.

Cheers guys

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