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# Design of Salt Retaining Wall

## Design of Salt Retaining Wall

(OP)
Refer to the linked picture. I am designing a retaining wall to support a salt pile. I am familiar with the procedure for calculating the force on a wall with sloped backfill but the problem here is that the salt being stacked at the angle of repose gives me a very large Ka value (case 1 in attached image). The actual condition of the backfill is constrained to "case 2" from the attached image due to geometry of the site. I would assume that the force for a pile that slopes to a peak is less than the force for a pile that slopes infinitely off to the distance. Does anyone here know how I would go about calculating the force on the wall in "case 2"?

https://imgur.com/a/BLXR1kp

### RE: Design of Salt Retaining Wall

You could probably use a "trial wedge" method (see Bowles book on foundation design). But if your angle of repose doesn't hit too far back from the peak (on the downside)......it's probably just faster/easier to do it by the same method as "Case 1".

### RE: Design of Salt Retaining Wall

Do it the graphical way as you would derive the orginal active earth pressure:

Vary omega till you get the bigges Earth Pressure E under equilibrium. The only difference to the known solution is the way you calulate the force of the soil G (which now is somehow restricted). You wont need a lot of iterations. Then you chose a reasonable distribution over the high of the wall for earth pressure to get the forces on the wall.

### RE: Design of Salt Retaining Wall

You can also look for references that talk about broken back slopes. There should be something out there either in your personal library or online that explains it.

### RE: Design of Salt Retaining Wall

For the proportions you have drawn, Case 2 looks like the larger of the two loads. Maybe that's just because the angles of repose are shown differently.

If the angle of repose is the same for both cases, the width (or diameter) of the pile would need to be pretty small for Case 2 to be appreciably smaller than Case 1.

I have been dragged into a couple of retaining wall failures, so be careful and be conservative. It's not an exact science.

### RE: Design of Salt Retaining Wall

The (horizontal) zone of influence of sloped backfill on a retaining wall is sometimes assumed to be twice the total height of the wall. If the top of the pile is at least that far from the wall, calcs for "Case 1" are reasonable:

If top of the pile is closer, assuming the backfill to level off at the high point will give a lower, but still conservative answer:

### RE: Design of Salt Retaining Wall

I would design for the peak height. Eg if the pile is 30ft high I’d assume 30ft rectangular block of soil.

Of if that was too excessive I’d average the soil height in the zone of influence.

### RE: Design of Salt Retaining Wall

Is there a need to consider the force of a front loader pushing against the pile as the supply dwindles?

### RE: Design of Salt Retaining Wall

Good point XR20.

I often visit loading yards and it’s the machines which smash the walls, not the piles of stuff!

### RE: Design of Salt Retaining Wall

Lascaris:
Given the salt storage application, I would be particularly careful with the rebar cover on the inner face, with the conc. mix design to limit salt migration into the conc. and maybe with some inner face surface treatment to limit the slat migration.

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