Retaining wall to retain liquid
Retaining wall to retain liquid
(OP)
At first when I did the overturning calculation and the sliding calculation, I added the weight of the water above the heel like if I was designing it to retain soil. But the more I think about it, I feel like I should not. If I do not add the weight of the water, it seems impossible to do this. Basically we want to build a secondary containment at a chemical plant. We want to build a wall around a large tank to make sure we can contain the largest tank if it breaks. Do you think I can use the weight of water above the heel?






RE: Retaining wall to retain liquid
Overturning and sliding results from wind or seismic forces, you will need to check cases for a full tank and an empty tank.
The secondary containment "tanks" I have seen typically have knee walls (relatively short walls, say 3' or 4' high) that are designed to contain the volume of the largest tank in addition to some allowance for rain water (say 10% of the tank volume). If this is your case, sliding or overturning of the secondary containment tank is not a problem.
RE: Retaining wall to retain liquid
I think what precast78 is talking about is a perimeter retaining wall that encircles some separate tank that, if it spills, will help retain the liquid. Thus, the retaining wall is serving as an isolated, cantilevered stem wall on grade, totally unlike a tank...with not continuous base across the enclosed area. (Is that correct precast78?)
To answer the original question - I would say that you shouldn't rely on the liquid as some sort of vertical dead weight helping to hold down the heel of the retaining wall as liquids have no internal shear resistance. The liquid would simply move out of the way if the heel were to rise upward.
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RE: Retaining wall to retain liquid
RE: Retaining wall to retain liquid
RE: Retaining wall to retain liquid
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
In my response, I'm assuming:
1) no dirt on the heel side and;
2) moderate pace of leakage. If the water's coming in tsunami style, that's another matter.
RE: Retaining wall to retain liquid
RE: Retaining wall to retain liquid
This is also assumed in the foundation design for the tank, by the way.
RE: Retaining wall to retain liquid
I think you should look at the situations with, and without, the water, and design for the worst case.
Mike McCann, PE, SE (WA)
RE: Retaining wall to retain liquid
If so, the heel of the retaining wall has weight on it from water, but once it rotates only a bit, you now have water under the heel too - thus a buoyant condition for your heel with the same pressure on both sides.
The water won't push down on the heel any more that the water below it pushes up (same water pressure at the same depth).
Think of a slab of concrete underwater. The only thing pushing down on it is the buoyant weight of the slab - not the water above it since there is similar water below it.
The water will simply flow out of the way of the heel which moves upward through the water.
Now if the heel had soil above it, that soil is interconnected to the surrounding soil with an internal shear stiffness/resistance. I think there's a big difference here between heel soil and heel water.
The sketch above by JStephen does show some soil on the back side. If there is full fluid coming to the wall above this soil, then conceivably that heel soil might become fully saturated and be a dead weight on the heel to some extent.
We've debated here in the past about how much soil can be counted on over tank footing extensions to counteract buoyancy uplift. The concern of taking a wedge of soil instead of only the soil directly above the footing extension is that the soil, being saturated, may become "mush" - i.e. the soil has lost its internal shear stiffness and only the soil directly above the lip will resist uplift.
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RE: Retaining wall to retain liquid
RE: Retaining wall to retain liquid
RE: Retaining wall to retain liquid
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Retaining wall to retain liquid
RE: Retaining wall to retain liquid
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Retaining wall to retain liquid
RE: Retaining wall to retain liquid
RE: Retaining wall to retain liquid
Dik
RE: Retaining wall to retain liquid
Of course you could do that with something like the sketch by J Stephen or simply lay it on the ground and back fill from beyond the heel / T to the top of the wall at a suitable angle to provide your static load.
~This would also reduce any shock loading from a wall of liquid racing to ward the wall from a catastrophic collapse. It reduces the bund volume, but only by a small amount.
This is bund wall design of which there are many examples.
As said a few times, a sketch of what you're thinking about / options would help.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Retaining wall to retain liquid