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Concrete Wall Soil Loading Question

Concrete Wall Soil Loading Question

Concrete Wall Soil Loading Question

(OP)
I have a common reinforced concrete wall between two detention vaults of differing elevations that I am designing. See the attached detail...

The active pressures given by the Geotech were 35 psf unrestrained, and 50 psf restrained for the wall.

My question concerns the portion of wall below the bottom slab of Vault "B" in the attached diagram, between levels 128.00 and 123.5. Considering the presence of the foundation drain, and the surcharge loading of the filled vault above, what lateral active pressure diagram would you impose on the short wall in question? Would you use the 50 psf value times the height of the soil retained clear up to the 142.04 foot level, or something different?

Just trying to get a reality check here... Thanks.

Mike McCann
MMC Engineering

RE: Concrete Wall Soil Loading Question

I would use the lateral water pressure at the higher elevation increased by the at rest pressure (water pressure + 50 pcf times height below 128.5) as it lowers elevation.
Bottom line is it's a pretty short span, so the reinforcing is probably controlled by the water above.

RE: Concrete Wall Soil Loading Question

Below Vault B, I would use the 50 psf restrained value because the wall is not free to rotate at the top in a classical cantilever sense. I assume when you are saying "50 psf up to the height retained clear up to the 142.04 level, you mean that the LEP at the 123.5' level would be (18.54')(50 psf)=927 plf/ft. I would say that this is the most conservative way to do it and the way I would typically do it. If you need to sharpen your pencil more, you could determine the surcharge loading from the vault and contents and reduce the LEP to some degree.

RE: Concrete Wall Soil Loading Question

(OP)
Thanks. I'm gong with the 20' X 50psf trapezoidal loading on the wall. Steel at center of wall works with the moments for both the full and empty conditions and it seems reasonable.

Mike McCann
MMC Engineering

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