the difference for the surcharge load of 1 feet area or 100 feet area behind the retaining wall

[johndeng]

There is 1 feet of distributed surcharge load 300psf, or there is 100 feet of distributed surcharge load 300psf right behind the retaining wall, what's the difference of the soil pressure due to the surcharge load? say wall retaining height 6'.
I can only figure they are the same with calculation, but I know they are not.

 

[PEinc]

How about giving us a sketch so that we are understanding you correctly?

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[johndeng]

Please see attached.

I think the additional soil pressure due to 1 feet surcharge is 100 times smaller than that of 100 feet, but it's not.

 

[johndeng]

no, actually i feel it's 6 times smaller, but the formula showed they are the same.

 

[PEinc]

Look up the Boussinesq equations for strip and area surcharge loads. You also may need to position the surcharges so that they provide the worst case loading. For overturning and sliding, the design will be more critical where the surcharge starts at the back end of the heel of the foundation. For design of the walll stem, the surcharge directly behind the stem would be more critical.

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