Retaining Wall Design

[tclat]

Hi All,

I have to design a retaining wall which has a large part of the stem below ground. The reason being we found somewhat questionable and suggested excavating down to more suitable depth for bearing purposes.

The height of the stem is 25 feet. however the soil over the toe is approximately 10 feet but tapers at a 4H:1V slope a distance of about 30 feet from the face of the retaining wall and then slopes at 2H:1V.

I'd like to use some of the material in front of the wall to resist not only overturning but to reduce the bending in the stem. I was thinking of ignoring the first 5 feet since the material to the front of the wall slopes and using a reducing the passive resistance to 50% as an additional factor of safety since I'm aware it takes more movement to develop the full passive resistance. Does this seem reasonable?

Thanks

 

[JAE]

Yes. The only concern would be if someone in the future saw the depth of footing and reasoned that they could excavate down further for whatever purpose, assuming the original designer (you) designed off the footing for stem bending and overall stability rather than with the front toe soil in place.

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[tclat]

Yes. Perhaps I can add a short wall where the slope of the material at the front of the wall changes.

 

[PEinc]

Can you use bearing piles with the footing/pile cap at a higher elevation?

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[Signious]

On the lines of JAEs post - this is something that has always bothered me. For a lot of walls it makes a pretty significant difference if you can use the soil above the toe in your design.

I have toyed with the idea of requiring the construction contractor to stain the concrete below your minimum toe backfill line with a note to not remove backfill, but a drainage matt and/or the ravages of time will throw that out the window.

In my jurisdiction they are brining in 'Retaining Wall Agreements' which are signed between the owner of the wall and any adjacent property, and a copy is permanently attached to the city files for those properties. Perhaps including the required toe backfill depth in any kind of design/ agreement can help.