Cantilevered Ret Wall - Gut Check

ACI 318-19 modified their one-way shear equation when Av < Avmin:

This equation applies to foundations of cantilevered retaining walls (the module I’m struggling with). I’m creating a baseline library of retaining walls for our company to pull from for residential projects because a geotech report requirement is often waived by our local building department on these. So, I am assuming minimum values like 1,500 psf soil bearing, 35 psf/ft active soil pressures, 300 psf/ft passive bearing pressure, 2,500 psi concrete, etc.

With all that said, my 8’ retaining wall requires an 8" stem but a 30" thick footing to pass. That’s with a 9.5’ wide footing. Something is off, it feels very disproportionate, but I can’t put my finger on a solution.

Any ideas? I can share more screenshots or let me know if I can share the calculation itself.

Hey Colton, nice to see you here!

That does seem like a really thick footing. The new ACI provisions in some cases more than halve the shear capacity of footings so that 30" thickness might have corresponded to a 16" footing before, which feels a lot more intuitive.

If you want to reduce the thickness, at this point, some ideas would be (if you can) to move the stem to the right so you have a longer toe and shorter heel, though you will hit a limit on sliding resistance at some point. You could also increase the reinforcement in the footing, but the capacity increases with the cube root so not very good bang for buck.

Would love to hear what others have found to solve solutions like this.

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