Possible Frost Heave Effects on a Unique Structure

[MrEngineerUS]

I was tasked with designing a concrete wall that has a bench projecting out from the side of it. They would like the face of the bench to extend to the ground. Essentially, an 18"x18" cross section of concrete that projects from the side of the wall face that people will sit on. The concern is that frost heave would act on the bench but not the wall (as the wall footing extends below to the frost line depth) and cause cracking.

Is it likely this would this actually occur or is this concern unwarranted? I have a hard time believing that pressure on the bottom of the bench from frost heave would be so great as to cause cracking. The bench protrudes 18" from the face of the concrete wall.

 

[oldestguy]

Easy fix. Since you will have an excavation for the foundation of the wall, backfill the zone below this bench with non frost susceptible material. I'd use clean fine aggregate for concrete, but place a 6" layer of clay soil at the surface to shed infiltrating water.

 

[MrEngineerUS]

I was thinking something similar but others were determined that the solution was structural. Just because we can design something to resist any possible loads doesn't mean we have to do so as other more cost effective solutions may be available if we can find them. Thanks for the insight, oldestguy!