garage/shop build at the angle of repose 1

[glandjr]

Hi, new here, what is the recommendation upon building a 650sq ft.structure as close to a 3' tall Lannon stone retaining wall? If I propose to set an 18" deep footer as a monolithic/floating 5" slab w/ #4 rebar, the 1 to 1, angle of repose, would be 18" lateral from face of said wall? correct? The 40' retaining wall has approx.8" of drainage gravel behind with 3" corrugated pipe to daylight. The 26' garage would start at one end. If this is not recommended based on loam and clay soils, what distance is best practice? does 2'-3' matter? or same unstable outcome? Here our frost line is 48". If a true frost-protected foundation is ideal, is my thinking correct that at that distance inward, I would need footing to be 7' from grade? Is this overkill and should I just go with the half stem wall, half mono pour?
see attached drawing, thanks for your help!
I appreciate your expertise!

 

[EireChch]

What you are proposing is fine. You will essentially have no load on the retaining wall as your rising wall beneath your slab edge will act as a retaining wall. Not sure what your frost depth needs to be but you only need to be below the retaining wall so as to not apply a load to it. Your new footing (not footer) could be 600mm deep where I practice. It saves you digging down 1.2m below bottom of retaining wall.

The only issue is construction, you will likely disturb the wall significantly, especially if going 1.2m below its base. It may be best to knock the wall completely and just let your new foundation wall take its place. Or knock the stone wall and rebuild it if you like the look of it

 

[glandjr]

Thanks for your reply
My frost line is 48" So you're saying build footing at 4' from buildings grade? not 7'?
yes this would just omit the stone wall.
Then this new wall tied in with rest of slab would act like new retaining wall?
For cost reasons, what depth and distance inward from wall face would a monolithic slab be safe?

 

[TigerGuy]

You have posted this in at least 4 threads. Since this is the one that is getting responses, I suggest you take down the others.