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Put down processed gravel to build up the fill again. Then put a layer of pea-stone down on the slope. Finally, but rip-rap stone over the whole slope.

Hey Gus -- If I read this right, you've got a slab poured on a slope and its washing away 14" high on the downhill side of an 11 x 15 slab?  How far back under the slab is it gone?  You can pour a slab on sand and gravel as long as the sand and gravel are contained, if not, you need footings of some sort, this would be the "wall" you're talking about.  How deep, wide, reinforced or not is a matter of local code and custom.

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In Kansas (north half), your frost depth is probably 36"-48".  Typical minimum design in your nothern neighbor is 40".  Do you want to support the edge of the slab or just put in a "retaining" structure.  Either one can be done with cmu block.  Be sure to ge tblock below frost line.  You might onsider pouring a thin leveling concrete leveling pad to begin laying your blocks on.  If supporting the edge of the slab a small footing should be considered.

Quoted: Put down processed gravel to build up the fill again. Then put a layer of pea-stone down on the slope. Finally, but rip-rap stone over the whole slope.

While it maybe cheaper, its stone. Your concrete club card is hereby revoked.



Dig a ditch, set a form, get some steel use fibers and pour a concrete wall to entomb the base material. Since its on a  grade, I would do the footing in the ditch maybe 12" subgrade, put some steel to tie the footing to the wall, and have the wall totally encase any exposed and all downhill area of the subgrade.