Crushed concrete backfill
Crushed concrete backfill
(OP)
I have a CMU "box" of dimensions 13'x28' with walls roughly 5' high. I'd like to fill it 90 percent with crushed concrete &then top it with some 8910, let it compact, then pour a porch slab on top. Does this sound reasonable? Clay backfill would be a no no in this instance as the walls aren't filled solid and I'm afraid the pressures would be too great. The slab will be 5"-6" thick and be reinforced to account for loads and the eventual settling of the fill below.
The crushed concrete pieces are roughly golf ball to tennis ball in size and VERY VERY irregular in shape.
The crushed concrete pieces are roughly golf ball to tennis ball in size and VERY VERY irregular in shape.





RE: Crushed concrete backfill
The six inch slab will have difficulty spanning thirteen feet if not engineered.
RE: Crushed concrete backfill
the walls are already up BTW ,unfilled and unreinforced.
RE: Crushed concrete backfill
Do not attempt to calculate the wall stresses because the aspect ratio of the wall, questionable fixity and assumed density would lead to a very accurate guess based on unrealistic assumptions.
Treat the walls like a common shallow basement wall and use empirical design parameters to show that is is adequate. Under this assumption, even a hollow block wall probably would be adequate.
The obvious problem is the ability of the slab to carry the aticipated loads assuming to support from the concrete fill. This should be a very straight forward design.
Dick
RE: Crushed concrete backfill
RE: Crushed concrete backfill
You hit it spot on!
It is a very basic, proven, garden variety structure with an unusual fill to make it interesting.
My 8' high basement is 12" unreinforced block with 6+ feet of clay/sand backfill and built intersecting a natural drainage pattern. No concrete slab for good top support. No cracks or problems for 30 years. When I tried to analyze it after I bought the home, it scared me, but I guess that is why there is a place for empirical design.
Dick
RE: Crushed concrete backfill