I think Eddie is dead on...
I have a little experience with some backfill in 2 areas...
1. Around the house foundation.
2. Carport backfill.
the foundation backfill was done by someone else and I did not see it done.
I think it was just dumped in and a trackhoe was used to push it in.
It has sank in really go in 2 spots..
the carport I did myself.
18 feet wide, 20 feet deep with some cutouts and narrowed and shallower areas.
Backfill was 6 feet at the deepest, and 2 feet at the shallowest.
concrete walls on all sides.
I used my
L3400 to do it all.
Large rocks, water, and dirt was used for most.
a ~3 inch layer of rock dust was used as a topper before concrete was poured.
Every rock was moved and dirt packed around it and water was used with a plate compactor after the first foot for 2 hours. and then again every foot past that for 30 min.
It has been two years since it was installed and no cracks, or settling is visible.
now my basement on the other hand, has a number of cracks in it....
So when you put dirt in the hole, I would pack it and pack it.
when I was growing up, my dad's best friend owned a grading company and he dug a hole to push trees and such in when building a subdivision per the lead contractor's wishes to not burn it for cost reasons. I remember that story well as this was just down the road from where I grew up. Dad and Russel talking about it as I road my minibike around the site. It was literally 1/2 mile from home and a great place to ride!!
well it's 30 years later and I was recently down there in Georgia. An old friend told me how the owner of the house down the street had recently spent a couple thousand dollars fill a growing hole in the front yard.
So I would take great care to fill that hole, and do it right this time!!!
J