Footings on fill

[RuralCRNA]

I'm planning to start a 30x30 detach in my backyard. The grade of my yard is going to require me to pour footings then a small foundation wall on top of them. My question... Should I dig the footings in the existing soil, pour them, then build a taller foundation wall and push fill up to them OR

Bring fill in and bring the area up to grade then dig footings in the fill and pour smaller foundation walls?

I can see the problem with option 2 as far as settling goes. The amount of fill I would need would be somewhere between two and three feet. The footings will be at least 30 inches deep.

Commentary is appreciated!

 

[RivennHewn]

Don't be one of those horror stories.

Call a geotech.

 

[canuckian]

I just made a similar decision and went with existing soil. There's something about building on compacted soil that gives me the willies. Sure, it can be done "right" and pass a compaction test but there's something about soil that's been compacted by mother nature for millions of years that doesn't give me those willies. I'm using a 6 foot foundation frost wall on the back and stepping up to a 4 foot wall half ways up the sides and across the front. Funny this topic came up today as my footings are scheduled to be formed up first thing tomorrow morning and hopefully run by the end of the day.

 

[7th Kahuna]

Engineering aside, if the existing soil were suitable for the projected load, I would expect to pour the foundation walls to height, be that slab height or curb height and then backfill with sand or another compacted base before finally pouring the slab over it. Drop in some steel rebar for good measure. If on the other hand the soil needed to be compacted in order to support the structural load, I would expect to excavate the entire area, re-compact, and import and compact additional soil to bring the elevation up to final height before digging the foundations. In this case you might then go with a monolithic pour.

If you are uncomfortable with this question, please consult an expert. If nothing else, you need to get the foundation right. Good luck.

 

[ConCretin]

You could place your foundation on properly constructed fill but it has to be done right and I doubt it's cost effective.

The cost of a foundation is driven more by length than height. You have the same footing and the labor to set a 4' panel is about the same as a 6' panel. The major expense is the additional concrete.

Now if your talking 12' retaining walls, that's a different matter but I'd still opt for placing on native soils.

 

[Milton Shaw]

One of the houses across the street from me. They filled and compacted it and then dug out the footings. Concrete truck was on the way when the inspector made them dig out the fill and original topsoil and dig footings about 4 foot underground to be into original subsoil for the footings. Ended up with about 4 feet of concrete in that area of the footing. Check with your inspector he has final say so on what he will pass.

 

[RuralCRNA]

Thank you everyone for the advice. I am just going to dig the footings in the native soil and then backfill the walls to make grade. I can just see a disaster doing it the other way. My next door neighbor poured on top of clay fill and he has some pretty good separation from the apron and the slab.

 

[canuckian]

good choice IMHO. The soil around here is a combination of red clay and what looks like sand. Also, mine's built on a bit of a slope so I figured I'd use as solid of a base as I could. Just had the frost walls poured on mine this afternoon. 4 ft dropped to 6 ft half ways back and all along the back.

 

[RuralCRNA]

good choice IMHO. The soil around here is a combination of red clay and what looks like sand. Also, mine's built on a bit of a slope so I figured I'd use as solid of a base as I could. Just had the frost walls poured on mine this afternoon. 4 ft dropped to 6 ft half ways back and all along the back.

Nice! I start mine this week!

 

[excavator]

I am a full time excavator and advise on option 1. After wall is built you want to back fill with a small compactor. Don't back fill with fine sand as it never compacts. You can use recycled stone with dust or use road stone with dust or bank run sand that compacts great

 

[RuralCRNA]

I am a full time excavator and advise on option 1. After wall is built you want to back fill with a small compactor. Don't back fill with fine sand as it never compacts. You can use recycled stone with dust or use road stone with dust or bank run sand that compacts great

Thank you for the advice!