Just finished excavation for an addition but the hole is 12 to 18 inches too deep because the rock kept breaking below the level we wanted. It is a very hard shale almost standing vertical. Will code allow me to fill to the proper level with 2B stone and pour on top of that? The footer will be 6 ft below grade.
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Replies
My gut tell me no, but the only good way to find out what code allows is to call the person that's going to do the inspection/approval and ask.
Don K.
EJG Homes Renovations - New Construction - Rentals
Properly compacted, yes, crushed stone can support footings. Superior Wall foundations, for example, are always installed directly on a crushed stone footing. You may need to verify compaction, and your AHJ may require paperwork. But it's done all the time.
Andy
"Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein
"Get off your dead #### and on your dying feet." Mom
Compact it in small lifts and U B fine
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Since you've already dug that deep why not just place your footings there and build with more headroom in the basement?
This is less about code and more about bearing competence and stability.
Some shales are expansive. Wouldn't hurt to investigate this before you backfill.
The choice of backfill material depends on the result you want and the existing conditions.
I use a variety of materials (sometimes crushed stone) depending upon what we are trying to accomplish.
Is there some reason why you would want to use stone rather than e-fill?
Is there any chance of groundwater getting to the shale?
Am I understanding correctly that you are only filling in 12" to 18"?
At 6' below grade you have a variety of considerations depending upon the size and shape of your excavation.
Is this a trench for footings? A hole for a basement?
Are the walls of the excavation Type A? If not, do you have the space on site to lay the walls back?
Dave, I don't know about this circumstance, but a lot of the world has no idea about e-fill. It's not something I ever encounter in the northeast.Andy
"Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein
"Get off your dead #### and on your dying feet." Mom
Makes sense. <G>E-fill is engineered fill. A well-graded mixture of material, usually 3/8-minus that is designed to have cohesive strength, a plasticity index below 15, and a density of about 125 pounds per cubic foot, and will hit 95% or better of a standard Proctor without undue effort.It's the one-size-fits-most answer to backfill.It's not so good for areas that will get wet, otherwise it's usually the cheapest way out.If you need high strength or good drainage, there are better choices.I think for this guy if he is working in trenches CLSM (lean fill) would be the best choice.No compaction, fast, really easy, amazing bearing competence, unaffected by moisture, much safer than getting in the trench with compaction equipment.Per cubic yard cost (in place) is comparable to dirt on small jobs in trenches.
Sounds like what we call dga (dense graded aggregate) in the northeast, although the size runs to 3/4 max in my experience. It's often used as fill around catch basins and the like on road jobs.
Otherwise, life on glaciated terrain mostly leaves very competent bearing soils. How much more compaction are you gonna get than what's left after half-mile thick ice moves over the land for a couple of millenia?Andy
"Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein
"Get off your dead #### and on your dying feet." Mom