Any footings experts?

[Pinusbanksiana]

I am building a 26x8 four season porch on sono tube pier footings. I am digging them down 4.5 feet and flaring the bottoms. Here is my situation. One of the footings has hit a solid rock down about 3 feet. It is solid and I can't even break it with a bar. Considering pouring it as is. If I move it one way to avoid it, I risk hitting a propane line, and the other side is a water line. Am I being foolish to pour it so shallow?

[MattL]

If it is bedrock you should be able to bear on that without issues. If it is just a large boulder it would be best to dig it out either by hand or with a mini excavator. If you have sandy soil it may be ok at 3' but if it were me, I'd be pulling that rock out and getting below the frost line. It will be a lot cheaper to do it now than later when the porch starts shifting.

[Pinusbanksiana]

No it isn't bedrock. In fact it is probably the worst case scenario. 3 feet of rocky gravel (glacial till) and then clay. There is no mottling of the clay. It is my last footing, all others are down deep and fine. I was just out there again pounding on it and I can't budge it. My thought process (probably wrong) is this: This rock is no doubt a foot or more thick, putting it below the frost line. If I expand the flaring around the top of the rock wouldn't the rock act somewhat like a footing itself. If I dig around it, it is likely that I couldn't lift it out of the hole anyway. I'm on a tight budget and the 300-600 dollars or more that a mini would take would hurt.

[CAMAN]

You could rent a jackhammer and remove it in chunks. Otherwise if it is very large and deep enough I have seen people drill holes and epoxy rebar in and pour the footing directly on top. Check with your building inspector to see which way they prefer.

[delcecchi]

I saw a "ask this old house" show where they had a similar problem and drilled holes in the rock and used some sort of expansion wedge bolts to break it.

or this

http://www.dexpan.com/dexpan-how-to-use-...t-breaking.aspx

[PurpleFloyd]

Pouring on tp of it might work but it would not meet code if the footing needs to be inspected which is the case in some cities. In the end you have to ask yourself if it is worth the risk to save the time and effort.If the rock is not below the frost and it heaves, how much might that cost later to fix?

[Pinusbanksiana]

I calculated the number of footings I needed, added one more in that span because I like to over build things like footings. And I am way up in Gods country where no building inspector is going to even care. I'll look into the hole drilling thing but I'm likely to just pour it on top. I measured it and it is actually 42 inches down to the rock. Triple the outer rim joist and call it a day is what I will likely do.

[CAMAN]

If that's the case I would at the very least drill a couple holes and drop some rebar in (no epoxy) just to make sure nothing moves laterally.

[Pinusbanksiana]

I saw a "ask this old house" show where they had a similar problem and drilled holes in the rock and used some sort of expansion wedge bolts to break it.

or this

http://www.dexpan.com/dexpan-how-to-use-...t-breaking.aspx

That is pretty neat stuff. My rock is buried, I don't think I could do that. It has nowhere to expand to.

[delcecchi]

It expands and breaks the rock into pieces so you can dig it out of the hole. A little dirt isn't going to stop it. I just thought it was really a cool solution of how to get that rock into manageable pieces that you could dig out of the hole.

[reddog]

Pour the footing on top of the rock and wish it well.

If youre worried about it, then dig a 4foot by 4 foot square 6 to 8 inches deep and place a piece of 2 inch extruded foam over the footing and make the footing think its in Kansas..

Ive got whole houses that are no deeper than 16 inches in the ground and my frost line to build to is 44"