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Underpinning a footing

Rio

Silver Member
Joined
Mar 31, 2010
Messages
224
The last two story addition we did the plan checker told us we couldn't underpin the single story footing to get it to carry the weight of the 2nd story. This took us by surprise as it had never come up before. Since then California has gone over to the CRC which is basically the IRC and now we have a possible 2nd story addition and would prefer to underpin the footing, tying it together with rebar dowels, rather than removing the footing and replacing it with a larger one. I've been reading through the code book and don't see where this is prohibited but don't see where it's condoned either. I've attached a stripped down detail showing what we normally do and are planning on doing.TIA for all comments,Rio

View attachment 1525

Underpinning (1).pdf

Underpinning (1).pdf
 
If the modified footing meets the requirements for the new construction we have and would accept it.
 
I don't see a problem with underpinning a foundation.

I'd work on the drawing a bit more though.
 
Yeah I don't see a problem with underpinning as long as the detail is submitted by a RDP.

I've never seen an underpinning detail like that; perhaps they are more opposed to the detail than to the actual underpinning?
 
Thanks for the comments. The time the plan checker wouldn't allow the underpinning was the first and only time it's come up. He's a senior structural engineer and usually works on large projects but there weren't any for him to pick apart so we were the subject of all of his attention; a very nice man and a walking dictionary of information but a bit overboard. On the detail, it has a lot more information but the file is too large to allow to be uploaded to this site so I had to strip it down.

On the not filling the entire excavation with concrete our experience has been that when we underpin it's impossible to dig out the area needed without having an angle similar to what is shown. When we pump in the crete it's been easier to just go ahead and fill up the entire excavation than to form (although we have done so previously with gyp. bd. as it doesn't have to be removed), and more importantly, to compact the excavated area sufficiently. Of course with the sky rocketing price of materials that is starting to occur again, maybe we'll consider forming, backfilling and compacting.

Thanks again for all the comments.
 
Have Designed this method and accepted and inspected this method; Key is width and segments of installation.

Have also used this methos to create sizeable loading dock areas on commercial mansonry or steel projects.

generally the only reluctance I have is doing this on prefab steel rigid frames.
 
I remember at the time he explained the reason why but I didn't pay too much attention to it as he as so adamant about saying no that there seemed to be no point in getting into it more with him; we had a lot of other issues we had to address to get the permit.

I'm thinking now that maybe it had something to do with the property being close to an active earthquake fault line however the engineer who was on our team knew about the fault and had designed the structure to comply with the code requirements regarding this situation.

I got a lot of good information from this plan checker but he was definitely a stickler and, as is the case with some senior structural engineers, had a tendency to go overboard. When I see him again I'll ask him to go over the project and explain his decision.
 
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