Footing on top of existing
Footing on top of existing
(OP)
Ive been working on a project with little nasty surprises along the way.
A retaining wall on a boundary with its footing.
I would welcome comments on the detail attached.
Soil properties stiff to very stiff qallow = 300kPa at least.
Footing of retaining wall competant (not sure of reinforcement).
A retaining wall on a boundary with its footing.
I would welcome comments on the detail attached.
Soil properties stiff to very stiff qallow = 300kPa at least.
Footing of retaining wall competant (not sure of reinforcement).






RE: Footing on top of existing
RE: Footing on top of existing
At the moment one owner has both titles. So no problems getting an agreement.
Maybe need an easement on the title if one of the blocks are sold.
Thanks.
RE: Footing on top of existing
RE: Footing on top of existing
RE: Footing on top of existing
The lean mix concrete footing (being new) will settle at a different rate than the existing retaining wall footing. Such a situation is obviously undesirable as it could (among other things) cause some tilt in the panel (no pun intended) and uneven bearing. Another thing about this detail that bothers me is: no connection between the “new footing” that the tilt up panel sits on and the retaining wall footing nor the new lean mix footing. I would expect some type of re-bar to tie that together. The detail shows some stirrups in it…..but no connecting re-bar. The code mandates a minimum for vertical transfer. (Not to mention some for the horizontal loads that are likely present.)
RE: Footing on top of existing
RE: Footing on top of existing
RE: Footing on top of existing
The tilt panel is dowelled into the footing its just not showed on this detail, also tied to the floor slab (not shown here)
RE: Footing on top of existing
I think I would negotiate with the owner of the fence to replace it after the tilt panel footing is in place.
Mike McCann
MMC Engineering
RE: Footing on top of existing
A concern of mine was the footing sitting on top of the joint, thats why I posted.
RE: Footing on top of existing
They sit on the same clay, but the soil under the wall footing has gotten more compacted over time than the new lean mix footing likely has (unless the contractor did an out of this world job compacting). This thing looks like a potential problem without it all being tied together with reinforcement. (IMHO.)
RE: Footing on top of existing
Mike McCann
MMC Engineering
RE: Footing on top of existing
RE: Footing on top of existing
Infact it would probably be about 3mm.
The pressure on the old footing from the retaining wall which is only about 1000mm high is about 10kPa (includes the footing load). So the settlement of the old footing would be about very roughly 5/20mm. 0.25mm.
Insignificant, Again to quote WARose "thats just nut" Differential settlement really is insignificant..... IMHO.
RE: Footing on top of existing
How tall of a building, ie, load on the footing?
Though I see Hokie's points in theory, and it may indeed be fine, but there seems to be a lot of unknowns for me to stick my neck out if I am the EOR. You can bet if you have any settlement issues down the road and someone sees this detail, you will get questioned on it big time. I fall on the side of the fence with Mike/WArose on this one. I would be concerned if you have only a cold joint between the retaining wall footing and the new concrete and no tie in that you could get a hinge effect there, and then you would have some unintended high edge bearing pressure on the retaining wall footing and the lean concrete.
Mike- I am not sure if civeng's sketch was implying rebar or no rebar in the transverse direction. Are there drawings of this wall? I would anticipate them to be there, but.... I would feel good if there were transverse bars and you tied the two sections of concrete all together into one foundation.
Also, if you have good soil (you indicated stiff clay), micropiles (steel augers) may be a good solution here, then design a grade beam to span between them. If there are contractors in your area that do this they can be surprisingly inexpensive. Then you are working with knowns and not touching the retaining wall.
RE: Footing on top of existing
As Gomer Pyle use to say: Shazam. And I also question that settlement number.....unless the Geotech is guaranteeing that number (i.e. 5mm) in writing, I would take it just as what it is: an approximate guess. Every time I've tried to get those guys to give an absolute limit on settlement (i.e. foundations (for equipment) where settlement would be a big issue).....they've been hesitant to do so and told me to go to piles instead. Settlement isn't an exact science.
RE: Footing on top of existing
RE: Footing on top of existing
You cannot pretend the existing footing doesn't exist. It is there already with slightly consolidated soil beneath its base. The soil beside the existing footing will not be consolidated the same amount and in fact may have been disturbed during the installation of said footing and therefore will not be as strong as the soil below the existing footing. I see issues all over the place with this proposal and would never try to partially rest a new building footing overtop of an existing retaining wall/fence footing.
RE: Footing on top of existing
RE: Footing on top of existing
Liability statements and assumptions can only go so far. What happens if there was no reinforcing put in the retaining wall footing (Just for argument sake) and the new load that you apply to it causes it to fail in shear. You now have two issues, one being that your current building is resting only partially on soil and partially on some random strength concrete, and two being that you have now damaged the retaining wall footing causing both the footing and retaining wall to be rendered useless.
RE: Footing on top of existing
RE: Footing on top of existing
An undesirable condition.
RE: Footing on top of existing
http://www.nceng.com.au/
"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."
RE: Footing on top of existing
I do not see any concern
"Structural Engineering is the Art of moulding materials we do not wholly understand into shapes we cannot precisely analyse, so as to withstand forces we cannot really assess, in such a way that the community at large has no reason to suspect the extent of our ignorance." Dr. Dykes, 1976