Footing on top of existing

[civeng80]

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).

 

[jayrod12]

Some call me conservative. I call it comfortable. How do you justify supporting a building you're designing on someone else's retaining wall/fence foundation that you did not design in the first place?

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.

 

[jayrod12]

I'm always leery about supporting new on existing unless I've designed (or at least know who designed and can confirm the details) the existing structure. If I can justify it by saying its a minimal load increase then that's one thing. In this case we're talking about supporting a "significant" amount of load on a foundation that you have next to no details about.

 

[civeng80]

Hokkie I was on your side until about 2 days ago but now have second thoughts. Concrete, even lean mix concrete is not earth and it has some bending strength (even unreinforced) so the 2 separate concrete bases could behave like 2 eccentically loaded footings (with load outside of the kern) and high localized pressure at the centre and separating on the outside.
An undesirable condition.

 

[rowingengineer]

I'm with Hokie, as long as the footing on top of the RW and weak mix is sized for bearing on clay I can see no reason to worry, if you are worried about differential settlement, dowel the two together.

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."

 

[aaronPTeng]

I agree with rowing and hokie,

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