2' Retaining wall?

[psychedomination]

Hi there,

I am a graduate engineer working on a basement project. I am currently stuck with an existing concrete column that was not cast on a proper footing. It was cast on a very thin slab perhaps 2 inches realistically. The client will be excavating down 2 feet from this concrete slab to increase the ceiling height by 2 feet. This will happen on all faces of the column. When they excavate down it will reveal 2' of sandy base material. I was thinking that this will need to be retained by a retaining wall or something. See the attached sketches. Are there any better solutions that would not protrude out much?

Would I need to take the load of the column on the soil as surcharge?

Any guidance would be appreciated.

http://files.engineering.com/getfil...c7-ab90-7b58b4b3076f&file=basement_column.jpg

 

[PEinc]

Can you pick up or brace the column and then excavate beneath it and install a real footing that is deep enough?

http://www.PeirceEngineering.com

 

[psychedomination]

Can you pick up or brace the column and then excavate beneath it and install a real footing that is deep enough?

The column spans to the top of the ceiling, I don't think it would be possible to lift it. The contractor was proposing to cut out underneath the column and place a footing but I am not sure how they can keep it propped up? They would have shoring jacks holding up the ceiling floor slab though.

This photo kind of shows the situation perhaps better than my sketch. The photograph is showing a wall that will require a similar fix to it.

 

[Okiryu]

Not sure if this makes sense: provide temporary supports for the ceiling or beams which are connected to that column, so “the column is not loaded”, then you can excavate underneath the column to place the new footing...

 

[psychedomination]

Not sure if this makes sense: provide temporary supports for the ceiling or beams which are connected to that column, so “the column is not loaded”, then you can excavate underneath the column to place the new footing...

Yes that makes perfect sense Okiryu. My only concern is that if it is done this way the column would be in tension under its own self weight. I am not sure if this would be an issue. Also how would the column reinforcement tie into the wall?

 

[PEinc]

Calculate the load on the column and see if you can grab the column with bolted connections and then jack it up until it just starts to move upward. Then remove and replace the existing "footing" with a deeper footing as I described above and as Okiryu reiterated. Also, look at his suggestion to support the beams that frame into the column. This is easier with steel columns but may also work for concrete if the loads aren't too great.

http://www.PeirceEngineering.com

 

[Okiryu]

You may add diagonal supports to that column if you are concerned about tension from its own weight.