Cutting Off 25 % of a Column Footing Projection

[cap4000]

I am involved with underpinning a corner column footing. In order for the new elevator cab to go past the corner footing, a 36inch x 36inch piece of the footing must be saw-cut off. The new elvator pit slab 5 foot down will now be dowelled into the underpinning pits with chemical anchors to assist as the new( 25%)footing. A NYC structural engineer(EOR) says this is no problem. Has anyone ever seen or done this before?? Your comments will be greatly appreciated.

 

[PSlem]

When we underpinned the footings of shigh rise buildings we typically dug pits under them 1/4 footing at a time, then proceeded when the first was concreted and drypacked, so I see no problem with the scheme. Only concerns would be is the footing oversize or marginal for the load? Of course I would sheet the pit as excavation proceeds to avoid a loss of ground. How much settlement do you anticipate?

Engineering is the art of not constructing...of doing that well with one dollar what any bungler can do well with two after a fashion.

 

[cap4000]

PSlem

The 25% sections of a column footing is the standard procedure,however the footing was 6ft. x 6ft. with a soil allowable bearing capacity value at just around 5,000psf max. Without the inside 25% it goes to 6500psf and thus the need to use the elevator pit slab dowelled to the underpinning. Settlement unknown, since there is no Geo-Tech for the job. Groundwater has become a major issue, so micro-piles may be a last resort.