increase very old undersized footing

huangyhg

increase very old undersized footing
i have a 4 story residential building with a very small footing built in the 1920's. the footing size is 16" wide x 5" thick. is underpinning it with a larger footing the only "practical" way to increase it in width. the major problem is the building has been totally renovated and its at the end of the bank financing it. the architect never required the existing footing to be checked. the buildings stucco and brick is cracked like a road map. i got the job to inspect it and  remediate from the owners lawyer. any tips will be greatly appreciated.
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is is possible to add additional new footings rather than increase the size of the existing?  that would be much simpler.
mike mccann
mmc engineering
by underpinning the entire continuous footing thats there now i am essentially making it all new.
what about using some piles that a lot basement repair guys use.  they are driven to refusal and seem to work??
ok - continuous footings...
you could use pin pile - 2 " diameter - per a geotech recommendation at the exterior continuous footings, and underpin any interior strip footings periodically along the footing.   
mike mccann
mmc engineering
i would talk to a specialty contractor who installs atlas brand resistance piers.  i think that would be a better solution in this situation.
daveatkins
daveatkins
resistance or push piers on a building thats looks ready to collapse and is already a lawsuit against the architect?? i don't think so.
this is an existing condition and if the use hasn't changed significantly, can the existing footings be left? what does the geotekkie say? we added an additional 4 floors to a building in downtown toronto that had been founded on spread footings.  can testing be undertaken that would indicate a higher bearing pressure considering the consolidation that has occurred over time. was the reason for checking the foundations a consequence of foundation failure? foundation failure will not likely be catastrophic. would the owner be accepting of any risk realising that future remedy may be more costly? would the authority having jurisdiction be satisfied?
i"ve been involved with a few projects that have been standing for the better part of a century and the foundations have been somewhat undersized.
just some ramblings...
dik
dik
the building is 90 years old and the owner is looking to get another 40 years out of it. the 12" brick walls have no lime mortar left in their joints and the rear wall is on the verge of collapse. something has to get done asap.
ok... then there is major renovation going on and it may be prudent to bring the building up to snuff.
is there any heritage value to the building and any heritage restraints?
also slideruleera has a pdf paper on historic masonry that i prepared.  you might want to take a gander at it. if you are planning to maintain the original masonry, you have to examine the issue of vapour barrier and existing mortar.  in old buildings, vapour barrier is not often used and the wall relies on the mortar to 'wick' moisture from within.  in addition, modern lifestyle creates a lot more humidity within a building.  someone (architect?) should look into this.
often damage is done to old buildings by a lack of understanding on how they function.
dik
a 16" wide by 5' thick continuous wall footing under a block wall is very minimal and almost useless.  helical piers might be a good way to underpin the building.  you would need to get the pier brackets up close to the wall by trimming off the edge of the thin footing.  however, the center to center helical pier spacing may be small because the footing probably is not strong enough to span a reasonable distance between helical piers.
you could also underpin the footing with alternate concrete piers - that is, maybe 4'w x 3' piers spaced at about 8' on center or closer.  this would provide at least the same bearing area, but hopefully at a deeper elevation with better bearing capacity.
however, whatever method you chose, there is the probability that the building will experience some additional settlement and damage. therefore, you want to make sure the owner is aware of this and that you are not responsible.