Interesting settlement in 1901 five story building 1

[StrucPatholgst]

Building is in a flood zone, constructed on fill. Exterior appeared to be fine, no cracks, well maintained, received a full repointing job about 10 years ago. Get inside on the first floor, notice the slabs are all pitching towards the center, with cracking at regular intervals. Found a 1 ft x 1 ft inspection hatch that looks like it was put in during the 1940's (had modern sized lumber frame, but plaster and lath under the newer layer of flooring). Get my 10,000 lumen flashlight and cell phone down there, and the entire field of slab base had settled about 10 inches. I could see clear across to the perimeter in every direction. Granite block pile caps were visible and still in contact with the center grade beams. Report is for a prospective leasing tenant who was thinking of making an offer on the building.

Anyone ever felt compelled to send a copy of findings to a building owner? I'm also concerned about the condition of the piles.

 

[SlideRuleEra]

1) Anyone ever felt compelled to send a copy of findings to a building owner?

2) I'm also concerned about the condition of the piles.

1) No, just the Client. Evaluated an 1885 seaport waterfront, brick warehouse for a Client with an option to purchase. Building had been cracked from top to bottom in the 1886 Charleston, SC earthquake (estimated 7.0+ Richter). Five year old, interior latex paint was stretching like chewing gum across fresh smaller cracks; probably from settlement caused by recent area large-scale changes to surface drainage patterns. Advised the Client not to buy... he did not buy.

Doubt the Owner would have appreciated receiving an unsolicited report that his building was slowly "tipping over" into the water.

2) It's possible that 1901 timber piles were pressure treated with creosote. If so, they are likely ok... at least from "rot".

 

[phamENG]

I guess it comes down whether or not you feel there's an immediate safety issue. If you think the building could collapse at any moment, then I would say you have a duty to report that. But if it's more of a 'this building is in rough shape and a really bad investment, they should do some work on it soon' then I'd leave it be.

 

[JoshPlumSE]

For what it's worth, I don't believe it is uncommon for a pile supported foundation to have the soil "pull away" from the slab a bit after freeze / thaw and moisture cycles and such.

Isn't the standard of practice to assume that (if you have a pile supported foundation) that the soil offers ZERO support for the slab?

I remember working on a nuclear project where we were supporting our structure on a pile supported slab. We were told that our project ended at the connection to the slab. They said their engineer would check the slab for the applied loads..... I talked to the EOR about this. He had done work for this client before. He explained that the slab was relatively thin (for nuclear work!) and would never calc out unless they accounted for soil bearing resisting under the applied loads. And, that the site had a long, complicated justification for this. Probably based on a long, complicated GeoTech report.... And, the site knew that any work we did in this regards wouldn't be accepted and they'd just have to re-do it themselves.

 

[bones206]

I've seen pile-supported buildings performing as designed with significant subgrade settlement voids. I've also seen pile-supported buildings with 4" slabs spanning 25-30 ft; some that failed similarly to the OP's building. Can only assume that some designers may not fully appreciate the potential of settlement and that slabs should be designed as structural elements rather than the usual slab-on-grade.

@StrucPatholgst - what's the thickness and span of this slab where it failed? Was it a regular grid of grade beams or just one along the center?