Lowering a leaning mat foundation

[CTW]

I've got a client who has a mat foundation supporting a 1,000 kip (fully loaded) silo that is leaning 10". The mat has rotated to produce the leaning silo. The client cannot raise the low end up and wants to investigate lowering the high side.

I don't think this is a safe route to take, but I thought I'd throw the scenario on this forum to see if anyone has any thoughts or suggestions. I've only seen pictures of the area and wanted to get some other opinions before I make a site visit.

 

[dgillette]

Didn't they lower the "high" side of the Leaning Tower of Pisa by augering out soil beneath it? Now THAT was living dangerously.

 

[lovethecold]

I believe it would be possible, but not sure how practical. The leaning tower of Pisa was fixed to an earlier more stable angle. I don't recall the specifics but it involved drilling holes on the high side, then allowing the holes to collapse to straighten it out. I think the holes were drilled at an angle.

At best I would say this seems easy but would be highly technical to accomplish without causing the silo to tilt the other way. To be safe it would likely be a lengthy process of drilling some holes, letting them collapse, then start again. The big technical questions are how many, how deep, what angle, and what diameter of hole should be used. Also, with the potential liability, who will do the work?

This is a rather peculiar request, I would start with a local geotech and also talk to a reputable professor in geotechnical engineering.

Would it not be possible to empty the silo then raise and support using a deep foundation system?

 

[Ron]

First determine if the "tilt" is caused by differential settlement or if it's caused by the beginning of a bearing capacity failure. Not sure why you can't raise one side with either slabjacking or jacking against needle piles and backgrouting.

 

[CTW]

lovethecold-
My concern exactly about causing the silo to tilt the other way.

The client actually has a contractor that suggested using high pressure water jetting to slowly remove layers of soil and allow the high side to settle. My concern with this was the water used would saturate the soil and cause too much settlement and the movement of the foundation would be uncontrollable.

I had forgot about the stabilization of the leaning tower of pisa. I'll have to research that a little.

Due to other ancillary equipment and structures on this foundation, the client cannot raise the low side.

 

[dgillette]

Look for publications by Michele Jamiolkowski. He was the leader on that effort. The sequence of when to remove how much soil from where would need some thinking. Could be a fun one to work on.

You have information on the soils? You would need that to determine whether it's differential settlement or the beginning of a bearing failure.

Jetting sounds pretty risky. I would be more inclined to try augers, plus disclaimers writ large.

 

[BigH]

Not sure of room, type of soil the foundation is sitting on, etc. But when the Indians (and other but the foundation is common in India) install well foundations, if they go off kilter, then the apply kentledge to the other side - sometimes at a moment arm - in order to bring the well foundation vertical again (a well foundation is a large caisson that is sunk into the ground by removing the soil inside). If the soils are settling differentially and you have the room, you might be able to do this - of course a detailed study of settlement, monitoring and the like would be needed.

 

[Prepakt1]

Suggestion.

First stabilize existing foundation. Piles or compaction grouting.
Underpin and support on adjustable piles or jacks then lower to desired level and leave on temp supports.
Grout underneath.
Jetting alone will give you a base that is saturated and no guarantee against settlement to the correct position or future movement due to bad existing foundation material.

Intrusion Prepakt /marineconcrete.com

 

[ishvaaag]

I woul likely propose build some new sound adjacent foundation, and then transfer the silo loads to it.

 

[oldestguy]

Hey guys: Ron is right. Ya gotta know what caused the thing to tilt before you try to fix it.

I'd bet some trench or other looseness nearby was at fault.

Jetting is for fools, Never do it.

 

[darthsoilsguy2]

do a geotechnical study outside of the silo ftg. confirm the silo ftg was built per plans with adequate soil cover. figure out why it failed. the solution will present itself once you've got the problem. i can't see what would be prohibitive about raising the low side.

 

[jheidt2543]

As background information you might check for articles on the Transcona Grain Elevator collapse (1913) and the Fargo Grain Elevator collapse (1955). Both were similar foundation failurs and were extensively studied by several engineers. A summary of both is in the book "Beyond Failure, Forensic Case Studies for Civil Engineer", by N.J. Delatte, Jr.

They saved the first elevator by jacking it back in place, so you may be able to gleen some good info. from that failure report.