underpinning help 2

[tarryn]

does anybody have a example drawing of underpinning panel supporting a footing for a large multi storey building.

 

[JedClampett]

First of all, underpinning is a dangerous business that should not be undertaken without careful thought and planning. There is no substitute for experience.
In the first edition of "Foundation Engineering Handbook" by Wnterkorn and Fang (1975), chapter 22 discusses underpinning and has a lot of drawings and photographs. If you can find a copy of that, you're in luck.

 

[csd72]

There was a good article on underpinning in Structure magazine or Structural Engineer last year.

 

[Doc08]

would this help. this is a job we did where we underpinned a 4 storey historical building.

 

[csd72]

Doc08,

Thats an awesome photo.

Where was that done?

 

[Prepakt1]

One thing you always have to consider when underpinning is earthquakes.Its not enough to provide just vertical support. You have to cross brace extensively to reduce possible sideways movement of your supports as much as possible. Even a minor quake can bring it all down.Your normal ground resistance to sideways movement is missing when you excavate below the building.

Intrusion Prepakt /marineconcrete.com

 

[Doc08]

This job was in Beirut, Lebanon, and we went 11.5m below the building where theowner built an entertainment area: pool, jacuzzi,.. the works.

 

[hokie66]

tarryn,

The photo attached by Doc08 is indeed impressive, but I would not take that as a good example of underpinning. My judgment is that that scheme was unstable and dangerous.

 

[csd72]

hokie66,

depends on the loads involved, I dont think we know enough about the specifics to make that sort of comment.

I understand what you are getting at though. A more adequate lateral bece at the concrete beam and a shorter unbraced length would probably be wiser.

But the numbers probably add up and I dont think this is a high seismic/wind zone.

 

[hokie66]

Lebanon does have earthquakes, and apparently a big one about every 1500 years, and the next big one is due. But I would have given Tarryn the same advice wherever the photo was located.

 

[DRC1]

Typically underpinning is not designed for earthquake or similar extreme events. It wll typically have a very short exposure period. Underpinning is typically conservatively designed based on live and dead loads and perhapps some lateral loads such as wind.The concrete mid frame I assume was designed to provide adequate restraint.
What type of piles are those? the bottoms loke like mini piles, and the tops look like augercast

 

[Doc08]

Hokie66

I appreciate your opinion and always apreciate a good advise especially that each and everyone of us is prone to mistakes. However, and strictly from a professional point of view, judging the system as "unstable and dangerous" just by looking at one picture and without asking for more details /clarifications is on its own, "dangerous". For what it is worth, about 15 years ago, I had the toughest time convincing structural engineers we dealt with that micropiles are more than just "tooth picks" and they indeed can function as decent structural elements. We have performed load tests up to 100 tons, on 22cm micropiles, with excellent results.

Indeed the next quake is due, in which case my primary concern would be about the integrity of the existing structure more so than the installed underpinning system. We cannot just shy away from challenges and wait around for the next big quake to come or design every structure, even if temporary, for a quake measuring 6 or more on the Richter scale. None of our proposals would be feasible and we would be quickly out of work. We can however, do our homework, trust our experience, follow the currently acceptable codes, and exercise sound engineering judgement.

DRC1:

you are absolutely right, the system was indeed temporary although we did adopt some out of the ordinary measures given that the structure itself was quite old and the structural frame consisted of bearing walls and arches made of only sandstone blocks (without any reinforcement) which does not permit much differential settlement between supports oterwise the arches would come apart and we'd end up with a pile of rubble. The piles were 25cm in diameter, cast with cement grout providing about 40MPa strength. These piles were braced every 2.5m on the way down and embedded a minimum of 5m into the limestone rock. The underpining system was in service a total of 13 months while the new structure was underway. The maximum recorded differential settlement was 3mm.

Cheers.

 

[aeoliantexan]

Another old reference, but a good one,is the chapter on Underpinning by Edward White in "Foundation engineering" by G. A. Leonards, McGraw-Hill, 1962. This was written prior to development of micro-piles and some other modern aids, but the methods described are low-tech and could be done anywhere.