Best piletype for statue 3

[Plantec]

Hello,

I have to design the foundations for a kind of statue. The statue is in fact a semi-arc (it's about 16m high, the arc is circular with a radius of about 30m) made of steel. There are three such semi-arcs, for the foundation of two of them I have all the space I want for counterweights. The third however is placed on a sidewalk, with many cables (electricity, gas, ...) underneath, so there isn't much space available. I thought that Franki-Bawang-piles (enlarged base tubular piles) were the best solution, as they work as tensile piles and compressive piles.

Do you agree or do you see a better solution? Would this be the cheapest solution?

Greetings
(hope you understand my question, my English isn't very good :-()

 

[Focht3]

Please describe the arcs - are they horizontal or vertical?

Yout English is just fine!

 

[Plantec]

The arc is vertical at the bottom, and describes a segment of a circle. So if you see it from the side it's something like this:
__
/
/
/
|
|

Greetings

 

[PEinc]

Depending on the soils, most piles can function in both tension and compression. Can the piles be driven deep enough to develop the required tension capacity? If not you may need tiedown anchors to resist uplift. You probably want a pile that is not a proprietory product and can be installed by local contractors. The cheapest pile will be a driven steel pile (H-Pile or pipe pile)if you have enough of them. If you have less than about 2 dozen piles, it may be cheaper to use reinforced, drilled shafts.

 

[Plantec]

Thanks PEinc and Focht3 for your comments.

The soil is sandy.

The reason I thought of tubular piles is that they have a very small diameter in the first few meters (where all the cables are).

The attacking forces aren't very big: the moment is about 400 kNm (hence the tension), so I thought that 3 tubular piles (two where the tension is, one on the other side) = stability.

The cheapest method I know for tension piles is probably screw piles (screw down, screw up). This piles however can't be placed here due to lack of space. This is also the reason I think that driven steel piles (there are too much of them) and reinforced drilled shafts (too big).

If there are any alternatives or comments to this I would be very thankful.

Greetings.

 

[DRC1]

It would seem to me the loads are relatively light, and I would consider H-piles. They can develop good tensile and compressive resistance in sands and are ussually cheap to install.However local conditions and customs will dictate what works bst in your area. I suggest calling a local piling contractor to dicuss it. he could probably suggest some alternatives and give you a feel for price.

 

[VAD]

Hello Plantec:

I would have thought that helical screw piles would be most appropriate. However, it appears that the site has many constraints. Another suggestion is grouted anchors or micropiles using small diameter bars, but these come with a price. As DRCI suggests, the opinion of a contractor should be sought as more than often he/she can come up with valid constructability solutions. Just another thought, can a deadman type of anchor be created using high yield steel bars and steel plates only, without impacting the utilities?. It seems that you have to ponder over the site conditions to create a solution. This sometimes takes a few days and pulling the hair out of your head. Stand back a bit and refocus.

Best of luck

 

[PEinc]

The proper pile choice depends on the tension and compression loads and on the actual amount of clearance between existing utilities. Either clearance or capacity may preclude helical piers. High bedrock may preclude helical piers and driven piles of any type. Although grouted mini-piles need the least amount of space, they may be very expensive if there are too few. In the end, you may have no choice but to use mini-piles. Whichever pile you use, don't forget to check the tensile bond of the pile in addition to the mass stability of the cone of soil that will resiste the uplift. Piles may need only a short "bond length" but the size and depth of the soil cone mass may be the controlling factor, especially if you have submerged soils around the piles.

 

[dgb]

Regarding micropiles/minipiles:
I have used micropiles of 6 or 8" dia for taking vertical loads. But unfortunately the ones used by me could take very less or almost zero horizontal load or bending moment. This is because they had a single centrally placed rebar and a thin steel sleeve for grouting(called tube-a-manchette).
With a small diameter and central reinforcenment, the moment capacity of such piles is insignificant. Since all structures have to be designed for horizontal forces, in many cases, this was the major hurdle that ruled out micropiles.
So micropiles could be used only in those cases where the hori. loads were resisted independently (by passive pressure against pilecap/by additional large dia piles/by separate horizontal supports, etc).
With this background, I would like to learn answers to the following -
(1) Are there any types of micropiles that have a good hori.load capacity?
(2) Is there is any way to increase the hori.load/moment capacity of micropiles described by me above?
Thanks in anticipation.
dgb

 

[Plantec]

Thanks everyone.

I called a local contractor and he suggested micropiles. I asked for the price, and just like VAD said, "they come with a price"! I would only need about 6, the price for the foundation of that one statue would be about 7500 euro!

Greetings.