Underground pump station number of piles required

[Aakalim103]

I am trying to find out the number and location of piles (steel piles) required for an underground pump station. We have a 800mm thick base slab which will be supported on piles. I have modeled the pump station in a FEM software and applied all the loads (traffic load on top slab, crane loads, pump loads, self weights, earth pressure, water pressure etc). As for the piles, the only information i have is the stiffness of the pile (in kN/m)

I am not sure if i should model the piles as nodal supports with the pile stiffness, or just pinned supports? Right now i am interested in only finding the number of piles required and their locations. Is there any example or reference where i can find how to model the piles in such a situation?

 

[oldestguy]

Total load divided by individual pile capacity equals the number of piles. . However, depending on your site, that individual pile capacity can vary significantly. Suggest a geotech give you that individual working pile load.

 

[r13]

What type of support assigned to the FEM model? You can assume it is pinned, but wouldn't be better by supporting on elastic (spring) foundation? Note the springs can resist compression only.

 

[Aakalim103]

Thanks for the replies. I have actually modeled them as nodal spring supports at the pile locations. I am not sure if i should use the soil springs under the base slab in addition to the nodal springs for piles.

Also i think i should be using SLS load combinations to check the number of piles.

 

[r13]

No, soil shouldn't relied upon. I think it is proper to use SLS combination for number of piles, and use ULS for design. At least, it was the old way.

 

[Aakalim103]

Thank you retired13. I am designing according to the eurocodes and the eurocodes ask us to use ULS load combinations to find the number of required piles.

I have one more question: the base slab of pump station is extended outside from the outer walls to assist in resisting the uplift pressure due to ground water. Do i need to include the load of back fill soil on this area for the calculation of number of piles?

 

[r13]

Yes. Everything supported on the base slab should be included.