Pile group efficiency for circular pattern
Pile group efficiency for circular pattern
(OP)
My name is jeff, and a fresh graduate structural engineer.
I'm facing a problem in reviewing a foundation for a fuel tank, the foundation is composed of 13 dia.400 m CSP pile, with the circular patterns as i attach below:
the problem is, i can't find the efficiency for circular patterned pile group, the only formula i know is the converse labbre which states that the formula is limited to rectangular groups.
I find some literature that in sandy layer soil (the layer of my soil dominated by sand), if the spacing of piles larger than 3x dia. of piles than the efficiency should be taken as 1, so the ultimate capacity of the pile group would be : n x single capacity piles.
is there any efficiency formula for circular patterns or is the n x single capacity would be true for my case?
thank you very much before,
regards,
jeff.
I'm facing a problem in reviewing a foundation for a fuel tank, the foundation is composed of 13 dia.400 m CSP pile, with the circular patterns as i attach below:
the problem is, i can't find the efficiency for circular patterned pile group, the only formula i know is the converse labbre which states that the formula is limited to rectangular groups.
I find some literature that in sandy layer soil (the layer of my soil dominated by sand), if the spacing of piles larger than 3x dia. of piles than the efficiency should be taken as 1, so the ultimate capacity of the pile group would be : n x single capacity piles.
is there any efficiency formula for circular patterns or is the n x single capacity would be true for my case?
thank you very much before,
regards,
jeff.





RE: Pile group efficiency for circular pattern
RE: Pile group efficiency for circular pattern
So basically if i find another case with pile group which has irregular pattern like this i can overlook it if the spacing larger than 3 times the diameter right?
And in my current design i use a statement from a journal which says that the basic formula for group effectivity:
Geometric effectivity = (perimeter of the group)/ (sum of the perimeter of pile)
so, in my case its:
(8 x 3.015)/(13 x 0.25 x 3.14 x 0.4^2) = 1.5 ( taken as 1)
which 3.015 is the distance between the outer pile..
Can this formula be applied for any irregular structures?
RE: Pile group efficiency for circular pattern
I am not familiar with the term "Geometric Effectivity". But it seems like this is a comparison of piles failing individually vs piles failing as a block. It means not only the perimeter but also the tip area should be compared to see which failure mode governs the design.
RE: Pile group efficiency for circular pattern
RE: Pile group efficiency for circular pattern
actually the Geometric effectivity stands for the pile group efficiency (Eg) which depends on the pattern of the pile, since the i can't use the converse-labbre equation, i use that one from the journal i found.
@Fixed earth
thanks for your suggestions, I'm not very knowledgeable in geotechnical problems, and my company doesn't have much literature about soil, we only have bowles 4th edition..do you have any journal about this?
RE: Pile group efficiency for circular pattern
I like the texts more than the journals. Go to Amazon and look for pile foundations books by Tomlinson, Canadian Foundation Manual, F.D.C. Henry, Teng and Poulos.
Your firm should start you off with combined footings or grade beam foundations.:) This design, you need to pick up the design steps from a senior engineer.
RE: Pile group efficiency for circular pattern