Batter Pile Foundations Example - Resolving lateral demands into pile reactions 1

[EZBuilding]

I am working on a building which must utilize batter piles to resist lateral loading as the upper soil strata are too weak to provide meaningful lateral resistance. I have found limited information regarding battered piles, especially worked out examples from a structural engineering perspective. Accordingly, the below and attached are my attempts at resolving lateral loads into a battered pile foundation system.

I believe there are two "methods" in which batter piles resist lateral loads, either through passive or active resistance (self described nomenclature here). Through passive resistance the batter piles resist lateral loads based on the horizontal component of the axial load in the batter pile. Through active resistance, the lateral load increases the axial load in the batter pile.

The attached worked out example attempts to work through the reactions on each of these methods.

Assumptions:

Reinforced concrete shear wall supported on pile cap with piles.
1 to 6 horizontal to vertical batter
0.6 D + 0.6W is the controlling load combination and the only one considered.
No seismic loading
No lateral resistance provide by pile bending or lateral earth pressure
Pile loads based on axial and moment demands are provided based on rigid pile group analysis

Generally, I am looking for feedback on my understanding of how to resolve lateral loads in a battered pile foundation. Specifically in the "active resistance case" as I appear unable to close the loop on the pile reactions. If anyone believes I am missing something in my worked out examples, please do share and I will aim incorporate the comments into this understanding.

 

[sticksandtriangles]

There is a large spike in shear in the "active" case as you described EZ building. Would keeping the battered pile under the shearwall chords help eliminate this large shear concern?

Shear - End Piles Battered

Moment - End Piles Battered

S&T -

http://www.re-tug.com

 

[EZBuilding]

I received this resource from a co-worker that had some good feedback on it.

https://www.researchgate.net/public...alysis_of_pile_groups_containing_batter_piles

This resource agrees with and shows the "Active Batter Pile" push-pull that myself and S&T observed in our models

It also provides a FBD that closed the loop across the active forces - but does so across the entire pile group versus my attempt to do it locally across the push pull piles. This reinforces the concern that to utilize batter piles - your pile cap needs to be capable of engaging them.

The resource does not go into discussion about the shear spike in the pile cap or for how to approach the topic across more complex condition with bi-axial bending, torsion, etc.

 

[KootK]

Nice score EZ, thanks for reporting back. For anyone interested, you can download a PDF here without having to log in or sign up for anything. The bit below is similar to what I was getting at when I mentioned the faux vertical piles and the system of equations.

Is it really practical to "amend the slopes of the batter piles"? In addition to the oddball angles, wouldn't it be different for each load combination?

 

[EZBuilding]

Kootk,

Maybe for bridge design or in other fields, amending the batter slope is a reasonable solution.

For vertical construction it would produce an optimization nightmare, not just from a analysis standpoint but also in providing a cost-effective solution. Not to mention that all your batter piles need to fit within your property lines and need to respect other vertical elements foundations...