Battered Pile in Compressible Soil

[tq3610]

For a site with compressible soils, a bridge abutment has lateral loads to be resisted by piles. FHWA states to avoid battered piles in this instance. If they can't be avoided (i.e., soils are too weak to get significant lateral capacity from vertical piles), does anyone have a reference as to determining what the additional bending moment applied to the battered pile due to compressible soil consolidation above the pile? I expect a significant portion of the allowable bending capacity for a given pile will be taken by the consolidating soil, and as a result a quite low allowable lateral capacity will result, but I need to vet this scenario.

 

[Retrograde]

i.e., soils are too weak to get significant lateral capacity from vertical piles

How are you calculating the lateral capacity of the piles? Normally the lateral capacity is governed by structural failure, not geotechnical failure. Unless you need to limit your serviceability lateral deflections.

 

[tq3610]

I haven’t yet analyzed it, but I am aware that FHWA says not to use battered piles in compressible soils due to the bending that would result to the piles from settlement.

So, I’m looking for some input as to how I can account for the load from settling soil on the battered pile (ie, apply an external distributed load along the pile length, for example).

Conceptually I could see applying a triangular load (narrow at shallow depth and larger at deeper depth) accounting for the weight of soil above the pile and some contributory area as a factor of pile
diameter. Example: a 7” dia pile gets assigned 3x the pile diameter x effective stress along the pile length to account for increasing load with depth).

 

[BridgeSmith]

If the FHWA says 'don't do it' there's a reason. Probably because the unpredictable soil pressures and resistance make the stability of the pile impossible to assess with any level of accuracy. I suggest finding an alternative foundation type.

Rod Smith, P.E., The artist formerly known as HotRod10