Approximate Lateral Analysis for a pile below an abutment

[BridgeE]

Hi Geotechs,

Am designing an abutment for a bridge and our geotech won't be able to give us anything for a month.

so am trying to size my piles until we hear back from him because we have to submit a design and I have all my loads ready. and I want to do an approximation of the lateral loads that would be generated (using assumed soil properties).

Is there a way I can do that ? , we don't have L-Pile so I need some other method, I tried treating the pile as a sheetpile and performed a flexible wall analysis but deflections were out of control, so do you guys have any recommendations?

Thanks,

 

[BridgeSmith]

Well, I'm not a geotech, but I am a bridge designer. Maybe I'm not understanding the question. Are you trying to approximate the soil load on the abutment that is applied to the pile and the moment in the pile from that load? If that's the case, conservatively you could assume a lowball phi angle for the soil to give you the max soil load. The geotechs can probably help with that if you provide a soil type. If you provide loading to the piles, and the material it's embedded in, perhaps they can also give you an approximation of the depth (length) to use to analyze the pile as a free head or fixed head cantilever. Without actual soil properties, you're not going get anything you can 'take to the bank', so I hope when you say you have to submit the design, you're referring to a preliminary design, and not something you're expected to put your stamp on. That would get a flat refusal from me.

If you're concerned about the axial capacity, or the moment generated by the pile deflection, I'll tell you this much, we always assume the pile forms a plastic hinge under the cap. If the soil around the pile is weak enough and the deflection small enough, it may bend elastically, but we design the abutment to handle the plastic moment of the piles. Because the pile is embedded in soil, we consider it fully braced and the axial capacity is .5 * Fy * A, even with a hinge in it.

 

[SlideRuleEra]

I want to do an approximation of the lateral loads that would be generated (using assumed soil properties).
Is there a way I can do that ?

Yes, determine the depth to the pile's point of fixity. See "How To Determing Lateral Load Capacity of Piles", on my website.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[canwesteng]

Do you have any FEA software? You model the pile with some springs representing subgrade modulus instead of L-pile.

 

[BridgeE]

Thanks all,

That was very helpful