Calculating Lateral Earth Pressure coefficient for piles

[TexastoTexas123]

I am trying to calculate the lateral earth pressure coefficients for piles. I have been looking at several different methods for calculating this number, but ideally I want to incorporate the angle of internal friction, the type of soil in which the pile is being placed, AND the type of material the piling is. I am using timber, steel, and/or concrete piling material. I just figured there might be a way to have both the piling material and type of soil factored in, instead of just having one or the other which seems to be the case in the various methods I've seen (Nordlund, Meyerhof, etc...). Thanks in advance for your expertise and input.

 

[Mccoy]

Texasto, do you mean lateral subgrade reaction like in the spring model (displacements, bending moments, shear) or lateral earth pressure like Ka and Kp (plasticity, soil failure).

 

[TexastoTexas123]

Thanks for your response, and I mean Ka and Kp. I think at this point I've accepted conservative values based on FEMA's standards for earth pressure coefficients that are usable in their formula for embedment depth, and since I am using their formula, then I figured I would stick within their earth pressure numbers so as to make the calculations more accurate. The only thing is I don't see anywhere else that has the types of earth pressure coefficients like they do. As I have understood it in my research, there is Ka (active), Kp (passive) and Ko (at-rest) earth pressure coefficients. FEMA has K-HC (earth pressure in compression) and K-HT(earth pressure in tension). I wasn't sure what the difference was ultimately. I decide that K-HT (Earth pressure in tension) correlates to Ka (active earth pressure) and K-HC(earth pressure in compression) correlates to Kp (passive earth pressure). Anyways, thats what I've got right now, and I just wanted to make sure I had thoroughly investigated the earth pressure issue. Where these earth pressures are relevant, is in an area of erratic soil types, but the soil type is majority medium-dense sand. We are in Galveston, TX area, and our construction is on the Galveston Island (Bolivar Peninsula, Crystal Beach, etc.).

 

[Mccoy]

Texasto, I agree with your interpretation of the FEMA guidelines, since the active pressure entails a realease of pressure= tension so Ka=K-HT and the passive pressure a thrust or compression, so Kp=K-HC. Right now I'm involved in the design of piles with a software which can define the plasticity treshold of the soil by passive and active pressure.
The type of soil is simply characterized by phi and c, there is no provision though for the pile material, since no friction along the shaft is considered in this plasticity model (only horizontal component, shaft friction is considered in a separate plasticity model).

 

[BigH]

One thing that might come into play is the effective width of the pile being pushed into the passive zone. I have seen several "widths" being used from 2x pile diameter to 3x. You might find Golder and Seychuk's paper in one of the old PanAm Geotechnical conferences where he and HQ Golder explain the design of a soldier pile. You might wish, too, to look at a very detailed analysis of laterally loaded piles in Poulos and Davis' book Pile Foundation Analysis and Design.

 

[TexastoTexas123]

McCoy- As I understand it, phi = angle of internal friction, and 'c'= cohesion? Out here the cohesion value is zero, so I really have no reason to use that. It seems weird how the material isnt taken into account more. I am thinking I need one more factor based on the material to include in this calculation, but really dont have much direction so I may end up just keeping things as they are. After my sheet is set I'll start testing the outputs with past piling depths. Does anyone maybe know where I can find records of piling depths to use as a test?

 

[fattdad]

the best estimation for the "effective width" is to multiply the actual width by phi/10. Of course you need to know phi to get your Ka and Kp.

f-d

¡papá gordo ain’t no madre flaca!