Finite Element Modeling of a Pier in Clay

[FixedEarth]

I have a site with CH soils with qu > 5 ksf, SPT > 20, and have given recommendations of 18 inch piers embedded 12 ft into the ground. Loading is approx. 3 kips vertical, 6 k horizontal & 14 k-ft moment. It is supporting 8 ft high panel. It is an individual pier and not a group.

Now I am trying to model it in Finite element program (strictly a client request).

Any guidance on applicable papers, references or websites are highly appreciated.

 

[kleo]

The only way to model this in using finite elements is with a 3D program. I would use LPILE instead which is based on a subgrade reaction approach.

 

[BridgeEI]

Agreed, LPILE would be the way to go since its made exactly for that problem. If you don't have access to LPILE use COM624P, its available from FHWA for free.

 

[FixedEarth]

Thank you ldeo & BridgeEI for your help.

I ran into a colleague who had PLAXIS 2D. We modeled it and got within 10% of the emperical values. We used unit weights, cohesion and modulus of elasticity as well as permeability. We modeled as a 3 layer material, since there was a 5 ft layer of SILT between the two clay layers.

I am now a fan of FEA.

Do you want to know something strange-My capacities were based on Teng method & the high vertical stresses dissapeared within 0.1 ft of Teng's result if there was no exclusion of passive resistance allowed.

 

[kleo]

I would like to know how you modeled a single pile with lateral loads in Plaxis 2D, as it is not possible.

 

[FixedEarth]

Kleo;

A better way to phrase the question would be "How did you model a lateral load on the 2D version?"

In the 2D version, you set up your axis and then pick on the node. In my case, the node at the center of the pier. Then you enter your later load as Fx and vertical load as Fy. I chose my coordinates, such that +x was to the right and -y was for downward vertical load.

 

[kleo]

FE,
Thanks for the explanation. Since you have a load in the x-direction I assume this must be plane strain model, yes?