PLAXIS3D - modelling of pile sleeves

Hi all,

PLAXIS3D question:

I am wanting to model several piles embedded in the ground, with the upper portion of the pile having an outer sleeve (steel casing with annulus being a void) around it so that it is not loaded by soil pushing on it laterally, due to an embankment nearby. The lower portion of the pile is embedded into the ground below the sleeve, like a normal pile.

I have tried modelling the sleeve as a cylindrical plate with an outer interface, around an embedded beam, with the soil volume between the plate and embedded beam deactivated. I think in theory this should work fine but I am having convergence issues perhaps due to the size of my model (& meshing?).

Basically I want a free connection along the length of an embedded beam and the surrounding soil, with a rigid connection to the embedded beam section that doesnt have a sleeve and is modelled typically. 

I think making the skin friction of the embedded beam equal to zero for the sleeved section will do this, connected to a second embedded beam with normal skin friction.

Any other suggested ways to model this? any ideas and information appreciated.

Thanks

Dan