Sorry Joe I can't help you but someone out there probably can. All I came across was a deformation analysis question under lateral loading of battered piles in rock.

An analysis approach can be taken if you know how to characterize the soils in contact with your piles. In all, the short term friction, adhesion and bearing point resistance would be input to your model as springs of the proper orientation and stiffness.

For long term behaviour you could do exactly the same but with the stiffnesses of the springs reduced in proportion to the secondary compression expected relative to the elastic one. Just the same than with n in composite beams, just that soil.

Alternatively of course you can model the soil itself (bricks, 2D vertical plates in a grill) and join the piles to the soil at nodes, what apart of precluding some relative movements for battered piles won't look nice.

Yet these models that include the soil directly modeled as an elastic continuum show that the calculated settlements (in theory of elasticity) are somewhat impervious to the nature of the foundation, especially if a stiff layer is not reached.

In any case, whichever the model used for the interaction, better use a range of soil stiffnesses to bracket the likely responses.

Settlement of groups of vertical piles are dealt with in

Bridge Substructure and Foudnation Design
Petros P. Xanthakos
Prentice Hall
p. 611...624