Modellilng Deep and shallow foundations in Abaqus

Dear All,

I decided to put this post since I am trying to model piles on granular materials with Abaqus and I am having LOADS of problems, some of them due to my lack of understanding in the subject and others becasue there is not enough information around. Some of my problems are:

1- convergence problems: I am using Mohr coulomb for the soil and elasticity for the pile. If the difference between Young's modulus for both materials is to big it does not converge on Abaqus Static. If I do not put a bit of cohesion in my soil it also does not converge.

2- Different failure mode or smaller than it should be.

I have done a few 2D simulations and the results I get from Abaqus are completely different than the results of the close form solution, even if I refine the mesh.

I decided to start with shallow foundations in 2D and, once again, the above happens. I am using the default solver parameters, NLgeom on, cohesion of 2kPa, friction angle of 42 degrees (dense sand), dilation of 20degrees and E=100MPa and the same Poisson's coefficient=0.3

The elements I am using are the C3D8R for the 3D and the  CPE4R for the 2D simulations. In order to get the displacement load curve I am displacing the pile or the shallow foundation, vertically, using the boundary condition option.

 Any expertise is extremely welcome.

Regards

Pedro