A soil test specimen is subjected to a vertical compression. On the lateral sides is is compressed by a constant pressure. The third direction is plain strain. We introduced a bit cohesion in this hypoplastic model.
Only a quarter of the mesh has been actually used in the calculations. The post processor is used to mirror the mesh around the x- and y-axis, in order to account for the symmetry conditions. It should be mentioned that no imperfections are a priori included in the mesh.
The first plot shows the development of the force for meshes with 16, 64, 256, 1024 and 4096 linear triangular elements respectively. For the total specimen this gives four times as much elements. Notice that the result for the force converges for an increasing number of elements.
The following plots shows the deviatoric part of the strain tensor, for meshes with 256, 1024 and 4096 elements. The shear band patterns still do change quite a bit while refining the mesh, but this doesn't change the force result much anymore, as could be seen from the force plot above.
This is ongoing research. Results may change.