Hi Oliver,

I am not an expert on cracking/crushing simulation using SOLID65, but I noticed that your solid mesh has only 3 elements through the thickness of the wall.

I suggest you try putting 12 elememt through the thickness and see if that helps.  If you simply make the element size 1/4 of the current size, the number of elements will go up by a factor of 64. If you are using the Student license, that may put the mesh over the limit on the number of nodes or elements of 128,000.  If that is the case, you can sweep 12 elements through the thickness, without changing the default element size.

That will make the element thin in one direction if you don’t change the height. You should also make the bottom layer of elements have the same height as thickness. In Mechanical, you would apply a Mesh Size control on the vertical edges of the wall and use a Bias factor of 4. I'm not sure how you do that in the APDL environment.