Tunneling simulation with ABAQUS

Hello

My research focuses on 3D
numerical simulation of tunnel excavation. I simulated it  by FLAC3D. But I need to investigate the interaction contact
between support and ground. I think that this is impossible in FLAC3D.
Therefore I need your help for modeling of tunnel excavation with ABAQUS. For modeling a tunnel excavation, I face to some problems.
First problem is that after
applying initial stresses (in situe stress) in first step, the tunnel should be
excavated in next step. It need to removing of meshes in tunnel section in this step. For removing
of meshes, or deleting of them, I don't know what can I do? The MODEL
CHANGE option may be used in this problem, But I could not use it because I
didn't see such as this option in next step (step 2). (please see the attached image file)

I will be very grateful if you can help me for solving these problems.

Thank you,