Problem in modelling shield tunnel in plaxis 2d ?


Hello
I'm working on modelling of a shield tunnel in Plaxis and design of its segmental lining... 
I am aware that for simulating the volume loss due to the tunnel boring process the "contraction" of the tunnel lining can be specified. 
Would you please help me about this problems:
1- In the "tunnel designer" option in plaxis the radius should be the inner radius of the "lining" or the outer one?
2- How can I implement the over-excavation? I mean is there any relation between the contraction ratio and the diameter of the cutter head of TBM? In my project the diameter of the TBM is 9.40m and diameter of the lining is 9.10 (out) and 8.40(in) .
I'm looking forward to your reply.
Best Regards.
 

Soil Mechanics / Geotechnical Analysis Design Tunneling & Underground Construction