Thick Lining Specified in PLAXIS 3D Tutorial Example 6

Question

Dear Support Team, 
 I would like to clarify for PLAXIS 3D Tutorial Example 6, what is the thickness lining specified in the text? 
 
 Is it the distance between the internal diameter and the TBM excavation diameter or the internal diameter and the external diameter of the tunnel lining? Please let me know. Thank you very much!

Stefanos Papavasileiou · Answer

Dear Wang, 
 In the PLAXIS 3D Tutorial Example 6, the thick lining is defined between what you mention as the TBM excavation diameter and the Internal diameter of tunnel lining. In this simplified case, we consider the thick lining as the final lining rings that follow the backfilling grouting. 
 The screenshot below can help you see what is being created in this specific example. 
 Note that you can define multiple thick linings, if required, in your project.

Dennis Waterman · Answer

Dear Jude, 
 Actually the reference point for the face pressure and grout pressure is the top of the cutter head, which is at -4.75. Since we model the TBM with a plate element that has no thickness and we want to inner diameter of the tunnel to be correct, the outer diameter of the whole construction is reduced with 0.25m because we don't model the thickness of the TBM and the overcut of the cutter head. This is where the difference comes from. 
 With kind regards, 
 Dennis Waterman