Abstract: Right type of TBM should be chosen so as to improve the construction efficiency of TBM boring in large diameter tunnels under high cover and complex geologies. The characteristics of the existing TBM types and their limitations for large diameter and long tunnels under mix conditions are presented. A general guideline for the selection of the proper type of TBM under different conditions is made. The 3 pilot innovation projects developed by SELI are presented, including DSU Compact TBM, DSU EPB TBM and SSU EPB TBM. Conclusions drawn are as follows: Traditional types of TBM are not specifically studied/designed to bore large diameter tunnels in complex geologies; To satisfy the market demand, new types of TBMs should be developed; 3 new types of TMB developed by SELI are specifically suitable for a certain geological range, and these new types of TBM allow coping with complex geologies as well as overcoming the most common criticalities that might be encountered when boring a long tunnel under variable cover.

Key words: large diameter and long tunnel, tunnel boring machine (TBM), open gripper TBM, double shield TBM, single shield TBM, open mode, dual mode, DSU compact TBM, DSU EPB TBM, SSU EPB TBM