TBM tunneling in mixed-face ground: Problems and solutions

Mixed-face ground encountered in Tunnel Boring Machine (TBM) tunneling presents great challenges and may trigger potential hazards without warning. A detailed understanding of such unfavorable conditions is therefore critical to a successful bored tunnel. In this paper, we firstly present a brief review of the definition, classification and the factors related to mixed-face conditions. Secondly, for a better understanding of this topic, we investigate the main difficulties and problems involved in TBM tunnelling under mixed-face ground with detailed cases. Thirdly, from the viewpoint of rock-machine interaction, we give some suggestions on the corresponding mitigation measurements from three categories: (i) selection of TBM type and modification of TBM, (ii) condition of ground and (iii) optimization of TBM operation.