A case study on TBM tunnelling in fault zones and lessons learned from ground improvement

TBM tunnelling in fault zones is one of the major challenges which affects the advance rate of TBM and sometimes leads to long TBM stoppage. The Zagros water transfer tunnel is under construction through the Zagros Mountains in Iran. During the excavation of the tunnel, the double shield (DS) TBM experienced overall rock mass properties worse than expected ones and a great geological event with unpredicted and unforeseeable collapsing encountered. The fault zones caused jamming of the TBM cutterhead and shield. Ground improvement and grouting techniques were implemented widely to release TBM. Applied techniques were fully successful and the TBM restarted excavation after eight months stoppage. This paper aims to share practical experiences about collapsing zones, consolidation grouting, and key elements of passing through the fault zone in TBM tunnelling.