Abstract: A sudden groundwater gushed into a tunnel which was under construction by using Tunnel Boring Machine (TBM) in a large water project.Approximately, the 50 liters/sec or 180 cubic meters/hour groundwater along the "thick debris flow material" consisting of with the running sand, gravel and yellow clay slurries trapped the TBM. Due to the large groundwater recharge area, the groundwater intrusions would last long time if the hazard was not engineering mitigated. The mitigation measure was a combination of plugging the front surface in the tunnel; drilling the investigation borings from the ground surface and the cement grouting of the surrounding rock mass to ensure the tunnel safety.This case history of a successful TBM tunneling technique underneath the ancient river, ditch and other poor geological conditions is one of the first constructions in the similar conditions in China.

Key words: TBM, Poor Geological Conditions, Groundwater (Mud) Intrusion, Drilling and Grouting Reinforcement Techniques