Abstract: Extralong waterdiversion tunnels are widely used in interbasin water transfer projects, and they are faced with many geohazard risks, such as water inrush, rock collapse, and large deformation. To study the geological prediction methods applicable to extralong TBM tunnels, the development history and technical status of geohazard prediction and early warning technologies are discussed. The challenges and issues faced in the development of adverse geological prediction for extralong TBM tunnels are summarized. To address these challenges, a fullcoverage geological prediction method system for extralong tunnels, namely, the "1 km+100 m+50 m" geological prediction system, is developed. Then, the main components and the implementation process of the "1 km+100 m+50 m" geological prediction system is presented. This system consists of "1 km" macroscale geological prediction (kilometer scale), "100 m" longdistance geological prediction (hundredmeter scale), and "50 m" shortdistance precise prediction (tenmeter scale). By means of multisource integrated inversion analysis, the realization of fullcoverage prediction of adverse geological conditions and possible geological disasters ahead of the tunnel face is achieved. The results from the engineering applications using the "1 km+100 m+50 m" geological prediction system in the water supply project Ⅱ in Xinjiang show that this system can accurately predict the adverse geological conditions and ensure the safe and efficient TBM tunneling operations for extralong tunnels.

Key words: extra-long tunnel, TBM tunneling; geological hazard, "1 km + 100 m +50 m" geological prediction system