Performance of Slurry TBM Tunnelling in Sandy Cobble Ground — A Case Study in Lanzhou

The slurry tunnelling boring machine (TBM) was used to construct the tunnel of the Lanzhou Metro Line 1 undercrossing the Yellow River, China. The ground is characterized by sandy cobble with high cobble content. There are many challenges for slurry TBM tunnelling in sandy cobble ground because the cobble is hard to break and transport. This paper focuses on the performance of slurry TBM tunnelling, summarizes the lessons of shield driving and suggests countermeasures for the cobble breaking and disposal including cutterhead improvement, double pebble crusher and clasts collection tank. The chamber pressure and grouting pressure during the driving process were recorded and compared with the theoretical ground stress. The key parameters including the thrust force of cylinders, advance rate, torque and rotation speed of the cutterhead were recorded and analysed. Field test results show that the surface settlement induced by slurry TBM tunnelling in sandy cobble ground can be well controlled and the longitudinal surface settlement can be predicted by the Attewell formula and modified Attewell formula. This paper provides a good reference for slurry TBM tunnelling in sandy cobble ground.