Abstract: The exit sections of the main and pilot tunnels of the Gaoligongshan tunnel are constructed using two different open tunnel boring machines (TBMs), and owing to the complex geologies and insufficient cutterhead torque, the TBMs are often jammed. Consequently, to improve the cutterhead torque for TBM jam release, a dualspeed reducer is arranged in the main drive system of TBM Caiyun #1. The speed reducers are installed between the main motor and the speed reducer. The speed reduction ratios in high and lowspeed modes are 1 and 1.47, respectively, and can be switched directly and easily. In the lowspeed mode, the jam release torque for the device can be increased from 6 150 to 9 225 kN·m. The field test shows that when the TBM is driven at low speed, the equipment can continue to drive under a torque of 7 000 kN·m, which significantly improves the jam release capacity of the equipment. The practical results indicate that by installing the dualspeed reducer on a TBM, the TBM jam release capacity can be significantly improved, providing a reference for TBM design in similar geologies.

Key words: Gaoligongshan tunnel, TBM jam release, dualspeed reducer, high and low speed, cutterhead torque, cutterhead rotation speed