Abstract: The extralarge diameter (over 14 m) slurry shield would be subjected to alternating loads when tunneling in soft and hard strata, which would lead to difficult tunneling parameters selection, frequent tool replacement, overload failure, and the loosening of the tool holder bolt, as well as seriously affect the tunneling safety. To achieve realtime load monitoring of tool replacement devices and guide the construction through sensing the load data, a suite of realtime load monitoring systems based on fiber Bragg grating technology are proposed based on the Su′ai tunnel in Shantou, China. The monitoring system measures the bolt load in a muddywater environment with smart bolts, then transmits the signal via wireless communication technology, and finally stores and analyzes the load data based on data acquisition software. The results show the following: (1) The electromagnetic environment has no harm on the system in a muddywater environment and the system can monitor the load stably and reliably. (2) When shield tunneling in soft and hard strata, the axial load of bolts changes periodically and varies greatly due to the different installation positions. The rock intrusion height can be estimated to guide the tool configuration according to the difference of the axial load of bolts in soft and hard strata. (3) By monitoring the bolt axial force, the phenomena of bolt loosening and pretightening force attenuation can be identified, which is conducive to timely conduct countermeasures for reducing the construction risk. The system can be used for realtime load monitoring, boltloosening identification, and rock intrusion height estimation of shield tunneling, as well as for providing guidance.

Key words: extra-large diameter slurry shield, cutter replacement device, real-time load monitoring system, axial load of bolts, fiber Bragg grating