Abstract: In recent years, the mountain tunnel collapse accidents occur frequently in China, which results in heavy casualties and huge property damage. Hence, the real-time field monitoring of surrounding rock stability and the early safety warning have become one of the key issues in current mountain tunnel constructions. Firstly, this paper clarified all the relating concepts of the remote online monitoring technology, including its signal collection, transmission and background processing principle, focus control system (FCS) and general packet radio service (GPRS). Then, a new type of tunnel remote telemetry system was proposed. The system adopted the wired and wireless networking schemes in the tunnels, including the signal collection and transmission subsystem, the management analysis subsystem and the remote receiving subsystem. Finally, the system was applied to Dashizi tunnel with the high-risk collapse, the longest road tunnel in Ningbo. All-weather real-time high-frequency monitoring was recorded, including the deformation of surrounding rock, the stress of bolts, and the shotcrete stress between surrounding rock and steel arch. In addition, server + client mode was employed to achieve a high-speed transmission of remote data and multi-unit real-time monitoring. The obtained time-history curves (i.e., deformation, stress and pressure) were analyzed. It indicates that the deformation of surrounding rock of Dashizi tunnel shows a change of the step-like fluctuation and exhibits a mutation after blasting excavation. Meanwhile, it is found that the deformation of surrounding rock and the pressure of the shotcrete layer are greatly affected by the tunnel excavation disturbance. However, the overall trend of change basically undergoes rapid change at the early stage, a slow change at the middle stage and the gradual stability at the late stage. Through the remote online monitoring of the tunnel for nearly one year, it shows that the technology can realize the long-range telemetry and unattended warning of the stability of underground engineering surrounding rock, which has great application prospect.

Key words: tunnel, remote monitoring, smart sensor, fieldbus control system, real-time warning