Abstract
Collapse or large deformation of fractured surrounding rock mass occurs frequently in underground tunnelling and results in many casualties and extensive property damage. This paper proposed a new type of remote telemetry system for monitoring the mechanical responses of underground tunnels during unloading. This system adopted both wired and wireless networking schemes, including a signal collection and transmission subsystem, a management analysis subsystem, and a remote receiving subsystem, in the tunnels. The application of this new approach in a subway tunnel indicated that the complete unloading performance of a surrounding rock mass can be captured in real time and high frequency using this method, recording the deformation of the surrounding rock, the stress in the bolts, and the stress in the shotcrete between the surrounding rock and steel arch. The in situ experimental study also found that deformation of the fractured surrounding rock mass in the Dashizi Tunnel showed a step-like fluctuating growth pattern. Additionally, the mechanical response of the surrounding rock mass during unloading tended to stabilize when the opening face was approximately 35 m away from the monitoring section, providing new ways to optimize the excavation process and support measure.
Highlights
A rock mass is a natural system composed of intact rock separated by a fracture network that can influence the physical-mechanical behaviour of the whole rock structure [1,2,3]
Based on the advancement of monitoring data information and the characteristics of underground tunnel engineering, a “wireline + wireless” networking scheme was used in the tunnel to propose a new remote online telemetry system architecture and method, mainly including an information acquisition and transmission subsystem, a management and analysis subsystem, and a remote receiving subsystem for monitoring data (Figure 1)
Data remote transmission subsystem material. e management and analysis subsystem manages all eld devices by issuing instructions that are mainly responsible for collecting, summarizing, and forwarding data information. e remote receiving subsystem uses General Packet Radio Service (GPRS) network technology, dynamic domain name resolution technology, and port mapping technology to realize the remote transmission and reception of data information between nonpublic Internet Protocol (IP) networks and to provide the major equipment required for the on-site monitoring centre; this equipment includes monitoring hosts, power supply equipment, and wireless transmission modules. is method e ectively solves the di cult problem of the incompatible use of di erent brands of monitoring equipment on-site while realizing the complete dispersion of the structural control functions and improves the robustness of the system
Summary
A rock mass is a natural system composed of intact rock separated by a fracture network that can influence the physical-mechanical behaviour of the whole rock structure [1,2,3]. Ji [14] veri ed the feasibility of a new displacement monitoring method and the stability of a wireless sensor network for fractured rock masses in underground structures. Ese technical developments and application attempts initially show that remote wireless telemetry is feasible in underground engineering, but the multisensor compatible monitoring method and corresponding analysis for the fractured rock mass induced by tunnelling are not yet su cient. Us, this article rst proposed a “wireline + wireless” networking automatic monitoring method, which is based on a focus control system (FCS) and General Packet Radio Service (GPRS), for fractured surrounding rock mass induced by underground excavation. En, the mechanical performance of fractured surrounding rock mass during unloading, including the unloading deformation, anchor stress, and spray pressure, is summarized according to the monitoring data by the multivariable smart sensors in tunnel engineering. Us, this article rst proposed a “wireline + wireless” networking automatic monitoring method, which is based on a focus control system (FCS) and General Packet Radio Service (GPRS), for fractured surrounding rock mass induced by underground excavation. en, the mechanical performance of fractured surrounding rock mass during unloading, including the unloading deformation, anchor stress, and spray pressure, is summarized according to the monitoring data by the multivariable smart sensors in tunnel engineering. e in situ experimental study indicated that the deformation of the fractured surrounding rock mass in Dashizi Tunnel showed a step-like uctuating growth pattern in the overall trend of change, and the mechanical response of the unloading surrounding rock mass tended to be stable when the opening face was approximately 35 m away from the monitoring section, providing new information and motivating new mitigation measures for excavation and support optimization
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