Based on the existing Canadian ESG microseismic monitoring system, a mobile microseismic monitoring system for a soft rock tunnel has been successfully constructed through continuous exploration and improvement to study the large-scale nucleation and development of microfractures in the soft rock of the Yangshan Tunnel. All-weather, continuous real-time monitoring is conducted while the tunnel is excavated through drilling and blasting, and the waveform characteristics of microseismic events are analysed. Through the recorded microseismic monitoring data, the variation characteristics of various parameters (e.g., the temporal, spatial, and magnitude distributions of the microseismic events, the frequency of microseismic events, and the microseismic event density and energy) are separately studied during the process of large-scale deformation instability and failure of the soft rock tunnel. The relationship between the deterioration of the rock mass and the microseismic activity during this failure process is consequently discussed. The research results show that a microseismic monitoring system can be used to detect precursors; namely, the microseismic event frequency and energy both will appear “lull” and “active” periods during the whole failure process of soft rock tunnel. Two peaks are observed during the evolution of failure. When the second peak occurs, it is accompanied by the destruction of the surrounding rock. The extent and strength of the damage within the surrounding rock can be delineated by the spatial, temporal, and magnitude distributions of the microseismic events and a microseismic event density nephogram. The results of microseismic analysis confirm that a microseismic monitoring system can be used to monitor the large-scale deformation and failure processes of a soft rock tunnel and provide early warning for on-site construction workers to ensure the smooth development of the project.
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