Abstract
The diversion tunnel of a hydropower station is characterized by low quality surrounding rock and weak structural planes. During excavation, rock mass spalling and cracking frequently occur. To evaluate the stability of a rock mass during tunnel excavation, high-precision microseismic monitoring technology was introduced to carry out real-time monitoring. Based on the temporal and spatial distribution characteristics of microseismic events, the main damage areas and their influencing factors of tunnel rock mass were studied. By analyzing the source characteristic parameters of the concentration area of microseismic activities, the rock fracture mechanism of the concentration area was revealed. The 3D numerical model of diversion tunnel was established, and the deformation characteristics of the rock mass under the control of different combination types of weak structural planes were obtained. The results showed that the microseismic event was active between 29 October 2020 and 6 November 2020, and the energy release increased sharply. The main damage areas of the rock mass were located at Stakes K0 + 500–K0 + 600 m. Microseismic source parameters revealed that shear failure or fault-slip failure induced by geological structures had an important influence on the stability of the surrounding rock. The numerical simulation results were consistent with the microseismic monitoring results and indicated that among the three kinds of structural plane combination types, including “upright triangle”, “inverted triangle” and “nearly parallel”, the “upright triangle” structure had the most significant influence on the stability of the surrounding rock. In addition, the maximum displacement of the surrounding rock had a trend of lateral migration to the larger dip angle in the three combined structural plane types. The research results will provide significant references for the safety evaluation and construction design of similar tunnels.
Highlights
The research results can provide a better understanding of the rock mass fracturing mechanism and failures of this hydraulic tunnel and other similar tunnels
The spillway tunnel on the right of occurred in the rock mass, which is prone to fractures and microseismic events in the the diversion tunnel was under construction simultaneously
To explore the impact of weak structural planes on the stability of surrounding rock in the diversion tunnel, no support measures were imposed on this numerical simulation model
Summary
The evaluation and research of surrounding rock deformation and stability in underground engineering is an urgent need for hydropower engineering construction in Southwest China. TBM boring in deep-buried tunnels; Tang et al [24] used the microseismic monitoring system to obtain the source information and applied the loading/unloading response ratio theory to predict the slope failure during water storage in the Dagangshan hydropower station; Tang et al [25] studied and predicted the hazard of rock bursts in the tunnel of the Jinping-II hydropower station using microseismic monitoring, indicating that the technology can be used to capture seismic activities in the stress formation and warning period; Xu et al [26,27,28] carried out microseismic monitoring in the Jinping-I, Shuangjiangkou, and Houziyan hydropower stations, studied the evolution process of microfractures and. The research results can provide a better understanding of the rock mass fracturing mechanism and failures of this hydraulic tunnel and other similar tunnels
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