## 6 Conclusions  
Microseismic monitoring was introduced into the diversion tunnel of a hydropower station to monitor, analyze and evaluate the stability of the surrounding rock during tunnel excavation. The following conclusions were drawn based on the analysis of the characteristics of microseismic activities and numerical simulation results. The diversion tunnel had frequent microseismic activities from 29 October to 6 November 2020, with up to nine microseismic events in a single day, along with a dramatic rise in the cumulative energy release curve. Microseismic events were mainly distributed at Stakes K0 + 500-K0 + 600 and particularly concentrated at Stakes K0 + 540 and K0 + 570, where damage of the surrounding rock was serious. Excavation unloading, structural planes and the group tunnel effect were the main factors causing microseismic events in the diversion tunnel. From 20 October to 10 November 2020, the diversion tunnel was excavated at Stakes K0 + 510-K0 + 565. The \(Es/Ep\) characteristics of microseismic events revealed that fractures of rock mass included tensile and shear failures. The stress was concentrated on the weak structural plane due to excavation and unloading, resulting in tensile cracks on both sides of the structural plane. Four structural planes and the loose rock mass near the structural plane was prone to slips and shear failure along the structural plane. The \(b\)-value of microseismic events was 1.0, indicating that there were microseismic activities caused by blast-induced stress migration and by slips on the structural plane. There are three types of structural plane combinations, namely \"nearly parallel\", \"upright triangle\" and \"inverted triangle\", at Stakes K0 + 500-K0 + 620. The numerical simulation results showed that the \"upright triangle\" structural plane had the greatest influence on the deformation of the rock mass within its range, followed by the \"inverted triangle\" structural plane, and finally the \"nearly parallel\" structural plane. In addition, the structural plane combination had an offset to the side of the structural plane with a  
Figure 12: Displacements at the intersection of structural planes and the diversion tunnel trunk: (**a**) Stake K0 + 607; (**b**) Stake K0 + 582; (**c**) Stake K0 + 542; (**d**) Stake K0 + 518.  
larger dip angle at the maximum displacement of the surrounding rock. The distribution of microseismic activities was in good agreement with the numerical simulation results. Surrounding rock damage was serious around microseismic clusters, which was prone to surrounding rock deformation and failure and had great guiding significance for site construction safety and engineering warning. It is worth noting that three structural planes with different combination types appear in a short tunnel. Secondly, microseismic monitoring technology is used to track the fracture damage of surrounding rock in this section, and the numerical calculation model is used to verify it. The results reveal which type of combined structure has the greatest influence on the tunnel. The research results can provide a better understanding of the rock mass fracturing mechanism and failures of this hydraulic tunnel and other similar tunnels. [PERSON] conducted the literature review and wrote the first draft of the manuscript. [PERSON] developed the overarching research goals and analyzed microseismic source parameters. [PERSON] edited the draft of the manuscript. [PERSON] investigated the geological and construction information of the engineering. [PERSON] carried out the numerical simulation. [PERSON] processed the microseismic monitoring data. All authors have read and agreed to the published version of the manuscript. The research is supported by the National Natural Science Foundation of China (No. 51809221 and No. 42177143), the Science Foundation for Distinguished Young Scholars of Sichuan Province (Grant No. 2020 JJQ0011) and the opening project (No. KFJ20-06M) of State Key Laboratory of Explosion Science and Technology (Beijing Institute of Technology).