## 5 Conclusions  
Through numerical analysis, the effects of blasting vibration on a TBM and its backup unit during TBM pilot and NATM extending parallel excavation were assessed according to rock type and powder factor, and the necessary length of the pilot tunnel was determined. Furthermore, the vibration speed transmitted to the tunnel face and ground surface was measured to determine its impact on the surrounding ground and structures. The main findings of this study and prospects for future research are summarized as follows. 1. Depending on the type of rock and powder factor, the transmitted vibration velocity differs significantly. The measured vibration velocity increased with denser rock or higher powder factor. Based on the characteristics of blasting using a TBM and the NATM in parallel, which only blasts a contour hole without center-cut blasting, the effects of blasting vibration were greater on the sidewalls than on the bottom of the TBM backup device. In cases where the blasting point was separated from the sidewall by 7 m or more, or a distance of 3 m or more was secured to the bottom point, the vibration values were measured to be lower than the regulated values for large RC buildings. Therefore, it was determined that the TBM backup device should have a minimum separation distance of 7 m to ensure safety. Otherwise, an appropriate protection device is required. 2. In our analysis of blasting vibration on the TBM, the results were lower than the permissible values for houses and apartments in the Seoul subway system, except for the case of hard rock with a powder factor of 2.0 kg. Regardless of the rock type, the effects of blasting vibration transmitted to the ground above the TBM were higher than the vibration regulation value applicable to shopping complexes, offices, and public buildings when the powder factor was 2.0 kg or more. The effect was lower than the vibration regulation value applicable to houses and apartments when the powder factor was 0.75 kg or less or when the length of the pilot tunnel was extended to 12 m. Consequently, in cases with aboveground sensitivities, the powder factor should be reduced for safer construction. An adjustment of the powder factor when the ground is solid will shorten the pilot tunnel and construction period, which is anticipated to be economically beneficial. 3. In all cases, except for hard rock with a load of 2.0 kg or more, the blasting vibration transmitted to the tunnel face and ground surface had lower vibration values than the regulated values for houses and apartments. Therefore, it is expected that the damage to the ground surface and structures would not be excessive. 4. This study was limited to a specific tunnel size. The size of the required tunnel varies according to the utilization of the underground space, and the effect of vibration is expected to vary according to the size of the TBM pilot tunnel. Therefore, in future studies, the interaction between various NATM and TBM pilot tunnel sizes should be studied. In addition, this study simulated only the minimal shell blasting caused by the pilot tunnel. Additional research will be conducted on the number of blast holes, spacing, and cross-sectional shape under various conditions. [PERSON]-M.K. drafted and performed the numerical analysis; [PERSON]-[PERSON] and [PERSON] investigated and reviewed the physical properties necessary for the analysis; [PERSON]-L.C. and [PERSON] reviewed and analyzed the existing literature and relevant materials; [PERSON]-W.L. analyzed the research concept and design, guided the dissertation, and conducted the final review. All authors have read and agreed to the published version of the manuscript. This research was supported by the Ministry of Land, Infrastructure, and Transport (Korea Agency for Infrastructure Technology Advancement) under the project \"Development of High-Speed Tunneling Technology for Long Tunnels Using Protective Shields (Parallel Excavation with a TBM Pilot and NATM Widening) (22 TBIP-C155615-03)\".