## 5 Conclusions  
To investigate the safety performance of the high-pressure gas expansion method in the process of rock breaking, a hard rock tunnel in China was taken as the research object, and a comparative analysis of the vibration caused by this new rock-breaking method and traditional rock breaking using explosives was carried out by means of on-site test, theoretical derivation, and numerical simulation. The main conclusions are as follows:  
1. Firstly, field tests were conducted on traditional blasting with explosives. The peak vibration velocity prediction formula was fitted based on [PERSON]'s formula. Combined with the maximum allowable vibration velocity given by the design, the maximum segmental loading of the project was calculated, and the force and vibration of the buildings near the tunnel during the maximum segmental loading of blasting under three working conditions were obtained through numerical simulation. 2. With reference to the dynamite blasting method, field tests of the high-pressure gas expansion method of rock breaking were carried out to determine its optimal hollowing method and rock-breaking effect. Based on the vibration velocities monitored in the field, the vibration attenuation law was explored and the prediction formula for the peak vibration velocity was established. 3. A comparative analysis of the dynamite blasting method and the high-pressure gas expansion method was carried out, with emphasis on the effects of different agent qualities, blasting center distances, and the application of engineering difficulties on the PPV. The relationship between the maximum agent quantity and the volume of rock breakage under the limit case, and a practical implementation scheme are discussed. 4. The study demonstrates that the high-pressure gas expansion method has low vibration and excellent rock-breaking effect, and is fully capable of replacing explosives in some special areas.  
Conceptualization, H.P., J.S., Q.D., B.D., L.Z. and L.T.; methodology, Q.D. and H.P.; software, Q.D. and H.P.; validation, J.S.; formal analysis, Q.D., J.S., B.D. and H.P.; investigation, Q.D., L.T. and B.D.; resources, Q.D. and H.P.; data curation, H.P.; writing--original draft preparation, Q.D. and H.P.; writing--review and editing, H.P., J.S., Q.D., B.D., L.Z. and L.T.; visualization, B.D. and Q.D.; supervision, H.P. and L.T.; project administration, H.P. and Q.D. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Nature Science Foundation of Hunan Province (2022)J40349); Open Project of State Key Laboratory of Safety Technology of Metal Mines, Changsha Institute of Mining Research Co., Ltd. (kft2023-03); the Postgraduate Scientific Research Innovation Project of Hunan Province (QL20220213); Key Project of Education Department of Hunan Province (22A0293); General Project of Education Department of Hunan Province (22C0235).  
The raw data supporting the conclusions of this article will be made available by the authors on request.  
Authors [PERSON], [PERSON] and [PERSON] were employed by the company Changsha Institute of Mining Research Co., Ltd. The remaining authors declare that the re-search was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.