###### Abstract
Previous research has shown that CO2 blasting technology has the advantages of little vibration, low noise and no harmful gas generation, which is a green, environmentally friendly and safe non-explosive blasting rock-cracking technology. However, it is cumbersome in use, has strict storage and transportation requirements, relies on special equipment, and cannot achieve efficient excavation in hard-rock projects [15; 16; 17; 18; 19; 20]. In order to find a new rock-cracking technology by gas expansion, that can overcome the disadvantages of CO2 blasting technology, the research group of [PERSON] from Central South University firstly proposed the concept of high-pressure gas expansion rock-cracking technology, invented the high-pressure gas expansion cracking method and its test method for cumulative damage to the surrounding rock [21; 22], and designed and produced the main rock-cracking equipment expansion pipe. Then the technology was actively applied to engineering projects and relevant tests were conducted to prove the feasibility of the technology. [PERSON] et al. [23] conducted a comparison test between high-pressure gas expansion rock-cracking technology and traditional explosive blasting technology in a hard rock tunnel, compared and analyzed the rock mass cracking effect and vibration speed of the two rock-cracking technologies, and concluded that traditional explosive blasting technology has smaller rock fragmentation while high-pressure gas expansion rock-cracking technology has less vibration. [PERSON] et al. [24] conducted the cutting tests of high-pressure gas expansion rock-cracking technology in a small section hard rock tunnel while the vibration was also monitored, and concluded that the technology can obtain an ideal cutting effect with reasonable cutting hole network parameters in a small section hard rock tunnel and the vibration caused by it has minimal influence on the surrounding buildings. [PERSON] et al. [25] used high-pressure gas expansion rock-cracking technology to excavate a hard rock connecting passage, optimized the rock mass cracking parameters to obtain the ideal rock mass cracking effect, and concluded that the technology can achieve the rapid excavation of the hard rock connecting passage and has the advantage of little vibration. Previous research has shown that high-pressure gas expansion rock-cracking technology has the advantages of little vibration, low noise, simple operation and convenient storage, and it can also realize hard rock tunnel excavation. However, it is still in the experimental stage, and there are few practical application cases at present [26; 27]. This study will take a hard rock tunnel project under the Great Wall in Hebei Province as the research background, theoretically analyze the rock mass cracking mechanism of high-pressure gas expansion rock-cracking technology and conduct field tests in the tunnel to determine the appropriate rock mass cracking parameters. Simultaneously, vibration monitoring will be conducted to ensure that the vibration does not affect the safety of the Great Wall. This paper aims at confirming the applicability of high-pressure gas expansion rock-cracking technology to the excavation of hard rock tunnels under the Great Wall and providing engineering experience for the application of the technology in hard rock tunnels near ancient buildings and historic sites.