# Formation Mechanism and Control Technology of an Excavation Damage Zone in Tunnel-Surrounding Rock
## 1 Introduction
This method can fully combine the results of field monitoring and theoretical deduction, which is a hot topic in the research of the measuring range of loose circles [15]. [PERSON] et al. [16], [PERSON] et al. [17], and [PERSON] et al. [18; 19] studied the deformation and failure characteristics of the surrounding rock by using particle flow and discrete element simulation methods that referenced a number of microfeature indicators, such as the microcrack field, crack propagation direction and final trend, and they provided a scientific explanation for the nature of many physical phenomena. In addition to blasting factors, the existence of in situ stress can also lead to stress fracture cycles in a tunnel excavation section. [PERSON] et al. [20] conducted research to distinguish between blasting and stress-induced fracture zones. Blasting technology has a great influence on the range and mechanical properties of tunnels surrounding rock loose circles. The tunnel blasting method can be categorized as either ordinary blasting, smooth blasting, or micro-vibration blasting. Through field tests and research, the loose circle formed by ordinary blasting has been deemed the largest, followed by smooth blasting, and the smallest circle is created by micro-vibration blasting [21]. However, there are few studies on the loose ring under the combined use of various blasting methods. [PERSON] et al. [22] believed that multiple blasting methods only produced cumulative damage at the cracks or fissures and increased the displacement at the joint surface, and the loose ring size depended on the maximum burst. [PERSON] et al. [14] and [PERSON] et al. [23] found that multiple explosions expanded the loose circle from 2.8 m to 3.2 m through the acoustic wave method and borehole peeping method and increased the degree of rock breakage, and the damage degrees of sidewalls and vaults can increase by 36-50% and 47-55% in loose circles, respectively. [PERSON] et al. [24] used field tests and finite element simulations to study the changes in the cumulative damage zones of tunnel-surrounding rock under multiple excavation and blasting conditions, and the damage degrees of the surrounding rock were sorted, divided, and summarized. [PERSON] et al. [25; 26] studied the difference between the blasting vibration on a tunnel surface and the blasting vibration inside the surrounding rock through field tests and the differences between the vibration peaks and dominant frequencies on the tunnel surface and the interior of the surrounding rock. At present, there is no unified and clear definition of a loose tunnel circle, and the disturbance zone, plastic zone, and loose circle are often muddled. The technical construction specification for rock foundation excavation in hydraulic structures stipulates that the change rate of wave velocity greater than 10% after blasting is the criterion of rock mass failure. This study used this standard to determine the loose circle of a tunnel. The loosening circle is formed under the dual actions of blasting and stress redistribution in the surrounding rock. However, the contribution of the two to the final loose circle remains unclear. In this study, referencing the construction of a tunnel, blasting construction tests of nonelectric detonators and electronic detonators are carried out. The vibration velocity and the range of the loose circle produced by the two blasting methods were tested. The field test data and numerical simulation method were used to explore the influence of the surrounding rock stress redistribution and blasting load on the range of the loose circle. The results show that the use of electronic detonators is more conducive to the protection of tunnel surrounding rock than non-electric detonators and can significantly reduce the rock damage range.