# Study on Vibration Effects and Optimal Delay Time for Tunnel Cut-Blasting Beneath Existing Railways
## 1 Introduction  
With the development of railway and highway transportation, it is common for new tunnels to be built close to existing structures, such as bridges, houses, and dams. The construction of new structures will have an impact on the neighboring buildings or sites. Urbansubways are generally developed after the city planning; thus, crossing existing structural spaces becomes inevitable. The commonly used methods for subway tunnel excavation are shield construction and the drilling-blasting method [1,2]. Between them, blasting is an efficient and economical excavation method in hard rock formations. However, blasting results in vibration to neighboring structures, which may damage or even destroy neighboring structures [3]. To understand the effect of blasting on existing structures, this paper will investigate controlled blasting against the background of blasting construction in the Zhongliangshan Tunnel in Chongqing, which crosses under existing railways. The impact of blasting on surrounding buildings is a major concern in tunnel blasting. [PERSON] et al. [4] analyzed the vibration response characteristics of tunnel blasting by taking the blasting project of the Chongli tunnel, which crosses under the existing railway, as an example. [PERSON] et al. [5] used monitoring data and numerical simulation to study the vibration of existing railway tunnels caused by blasting of the tunnel in the neighboring area. [PERSON] et al. [6] used the numerical simulation method to analyze the dynamic response of subway tunnels crossing under the existing railway tunnel by the full-face excavation method and the center diaphragm method. [PERSON] et al. [7] analyzed the impact of the blasting vibration effect of undersea tunnels on the structure of neighboring service tunnels and the characteristics of shock wave pressure distribution in the water excited by blasting vibration. [PERSON] et al. [8] analyzed the influence of blasting construction on the vibration velocity and stress distribution of existing subway tunnels based on numerical simulation and on-site monitoring data. [PERSON] et al. [9] analyzed the impact of more complicated working conditions, where a new tunnel construction crosses over the existing tunnel and under the existing railway. In addition, [PERSON] et al. [10] used the numerical simulation method to discuss the dynamic response of metro station pit blasting on adjacent foundations, and analyzed the influence of the length, width, depth of adjacent pits, and the depth of the blasting pit. Generally, a portion of the energy generated during tunnel blasting is utilized in the rock fragmentation process, while the remaining energy propagates through the rock medium as elastic waves. These waves subsequently trigger the dynamic response of the surrounding rock mass and the adjacent environment. When the intensity of vibration exceeds the limit of the load-bearing capacity of the existing structure, blasting may significantly affect the structural stability of the structure and even cause a safety threat. Therefore, reducing the vibration effect has been the focus in the field of blasting [11,12]. [PERSON] et al. [13] carried out the inversion of key parameters based on field data and the BP neural network, and analyzed the propagation and attenuation of tunnel blasting vibration waves under different blast center distances with the help of numerical simulation. [PERSON] et al. [14] carried out two-hole time-delayed blasting of granite plates and analyzed the evolution of the explosive stress wave and vibration wave between the two holes. [PERSON] et al. [15] compared the surface vibration velocity and instantaneous energy obtained from millisecond delayed initiation of cut-blasting and initiation of different charging schemes, and found that the free surface condition, the amount of the single section, and the depth of the tunnel had a significant effect on the surface vibration. [PERSON] et al.