# Research on Optimization Design of Tunnel Blasting Scheme Adjacent to Buildings
## 2 Project Overview  
The tunnel of the Jialingjiang Road Station-Xiangjiang Road Station section starts from Jialingjiang Road Station, which is in the east along Jialingjiang West Road, then turns into Jinggangshan Road, and ends at the intersection of Jinggangshan Road and Xiangjiang Road. Two shafts are set in this section, with a total length of 1211.124 m. A single-hole double-line horseshoe tunnel occupies the first 407.9 m, and a single-hole single-line horseshoe tunnel occupies the last 803.2 m, with a buried depth of 10.56 m-21.86 m.  
The tunnel between Jialingjiang Road Station and Xiangjiang Road Station is facing geological fragmentation and other problems. For example, it passes through heavy industrial plants and other dense buildings, in addition to encountering other problems. The stratigraphy along the line is complex; where the groundwater is serious, the rock fragmentation strength is low, and the fracture's structure has great influence on this project. All the tunnel intervals are located in class V rock sections. The section in this study is from ZSKS5 + 376.877 to ZSK5 + 799.997. The schematic diagram of the surrounding environment of the metro intervals is shown in Figure 1.  
Since the tunnel will laterally pass through a section of dense buildings, the vibration velocity needs to be strictly controlled. In this project, more stringent blasting vibration control is adopted than what is stated in the Blasting Safety Regulations (GB6722-2014) [24]. In order to ensure the safe completion of the blasting operation while minimizing its impact on surface buildings, a combined mechanical excavation and blasting scheme is proposed.  
The tunnel is excavated in several steps, and the upper guide hole is in a soft stratum. Therefore, the mechanical method is used for excavation. After the mechanical excavation process is completed, a critical surface will be formed to facilitate the blasting operation, which, at the same time, can take advantage of the roundness and smoothness of the mechanical method for the excavation contour line, effectively solving the problem of over (under)-ex excavation. The initial support leveling is improved, with the installation velocity of grating greatly improved and the quality of shotcrete ensured. The lower guide hole was constructed using the drilling-and-blasting method. Due to the proximity of the mechanical excavation of the upper guide hole, the vibration impacts the surface buildings. At the time of the lower guide hole blasting, because part of the energy will be dissipated into the air from the existing free surface in the upper part, it results in the reduction in the vibration  
Figure 1: Schematic figure of subway section building environment.  
velocity at the work surface directly above the measurement point, thus protecting the buildings. At the same time, the drilling-and-blasting method of excavation can be used to solve the problem of hard rock excavation in the lower section. The drilling-and-blasting method not only has characteristics such as a low cost, and high efficiency and velocity, but with the use of light surface blasting and differential control blasting, the profile of the section can also be controlled. The actual view of the adjacent buildings is shown in Figure 2.