## 3 Rock Breaking Design Program  
### Dynamic Blasting  
#### 3.1.1 Schematic Design  
Since HPGEM is an emerging rock-breaking method with little engineering experience to draw on, this study first carried out the design of the rock-breaking scheme by explosive blasting (No. 2 rock emulsion explosive), to provide a reference point for the subsequent design of the HPGEM. Due to the constraints of the construction project's environment, dynamite blasting cannot be performed in the case study tunnel. Therefore, all blasting tests in this study were conducted in another tunnel about 1 km away from the case study tunnel (with almost the same geological conditions as in the study area). The blasting vibration velocities in three directions are monitored during the blasting operation. The peak particle velocity [22,23] is usually taken as the key factor for determining the impact of blasting vibration. Determination of the PPV is the basis for measuring whether the blasting operation causes damage to adjacent buildings (structures), which the Sadowski formula is commonly used to predict [24,25] (Equation (1)). \[PPV=K\bigg{(}\frac{\sqrt[3]{Q}}{R}\bigg{)}^{\alpha} \tag{1}\]  
where the characteristic coefficient \(K\) and \(\alpha\) are the coefficients related to the site topography (geological conditions and other factors are shown in Table 1). PPV is the peak particle velocity (cm/s), \(R\) is the distance from the blasting center (m), \(Q\) is the maximum explosive charge in all sections (kg). Figure 4: Overview of the study area. (**a**) Geographic location of the study area; (**b**) elevation map of the study area; (**c**) satellite view of the study tunnel area; (**d**) inside the tunnel; (**e**) outside the tunnel. Taking the logarithm of both sides of Equation (1) gives the following:  
\[lgPPV=lgK+\alpha lg\left(\frac{\sqrt[3]{Q}}{R}\right) \tag{2}\]  
\[\text{Let }y=lgPPV;x=lg\left(\frac{3/Q}{R}\right);b=lgK;k=\alpha\]  
Then:  
\[y=kx+b \tag{3}\]  
The regression calculation yields the following:  
\[k=\frac{n\sum_{i=1}^{n}x_{i}y_{i}-\sum_{i=1}^{n}x_{i}\sum_{i=1}^{n}y_{i}}{n \sum_{i=1}^{n}x_{i}{}^{2}-\left(\sum_{i=1}^{n}x_{i}\right)^{2}} \tag{4}\]  
\[b=\frac{1}{n}\left(\sum_{i=1}^{n}y_{i}-\alpha\sum_{i=1}^{n}x_{i}\right) \tag{5}\]  
The correlation coefficient can be expressed as:  
\[\gamma=\frac{\sum_{i=1}^{n}\left(x-\overline{x}\right)\cdot\left(y-\overline{ y}\right)}{\sqrt{\sum_{i=1}^{n}\left(x-\overline{x}\right)^{2}\cdot\sum_{i=1}^{n} (y-\overline{y})^{2}}} \tag{6}\]  
where \(n\) is the total number of monitoring; and, each \(x_{i}\) and \(y_{i}\) represents the size of a particular experiment \(x\) and \(y\). If the full section excavation is used, the PPV will exceed the specified limit. Therefore, the proposed tunnel is divided into a drilling and blasting excavation area and a mechanical and drilling and blasting excavation area, according to the distance from the highway and underground pipelines. Excavation operations are carried out in the areas within 34 m from the left and right sides of the highway centerline, and drilling and blasting excavation is performed outside the area. Since the PPV is the direct cause of damage to buildings (structures), the analysis is conducted on vibration monitoring and the blasting effect of the drilling and blasting method. In this blasting design, the wedge cutting technique was applied to blast excavate a section of the upper and lower benches. The spacing of the cut holes was 0.9 m, with a plum-shaped arrangement and a row spacing of 0.7 m. Each hole was charged with 0.4 kg of explosives (calculated based on the design of the drilling and blasting excavation). The first section of the charge was slightly larger, with a charge of 0.6 kg per hole, and an advance of 1.0 m per cycle. Refuge blasting is used at the center of the empty hole by spiral hollowing, with a maximum charge of 0.6 kg per hollowing hole. Each cut and peripheral hole is charged with 0.2 kg of explosives, and the guide mine for each advance cycle is 0.8 m long.