# Safety Assessment of the Cover-and-Cut Method Under Blasting Vibration Induced by Tunnel Excavation
## 4 Vibration Analysis of Subway Tunnel Construction
### Summary and Analysis of Results
#### 4.3.6 Comparison with China's Blasting Safety Regulations  
During the excavation of the subway tunnel, vibration velocities at the diaphragm wall and central pillar were directly measurable; however, monitoring at the tunnel roof was not feasible. To address this limitation, a three-dimensional numerical simulation was conducted using FLAC3D to predict the particle velocities at the roof. The predicted vibration velocities at various points are shown in Figure 13, with the maximum vibration velocity at the roof predicted to be 1.537 cm/s. Comparative analysis of the measured roof velocities and center pillar data revealed that the roof experienced higher vibration velocities, with both the roof and central pillar velocities surpassing those of the diaphragm wall.  
These findings are consistent with the stress cloud analysis results, which indicate that the tunnel blasting generates a maximum predicted vibration velocity of 1.537 cm/s at the roof, followed by 1.482 cm/s at the central pillar and 1.424 cm/s at the diaphragm wall.  
Assessment of Safety Criteria: In order to assess the safety of the measured vibration velocities, it is essential to evaluate these values against established safety standards. The Chinese Blasting Safety Regulations provide guidelines for controlling vibration during construction activities, including permissible peak particle velocity (PPV) limits for blasting-induced vibrations. According to these regulations, the allowable PPV for newly poured concrete in foundation pits is between 2.0-2.5 cm/s, depending on the type of structure and its proximity to the blast. This threshold aligns with international standards such as those set by the U.S. Bureau of Mines (USBM), German Industrial Standards (DIN), and British Standards (BS).  
The Chinese regulations also recognize the relationship between vibration frequency and structural safety. Specifically, if the vibration frequency falls within the 40-80 Hz range, the allowable PPV is typically set at 2.0 cm/s, which is consistent with international standards. However, for higher frequencies (e.g., above 100 Hz), the regulations adopt a more conservative approach, requiring further attenuation of vibrations to prevent potential structural damage.  
The results of this study, which show maximum predicted PPV values of 1.537 cm/s at the roof, 1.482 cm/s at the central pillar, and 1.424 cm/s at the diaphragm wall, all fall well within the safety limits set by China's Blasting Safety Regulations. These values are also well below the limits recommended by international standards such as the USBM, DIN, and BS for newly poured concrete structures.  
Additionally, the vibration frequencies observed in this study (ranging from 40 to 80 Hz) are within the safe range according to both Chinese and international guidelines. This ensures that the measured vibrations do not exceed the permissible PPV thresholds for the observed frequency range.  
Thus, based on the comparison with both Chinese and international safety regulations, the blasting-induced vibrations measured in this study fall within the safe zone, confirming that they are unlikely to cause any structural damage. The results demonstrate that the structural safety of the subway tunnel, as measured in this study, remains within acceptable limits according to both national and international standards.