# Safety Assessment of the Cover-and-Cut Method Under Blasting Vibration Induced by Tunnel Excavation
## 3 Field Blasting Vibration Monitoring and Analysis  
To analyze the in situ blasting vibration results, monitoring points were established on the central pillar and diaphragm wall to measure peak vibration velocity (PPV). A vibrometer was placed on both the central pillar and diaphragm wall, positioned 30 m from the blast site. Measurement points 1 to 5 were suspended along the diaphragm wall, while points 6 to 10 were set near the central pillar, each spaced 10 m apart. These monitoring locations align with those in the simulation model, as shown in Figure 6. Due to challenges in directly measuring PPV on the roof, a model was used to simulate it. Figure 9 illustrates the field setup for monitoring on the diaphragm wall. The NUBOX-8016 vibrometer from Sichuan Topu Measurement and Control Co., Ltd., equipped with three channels, recorded data in the horizontal (x, y) and vertical (z) directions, capturing particle velocity, frequency, and duration in each direction. In this  
Figure 8: Vibration speed peak of the bottom measuring point at the bottom of the neutral column. Figure 9: Diaphrag wall measurement diagram. study, point 6, which experiences higher vibration levels, was selected for detailed analysis. A comparison of field and simulated PPV values (Figure 10) reveals that the simulation closely matches the trend of field vibration velocity, reflecting the impact on the structure. The installation of sensors plays a critical role in ensuring the accuracy of vibration measurements and the overall reliability of the data. Proper installation is essential to correctly assess the impact of blast-induced vibrations on the tunnel structure. In Figure 9, while the sensor setup is illustrated, the details regarding the sensor installation procedure are not fully described. To address this, the following description outlines the key steps involved in installing the geophones and related equipment. First, a base plate was used as the foundation for mounting the geophone sensors. This base plate provides a stable and rigid surface for the sensor, ensuring that measurements are not affected by any movement or instability during the installation. The geophone was carefully aligned on the base plate, ensuring that its orientation was correct to measure vibrations in the desired direction. To ensure precise positioning and to account for any surface irregularities, leveling screws were incorporated into the installation. These leveling screws were adjustable and used to fine-tune the alignment of the geophone, ensuring that it was perfectly level and aligned with the direction of vibration measurement. The screws allowed for minor adjustments, which is crucial in obtaining accurate readings, especially when measuring low-frequency vibrations. Once the geophone was positioned and leveled, it was securely fixed to the base plate using a set of mounting screws. These screws were tightened to ensure that the geophone remained in place throughout the entire measurement process. This installation procedure ensures that the geophone is firmly attached to the base plate and maintains its stability during the duration of the measurements, preventing any potential movement that could distort the data. This detailed installation procedure was carried out at all monitoring points, ensuring that each sensor was positioned optimally for accurate measurement of vibration velocities. The precise alignment and secure mounting of the geophones, as described, are essential for obtaining reliable data that can be used to assess the safety of the tunnel structure under blast-induced vibrations. Figure 10: Comparison of PPV curves between numerically simulation and field test on the No. 6 point. Table 4 lists the PPV values from both field measurements and simulations for all monitoring points. The analysis reveals that simulated PPV values are generally higher than field measurements, with a maximum deviation of 16%. This discrepancy may be due to unmodeled factors, such as rock joints and weak surfaces, which could attenuate vibration waves.