# Recognition of Tunnel Fracture Zones in Seismic Waves and Ground-Penetrating Radar Data
## 4 Advance Forecasting and Verification of Fracture Zones in Liangwangshan Tunnel  
The starting and ending mileage of the right line tunnel of Liangwangshan Tunnel has a total length of 7978 m. The starting and ending mileage of the left tunnel has a total length of 7961 m. The maximum burial depth of the tunnel is determined to be 384.6 m, which belongs to an extra-long tunnel, by analyzing the stability of excavation, the degree of fragmentation, and the development of cracks. Based on the characteristics of rock extension, the information of the rock layer in front of the tunnel face can be inferred. This method is highly accurate in determining faults and fracture zones, usually revealing the direction of fracture zones. The seismic wave method's work arrangement is shown in Figure 11. Starting from the tunnel face, 12 seismic source points were established on both the left and right tunnel walls, with a spacing of approximately 1.5 m between points. Three-component detectors were placed at a distance of about 3.0 m from the first seismic source point, using a hammer strike as the seismic source. Additionally, one three-component detector was installed at a height of approximately 1.0 m on both the left and right tunnel walls and at the crown of the tunnel. The tunnel's axis was used as the reference line. The seismic reflection signals generated by the hammer strikes were collected, and preprocessing techniques were applied to filter out noise and unwanted signals. This process resulted in the acquisition of effective seismic reflection signals from the front of the tunnel face. Based on the characteristics of seismic wave propagation in the fracture zone, the fracture zone in front of the tunnel working face can be preliminarily identified. Figure 11: Work arrangement for seismic wave method. The seismic trace data collected from tunnel K37 + 537 to K37 + 417 were processed. The clutter signal was eliminated by bandpass filtering, and the direct wave signal was suppressed by F-K filtering. The stack velocity spectrum was obtained by the velocity scanning stack. The peaks and troughs in the channel record are continuous and dense, as shown in Figure 6. There are many energy bands and interference bands in the calculated velocity spectrum. This shows that the rock in front of the tunnel is relatively broken. The recognition results show three abnormal reflection regions. A three-dimensional imaging result for the area between K37+537 and K37+417 was obtained by the principles of seismic wave common reflection surface stacking and diffraction scanning offset superposition, combined with the wave velocity scanning analysis results, as shown in Figure 7.  
From the extracted three-dimensional superimposed reflection surfaces, it is observed that there are three anomalous reflection areas within the entire detection range. The positive and negative reflection interfaces within these three areas exhibit a chaotic pattern, with alternating red and blue interfaces discernible in the 3D image. The positive and negative reflection amplitudes inside the areas are relatively large, indicating the presence of rock fragmentation zones in front of the tunnel. Based on the tunnel face's geological conditions, wave velocity scanning, and three-dimensional imaging results, the following conclusions are drawn for the region between K37+537 and K37+417: within the predicted range, the integrity and stability of the surrounding rock in the three areas are weak, and there are areas of rock fragmentation. Ground-penetrating radar detection was performed on three areas to identify the fracture zone area in front of the tunnel face. Ground-penetrating radar was used for data collection. The radar data underwent preprocessing, such as editing and zero-point correction. The layout of the survey lines is shown in Figure 12b. The fracture zone features of the radar signals in the three abnormal reflection areas were identified according to the collected radar reflection signals.