Shield Tunnel Face Visualization System Development for Geological Assessment: Application to Real-Time Determination of Ground Composition

Recently, the demand for long-distance underground tunnels constructed using the shield tunneling method has increased, raising the chance of encountering significant changes in ground composition during excavation. Ground composition is commonly evaluated based on discharged soil characteristics, earth pressure at the tunnel face, and cutter torque. However, these approaches generally provide average information about the excavation face and may not accurately represent local geological variations. Particularly, maintaining the vertical and horizontal alignment of shield machines can become difficult when hard ground is encountered, increasing the risk of machine climbing, sliding, and reduced excavation efficiency. To address this limitation, this study reports on the development of a real-time face visualization system for evaluating and visualizing ground composition at the tunnel face using measurements obtained from accelerometers installed directly beneath the cutter bit. The developed system was subsequently implemented and evaluated in an earth-pressure-balance shield tunnel excavated using a 2.36 m diameter shield machine. The results demonstrated qualitative correspondence between measured acceleration responses and observed ground compositions, indicating the potential of the proposed system for real-time visualization and prediction of major ground transitions ahead of the excavation face. At the same time, detailed field validation remains limited to the investigated projects, and further validation is needed to evaluate discrimination and prediction performance under different geological conditions. Therefore, the system should be regarded as a supplementary tool that complements conventional geological investigations and supports excavation management.