Deformation monitoring of large tunnel wall under construction by digital photogrammetry measurement at Ritto Tunnel

The second Meishin (Tokyo-Kobe) highway that will be the most important to Japanese economy in the 21st century, is under construction. In this highway tunnels are the major structures which go through many mountainous areas. The standard cross-section of the tunnel in this highways is very large (250 m ²) compared to ordinary tunnels and the tunnel width is very wide (18 m). The tunnel is first bored by 5 m diameter TBM and it is enlarged later. Photogrammetry measurement with a CCD camera is applied to deformation monitoring of large tunnel. Tunnels on construction sites like highways must be carefully and continuously observed for deformation during construction. Although geology is granite, it has many fractures under Tectonic process in Japan. In the tunnel, the fractured zone was detected widely by investigation by TBM pilot tunnel, we needed to check the stability of tunnel wall after enlarge section process. Conventionally proposed monitoring methods include total station. However, none of these are widely employed because of poor workability, insufficient precision and/or high running cost under tunnel work. For this reason, it decided to apply precision photogrammetry and the technique of investigating the tunnel deformation of the whole visually by three dimensions was developed. The reflective target of 121 or more sheets was stuck on tunnel wall, by taking a photograph, the 3-dimensional coordinates of a target were acquired and deformation of tunnel wall was visualized. In this paper, we show an example of the result.