It is difficult to predict detailed ground conditions of a mountain tunnel with a large overburden from a surface geological survey only. The ground conditions ahead of a tunnel face must be predicted for efficient and safe tunnel construction. The authors have proposed a simple forward prediction method that uses tilt sensors installed at the tunnel crown near the cutting face. Moreover the effectiveness of the method has been verified in practice. The field tests have been carried out at three mountain tunnel projects under construction to confirm that the trend of the inclination angle variation shows the transition portent of the ground ahead of the face, as predicted by a preliminary numerical study (Kudoh et al., 2012a). The trends of inclination angle measured in the field are practically consistent with those in the numerical analysis for an unsupported elastic ground (Tani et al., 2012).
This paper first shows the proposed prediction method and the necessary measurement devices, and mentions the principle of prediction by tilt sensors. It then presents the capability of prediction, and discusses the effectiveness of this method in two different types of deformation modes.