On the Case Example of the Application of the Handheld Laser Scanner to the Geological Risk Assessment of the Unlined Tunnel

Abstract

Many hydropower plants of J-Power were constructed more than 50 years ago. The geological risk assessment of the unlined tunnel such as waterway tunnel has been carried out for the steady maintenance of these old power plants since 2015. The laser measurement by the Handheld Laser Scanner was conducted in the unlined tunnel to improve efficiency and accuracy of the geological survey for the geological risk assessment. This report describes the method and the results of the measurement.

Firstly, a preliminary measurement by the Handheld Laser Scanner was conducted in access tunnels with unlined parts of two underground power plants to confirm performance such as accuracy at the measurement. The accuracy of the measurement was within about 10 cm of actual measured value. Later, the Handheld Laser Scanner was applied to a collapsed unlined waterway tunnel. Surface roughness and discontinuities on the bedrock can be visualized by computer from the acquired high density point cloud data. As a result, it was possible to grasp three-dimensional shapes of the tunnel conveniently and efficiently. Furthermore, we confirmed that highly accurate geological model can be produced by combining geological observation.