Application of 3D laser scanning on NATM tunnel deformation measurement during construction

The 3D laser scanning technology is implemented to multi-temporally scan the lining of a NATM tunnel during construction. An improved moving average method (IMAM) is firstly proposed for downsizing the scanned point clouds. The correspondence between two temporal point clouds is determined by the iterative closest point (ICP) algorithm, and then the deformation between each paired points was obtained throughout the data. Subsequently, the full-space deformation field of tunnel lining can be calculated, which provides extensive deformation information of the complete tunnel lining for construction. The verification is conducted by a 20-mm convergence test, and it shows that the IMA method can maintain the accuracy at 78% when the reserved ratio is as low as 3% in NATM tunnel, which is significantly better than the random sampling method and the curvature sampling method. The results also indicate that proposed deformation analysis method performs well even for rough linings. The validation of the proposed method is carried out by comparing the 3D laser scanning and total station measurement of the Nanshan Tunnel. The measurement using the proposed technology has a good agreement with that obtained by using traditional total station monitoring method. In addition, the full-space deformation field of tunnel lining can be obtained for more extensive discussion on the development of deformation.