Monitoring of retaining structures on an open excavation site with 3D laser scanning

Three-dimensional (3D) laser scanning techniques evolved significantly in terms of accuracy and resolution in recent years and now demonstrate a great potential for structural displacement monitoring. Laser scanners can capture the 3D profile of a structure and can be used for displacement monitoring of all visible surfaces. While the traditional techniques (total station, inclinometer, and theodolite measurements) measure displacements sparsely at several sampled points on the structure. In this work, a 3D laser scanner was used to monitor displacement of a ring beam and a reinforced soil mixing wall (SMW) at an open excavation site. Seven scans of the SMW were taken during the excavation. 3D point clouds of the SMW produced with these scans are placed in one consistent coordinates system and the difference between each pairs of consecutive scans were analysed to determine displacements of the SMW. Several cloud comparison methods were applied including C2C, C2M and M3C2 techniques to identify displacements along the height of the SMW. The displacement obtained were validated against displacement measured by inclinometer and total station. It is concluded that the displacement monitoring with 3D laser scanner are sufficient for monitoring of cumulative displacement but not for increment displacement.