Aerial Close-Range Photogrammetry to Quantify Deformations of the Pile Retaining Walls

Today, as structures with life expectancy of more than 100 years are being constructed, it is vital to gain knowledge about the gradual decline in material properties. Accordingly, to ensure the longevity and safety of these structures, monitoring has been incorporated as a fundamental part of their service life. To monitor structural deformation, various methods have been developed, with the most common being the survey of certain points of a structure during and after construction using a total station. New techniques are now being developed, and one of the most promising ones is photogrammetry because it provides a simple method to monitor a structure using unmanned air vehicles (UAVs). This paper is aimed at sharing the strategic steps followed in monitoring the deflection of a simple secant pile retaining wall during excavation and construction of a basement. The monitoring is performed using a commercial UAV in combination with point cloud formation, georeferencing, and comparison software (cloud compare, I-Site Studio, 3D Reshaper, etc.). The monitoring results show very good agreement with the traditional inclinometer deflection measurements and numerical analysis, thereby demonstrating the feasibility of the proposed method. The authors believe that in the future, photogrammetry using UAVs can become the standard method for geotechnical monitoring because of its speed, lower cost and ease of use, when compared to conventional methods, a non-destructive method, and is easy to learn and use