Reconnaissance of Two Liquefaction Sites Using Small Unmanned Aerial Vehicles and Structure from Motion Computer Vision Following the April 1, 2014 Chile Earthquake

Small unmanned aerial vehicles (sUAVs) were used to reconnoiter, image, and model the effects of soil liquefaction at two separate sites following the M8.2 and M7.6 earthquakes near Iquique, Chile, on April 1 and 2, 2014, respectively. Geotechnical investigators performed conventional observations/measurements at the two sites using traditional reconnaissance methods, and virtual observations/measurements using sUAV-based remote sensing and structure from motion (SfM) computer vision. Two types of sUAV platform/sensor combinations were evaluated for this study. Comparisons between the traditional and sUAV-based reconnaissance methods were performed and observations are discussed. The sUAV-based point cloud models of the sites were between 770 and 2,600 points per square meter depending on the camera that was used, with average model dimensional error ranging from +/- 1.0 to +/- 3.5%. Lateral spread displacement measurements from the UAV-based three-dimensional models were generally within 9cm of the lateral spread displacements measured in the field, and measured vertical deformations from the models generally agreed well with the deformations reported by previous investigators. This study demonstrates that sUAVs can be useful instruments for post-disaster geotechnical surficial site reconnaissance. (C) 2016 American Society of Civil Engineers.