Abstract
Dams are a critical infrastructure system for many communities, but they are also one of the most challenging to inspect. Dams are typically very large and complex structures, and the result is that inspections are often time-intensive and require expensive, specialized equipment and training to provide inspectors with comprehensive access to the structure. The scale and nature of dam inspections also introduces additional safety risks to the inspectors. Unmanned aerial vehicles (UAV) have the potential to address many of these challenges, particularly when used as a data acquisition platform for photogrammetric three-dimensional (3D) reconstruction and analysis, though the nature of both UAV and modern photogrammetric methods necessitates careful planning and coordination for integration. This paper presents a case study on one such integration at the Brighton Dam, a large-scale concrete gravity dam in Maryland, USA. A combination of multiple UAV platforms and multi-scale photogrammetry was used to create two comprehensive and high-resolution 3D point clouds of the dam and surrounding environment at intervals. These models were then assessed for their overall quality, as well as their ability to resolve flaws and defects that were artificially applied to the structure between inspection intervals. The results indicate that the integrated process is capable of generating models that accurately render a variety of defect types with sub-millimeter accuracy. Recommendations for mission planning and imaging specifications are provided as well.
Highlights
Dams provide vital service and protection for many communities, their complex nature poses many challenges for an efficient and reliable inspection
Both of the aforementioned studies proved the value of 3D modeling using Terrestrial Laser Scanning (TLS) for dam inspection, they were not able to capture the overall geometry and resolve the fine-scale (1-mm) details needed for accurate visual inspection
The evaluation results showed an accuracy within 2 cm, but the surface resolution of the model was estimated to be an average of one point every 1 cm2 which may be inadequate for detailed visual inspection of smaller scale damages such as cracks
Summary
Dams provide vital service and protection for many communities, their complex nature poses many challenges for an efficient and reliable inspection. In the study by Colombo and Comi (2016), a bi-phase damage model of an existing concrete arch dam subjected to ASR was generated by taking into account the effects of both temperature and humidity on the hydraulic structure through a heat diffusion analysis and a moisture diffusion analysis, respectively These NDE methods can be used to further evaluate the condition of the concrete structures, periodic visual inspection is still the dominant method to assess the structural integrity of dams and appurtenant structures These digital models capture current conditions of the entire structure that can be used for archival and analytical purposes (Ghahremani et al, 2016; Jafari et al, 2017; D’Altri et al, 2018) Both 3D imaging approaches suffer from the same access challenges that hinder conventional visual inspections. The nature of both UAV and 3D reconstruction methods necessitate careful planning and coordination to properly integrate and tailor these technologies for dam inspection
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