Terrestrial Scanning / Topography & Monitoring

J. Boavida, A. Oliveira, A. Berberan
"Dam monitoring using combined terrestrial imaging systems", Civil Engineering Surveyor (CES) December/January 2009 11.02.2009

Thousands of registered large concrete and embankment dams have now more than five decades of operational and age related problems. Monitoring plays an essential role in evaluating the structural safety condition of dams. Monitoring activities are also useful for the collection of valuable data to enhance the understanding of the behaviour of these structures.
Embankment dams can suffer from surface displacements related to internal deterioration, such as internal erosion or slope failure. Surface displacements are important quantities to be determined, especially in relation to safety and long term behaviour. The determination of these values is made by measuring surface marks located at regular space intervals, usually in the dam crest and downstream face. However this methodology is based on a discrete sample instead of the surface itself.
Up until now, concrete dam visual inspections have been carried out by expert personnel, without the assistance of any dedicated device or system. Due to operational difficulties, the collected information is often inaccurate, from a positional point of view, rather subjective and costly, yet very important. Laser scanners combined with calibrated reflex digital cameras provide accurate and dense 3D numerical models as well as spatially continuous high-resolution colour (RGB) information of the objects under study. These combined terrestrial imaging systems (CTIS) provide a huge amount of geometric and radiometric well structured data in a short period of time. A 3D scanning company, Artescan, and a research organization, the Laboratório Nacional de Engenharia Civil, in Portugal (LNEC) have been developing positional monitoring methodologies for embankment dams and assisted visual inspection methodologies for concrete dams since 2003. This paper presents three case studies (two concrete and one embankment dam) of the developed methodologies as applied to dam monitoring.