A general review of the deformation monitoring techniques and a case study: Analysing deformations using GPS/levelling

Being sure is very important that the movements of an engineering structure, which serves the human life of today's modern world, are exhibiting safe behaviours. So, a lot of deformation monitoring studies for determining and analysing different kinds of engineering structures such as high-rise buildings, dams, bridges, viaducts, industrial complexes etc., are implemented. During these studies, the used measurement techniques and systems, which could be geodetic or non-geodetic, are determined considering the type of the structure of which deformations will be monitored, its environmental conditions and expected accuracy from the measurements. As related the used monitoring techniques, the deformation measurement equipments are varied. Also according to professions who use the deformation monitoring techniques, these techniques and instrumentation have traditionally been categorized in to two groups: geodetic surveys, which include conventional (terrestrial such as precise levelling measurements, angle and distance measurements etc.), photogrammetric (terrestrial, aerial and digital photogrammetry), satellite (such as Global Positioning System-GPS, InSAR), and some special techniques; geotechnical/structural measurements, using lasers, tiltmeters, strainmeters, extensometers, joint-meters, plumb lines, micrometers etc. In this paper, some of these deformation measurement techniques which are thought as more important and mostly used by the geodesy specialists will be reviewed. The importance and need of carrying out the deformation measurements periodically in engineering structures will be emphasised. Besides, a case study that is about implementing the deformation analysis of a large viaduct using GPS and Precise Levelling measurements will be discussed here. As it is well known, engineering structures (such as in this viaduct) are subject of deformation due to factors such as changes of ground water level, tidal phenomena, tectonic phenomena etc. In this study, the design, execution and analysis of deformations in a high-way viaduct are going to be mentioned in detailed explanations as an example of implementing the two geodetic techniques in deformation monitoring of large engineering structures. During the study, the control network points were positioned with GPS measurement technique and height differences were supported with precise levelling measurements. As the result of measurement campaigns, the X, Y, Z cartesian coordinates and height differences were determined from the GPS measurements and precise levelling measurements respectively. Later on, deformation analysis using the height differences according to provided data from the GPS and the data from the precise levelling were carried out separately. Then, the 3D deformation analysis using the GPS measurements data was carried out too. Founded results will be given in the paper.