A GENERAL REVIEW OF THE DEFORMATION MONITORING TECHNIQUES AND A 
CASE STUDY: ANALYSING DEFORMATIONS USING GPS/LEVELLING 
S. Erol* *, B. Erol®, T. Ayan* 
? [TU, Civil Engineering Faculty, Geodesy Division, 34469 Maslak Istanbul, Turkey - (erol, bihter, ayan)@itu.edu.tr 
Commission VII, WG VII/5 
KEY WORDS: Geodesy, Engineering, Structure, Disaster, Monitoring, Analysis 
ABSTRACT: 
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. 
measurements, are easier to adapt for automatic and continuous 
monitoring than conventional instruments of geodetic 
Engineering structures (such as dams, bridges, viaducts, high measurements. Geodetic techniques have traditionally been 
1. INTRODUCTION 
rise buildings, etc.) are subject to deformation due to factors 
such as changes of ground water level, tidal phenomena, 
tectonic phenomena, etc. Monitoring and analyzing 
deformations of these structures constitutes a special branch of 
Geodesy Science. There are several techniques for measuring 
the deformations. These can be grouped mainly into two as 
geodetic and non-geodetic techniques. 
Each main measurement technique has its own advantages and 
drawbacks. Geodetic techniques, through a network of points 
interconnected by angle and/or distance measurements, usually 
supply a sufficient redundancy of observations for the statistical 
evaluation of their quality and for a detection of errors. They 
give global information on the behaviour of the deformable 
structure while the non-geodetic techniques give localized and 
locally disturbed information without any check unless 
compared with some other independent measurements. On the 
other hand, the instruments, which are used in non-geodetic 
  
used mainly for determining the absolute displacements of 
selected points on the surface of the object with respect to some 
reference points that are assumed to be stable. Non-geodetic 
techniques have mainly been used for relative deformation 
measurements within the deformable object and its 
surroundings (Anonym, 2002). 
The major motivation of this study is geodetic techniques in 
monitoring deformations of engineering structures and 
analyzing. In determining deformations according to geodetic 
techniques constitutes terrestrial measurement techniques or 
space based positioning techniques and/or combination of both 
techniques. Until the very beginning of 1980’s, the 
deformations in engineering structures had been determined just 
using conventional measurement techniques. After that, by 
starting to use GPS measurement technique in geodetic and 
surveying applications, this very precise satellite based 
  
* Corresponding author. This is useful to know for communication with the appropriate person in cases with more than one author. 
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