Deformation Monitoring of Engineering Structures: Assessing Causes and Measuring Methods

Introduction

The surface of the planet is not at rest, but slowly changing, probably because of several factors such as man-made structures and earth's nature itself. Hence, it is necessary to be certain of the engineering structures' motions, which serve for human existence. Therefore, most deformation monitoring studies analyse various types of engineering structures, for instance, dams, bridges, high-buildings or infrastructures, tunnels, manufacturing subdivisions, etc., which are frequently applied. The measuring methods are used in these analyses, which either is geodetic or non-geodetic, and these are decided depending on the type of structure to be observed, the predicted accuracy of the observations and their environmental factors. Some reasons of these motions are a volcanic explosion, which falls down a sloping rock layer, eventually triggering a land subsidence; a rise in groundwater level, which can react to the consolidation of intersecting soil layers; soil oxidation and drainage; decay and failure of sensitive stones; tectonic and tidal natural events; etc. Most of the main consequences of subsurface movement are decrease of freeboard level thus causing reduction in flood controlling, gradient, varying across channels of water transport and breakdown of engineering structures (Richardus, 1977). Among all the complex dynamics of engineering their communication and association with the environment is enhanced by the expertise offered by Engineering Dissertation Help becomes indispensable. They provide them with tailored assistance to make the research journey smooth including high proficiency.

Investigating the engineering structures deformation (like dams, viaducts, bridges, towers, etc.) is a special challenge for geodesists. Deformation of structures can be measured by different techniques. Commonly, these methods were commonly categorised into two sections: (i) geodetic surveys, including conventional (terrestrial, like angle and distance observations, precise measurement of the levelling, etc.), photogrammetry (digital and aerial photogrammetry), satellite (like Interferometric Synthetic-Aperture Radar (InSAR), Global Positioning System ( GPS)) and several other specific methods; (ii) geotechnical measurements via tilt meters, lasers, joint meters, micrometers, plumb-lines, strain meters, etc. Any method of measurement has its pros and cons. In general geodetic methods, adequate redundancy of measurements is taken for the statistical analysis of their accuracy, also for the identification of errors that are observed via a network of points, linked by direction and/or length. It further provides details on the deformable structure’s behaviour as compared with some other independent measurements. Non-geodetic techniques provide spatial and geographically disrupted information without any survey. However, equipment that is used for the non-geodetic measurements is better to handle for automated as well as repeatable tracking than traditional geodetic measurement devices. Traditionally, geodetic instruments were used mostly to measure the absolute deformations of chosen points on the surface of the structure in relation to other reference points, which are considered to be stable. Non-geodetic methods are usually used for estimating relative displacements in and vicinity the deformable structure (US Army Corps of Engineers, 2018)

Recently, surveys of surface displacement at unstable areas have focused on horizontal deformation determined by GPS. The focus on horizontal deformation is due to inadequate precision using GPS in determining vertical deformation (Verdonck, 2004). This is due to the fact that, the height component is always the poorest accurately measured GPS coordinate, mainly because of intrinsic geometric deficiency as well as atmospheric errors (Çelik et al., 2001, Featherstone et al., 1998). The above, precise levelling can be used in the current time of GPS as an indispensable method for measuring deformations. The Duhok Dam is an earth-filled embankment dam built on Duhokriver, which is located in Duhok city, in the northern part of Iraq. The dam was abolished in 1988 with the main aim of providing irrigation water.

In literature, various instruments, and procedures for monitoring the dam behaviour were developed. Mostly, they are based on geodetic research. For instance, (Gikas and Sakellariou, 2008) did comparison between actually observed deformations due to continuous geodetic monitoring record with a simulated back analysis of Mornos dam behaviour. Their research tried to explain the real history of deformation on the basis of the dam's mechanical behaviour. The study focused on vertical shifts, whereas the available geodetic data covered cumulative 30-year duration. The results of the geodetic monitoring analysis have been compared with the observations of the finite element back study simulating distinctive steps in the lifespan of the structure, indicating a very strong correlation (on average 0.03 m) between the measured and computed deformations. In a study by (Guler et al., 2006) based on geodetic and geotechnical techniques, analysis of the surface shifts that occurred after construction of an earth fill dam, which had been evaluated. Using the Karlsruhe method, horizontal and vertical observations of movement collected during 1987–1991 and 1991–1996 were geodetically analysed. Similarly, the dam’s behaviour and its base layers were checked using the finite element method (FEM) to determine the deformation. The results of the geodetic observations were compared to the numerical analysis, and it is noted that, there had been a high correlation between the field data and the computed measurement values. It can be seen in (Kalkan et al., 2016) the research that, the efforts and results of the geodetic measurements of Atatürk dam, the largest volume structure in Turkey as well as the world's ninth largest dam. Geodetic techniques have been used to

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