GEODYNAMICS

The paper analyzes the vertical displacements of the GNSS sites of civil engineering structures caused by non-tidal atmospheric loading (NTAL). The object of the study is the Dnister Hydroelectric Power Plant №1 (HPP-1) and its GNSS monitoring network. The initial data are the RINEX-files of 14 GNSS stations of the Dnister HPP-1 and 8 permanent GNSS stations within a radius of 100 km, the NTAL model downloaded from the repository of German Research Centre for Geosciences GFZ for 2019-2021, and materials on the geological structure of the object. Methods include comparison and analysis of the altitude component of GNSS time series with model values of NTAL as well as interpretation of the geodynamic vertical displacements, taking into account the analysis of the geological structure. As a result, it was found that the sites of the GNSS network of the Dnister HPP-1 undergo less vertical displacements than the permanent GNSS stations within a radius of 100 km. This corresponds to the difference in thickness and density of the rocks under the GNSS sites and stations, so they undergo different elastic deformations by the same NTAL. In addition, the research detected different dynamics of vertical displacements of GNSS sites on the dam and on the river banks. It leads to cracks and deformations of concrete structures in the dam-bank contact zones. During the anomalous impact of NTAL, the altitude of even nearby sites can change if the geological structure beneath them is different. The work shows that for civil engineering structures it is necessary to apply special models to take into account NTAL deformations for high-precision engineering and geodetic measurements.

Vibration Monitoring of Civil Engineering Structures Using Contactless Vision-Based Low-Cost IATS Prototype

The role and importance of geodesists in the planning and building of civil engineering constructions are well known. However, the importance and benefits of collected data during maintenance in exploitation have arisen in the last thirty years due primarily to the development of Global Positioning Systems (GPS) and Global Navigation Satellite System (GNSS) instruments, sensors and systems, which can receive signals from multiple GPS systems. In the last fifteen years, the development of Terrestrial Laser Scanners (TLS) and Image-Assisted Total Stations (IATS) has enabled much wider integration of these types of geodetic instruments with their sensors into monitoring systems for the displacement and deformation monitoring of structures, as well as for regular structure inspections. While GNSS sensors have certain limitations regarding their accuracy, their suitability in monitoring systems, and the need for a clean horizon, IATS do not have these limitations. The latest development of Total Stations (TS) called IATS is a theodolite that consists of a Robotic Total Station (RTS) with integrated image sensors. Today, IATS can be used for structural and geo-monitoring, i.e., for the determination of static and dynamic displacements and deformations, as well as for the determination of civil engineering structures’ natural frequencies. In this way, IATS can provide essential information about the current condition of structures. However, like all instruments and sensors, they have their advantages and disadvantages. IATS’s biggest advantage is their high level of accuracy and precision and the fact that they do not need to be set up on the structure, while their biggest disadvantage is that they are expensive. In this paper, the developed low-cost IATS prototype, which consists of an RTS Leica TPS1201 instrument and GoPro Hero5 camera, is presented. At first, the IATS prototype was tested in the laboratory where simulated dynamic displacements were determined. After the experiment, the IATS prototype was used in the field for the purpose of static and dynamic load testing of the railway bridge Kloštar, after its reconstruction according to HRN ISO NORM U.M1.046—Testing of bridges by load test. In this article, the determination of bridge dynamic displacements and results of the computation of natural frequencies using FFT from the measurement data obtained by means of IATS are presented. During the load testing of the bridge, the frequencies were also determined by accelerometers, and these data were used as a reference for the assessment of IATS accuracy and suitability for dynamic testing. From the conducted measurements, we successfully determined natural bridge frequencies as they match the results gained by accelerometers.