Tomaž Ambrožič

Prediction of subsidence due to underground mining by artificial neural networks

Alternatively to empirical prediction methods, methods based on influential functions and on mechanical model, artificial neural networks (ANNs) can be used for the surface subsidence prediction. In our case, the multi-layer feed-forward neural network was used. The training and testing of neural network is based on the available data. Input variables represent extraction parameters and coordinates of the points of interest, while the output variable represents surface subsidence data. After the neural network has been successfully trained, its performance is tested on a separate testing set. Finally, the surface subsidence trough above the projected excavation is predicted by the trained neural network. The applicability of ANN for the prediction of surface subsidence was verified in different subsidence models and proved on actual excavated levels and in levelled data on surface profile points in the Velenje Coal Mine.

Use of Terrestrial Laser Scanning Technology for Long Term High Precision Deformation Monitoring

The paper presents a new methodology for high precision monitoring of deformations with a long term perspective using terrestrial laser scanning technology. In order to solve the problem of a stable reference system and to assure the high quality of possible position changes of point clouds, scanning is integrated with two complementary surveying techniques, i.e., high quality static GNSS positioning and precise tacheometry. The case study object where the proposed methodology was tested is a high pressure underground pipeline situated in an area which is geologically unstable.

GPS-derived Geoid using Artificial Neural Network and Least Squares Collocation

Abstract The geoidal undulations are needed for determining the orthometric heights from the Global Positioning System GPS-derived ellipsoidal heights. There are several methods for geoidal undulation determination. The paper presents a method employing the Artificial Neural Network (ANN) approximation together with the Least Squares Collocation (LSC). The surface obtained by the ANN approximation is used as a trend surface in the least squares collocation. In numerical examples four surfaces were compared: the global geopotential model (EGM96), the European gravimetric quasigeoid 1997 (EGG97), the surface approximated with minimum curvature splines in tension algorithm and the ANN surface approximation. The effectiveness of the ANN surface approximation depends on the number of control points. If the number of well-distributed control points is sufficiently large, the results are better than those obtained by the minimum curvature algorithm and comparable to those obtained by the EGG97 model.

An alternative approach to control measurements of crane rails

Horizontal and vertical positions of points for the control assessment of crane rails are classically determined separately. The procedure is time consuming and causes non-homogenous accuracy of the horizontal and vertical position of control points. The proposed alternative approach is based on polar measurements using a high accuracy total station instrument and a special platform with two precise surveying prisms fixed on it. Measurements are carried out from a single station thus ensuring a common coordinate system and homogenous accuracy. The position of the characteristic point of a rail is derived from the measured positions of both prisms with known geometry of the platform. The influence of platform non-horizontality is defined, along with its elimination procedure. Accuracy assessment is ensured with redundant measurements. Result of the proposed procedure is a numerical and graphical presentation of characteristic points. The control parameters required in international Eurocode standards are easily determined from them.

Statistical Properties of Strain and Rotation Tensors in Geodetic Network

This article deals with the characteristics of deformation of a body or a figure represented by discrete points of geodetic network. In each point of geodetic network kinematic quantities are considered normal strain, shear strain, and rotation. They are computed from strain and rotation tensors represented by displacement gradient matrix on the basis of known point displacement vector. Deformation analysis requires the appropriate treatment of kinematic quantities. Thus statistical properties of each quantity in a single point of geodetic network have to be known. Empirical results have shown that statistical properties are strongly related to the orientation in single point and local geometry of the geodetic network. Based on the known probability distribution of kinematic quantities the confidence areas for each quantity in a certain point can be defined. Based on this we can carry out appropriate statistical testing and decide whether the deformation of network in each point is statistically significant or not. On the other hand, we are able to ascertain the quality of the geometry of the geodetic network. The known characteristics of the probability distributions of two strain parameters and rotation in each point can serve as useful tools in the procedures of optimizing the geometry of the geodetic networks.

Control Measurements of Crane Rails Performed by Terrestrial Laser Scanning

This article presents a method for measuring the geometry of crane rails with terrestrial laser scanning (TLS). Two sets of crane rails were divided into segments, their planes were adjusted, and the characteristic rail lines were defined. We used their profiles to define the positional and altitude deviations of the rails, the span and height difference between the two rails, and we also verified that they complied with the Eurocode 3 standard. We tested the method on crane rails at the hydroelectric power plant in Krško and the thermal power plant in Brestanica. We used two scanning techniques: “pure” TLS (Riegel VZ-400) and “hybrid” TLS (Leica MS50) scanning. This article’s original contribution lies in the detailed presentation of the computations used to define the characteristic lines of the rails without using the numeric procedures from existing software packages. We also analysed the influence of segment length and point density on the rail geometry results, and compared the two laser scanning techniques. We also compared the results obtained by terrestrial laser scanning with the results obtained from the classic polar method, which served as a reference point for its precision.

Use of Automatic Target Recognition System for the Displacement Measurements in a Small Diameter Tunnel Ahead of the Face of the Motorway Tunnel During Excavation

During construction of the Šentvid tunnel a unique opportunity arose to measure the 3D displacements ahead of the motorway tunnel excavation face, since the exploratory tunnel was already constructed in the axis of the main tunnel. According to reviewed literature such measurements had not been performed yet and several problems regarding equipment and complete scheme of the experiment needed to be overcome. The paper gives a brief description of the Šentvid tunnel project, presents significant factors that affected the choice of the geodetic equipment and describes the scheme of the experiment. A special attention is focused on the problems relating to the operation of the instrument in demanding environmental conditions (water, dust).

Measuring meteorological data along the ray path of a distance meter with an ultra-light aircraft

Abstract When measuring distances, the density of the air that electromagnetic waves travel through is important. In practice, the meteorological parameters usually measured at the endpoints of the measured lines, which may be oversimplified for long distances. Thus, the basic idea behind our research was to measure the meteorological parameters along the path of the measuring beam through the air by using an ultra-light aircraft flying at low speed. The test measurements were carried out on two lines of a small geodynamic network of the Coalmine Velenje, where the observations are used to determine displacements due to mining in this area. Three flights were done in different conditions of the atmosphere. Within one flight, we conducted two independent measurements of two lines. In this way, we wanted to obtain more precise data on the actual conditions of the atmosphere. The aim of our analysis is to critically evaluate the calculations found in literature and to find an optimal way on how to account for the meteorological parameters in the calculation of the actual atmosphere when measuring longer distances in difficult measuring conditions. We expect that the obtained data, which reflect the actual conditions in the atmosphere, can have a significant influence on the measuring of longer distances.

Deformation analysis: The Fredericton approach

In this article, the Fredericton approach to deformation analysis is presented. It is possible to use several deformation models to determine the differences between the geodetic observations or between the coordinates of points in geodetic network in more epochs. The most appropriate deformation model has been chosen based on statistical testing and available information about dynamics at the area of interest. First, a theoretical background of the approach is described. Then it is applied to the generated observations in two epochs. In the present example, the results of the Fredericton approach differ only slightly from the results obtained with the Delft, Karlsruhe in Hannover approaches

Geodesy in Geotechnics

Geodetic methods are one of the possible means of determining the stability of geotechnical objects. The determination of the displacements of the geotechnical objects is specific due to the size and the expected displacements. The expected size of the displacement determines the necessary precision of the displacement determination, whereas the size of the object determines the method of the geodetic measurement. We choose either the terrestrical or the GNSS methods. There is no relevant legal framework for geotechnical measurements. For this reason, we present the characteristics of the single methods and suggest general recommendations regarding the implementation of the geodetic procedures when monitoring the displacements of the geotechnical objects. The recommendations are intended for geotechnical engineers planning the geotechnical objects and the operators of geodetic measurements and investors. The recommendations the facilitate supervision of the geotechnical projects.