Zbigniew Szczerbowski

The monitoring of the process of converging historic mining excavations in the medieval and still-active Bochnia Salt Mine, conducted for years using classic geodetic measurements, allows for determining the results of point displacements. The movements of the selected fragments of the excavation over time, determined on the basis of these displacements, allow for estimating the displacement field, characterizing the entire excavation together with the often-complicated surface layout of the sidewalls, roof and floor. However, this is a certain simplification of the model of this field, and so far, no stress field has been determined that would characterize the compressive forces and would correspond to the characteristics of the measured deformations. This issue has both scientific and practical importance. The latter involves determining the model characteristics of deformations that would be used in the strategy of the conducted protective works. The authors concluded that in modeling displacements, the results of classic geodetic measurements are insufficient for a precise description of the displacement field and reliable simulations of the stress field model. The use of a laser scanner made it possible to obtain an appropriate image of the geometry of the selected excavation and displacements over time. From a scientific point of view, it is interesting to explain the differentiation of displacements in different directions, and determine the nature and share of the acting compressive forces (gravitational forces, the impact of other excavations, tectonic forces).

Many papers have been devoted to the problematic tectonic stress regime of the Upper Silesian Coal Basin (USCB), particularly relating to the interrelation between the tremors triggered by mining activity and the natural seismicity in the rock mass. This problem is analysed here on the basis of geodetic data in light of the tectonic setting. The author determined the horizontal strain regime in the USCB area with the application of triangular arrays that are formed by a network of GPS/GNSS stations. The primary geodetic data used in this research are the coordinates recorded in time by the stations. They enabled the calculation of the easting and northing components of displacement velocity vector and their errors. 16 permanently installed GPS/GNSS stations are located into the study area and this set led to the construction of 23 different triangles, while the centroid of each triangle was extracted. For each centroid, the deformation parameters were determined: maximal horizontal extension, azimuth of maximal horizontal extension, minimal horizontal extension, maximal shear strain, and area strain. These results were applied to estimate the spatial distributions of the parameters. The distributions reveal that the central part of the study area (the Upper Silesian Trough) is under compression, and is surrounded by extension zones. In general, the distributions of strain estimates correspond to the tectonic pattern of the area. These findings provide a different perspective on former studies on tectonic stress by geological surveys and tectonic influence on seismicity in the USCB area. They confirm earlier assumptions about the occurrence of tectonic stress in the studied area. The determined deformation parameters and their spatial distribution provide an explanation for the occurrence of high-energy tremors in the USCB area.

The authors discuss a case that is full of examples of the problems faced by civil engineers whose task is to develop areas in the face of natural, technological, or post-mining hazards. The study area is in the central part of Inowrocław, a town located on a massive salt dome of Zechstein salts. A strong deformation zone expanded in its upper part; this was caused by a natural process (related to so-called salt karst) and by mining activities that occurred in the past, creating a problem with regard to any potential spatial development in the town. The authors show a combination of data obtained using gravimetric and geodetic methods, which helps us to assess the geohazard risk. These include remote sensing data, which can be used to evaluate displacements of the ground surface. The authors used an approach that they term the Elevation Difference Method. This consists of determining displacements between ground surfaces: estimated on the basis of remote sensing data and on the basis of the historical data, when mounted measurement points (and remote sensing data) did not exist. The authors discuss the results in the light of the geological background. Within the area of the study, the displacements of the positive values dominate. The displacement occurs at 6 mm/yr on average and indicates diapiric uplift movement. The results are important for the town authorities for planning and development and for infrastructure management.

The measurement method with the application of an extensometer for the detection of the manifestation of tectonic strain is presented in this paper. The instrument is operated in underground construction for engineering purposes, and the authors applied it in a deeply placed underground old mine gallery in the Bochnia Salt Mine, just at the tectonic boundary of the Outer Carpathians which is commonly considered to be a tectonically active zone. The presented study is characterized by two basic features. The first is the placement of the measurements deep in an old mine which is an environment free of atmospheric factors disturbing the detection of a tectonic signal. The second is a combination of routine measurements carried out for engineering purposes and research measurements enabling the extension of the observation of displacements in the space outside underground workings, inside the rock mass that has been penetrated by extensometer probes. The extensometric measurements have been made using three 7-meter long sections. The results showed the differentiation in the displacement rates of points placed in the side walls: in the southern profile, the annual displacements are approximately 1.5 mm and in the northern one – approximately 1 mm. The combined result corresponds to the amount of the annual convergence value which has been determined by the classical surveys in the excavation where extensometric measurements have been made. What is more, the ongoing displacements in the southern side wall involve the entire part of the rock mass which is penetrated by an extensometric probe, but the displacements in the northern side are only observed in the first 2 m of the penetrated part of the rock mass. This differentiation is interpreted by the authors as being the result of tectonic strain acting from the south exerted by the Carpathians.

Special regulations have been laid down to establish the principles and requirements for the safety and serviceability of old mining workings which are adapted for tourism. To comply with these regulations the measurements were taken in the Bochnia Salt Mine, which has been in use for 800 years. The presented work demonstrates the use of a sonic probe extensometer in connection with the obtained results of displacement measurements in intact rocks surrounding the gallery. There were also test measurements carried out for determination of the real accuracy of the instrument. The presented study of deformations detected by electromagnetic extensometer measurements is presumed to be the first time that research has been made in salt mines operating in rock mass affected by tectonic stress. The paper presents the process of rock salt flow into the gallery observed over a period of 3 years. It is an unprecedented depiction of salt deformation subjected to natural stresses. One of the more surprising results presented here is the discovery of the occurrence of a specific distribution of strain around the measured gallery. The results of measurements showed that the southern part of the intact rock mass surrounding the passage is more compressed (strain rate 3.6 mm/m/year) than the northern one (strain rate 1.6 mm/m/year). This illustrates the presence and influence of additional tectonic effects resulting from the Carpathian push. These observations represent a new kind of research into tectonic stress and tectonic activity in underground measurements.

The presented work deals with the problem of terrain surface and rock mass deformation in the area of the Bochnia Salt Mine. The deformations are related to natural causes (mainly the tectonic stress of the Carpathian orogen) as well as anthropogenic ones related to the past mining activity conducted directly under the buildings of the town of Bochnia. The discussed characteristics of land surface deformation are important from the point of view of threats to surface features and contribute to spatial development. Particularly anomalous zones of observed subsidence basins are examined as places of second order deformation effects. The author presents a method of determinations of these anomalous areas and he discusses their origins.

Area of Inowrocław town is considered as tectonically active due to halotectonic movement of salt dipair situated there. The geodetic surveys carried out for the determination of terrain surface deformations over the years revealed characteristics of the movement. The evaluated vertical displacements based on measurements of benchmarks show different characteristics, depending on distant points assumed as reference benchmarks. This raises problems in analysis, interpretation of the results and decision makings in master planning. The authors demonstrate a method of adjustment calculations that minimize the inconsistencies between previously elaborated heights and inconsistencies of points considered as stabile benchmarks. Thanks to the new approach the point considered as reference were recognized as unstable. And for the others more consistent values of the displacements were obtained: several benchmarks demonstrated higher difference of displacement values in compare to the initial approach in adjustments ranging in the interval of –9 mm – +3 mm.

Seismic events in the area of Poland are related mostly to copper and coal mining, and they are regarded as the most dangerous natural hazard. Although development of geomechanical modelling as the development of geophysical methods determining seismic hazard are evident, low predictability of the time-effect relationship still remains. Geomechanical models as geophysical data analysis highlight the interaction between parts of rock mass or allow to reconstruct the way of rock mass destruction and to understand the processes that take place in the high-energy tremors. However, the association of larger mining tremors with pre-existing geological features has been reported by many investigators; in geomechanical practice, investigations of rock mass condition concentrate on this problem in the local scale. Therefore, the problem of relations between high-energy seismic events in Legnica–Głogów Copper District (LGCD) and regional scale deformations of terrain surface resulting from possible tectonic activity is discussed in this paper. The GNSS data evaluated from the observations of ASG-EUPOS (Active Geodetic Network – EUPOS) stations in the area of LGCD and in the adjacent areas is analysed in this study. Temporal variation of distances between the stations and evaluated on that base so called apparent strain was combined with the occurrence of high-energy tremors. Consequently, after the examination and analysis of occurrences of mining tremors, it is found that high-energy seismic events and periods of strain accumulation evaluated from GPS/GNSS data have temporal relations. Although the seismic events were triggered by mining, nearly all the events with energy E > 10 ⁸ J occurred in the periods when the analysed stations’ positions demonstrated a decrease in the baseline length.

The GNSS data evaluated from on observation of ASG EUPOS stations in the Sudety Mts. and in adjacent areas is analyzed by the author in the scope of disturbances in daily solutions that can be induced by tectonics stress. The daily position changes derived from GNSS data demonstrate the long or short term trends, which are affected by offsets of different nature. Author presents an analysis based on frequency of parameter – displacement vector azimuth. The aim of the analysis is to show statistical significance of observed small values of temporal displacements, which values are not normally distributed. There are “outliers” of the normal distribution of displacement azimuths, which values show a certain reproducibility, which corresponds to orientations of tectonic lines. That suggests small, short time movements along boundaries of horsts and grabens – a crustal-extension structure of the area. However derived results (values of displacements) are less than a limitation error, temporal distributions of coordinates are not random as usually data errors. So in author’s opinion the spatial-temporal evolution of horizontal displacements of ASG EUPOS stations in the Sudety Mts. and in adjacent areas are determined by expressions of underlying geological structures