Abstract
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.
Highlights
Conducting the appropriate monitoring of technical facilities is one of the most important activities affecting the safe use of these facilities and their long-term maintenance.Depending upon the complexity of the facility and its intended use, the monitoring may be only visual, or it may be carried out with the use of survey equipment with the periodic or continuous recording of a parameter [1,2,3]
Laboratory tests proved the high accuracy of the extensometer, and field surveys carried out on the condition of the salt rock mass provided some results in initial measurement series which were affected by interference
The presented studyofofthedeformations detected by electromagnetic to another effect of the tectonic stress: northward inclination of the mining shafts whichopis measurements is presumed to be the first time research has occurred into salt mines discussed in the erating in rock mass affected by tectonic stress
Summary
Depending upon the complexity of the facility and its intended use, the monitoring may be only visual, or it may be carried out with the use of survey equipment with the periodic or continuous recording of a parameter [1,2,3]. This problem of monitoring is of particular importance when the object under observation is an underground mine. Distance and angle measurements are carried out on observational lines comprised of control points Evaluated changes in their coordinates are used in the estimation of orientations and rates of displacement. There is a specialized engineering service involved in measurements: either stationary, which uses tubular, rod, tape or wire convergometers (for deformation measurements of bases in caverns, headings, pillars), or portable, which uses a spring tool for reading the measurements made using typical measuring tape (wire) or the even more popular laser rangefinders
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