Wojciech Bochenek, Zbigniew Motyka, Henryk Passia, Adam Szade. Central Mining Institute, Katowice, Poland ABSTRACT

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Reaction of various types of buildings to diversified environmental conditions, including mining and geotectonic, on the basis of continuous monitoring with the use of laser tilt and vibration

1 Reaction of various types of buildings to diversified environmental conditions, including mining and geotectonic, on the basis of continuous monitoring with the use of laser tilt and vibration sensors Wojciech Bochenek, Zbigniew Motyka, Henryk Passia, Adam Szade Central Mining Institute, Katowice, Poland ABSTRACT Continuous monitoring of long-term and sudden changes of tilt of building structures located in mining areas with various geological-tectonic conditions and forms of effects of underground mining operations, also reveals the influence of a number of other environmental and operational conditions. The following can be counted among them: climatic, road traffic, hydrogeological. They can be distinguished with a relatively high precision. Finally, the recorded changes (reaction of buildings) are the resultant of environmental (mining and others) conditions, type of the structure itself, its appropriation, and technical- operational conditions. High structures, e.g. chimneys, hoisting towers, react in a basically different way than the extended ones such as monumental (as an example) or residential blocks, especially of large-panel construction. Keywords: tilt, building structures, mining, environmental conditions 1. LASER TILT AND LOW-FREQUENCY VIBRATION SENSOR WITH ACCELEROMETRIC ATTACHMENT The structure and operational principle of the CMI-developed laser tilt and vibration sensor, together with its operational characteristics, have been widely described elsewhere [1]-[5]. Here, the additional information will be provided concerning an extended version of the sensor which enables to measure three-axial acceleration in parallel with the measurement of the tilt. The two versions of the sensor are shown in Figure 1. Figure 1. The photograph of the tilt-only sensor (on the left) and combined tilt and acceleration sensor (on the right). The latter is new optional solution. The cylindrical metallic element in the foreground is the casing fitting to both versions. The measuring parameters of the combined version are the following: - tilt measurement range + 5 mm (with the possibility to be adjusted from 2 to 50 mm/m), - resolution mm/m, - vibration frequency to be measured < 10 Hz, - acceleration measurement range + 1g or + 5g (optional), - resolution of acceleration measurement g, - power consumption < 3W (without the digital recorder), - dimensions of the cylindrical casing: diameter 90 mm, height 200 mm - weight of the instrument ca.2 kg. The possibility of acceleration measurement is an option not available in the tilt-only sensor, although the latter is sensitive for rapid tilt changes as well. The digital recorder associated with the tilt-only sensor is able to store the maximum and minimum amplitude of tilts that occur during every whole minute.

2 The system is composed of the laser tilt and (optional) vibration sensor, measuring amplifier and analog or digital recorder. In special applications, the sensor elements can be contained in a dust-and-waterproof casing (type IP55). The operation principle of the tilt-only sensor is based on determining the deflection of the laser beam from its initial vertical position after it has passed through the liquid wedge. The layer of the liquid is an absolute reference system in the measurements. The displacement of the beam spot on the photodetector is a function of the inclination angle assumed by the liquid level when the instrument (together with the controlled structure) is tilted, and index of refraction of the liquid. The electrical signal is, in turn, a function of the illuminated quadrant areas of the detector. After being amplified, it is fed into a PC-type digital recorder through an A/D card for further processing and storage of processed data. The measurement results, in a form of a graphic printout, provide the full pattern of changes both in terms of the deflection values and their directions, and the time of their occurrence. An analysis of the measurement data obtained by using the sensor system enable to identify the factors influencing the stability of the object, as well as, e.g. decision taking about applying building protection measures. For many objects and engineering structures located in seismic and mining-influenced areas, continuous measurements are required with the use of continuous recording of amplitudes and directions of changes. The structures (objects) located within mining-influenced zones are liable to various deformations differing in their kind and size. The deflection from the vertical direction, when kept within the limits defined by the standards, is a condition of their safe operation. This deflection can proceed either gradually or to be of periodical and dynamic character. Uneven subsidence, shock and vibration can be a result of other causes, apart from mining operations. As demonstrated in the figures enclosed in the next section, these are, as an example: hydro-geological, climate and road traffic. 2. EXAMPLES OF RECORDING OF THE EFFECTS AT THE VARIOUS STRUCTURES ON LOCATIONS IN POLISH MINING AREAS The examples below present applications of the laser tilt and vibration sensor in several measuring situations relating to different types of structures. These are: - monumental structures located in the mining-influenced areas, namely the medieval 14-th century castle of Będzin and 19-th century church in the town of Rydułtowy, both Upper Silesia region, south of Poland, - residential blocks, especially high-rise buildings and blocks of large-panel construction in the city of Katowice, - high industrial structures, with shaft mine towers and chimney of thermal power station as the examples. The first example in the first group is influenced mainly by post-mining occurrences, the other by currently conducted mining right under the structure. The subsequent figures demonstrate various effects observed at these two objects. Figure 2 presents a sudden change of tilt resulting from ground movement caused by water from heavy rains flowing into the cavities under the castle, created by previous mining operations(watering of the basement). As mentioned above, the second example of the first group refers to monitoring of the church (late 19-th century) strongly influenced by current mining operations conducted right under the structure. Figure 3 shows a very strong momentary change of the tilt caused by an underground rockburst (break of the rigid sandstone plate above the mine working). Worth mentioning is the occurrence of the pair of foreshocks recorded several hours earlier. Weather conditions, especially temperature differences (e.g. by illumination of one part of the structure) can cause remarkable changes of the tilt. Such an example is also presented in Figure 3, as the effect of the sun beginning from 11a.m. The second group presents the effects recorded on residential blocks, especially high-rise buildings and blocks of largepanel construction. The presentation is based on the examples from measuring locations in the city of Katowice. Figure 4 presents an example of recording of a periodical tilt change and shocks at 11 th floor of the residential building of large-panel construction. Subsequent figures describe the behaviour of the third group of structures. These are: high industrial structures, with steel mine s shaft tower (Figures 5-6), reinforced concrete mine s shaft tower (Figures 7), and chimney of thermal power station (Figures 8-9) as the examples.

and effects of the insolation beginning from 11 a.m. Figure 4.

3 Figure 2. Major change of tilt fixed resulting from the ground movement caused by water inflow. Figure 3. Rapid change of tilt caused by underground mining rockburst and effects of the insolation beginning from 11 a.m. Figure 4. Example of recording of a periodical tilt change and shocks at 11 th floor of the residential building of large-panel construction.

Comparison of recordings of the reinforced concrete shaft frame behaviour during week-end 16-01-2000 and the subsequent weekday.

4 Figure 5. Examples of the influence of weather conditions (sudden drop of temperature below 0 o C) on the stability Figure 6. Comparison of recordings of the shaft frame behaviour during holiday and week day. Figure 7. Comparison of recordings of the reinforced concrete shaft frame behaviour during week-end and the subsequent weekday. The central parts of each diagram are the magnifications of the shadowed one-hour duration parts of the 24-hours windows on the left. The parts on the right are the resultant 1-hour polar diagrams referring to tilts recorded in channels N-S and E-W. The split curves denote minimum and maximum values of tilt in every minute for both channels.

gallery (right) of the chimney. Figure 9. The 5s-duration of the tilt record section obtained at the measuring location shown above and their Fourier analysis.

5 Figure 8. The measuring location of the laser tilt and vibration sensor at the top of the 200 m high chimney at electric power plant (left) and the Trollex ultrasonic anemometer at the top gallery (right) of the chimney. Figure 9. The 5s-duration of the tilt record section obtained at the measuring location shown above and their Fourier analysis. The top diagram presents the tilts in the directions N-S (Ch.1) and E-W (Ch2) and the records of the wind velocity (Ch.3) being in average 14.5 m/s. The middle diagram presents the Fourier transform of the N-S record revealing the dominated frequency of Hz. The bottom diagram presents the Fourier transform of the E-W record with the marker pointing at the frequency of 2.05 Hz.

6 CONCLUSIONS The presented examples demonstrate various effects both of mining and environmental origin. In general it is easy to distinguish between mining-induced effects and environmental ones, of course some experience is needed in every single case. The instrumentation and methodology applied enables to point exactly at the size of the effects and their nature. It is possible to analyze equally the short-duration (e.g. mining shocks and vibrations originating from machinery) and long-term phenomena as influence of whether, ground subsidence due to changing water conditions in the ground as result of postmining activities, and direct ground subsidence resulting from currently conducted underground excavations. In case of necessity, the construction parameters may also be analyzed including the pattern of constructional vibration, decrement of damping, resonance frequencies etc. REFERENCES 1. Szade A., Passia H., Lipowczan A., Laser sensors for continuous control of tilting of buildings on mining-influenced and seismic areas; construction and field experience, Proc. SPIE, 2868, pp , Polish patent N o : Instrument for continuous measurement of tilt of buildings. 3. Szade A., Passia H., Lipowczan A., Bochenek W., Intrinsically-safe laser-based system for continuous measurement of low-frequency vibration of mine shaft installations, Proc. SPIE, 3411, pp , Szade A., Passia H., Bochenek W., Pytlarz T., Continuous, automatic measurement of influence of mining - exploitation on objects on surface area with the use of laser sensors of vibrations and tilting (Only in Polish) Polish Academy Of Sciences, Conference Preceedings, Workshops' 98, Ustroń, Polska, pp , Szade A., Passia H., Bochenek W., Laser sensor for continuous three-axial measurements of low frequency vibrations and tilt of buildings (Only in Polish), Polish Academy Of Sciences, Conference Preceedings, Workshops' 99, Jaworze, Polska, pp , 1999.

Measurement methods of building structures deflections

Measurement methods of building structures deflections Magdalena Wróblewska 1,* 1 Silesian University of Technology, Faculty of Civil Engineering, Department of Geotechnics and Roads, Gliwice, Poland Abstract.