Mining Geophysics. Proceedings of the XXVI Polish-Czech-Slovakian Symposium, Wisła, Poland, September 23-25, 1998 *** Geofizyka Górnicza. Referaty Przedstawione na XXVI Polsko-Czesko-Słowackim Sympozjum w Wiśle (23-25 września 1998)

Abstract:

The volume contains the majority of papers presented at the XXVI Polish-Czech-Slovakian Symposium on Mining Geophysics held in Wisła, Poland, from 23rd to 25th September 1998. All the papers have been reviewed by Polish and Czech experts and some of them have been significantly revised by the authors, taking into account the reviewers' recommendations and suggestions. Such a procedure has delayed the publication of the proceedings but it should hopefully increase the scientific and technical values of the published contributions. Not all the papers were accepted for publication.

Abstract:

The empirical Green's function deconvolution technique is used to retrieve the source time function from thew records of large seismic events induced by mining. The records of small events, generated near the larger events with similar source mechanism, are accepted as empirical Green's functions. The applied procedure, based on numerous trials and tests performed on real data, is described. Several examples of source time function determination for seismic events from Polish copper mines are given. The relative source time functions retrieved at several stations depend as a rule on the station azimuth. In such a case, several rupture parameters (the azimuth of rupture propagation direction, rupture velocity) can be calculated. The obtained source time functions are convolved with the corresponding records of small events, serving as empirical Green's functions, to generate the original wave-forms of the larger event as a final check-up of the applied procedure.

Abstract:

Focal mechanism of 543 mine tremors occurred in 1995 in Halemba coal mine area (the Upper Silesian Coal Basin, Poland) were determined using the seismic moment tensor inversion method. The DC component was dominant in mechanism of majority of tremors. On the basis of focal mechanisms solutions, mean local stress tensors in one-month time intervals were calculated applying direct inversion method developed by Angelier (1979). The research showed that the state of stress in the investigated area was very unstable. Fast and sweeping changes of main stress axes orientations were observed. The mining put the rock mass in the state of unstability. The state manifests itself by instantaneous interchanging of the positions of maximum and mininum axes.

Abstract:

The paper presents results of calibration blasting investigation in Polkowice-Sieroszowice copper mine. Source parameters obtained from seismic wave spectra and mechanisms calculated by using seismic moment tensor inversion were analysed. On the basis of an analysis of results and comparison of mean values of some parameters of blasting sources compared with the values obtained for mining-induced seismic events, the correctness and effectiveness of the applied method was evaluated.

Abstract:

The values of uniformly estimated apparent stress, σ_a, and Brune's stress drop, taken as a measure of static stress drop, from 850 seismic events, with moment magnitude ranging from -3.6 to 3.6, induced at the Underground Research Laboratory (URL) in Canada, Western Deep Levels (WDL) gold mine in South Africa, and two coal and two copper mines in Poland, were collected to study the stress release mode in various mining environments. For this, the quantitiy epsilon, ε = Δσ/(σ_a + Δσ/2), where Δσ is the static stress drop, proposed by Zúñiga (1993) as an indicator of stress drop mechanism was used. The events induced at the URL are characterized by low values of epsilon corresponding to a partial stress drop mechanism, whereas all the events at WDL display frictional overshoot mechanism in which final stress reaches a lower value than that of frictional stress. The events at Polish coal and copper mines, on the other hand, are in good agreement with the well-known Orowan's condition that the final stress is equal to the dynamic frictional stress.
   The Brune stress drop, however, is heavily model dependent through the source radius-corner frequency relation. The Orowan's condition for the events from the URL would be met if a constant in the source radius-corner frequency relation is equal to 1.82 ± 0.12, and for the events from WDL if it is equal to 3.92 ± 0.40, in contrast to Brune's constant of 2.34.
   The smoothed values of epsilon displayed as a function of time, represented by the consecutive event numbers, for selected sets of events imply that the largest seismic events in a given set occur when the epsilon is low and a partial stress drop mechanism is dominant. The large events are then followed by high epsilon values when a frictional overshoot mechanism begins to dominate.

This paper was published in Pure and Applied Geophysics, 1998, 153, 5-20.

Abstract:

The Zofiówka coal mine located in the Rybnik Coalfield is known as seismically active. Numerous low- and intermediate-energy mine tremors (energy E < 10⁵ J) occur there; however, high energy seismic events are absent. The tremors focal mechanism determination has been performed for the events as occurred during mining of seams No. 404/4 (longwall D-10) and No. 406/1 (longwall H-12). It follows from the study on focal mechanism of mine tremors as occurred during the exploitation that the tremor focal mechanisms vary depending on the tremor  source location. This has been confirmed by the consistency of the focal mechanism types of the tremors located within the strip parallel to the water reservoir situated in the overlying coal seam No. 404/4. In general, those were the normal slip focal mechanisms. The nodal plane the azimuth of which was consistent with that of the water reservoir boundary was considered to be the fault plane. On the other hand, the focal mechanisms of the tremors as occurred during exploitation of longwall No. D-10 were, in general, determined by the failure processes associated with the mining-related roof break-down. Those mostly were the reverse slip type focal mechanisms, the fault planes of which were chosen as the nodal planes that were consistent with the longwall face line orientation. In the case of those events, the predominant stresses were the NW-SE trending compressive stresses. The tremor sources of this type of focal mechanisms are likely to occur as a result of the processes associated with the failure related roof displacement. The results of this type of studies contribute to the improvement in informativeness of the seismological method and to the improvement in effectiveness of mining assessment of the state of rockburst hazard.

Abstract:

The rockbursts are a serious danger to coal-mining. They are associated with high stresses caused by multiple factors. In general, the high stress level is produced by the combination of natural stresses and the induced stress. The former are caused by specific geological rock mass properties while mining process is responsible for the latter. The reason of our work is to endorse or to refute the opinion on the influence of geological, mainly structural-tectonic factors, on the recent stress distribution. The seismic observations make it possible to determine the principal stress orientation in the focus field which can be compared with the direction of paleostress derived from the structural-tectonic analysis in the Karviná region.

Abstract:

It is possible to obtain, in areas of active induced mine seismicity, within a short time interval, a sufficiently large data set of seismic and other physical parameters. These data can be used as input for multi-channel statistical extrapolation methods, which appear most suitable for the very reason that all the effects and parameters which enter in the process and affect the preparation and inception of a seismic event are not exactly known until now. Seismic and mining parameters obtained from January 1, 1944 to April 3, 1997 were used as input data for the application of linear extrapolation (Wiener filter) and non-linear methods (neural network). This proved that the seismic data completed by parameters of mining activities do not contain sufficient information on the development of seismic parameters within a future time interval and the prediction, from the statistical viewpoint, is on the average only by about 30% better than that obtained with the use of a primitive predictor, such as the last or average value.

Abstract:

Tremors that occurred in two structural units of the Upper Silesian Coal Basin from 1987 to 1996 have been analysed. The b-value of Gutenberg-Richter relationship for Bytom Syncline and Main Anticline has been estimated. It has been calculated for the ten year period and for each one-year period for the whole area of selected geological units and for a few selected mines situated in these units. The differences of b-values for these units have been observed for the whole area and for selected coal mines. In all cases, the b value for Bytom Syncline is greater than that for the Main Anticline. This means that there is different ability to release accumulated energy in these units. The difference could be connected with geological structure of units.
   The Main Anticline is located above central zone of active fault in deep basement of USCB. In this area, the dynamics of processes connected with fault zone is the most intensive. This may result in a considerable number of strong shocks in this region. On the other hand, active is only part of fault network, which makes it difficult to release the accumulated energy. The Bytom Syncline is situated in the peripheral part of this zone. Hence, the dynamics of processes is less intensive and strong tremors are less frequent. In the area of Bytom Syncline, the whole fault network may be engaged in generating of tremors, producing a great number of shocks with the same energy. This means that the b-value will be greater than that for Main Anticline.

Abstract:

The seismoacoustic and seismological energy-frequency distributions were compared in one coal block of a coal mine. It was shown that seismoacoustic monitoring extends the measured band towards the small seismic events, below 20 J, which is the threshold of seismologic monitoring in the area. 
   The seismoacoustic energy-frequency (E-F) distribution consists of at least two independent distributions, formed by seismic events from coal seam and coal roof, respectively. The total E-F distribution represents the weighted average of both distributions. By evaluating the total E-F distribution line slope it is possible to determine only the ratio between the coal seam and the coal roof seismic activity.

Abstract:

A comparison of two apparatuses with the different types of notch filters and spectral analysis of some waveforms have been made out. Then the dependence of forms of spectra on distance and/or energy has been analyzed. Based on this analysis, empirical relation between the corner frequency of S waves and event energy as well as epicentral distance has been determined. 

Abstract:

The generalised correlation exponent dimension D_q is used to study multifractal properties in energy domain of different scale seismic activity induced by mining operations and seismoacoustic emission of rock samples in compression tests. It was shown that the distribution of seismic energy is multifractal regardless of the scale of fracturing process. Some interesting relations between D_q vs. q curves were obtained for different scale seismicity.

Abstract:

The occurrence of rockbursts in the Kladno deep coal mine displays very similar sequences to those observed for tectonic earthquakes in Europe. The types of these sequence are the following: single shock, main shock and aftershocks, main shock and foreshocks, double shocks, swarms and multiple events. No simple and clear relations between the occurrence of individual types and time variations of mining activities were detected. From this fact it follows that we should not much hope to utilise some of the known simple earthquake precursory phenomena for prediction of large rockbursts.

Abstract:

During the exploitation of the Kladno mine, digital seismic network in years 1993-1997 has localised 7700 rockburst events within the safety shaft pillar under liquidation, by drifting 1527 meters of new adits. The correlation between the time- and site-distribution of rockburst foci and the variations of mining activity were found to be very complex and not easy to understand. The prevailing part of foci occurred about 80 meters above the exploited coal seam. The rockburst activity rate does not much depend on the mining activity rate, but depends on the site and direction of new drifts. For practical reason, a software KLADBIO was written, that enables the live overview over both mining and rockburst activities.

Abstract:

Seismic measurements are a widely used method for precise evaluation of subsurface structure. This is essential in a wide range of geophysical problems, such as hydrocarbon exploration, geothermal reservoir characterisation or detection of discontinuities in coal beds. Very appropriate means for characteisation of the fracture system of gas reservoirs or hot dry rock geothermal sites are engineering seismology and crosswell seismic prospecting. The resolution of these methods depends on the frequency bandwidth of traces, the acquisition method and the particular setup of the experiment. Engineering seismology and crosswell seismic prospecting offer better resolution than surface seismic prospecting or vertical seismic profiling (VSP).
   A single fracture or fault affects the seismic wave propagation only for short wavelengths as compared to the fracture equivalent thickness. Shear wave splitting caused by anisotropy, wave transmission/reflection coefficients of a fracture system and resolution of the seismic prospecting are also frequency dependent.
   In order to precisely characterise a single fracture, a fracture system or to locate reflection boundaries, measurements made over short distances from the wave source are preferred due to their higher signal-to-noise ratio (SNR) and smaller attenuation is subsurface structures. For such measurements, the different modes of the signals overlap each other in time and give rise to problems in the identification of their onsets. Resolution is also decreased due to small scale variation of elastic parameters, which generates scattered waves.
   The scattered waves recorded after the passage of each mode (such as P, S or tube waves) are called coda waves and are intensively studied in seismology. It is essential to divide the recorded signal to coherent and incoherent parts and analyse both of them. A processing method which eliminates the coda component from a wideband seismic wave and reduces the length of the wavelets related to each mode is presented in the paper. An original method of interpretation of sathe coda is also proposed.
   A method of eliminating coda waves from three component (3C) wide-band signals based on the coherence of waveforms over adjacent raypaths is presented. Coherency analysis is a popular technique to quantitatively express the similarity of time series data. In geophysical exploration it is used to detect and classify signals or evaluate the delays between them. Coherency based filtering has also been proposed for narrow band reflection data where body waves are stationary and their parameters, like instantaneous variance or frequency do not change in time. In this paper we deal with wide-band crosswell data, which are not stationary. Our aim is to evaluate the instantaneous parameters of the recorded wavefield which vary in time. We use the time-frequency coherency function to distinguish between the parts of the signal that consist mainly of coda and the parts that are similar on adjacent raypaths. It is then possible to eliminate the coda and other incoherent noise from the time section. Then coherent and incoherent components of the signals are separately analysed. The identification and picking of direct P and S body waves and reflected waves are possible using coherent part of the signal. On the other hand, the coherency of the coda characterises the spatial scale of inhomogeneities.
   Field experiments were carried out to thest the method. The time-frequency coherency analysis of the data demonstrates the effectiveness of the proposed methods.

Abstract:

An approach known from exploration geology is used to identify the P phase arrival of seismic events. This approach was derived by Robinson and Treitel (1980). They used it to increase the number of details available on a time series by the so-called shaping filtration or spiking filtration. The author of this paper uses this method to determine P-phase arrival time in a seismic signal from coal mine. The accuracy of detection of the P-phase determines the epicenter localization accuracy in some method of epicenter locatiozation. The aim of the investigation is to evaluate the efficiency of this method for this problem.

Abstract:

The main goal of this work was to verify a possibility of observation of changes in the vibration modes frequencies for the purpose of seismic stress monitoring. It has been shown that for series of events of a similar location, these frequencies are much the same, and also are time-dependent. Unfortunately, no relationship between these frequency changes and the occurrence of seismic events of large energy has been established.

Abstract:

In this contribution, a record of mining induced seismic event is used to demonstrate effects of the wavelet transform. The time-frequency decomposition of wavelet coefficients is conceived as a successive decomposition of the signal on particular levels of wavelet frequencies. The main results are shown graphically in figures that represent the decomposition of record of the seismic event induced by a quarry blast in the Chomutov region.

Abstract:

The present paper reports on instrumentation of the new local seismic stations Hradec nad Moravicí (HRMC) and Zlaté Hory (ZLHC) - later moved to Žáry (ZARC), located in Northern Moravia. The stations are equipped with self-contained apparatuses with the triggered digital recording of seismic events to PC. A remote fed telemetric transmitter for digital data transmission from the underground mine is described.Initial information about registration at these stations is presented.

Abstract:

The paper presents a modem digital transmission system of seismic signals, DTSS, designed by EMAAG Centre to be used in hard coal mines. The system  enables central intrinsically-safe supply of underground transmitting stations from the surface. The stations amplify and process, in many channels, near sensors, synchronously in time, seismic signals to a digital form. The stations transmit in series, along supplying lines, a signal suitably coded in figures, to the receivers placed on the surface. The seismic signals transmission system provides 100 dB transmission dynamics and frequency band of 0 to 200 Hz. It enables automatic or controlled from-the-surface setting of amplifications in channels and testing of seismometers. The presented system ensures a principal qualitative jump of the presently used apparatus for recording of rock mass vibration and tremors, thus enabling correct record of both the slight and strong seismic events. The paper describes the system's potentiality for digital transmission of signals from traxial sensors along a single telecommunication line.

Abstract:

The new isometrical algorithm for nonlinear inverse problems which is suitable for tomographic location was developed. This method was applied at the mining region of Kladno. The optimal velocity model is the anisotropical model with vertical velocity  v_v = 1.96 km/s  and horizontal velocity  v_h = 2.66 km/s. This strong anisotropy has to be considered to achive precise location of rockbursts.

Abstract:

Neural Networks provide very convenient methods for seismic source location. The back propagation neural networks allows to find seismic source location even in case of very complicated seismic ray geometry, if only the user is able to present to it a sufficient number of known events for training session. The process of training is often very long, especially when the training aims to teach the net to recognize the location for a big area and with a high precision. To avoid such difficulties one can use neural network in a slightly modified manner, introducing additional nets. To do this, the investigated area is divided into small cells. The first net has to be taught to recognize the cells. The set of secondary nets, where each set is used for a single cell only, is easier to train and they are able to perform localization with a high precision. Such a modification allows to perform fast and reliable source location, when at the same time the training process is short and the needed computer memory is smaller than in the case of typical methods.

Abstract:

The paper presents the manner of search for optimal solution in the case of difficult and complicated tasks. The developed method belongs to the group of stochastic and iteration algorithms. The method searches for both global minimum and maximum of the  multi-variable function (every one, if there appears many local minima and maxima). For the purpose of the optimal solution search, the space of the possible solutions is scrolled in the parallel mode by group of points. These points represent the potential solutions. The better solutions are preserved while the worse ones are eliminated. In the area of better solutions the new solutions are found in the surroundings of the above mentioned points.
   The paper presents two examples for the application of the developed method to calculate the maximum function:  f(x) = x · sin(10πx) + 1 (x ͼ [-1, 2])  (example 1)  and   f(x₁, x₂) = 21.5 + x₁ · sin(4πsx₁) + x₂ · sin(20πx₂) (x₁ ͼ [-3.0, 12.1], x₂ ͼ [4.1, 5.8])  (example 2).
   Subsequently, two examples for the application of this method to determine the hypocentre of tremors in a coal mine are provided. Example 3 involves the location of tremors according to the S-P method, and example 4 involves the location of tremors according to the P method.

Abstract:

The goal of this contribution is to present the way and the records of seismic manifestations evoked by small blasts of explosives in a deep mine. These blasting operations were done as a part of technology of exploitation in the Rozná uranium-ores mine. The depth of places was about 1200 meters for both the seismic station and shot points. The recording apparatus worked under the triggered regime of the three-component digital record of vibration velocity of the seismic signal. Examples of the obtained wave patterns are given.

Abstract:

The exploration of primary stress fields within the territory of Czech Republic is not much advanced. The nature of such stress fields in the Carboniferous of Czech part of Upper Silesian Basin (i.e., their magnitude, orientation and proportion of individual components) was unknown until recently. The change has been brought by a number of successful measurements. They were carried out mainly in relatively intact, non-worked areas (but not only there), including unique measurements in the vicinity of Frenštát shafts. It is clear that the measured values were influenced by local geomechanical and geological situation, well direction etc. These measurements seem to be more acceptable for practical use than an approach based on the elastic model and overburden stress (hρg). The horizontal stresses exceed values derived from the particular elastic model for a specified depth ((S_H + S_h)/hρh ≈ 2). The measured horizontal stresses indicate significant variability in S_H /S_h  ratio  (S_H /S_h) = 1 ÷ 3), that depends on particular geomechanical situations. 
   In the present paper, results of measurements by hydrofracturing method in the above mentioned area of trhe Czech part of Upper Silesian Basin are discussed.

Abstract:

During the last 6 years almost 12 thousand measurements of test holes deformation located in the roof excavations of copper and coal mines, in three different mining basins were made. The outline of the method potentially useful for bumps hazard evaluation is presented in the paper. The essence of the method is, associated with seismic activity registration, observation of roof test holes deformation, as probable representation of vertical roof deflection changes in the working front, caused by front progress interaction, by creating of alleged rock destruction zones before bumps occurrence and by bumps influence itself as well.

Abstract:

The need to control ground movements induced by mining activities is necessary for prevention or reduction of damages to structures on the arth surface. The surface monitoring programme of vertical and horizontal movements by conventional survey methods is in general used at many mining regions. In the paper a new method in deformation measurements is presented. The surface movements are determined by means of tiltmeters ‒ the special electronic sensors developed by the Applied Geomechanics, Inc., USA. Some results of deformation measurements by tiltmeters from the Slovak coalfields are presented.

Abstract:

Very simple and inexpensive hardware and software AIREGI was constructed for recording the onset times of both seismoacoustic impulses and seismic transient ground motions (blasting, technogenic vibrations). A four-channel version AIREG4 is recommended for recording of onset times of motions distinguished to four amplitude classes. The very easy and fully automated exploration of great number of such devices in the neighbourhood of expected sources of technical seismicity is important for discrimination of useful local tectonic events such as local microearthquakes.

Abstract:

Nonlinear rheological model (MRSK) is introduced and, as its linear approximation, a known (linear) standard model with emission generator is suggested. The model makes it possible - under appropriate assumptions - to describe quantitavely emission in the longwall with a shearer, by connecting the cumulated activity with the stress averaged alongside the heading. Systematic observation of changes of the cumulated emission is then equivalent to the observation of stress changes, which constitutes the fundamentals of seismoacoustic method of stress and hazard assessment. Analogous relation connects the emission generated after blasting with the stress in the region of measurements, which constitutes the basis of the active seismoacoustic method (WAS) of seismic hazard assessment.

Abstract:

Many longwalls in the Ostrava-Karviná Coal Basin are mined under conditions of rockburst hazard. Therefore, as a part of the rockbursts preventative measures, large scale torpedo blasting operations carried out in the overlying strata have been applied. The main objective of these operations is to influence the stress-strain state of the rockmass on the basis of breaking up the roof rocks. The effectiveness of these preventative measures depends on the efficiency of individual explosions. The investigation into effectiveness of large scale torpedo blasting operations was performed using data gathered during mining operations of longwall No. 16419 in the Dukla mine. Efficiency has been calculated according to the empirical formula  η = E_s [J] / (2.6 × Q [kg])  and the explosions were considered as effective when  η ≥ 3  and as ineffective when  η < 3.

Abstract:

In coal mining, rockburst prevention methods are, first of all, used to improve safety of the mining personnel, but they can also unprofitably unbalance costs of coal recovery. The maintenance of equilibrium between the work safety and the costs involved in supporting it will be compulsory in the times of future reforming of the mining industry. Therefore, it is advisable to apply the methods for forecasting the state of rockburst hazard and for assessing the effectiveness of the utilized rockburst prevention measures to the mining situations affected by the prevaling high seismicity of the rockmass. In this paper, and example of a mining situation, from which the seismic monitoring data have provided information on the state of rockburst hazard and on the effectiveness of the utilized rockburst prevention techniques, is shown.

Abstract:

The problem has been solved based on the analysis of seismicity recorded during the mining of longwalls with caving and hydraulic backfilling. From the analysis of the results it follows that in the case of the rock mass that was earlier disturbed by repeated mining and therefore considered to be destressed and unstable, the extraction of a successive seam with caving should be more advantageous. A higher rockburst hazard during mining with hydraulic backfilling has been observed. The study indicates that it may be possible to modify the rock mass seismic activity by the way of the roof control consistent with existing conditions.

Abstract:

Methods of statistical analysis in mining geophysics are often used to search for new parameters whose anomalous changes would be connected with  the occurrence of strong events and which could be used as precursors to strong tremors in mines. Following the earlier works, the following three parameters of epicentre distribution have been studied to determine their possible suitability as statistical precursors:
      - the directional coefficient, a, of the temporary linear trend of epicentre distribution;
      - the root-mean-square dispersion, RMS, of distribution around the trend;
      - the statistical coefficient, d, of seismic diffusion.
   The studies were made on seismic events series recorded close to active mining regions of Wujek and Halemba coal mines in Upper Silesia, Poland, Rudna and Polkowice-Sieroszowice copper mines in Lower Silesia, Poland and a gold mine in South Africa.
   The analysies were designed to test whether the investigated parameters estimated on events that occur just before strong tremors differ statistically from their values obtained for a "quiet" time period. There were used two methods of analysis to check these differences and to make the results more probable. In the first method, Shapiro-Wilk's test and t-Student's test were used in analysis of a-parameter distribution, and Kolmogorov-Smirnov's test and Mann-Whitney's test were used in analysis of RMS and d-parameter distributions. In the other method, Wilcoxon's test tested hypothesis about zero central value of parameters distributions and Shapiro-Wilk's test and Kolmogorov-Smirnov's test tested the normality of parameters distributions.
   The statistical tests in both methods have proved that the three parameters studied change significantly before the occurrence of a strong event and can be used as statistical precursors to strong tremors in different types of mines.

Abstract:

The aim this study is to obtain ground motion characteristics for near distances, i.e., at locations affected by the rockburst-related failures. Such characteristics and the knowledge of the ground motion peak particle velocity (PPV) are of great practical importance for the comprehensive rockburst prevention. Also, it follows from the experiments that the PPV values can be utilized to estimate the state of rockburst hazard.
   The results of special seismic measurements conducted in several hard coal mines show that in rock mass regions at short distances from the tremor sources the ground motions are characterized by very high PPA and PPV values and by the prevalent high frequency spectral components.
   In the Upper Silesian Coal Basin, the results of the study of mining tremors close to the sources can be summarized as follows:
      - the PPV values are 150 mm/s (when prevalent frequency f_D does not exceed 100 Hz) and 380 mm/s (when f_D exceeds 100 Hz),
      - the PPA value (obtained after differentiation of the velocity seismogram, filtered in the frequency range of 1-100 Hz) is 42 m/s² (almost five times  as large as the acceleration of gravity),
      - the amplification of the PPV at the boundary between the cracked coal zones around openings and hard rock (sandstone) was often fourfold.
   It is expected that these parameters will allow to develop more real empirical and analytical criteria of the ground failure (rockburst) occurrence.

Abstract:

Radar interferometry is a technique for extracting information about the Earth's surface using the phase difference between the signals arriving at the antenna during repeated observations of the same platform. SAR interferometry has a high potential for the measurement of land subsidence and other surface changes. It is a relatively new method but results of tests and experiments demonstrate the capability of this technique to measure man-induced surface movement to centimetre resolution. Application of SAR interferometry to study the impact of underground mining has been discussed by Ostaficzuk (1995) and first tested in Selby Coalfield in the UK. An exhaustive test of the applicability of InSAR techniques in the Upper Silesia Coal Basin in Poland has been carried out in ESA/ESRIN. The results of this work clearly show that subsidence in the Upper Silesia mining area can be detected and measured using ERS InSAR.

Abstract:

Ground vibrations caused by mining induced seismicity in the area of Polkowice-Sieroszowice mine of Lubin-Głogów Copper District were analysed. The seismic signals were decomposed into frequency band components of one-third octave bandwidths and the attenuation relationship for estimation of peak ground horizontal acceleration was developed for every frequency component. Such a combined one-third octave model of propagation of vibrations was used to estimate an extent of damaging effects of selected mine tremors.

Abstract:

Characteristics of surface vibrations induced by mining in the Upper Silesian Coalfield and Legnica-Głogów Copperfield and vibrations excited by quarry explosion are described. Seismological investigations are discussed in terms of their usefullness for the assessment of possible harmfulness to designed or existing constructions on the surface in areas subject to vibrations. The necessity of co-operation between geophysicists and building engineers is pointed out.
   To make an analysis of the effect of vibrations on buildings, one has to know the entire records of all components of vibration, the horizontal ones being the most important. An approximate but sufficiently accurate evaluation of the effects of mining tremors on buildings may be obtained with the use of response spectra. Exemplary response spectra are given.

Abstract:

For the investigated earth section the mining damages may be detected by means of visualisation of the chosen electrical parameters distribution. The tomographic image of the distribution of electromagnetic waves attenuation coefficient is reconstructed by measuring the field strength of the electromagnetic waves propagated  in the earth. The scope of applicability for this purpose of the image reconstruction methods, resulting from the reduction of the limited angular lightning of the investigated are, was presented. The following algorithms were chosen for the reconstruction: EM, MAP and RAMLA likelihood maximisation algorithms. The reconstruction results, obtained by these methods for the chosen areas where the measurements were carried out, were presented. The comparative representation of the effectiveness of the particular algorithms was presented for this purpose.

Abstract:

A continuous checking of analytical, geochemical, and geophysical measurements has been performed in connection with maintenance of the burning dump pile in Kateřina mine near the community of Radvanice in Bohemia. The acquisiton of complex data on the dump pile is the main purpose of the measurement. These data will enable us to evaluate the influence of this dump pile on the environment and to rationalize the planning and maintenance work with the aim of its successive liquidation. Some results of thermal and radiometric measurements are presented.

Abstract:

In the computational example, the effects of mining induced seismicity on the safety of the designed embankments are shown. The slope stability tests have been done using the Fellenius method. The calculations have induced the effects of the predicted ground motion on the slope stability coefficient in the most endangered geologic sections, depending on the considered types of embankment soil. 
   The calculation results show that, under some circumstances, the mining induced tremors can reduce the safety factor so much that its values may be lower than those of the standardized ones. This means that the strongest mine tremors from the Polish mining districts can influence the safety of hydrotechnical and other civil engineering structures requiring stable slopes.

Abstract:

Surface deformations due to underground mining considerably complicate the construction and reconstruction of engineering objects. A complex exploration and control are required in the areas influenced by mining. To deal with the above-mentioned problems it is possible to take advantage of geophysical methods which enable us to discover the deformations in the early stage without their evident surface occurrence. We point out the efficiency of the use of geophysical methods, above all geoelectrical methods, within the set of exploration works on the following case studies: (i) exploration of an extensive deformation zone in Slezská Ostrava, (ii) exploration aimed at choosing of an acceptable area for the replacement of a high-voltage mast in Orlová, (iii) control of the formation of a homogeneous large aerial fill designed to be the fundation soil for the construction of an industrial complex in Ostrava.

Abstract:

Acoustic (ultrasonic) tomography is a very powerful method for investigating the internal structure of rock samples and rock masses. In this article, preliminary results of tomography imaging of Lac du Bonet granite sample from Underground Research Laboratory (Canada) are presented. The presented velocity images have been obtained in a classical way by inverting wave travel times. On the other hand, the quality factor distributions were calculated by inverting pulse rise time data. This technique provides better numerical stability than the classical attenuation tomography based on measurements of wave amplitudes and does not require special calibration of equipment. The general belief that attenuation tomography is more sensitive to the internal rock micro-structure then velocity tomography is confirmed in the considered case. It has also been highlighted that attenuation tomography requires very carefull data collection and in some cases it is necessary to use very advanced inversion technique in order to obtain reliable results.

Abstract:

The laboratory investigation of rheological processes of Carboniferous sandstones brought first results as to the possibility of application of seismic methods for monitoring long-term stress alterations and fractured state of a rock massif. The method of complex measurements has been checked, which enables, in rheological tests on the same rock specimen, not only the deformation and strength characteristics, but also kinematic and dynamic parameters of ultrasonic waves to be assessed and the process of fracturing by means of seismoacoustic emission measurements to be observed. These properties correlate, in many parameters, with the course of rheological deformations.

Abstract:

An attempt is presented to describe the time distribution of acoustic emission in sandstone specimens subjected to incremental uniaxial compression. It was found that after the ultimate long-term compressive strength is reached, a sequence of impulses occurs which resembles a series of earthquake foreshocks. The obtained empirical function describing the time distribution of AE spacing time intervals enabled to propose a modification of Gu's interpretation method not demanding the preliminary classification of fore-and after-shock categories.

Abstract:

The objective of the paper is to discuss the results of geomechanical research into rock mass behaviour, where multi-seam coal extraction is conducted in the vicinity of major faults. The research was undertaken to verify the hypothesis of such faults being a possible source of intense rock mass tremors which in turn lead to rockbursts. The investigation was occasioned by the tragic consequences of the rockburst that occurred at 13:57 on September 11, 1995, in the vicinity of Fault III in Nowy Wirek Colliery (in the autumn of 1995 Nowy Wirek Colliery merged with Polska Colliery, henceforth became known as Polska-Wirek Colliery), the Upper Silesia Coal Basin, Poland. The energy of the seismic event was 8×10⁷ J, resulting in a rockburst in a setup entry in the working face 2A/II located in the upper slice of seam 502 at a depth of about 670-680 m. The consequences involved the destruction of the setup entry and damage to a part of the adjacent upper panel entry, and a serious accident in which 5 miners were fatally injured and died instantly, whereas 4 others remained trapped underground for nearly four days.

Abstract:

The paper deals with wave propagation through a layered medium and an assessment of dynamical effects of a mining-induced tremor on excavation. Two-dimensional modelling was made in an elasto-plastic medium; the Coulomb-Mohr strength criterion was used. Calculations were made with the finite-difference method, the source impulse was simulated with a Ricker signal, and the wave propagation was based on the solution of motion equation. The assessment was made of the amount of displacement and vibration velocities nearby the excavation that may be attributed to the onset of a tremor and the assumed energy. The modelling was made taking as an example a rockburst that occurred on August 23, 1997, in seam 510 of the Katowice-Kleofas mine.

Abstract:

Radon is a noble radioactive gas, which can be useful in prediction of seismic events. Investigations concerning correlation between changes of radon concentrations in ground waters and earthquakes have been performed in seismic zones of many Asian countries and in the United States. We suppose that changes of radon concentrations in the ground are related with smaller seismic events induced by mining industry. Within the frame of presented work the measurements of radon concentrations in soil gas have been carried out. Investigations were performed in Upper Silesia, area strongly affected by mining activity. As the investigation site, the vicinity of the Kłodnicki fault has been chosen. The fault runs through the area, in which several underground mines are operating. Measurements were done in the ground along several traverses crossing the fault.
   The results show that in most cases the significant changes of radon level in soil gas correspond to the zones of seismic dislocations and faulting. The continuous measurements will be carried out with the aim to find out the possible correlation between changes of radon concentrations and seismic shocks induced by mining.

Abstract:

In connection with the plan of closing the iron ore exploitation and processing in the Medenec mine, it became necessary to construct hydraulic insulation of part of mining field. This task was solved by complex hydrogeological exploration. Quasi-homogeneity of parts selected for construction of insulation objects was also assessed on the basis of geophysical measurements in the mine. With a view to complicated local conditions, this task was solved by means of symmetric resistivity and combined resistivity profiling.

Abstract:

In this article we give a brief overview of geophysical courses at the VŠB-Technical University of Ostrava, information on geophysics study program in specializations of Drilling and Geophysical Exploration within the framework of the Geological Engineering Branch as well as the present state of geophysical courses at the Faculty of Mining and Geology and the Faculty of Civil Engineering.

Abstract:

We are pleased to acknowledge the assistance of the following people who reviewed the papers submitted to this publication.