Mining Tremors Research Articles

Case Studies of Seismic Energy Release Ahead of Underground Coal Mining Before Strong Tremors

We would like to test the concept that induced seismicity prior to relatively large mining tremor (ML > 2.5, E > 106J) can be inferred from the cumulative Benioff strain release (BSR) as power law time-to-failure before the strong event. This study presents the application of accelerating BSR prior to a large earthquake, widely used in natural seismicity, for analysis of this phenomenon in induced seismicity. The Benioff strain release is quantified as accelerated releases of cumulative (square root sum) of seismic energy in the time series. During the study, five sequences were extracted from the seismic catalogues from two Polish hard coal mines: exhausted Bobrek Mine (data form the IS-EPOS Platform) and from a mine belonging to the Polish Mining Group. Next, a search radius was used to select precursory events and to indicate the type of processes occurring in the coal seam and its vicinity. The fitted power law of cumulative Benioff strain release showed changes of m-parameter. If the value of m was lower than 1.0, the process was regarded as an accelerating-like and if m was higher than 1.0—as a quiescence-like. The investigation of m-parameter vs. the search radius showed the general behaviour of the rock mass in the studied areas and allowed to evaluate the relationship between the critical radius and magnitude of the target event. The obtained scaling relation log(Rc) ~ 0.35 ML is similar to these reported by other authors who analysed natural seismicity which might suggest that the scaling relation works in a wide range of magnitudes.

Estimation of Tropospheric and Ionospheric Delay in DInSAR Calculations: Case Study of Areas Showing (Natural and Induced) Seismic Activity

The article presents a proposal to make simultaneous allowance for both ionospheric and tropospheric corrections in differential synthetic aperture radar interferometry (DInSAR) measurements. Atmospheric delay in the interferometric phase may cause the detection of terrain-surface changes to be impossible or significantly distorted. This fact remains of special importance in the case of surface changes that show limited amplitude and spatial range. Two areas were chosen to verify the validity of the proposed solution. The first area includes terrains affected by underground copper-ore mining activity (Poland), which shows high induced seismic activity. Mining tremors recorded in this area cause the terrain surface to locally subside. The authors analyzed three tremors that were recorded in 2016, 2017, and 2019. Each of the tremors exceeded a magnitude of Mw 4.0. The second area is located in the coastal region of Chile, in the Cardenal Caro province. In this case, the authors focused on a series of three earthquakes recorded on 11 March 2010. The strongest of the earthquakes was of Mw 7.0 magnitude. In the first case, calculations were based on obtained data from the Sentinel 1 satellites, and in the second case from the ALOS-1 satellite. It is demonstrated that simultaneous allowance for both the tropospheric and ionospheric corrections significantly improves the final results. The authors were also able to use the analyzed cases to demonstrate that implementation of the corrections does not have negative influence on the range and magnitude of local ground-surface deformations. At the same time, such implementation minimizes local displacement fluctuations and reduces displacement values in areas affected by deformations. The examples used in the article served to show that tropospheric correction is mainly responsible for global corrections (i.e., within the whole analyzed spatial range), while ionospheric correction reduces local fluctuations.

Assessing the Influence of Mining Impacts on Buildings using SVM and MLR Method

The article presents research studies, the aim of which was to assess the influence of mining impacts in the form of surface deformation, as well as mining tremors, on technical wear of traditional residential development in a mining area. A group of 170 single-family masonry residential buildings located in the mining area of the Legnica-Głogów Copper District (LGOM) were analysed. The assessment was based on the model of technical wear, developed using SVM (Support Vector Machine) method in ε-SVR regression approach. In order to interpret the metrics describing the monotonicity of the nonlinear ε-SVR model and to confirm the established trends, they were confronted with the results obtained using a multiple linear regression model (MLR - Multiple Linear Regression). The results confirmed the view that it was the age of the masonry buildings located in the Copper District which had the dominant influence on their technical wear, while the influence of mining impacts was to be considered secondary, however, significant in the statistical sense.

The influence of vibration duration on the structure of irregular RC buildings

In the twenty-first century, the seismic design of buildings seems to have become a fully recognised topic. There are guidelines and standards which should be taken into account by designers in seismic areas. Designers using modern international guidelines have ascertained that the behaviour of structures is not as expected. This may be the result of not taking into account the duration of the shock. The duration of surface vibrations could be one of the basic reasons why some buildings collapse or suffer severe damage to bearing systems as a result of long-duration earthquakes despite being properly designed in accordance with current understanding. Another primary reason for such collapse or damage is that some buildings in seismic areas have irregular structural systems that are sensitive to torsional vibrations. In this paper, a five-storey, irregular-shaped RC building model was subjected to different types of excitations: mining tremors, short-duration earthquakes, long-duration earthquakes. The first stage was a modal analysis based on in situ measurement. After model verification using in situ measurements, the building was then subjected to the three forms of excitation. Numerical studies were performed using a verified FEA model of the building in the time domain. The results of the calculations prove that the duration of the intensive phase of extortion is one of the reasons for the lack of building collapse in mining areas. In cases of mining shocks with a short duration of surface vibration, damage to buildings may occur which does not threaten the safety of their construction. Building collapses occur with earthquakes which are characterised by a much longer duration of the intensive phase of excitation compared to mining shocks. The results of in situ observations of RC structures that have survived a history of mining shocks of varied intensities confirm the results of numerical analyses.

Dynamic Response of a Road Viaduct to a Mining Tremor Using Multiple Support Response Spectrum Method

In this study the dynamic response analysis of a concrete road viaduct subjected to a mining shock is presented. The dynamic analysis was performed using different methods of analysis, i.e. the Time History Analysis (THA), the Response Spectrum Analysis (RSA) and the Multiple Support Response Spectrum Analysis (MSRS). On the basis of analyses, the effectiveness and the suitability of these methods in case of non-uniform kinematic excitation were determined. For the analysis of dynamic response, a real road structure was chosen. The object is a three-span bridge, 40 m long. The structure was subjected to a real, representative mining shock as a kinematic excitation. The typical shock from Upper Silesian Coal Basin was taking into account. The dynamic calculation of the viaduct to the mining shock were performed using the THA, RSA and MSRS methods. For the THA method two kinds of ground motion models were used: the uniform and non-uniform model. For the non-uniform excitation model two wave velocities were taken into account: 500 and 1000 m/s. For the RSA and MSRS analysis the spectral curves, created on the basis of the mining shock acceleration, were used. In the RSA method, the same spectra were used at each supports. In the MSRS method, the response spectra were modified, due to the occurring non-uniformity of excitation effects. For the MSRS analysis the wave passage effect, the attenuation effect and the incoherence effect were taken into account. As the results of the analysis, principal stresses in representative points were determined. To compare the obtained solutions, the results of each analysis were correlated. This comparison clearly presents the significant influence of the non-uniformity effects. On the basis of the results obtained for chosen elements it was easy to notice that the non-uniform excitation model results in much greater values of stresses than the uniform excitation model. The presented results also prove that the MSRS analysis led to significantly greater values of stresses than the RSA method. The conducted response spectrum analysis has shown that the RSA method may lead to underestimation of the dynamic response of structures, whereas the MSRS method provides the proper quasi-static way to estimate the stress level in a structure subjected to a nonuniform kinematical excitation. The key conclusion of this studies is that the non-uniformity effects has important influence on the dynamic behaviour of multiple-support structures. Neglecting of these effects may results in underestimation the maximum response of a structure. In addition, the comparison of results obtained by different methods shows that the MSRS method may be used in estimation of the dynamic response of large-dimensional structure subjected to non-uniform mining shock.

Analysis of Influence of Geometric and Material Properties on Dynamic Resistance of Overpasses Subjected to the Impact of Mining Tremors

This research paper presents the results of the analysis of the influence of geometric and material properties on the dynamic resistance of road overpasses of reinforced concrete slab span structure. The research was based on the database regarding the resistance of 3,000 structures with different geometric and material properties. The database compared the results of multiple numerical FEM simulations using the response spectrum method and a set of criteria for assessing dynamic resistance. The requirements set forth in Eurocode 8 and its adaptations to the seismic conditions prevailing in Legnica-Głogów Copper District (Poland) were applied. Reasons were given for the selection of 1,499 structures with properties which were characteristic for the existing bridges located within the range of mining impacts which took the form of continuous surface deformations. Then, the selected group of structures was subjected to a detailed analysis of dynamic resistance based on the criterion condition regarding the strength of the spans. The influence of geometric and material properties of a selected group of bridge structures on shaping the permissible values of vertical accelerations of ground vibrations (av,dop) was analyzed. The results of preliminary analyzes made it possible to build a statistical predictive model. It was demonstrated that this model, using only basic geometric and material properties, allowed to replace the complex dynamic analysis of the discussed criterion. This paper also outlines further research studies on the analyzed issue.

Precursor of Spatio-temporal Evolution Law of MS and AE Activities for Rock Burst Warning in Steeply Inclined and Extremely Thick Coal Seams Under Caving Mining Conditions

Rock burst is one of the main coal and rock dynamic disasters in steeply inclined and extremely thick coal seams (SIETCS). Timely identification of potential precursor information enables effective and specifically targeted measures to mitigate hazards. To provide a reference for the determination of precursor information in SIETCS with similar conditions, an in situ investigation that lasted for more than 1 year was conducted on the + 450 horizontal no. B3 + 6 fully mechanized top-coal caving face of the Wudong coal mine. This mine has an average dip angle of 87° and experienced a total of three rock bursts. The investigation focused on the consequences of rock burst (including the source location, energy, damage range, and modes of ensuing damage), the temporal and spatial evolution laws of the monitoring parameters of microseismic (MS) and acoustic emissions (AE), and the relationship between precursory information of both the AE and MS monitoring systems. Furthermore, a comparison of the evolution laws of the precursory characteristics between steeply and gently inclined coal seams was conducted. The obtained results indicate that rock burst failure mainly shows a directionality from south to north of the roadway, and the main factor causing the rock burst was the suspended rock pillar. Prior to the rock burst, sources of MS events gradually clustered and congregated around the rock pillar or coalface, and high-energy events (energy > 103 J) noticeably increased. Similar variations of sharp rise–sharp drop were found for both daily total energy and event counts. Prior to rock burst or large energy mine tremors, the AE energy deviation continued to rise, a peak was observed in the total number of high-value daily AE deviations, and the precursory information of AE was ahead of the precursory information of the MS monitoring system. The evolution laws of MS precursor information prior to rock burst differed between SIETCS and gently inclined coal seams. These evolution laws can be used as precursory warning for rock burst in SIETCS. Integrated monitoring of the AE and MS monitoring systems realizes the real-time monitoring and early warning from the germination stage to the occurrence of rock burst, and can determine the danger area in space. This can improve the early warning efficiency and provides a solid foundation for safe mining in SIETCS.

Dynamic response of a cable-stayed footbridge to high-energy mining tremors

In this work an analysis of the dynamic response of a cable-stayed footbridge to mining tremors typical for two main regions of mining activity in Poland, i.e. the Legnica-Glogow Copper District (LGCD) and the Upper Silesian Coal Basin (USCB) is presented. For analysis, a 3-D finite element (FE) model of the structure was created in the ABAQUS/Standard software program. As a final result, the dynamic responses of the footbridge to the typical mining tremors were delivered. For this stage, the numerical simulations were conducted with the non-uniform kinematic excitation as well as with the uniform kinematic excitation. Finally, the evaluation of two calculation approaches was also made for the studied structure.

Strengthening of masonry and concrete structures working in elevated temperatures and mining tremors area

In this paper, comparison of behaviour of composite strengthening bonded to concrete and masonry substrate are presented. Specimens are tested in single lap shear tests under constant load and action of elevated temperatures. Obtained results showed that tested stiff epoxy adhesives are vulnerable to elevated temperatures, changing strain distribution, whereas the tested flexible polyurethane adhesive works stable in the whole tested temperature range. The carried out analysis concerns cracked industrial chimneys working in mining areas, which are strengthened with composite materials and carry thermal and dynamic loads, and can be responsible for the composite strengthening detachment.

Powered roof support in conditions of mining tremors in Upper Silesian Coal Basin – current state in terms of statistical analysis

Powered roof support in conditions of mining tremors in Upper Silesian Coal Basin – current state in terms of statistical analysis

Edges of overlying seams as a factor responsible for strong mining tremors occurrence during underground hard coal extraction in the light of seismic moment tensor inversion method

Physical processes occurring in the focus of tremor can be identified by solving a focal mechanism via the seismic moment tensor inversion method. In this article the estimation of focal mechanisms of strong mining tremors (according to Polish law tremors of energy higher or equal 1·105 J), which occurred during longwall mining of coal seam no. 507 in one of the hard coal mines in the Polish part of Upper Silesian Coal Basin was performed. Totally 7 strong mining tremors with the local magnitude from 1.84 to 2.52 were analysed. The most probable geomechanical processes in the foci of these tremors have been reconstructed. An attempt to determine the correlation between the edges of overlying seams no. 502, 504 or 506 and strong mining tremors occurrence has been made. The strike of determined nodal planes is in accordance with the azimuth of mentioned edges. The difference between them (absolute value) varies from 0.3° to 34.1° (on average approximately 19°).

Application of Seismic Monitoring and Numerical Modelling in the Assessment of Possibility of Seismic Event Occurrence in the Vicinity of Ore Remnant

Seismic and rockburst hazard is one of the basic problems associated with deposit exploitation in many underground mines. Rockbursts are responsible for many mining accidents, and their effects, which include damaged excavations, destroyed equipment and machinery, generate financial losses and disrupt the operational continuity of the mining facility. Dynamic phenomena occurrence is one of the major natural hazards in Polish underground copper mines in the Legnica-Glogow Copper Belt (LGCB). The degree of seismic hazard in the LGCB results, among others, from the great depth of the copper deposit exploitation, high-strength rock layers in the roof strata and the ability of rock mass to accumulate elastic energy, as well as from an increasing amount of mining works to be carried out in difficult geological and mining conditions, for instance in the vicinity of remnants. The purpose of this paper is to show the influence of ore remnant on the possibility of seismic event occurrence by seismic activity analysis and numerical modelling. The possibility of using numerical modelling to back-calculate the occurrence of a seismic event due to sudden shear rupture is also presented. Analyses were conducted for the case study of the Polkowice-Sieroszowice Polish underground copper mine for the room-and-pillar mining system with room deflection. For the selected mining field, quantitative analysis of seismic activity was performed in connection with the assessment of the mining situation in this field. The location of tremor epicentres in the context of the existing geological and mining situation was also analysed, with special attention paid to the impact of remnants and dynamic phenomena in their vicinity. Subsequent investigations focused on the back analysis of deposit exploitation by room and pillar mining system with roof deflection in the selected mining field. Numerical simulations were conducted in a plane deformation state by means of Phase2 v. 8.0 software, which is based on the finite element method. The results of seismic and numerical analyses show that undisturbed rock remnants may have a negative impact on the seismic and rockburst hazard in the mining field. The analyses also show that on the edge of a rigid remnant, sudden fracturing of roof strata may occur, as a result of exceedance of shear strength (shear rapture). This may cause a high-energy mining tremor, and under appropriate conditions, may result in a rockburst phenomenon.

Assessing the dynamic response of a steel pipeline to a strong vertical mining tremor using the multiple support response spectrum method

Assessing the dynamic response of a steel pipeline to a strong vertical mining tremor using the multiple support response spectrum method

Effect of Near-Wave Field Mining Tremors on the Rock Bolt Support Behaviour within Stress Domain

One of the most serious hazard in the underground copper mining in Poland is the roof fall hazard. The scale and intensity of this type of events depends on several factors. Due to seismic activity, weaker roof strata can loosen and deform, generating additional load on the rock bolt support. The type of load depends strictly on the course of stratum deformation as well as on the intensity of the dynamic effect in the form of a seismic wave. Continuous monitoring is then necessary to determine the risk level of stability loss within existing excavations in order to minimize the probability of serious accidents. The following study analyses the impact of tremors recorded within the near-wave field upon the stress change in the instrumented rock bolts.

Comparison of approximate assessments of the harmfulness of mining shocks using ground and building foundation vibrations

Mining tremors belong to so-called paraseismic sources of vibrations and can be classified as the most intensive of such type sources of surface structures vibrations, hazardous for buildings. According to the soil-structure interaction effect, the ground vibrations are modified during their transmission to foundations of building. In consequence, the differences between the records of vibrations registered on the ground next to a building and at the building foundation (simultaneously), can be significant. The paper is focused on the analysis of the differences in the approximate assessments of the harmfulness of mine-induced rockbursts on the basis of simultaneously occurring free-field vibrations next to the building, or building foundation vibrations. The analysed vibrations were induced by shocks in the Upper Silesian Coalfield (USC), one of the most seismically active area in Poland. Typical administrative, masonry, low-rise actual building was taken into account. The harmfulness of mining-induced vibrations to the building was estimated using appropriately prepared scales for this region. Results corresponding to two versions of the scales were analysed: the new proposition – Mining Seismic Intensity Scale GSIS-2017, as well as its former version – the Mining Intensity Scale GSI-GZWKW-2012. Both of the scales were considered in two versions: velocity version (basic), and acceleration version (auxiliary). It is worth mention that these scales base on the ground vibration parameters. However, for research and comparison purposes, they were applied also for building foundation vibrations.

SEISMICKÉ JEVY REGISTROVANÉ STANICÍ VRAC V ROCE 2017

Broadband seismic station VRAC, operated by Institute of Physics of the Earth (Masaryk University) and situated westwards of village Vranov u Brna, is equipped with seismometer STS-2 high gain and by digitizer Quanterra Q330. This instrumentation allows recording of broad band of frequencies from tenths of Hz to hundreds of seconds. It is important for usage of the VRAC station, which is part of several seismic networks, including Czech regional seismic network and global International Monitoring System of the CTBTO. In frame of these networks, station VRAC has to record of seismic signal of both local and teleseismic events. During year 2017, station VRAC recorded 6 855 seismic events (10 699 picked seismic phases). More than 70% of recorded events were represented by local events with epicentral distance less than 360 km. Induced events (mining tremors) and quarry blasts dominated among these local events. In addition, 197 natural tectonic events were recorded (89 on the territory of the Czech Republic). In the region of the Bohemian massif, most important natural seismicity was observed in the area of west Bohemia, where seismic swarm occured in July 2017. Exceptional tectonic event (10. 12. 2017, ML = 3.5) was recorded from the NE part of the Bohemian Massif (near Hlučín). About 25% of events registered by station VRAC were represented by teleseismic events with epicentral distance exceeding 2 000 km, including Korean nuclear test from 3. 9. 2017. Records of relatively small teleseismic events show signifi cant eff ect of the PKP caustic zone in respect of detectability of station VRAC.

Reconstruction of the acceleration field of ground vibrations taking into account the directivity of vibrations’ propagation

Many times, commonly used attenuation relations do not allow to obtain a sufficiently practicable accuracy of the results’ description of the observations. This may be an evidence of the attenuation directional nature of ground vibrations caused by tremors. In such cases, using the attenuation relationship that takes into account the directivity of the propagation of vibrations may allow to increase the accuracy of the reconstruction of ground vibrations accelerations. In the article there are presented the reconstruction’s results of recorded accelerations of ground vibrations caused by mine tremors, occurring in the area of one of the Polish mine. In all cases, the directivity of vibrations propagation was observed. The results of the calculations show that the direction of lower surface vibrations attenuation is parallel to the direction of the tectonic fault adjacent to the epicentre of the tremor inducing these vibrations.

Ground-motion prediction equation and site effect characterization for the central area of the Main Syncline, Upper Silesia Coal Basin, Poland

Abstract The aim of the study was to find the best model of ground-motion prediction equation (GMPE) forecasting peak ground acceleration (PGA) caused by induced seismicity. The maximum values of PGA on the surface are a major seismic threat for the infrastructure, especially in the highly urbanized areas, such is the Upper Silesian Metropolitan Area. The forecasting equations were estimated based on the values of PGA, epicenter distances and mining tremor energy registered by 14 surface seismometer stations located in the central area of the Main Syncline of the Upper Silesia Coal Basin. Data were collected within the period from January 2010 to December 2016, and the total number of seismic events used in the calculations was 15 541. The final model predicted the PGA values and amplification coefficients representing the characteristics of the site effects under seismometer stations.

Wpływ wybranych czynników na intensywność uszkodzeń przewodów podsystemu dystrybucji wody, zlokalizowanych na terenie oddziaływania wstrząsów pochodzenia górniczego

The article presents the influence of the selected factors, including mining tremors, described by the parameter PGVHmax on the failure rate of the water distribution pipelines. In created multiple regression models, the following independent variables were used: diameter and material from which the pipes were made, operation time without failure, the age of pipes, the value of pressure and PGVHmax. The values of PGVHmax in places with damaged water pipelines were determined by constructed the seismic wave propagation models. The analysis was carried out for a random sample of all water pipelines and extracted from this sample new groups: steel and gray cast iron pipes, their diameters, diameters and materials, and their construction time.

Effects of strong mining tremors, and assessment of the buildings' resistance to the dynamic impacts

A particularly important element in the assessment of the actual state of the threats which is caused by conducting the mining exploitation of seams bumping under the urban areas is to diagnose the condition of the land development after hard shocks. In the buildings, for which the impact of the mining activities, including the tremors, is not taken into account at the stage of design and formulation of the strength and use conditions, conclusions from the structure behaviour under the tremor influence are an essential part of the assessment of the possibility for transferring the further dynamic impacts. The use of conclusions from the in situ research has its role in anticipating the behaviour of the buildings in case of the forecast of the mining tremors effects in the regions of their impacts. These conclusions should also provide ground for the assumptions to the scope of the building prevention necessary to be taken in case of forecasting the tremors with big intensity. Based on the analysis of effects which occurred in the land development after the highenergy mining tremors, the elements of the dynamic resistance assessment for the buildings with traditional structure were discussed.