Mining Panel Research Articles

Panel Destressing Strategies for Remnant Pillar Extraction

Large-scale panel destressing is a rockburst mitigation technique employed in deep hard rock mines during remnant pillar extraction. Panels are choke blasted in the pillar footwall to cutoff the far-field major stress in the mining area and deviate them around the pillar. In this study, the effects of panel geometry and far-field stress magnitude are investigated. Destress blast performance is assessed by measuring change to the energy release rate (ERR) of all mining steps during the extraction of a simplified remnant pillar due to destressing. It is demonstrated that the energy release rate (ERR) of critical stopes is reduced by 30% with the base panel geometry. The panel thickness is shown to have the most influence on the efficiency of destressing, followed by the stand-off distance between the panel and the pillar and the overhang length of the panel. The effect of far-field stress magnitude on the ERR is also investigated, and the destress blast performance is expressed as an equivalent major principal stress reduction. It is shown that with the base panel geometry, the destressing program offers the same ERR reduction as a 9.6 MPa reduction in the far-field stress for the most critical stopes. Finally, the Copper Cliff Mine (CCM) panel destressing program is presented as a case study. The ore at risk and ERR are calculated over the extraction and destressing sequence in the pillar with a pillar-wide numerical model.

Defects and Improvement of Predicting Mine Water Inflow by Virtual Large Diameter Well Method

In order to prevent the occurrence of water inrush accidents, it is particularly important to predict the mine water inrush, especially the accurate prediction of the mine water inflow in the coal mining process. Mine water inflow is caused by mining disturbance, groundwater flows into mining panels along the mining-induced fissures, and a depression cone of water table is formed in certain range around the mining sites. Mining panel is usually regarded as an irregular “virtual large diameter well” so as to calculate mine water inflow in China. However, in the mining process, the area, shape, and cross section of goafs are constantly changing, so is the water inflow. Therefore, the central position and influence radius of the “virtual large diameter well” in the spatial and temporal distribution are in a dynamic process of continuous movement and expansion, rather than being confined to a static position. This paper firstly analyzes the formation mechanism of coal mine roof water inflow and the errors and defects in the calculation of mine water inflow by virtual large diameter well (VLDWM). Then, based on the theory of steady flow and combined with the dynamic change process of goaf area and depression cone of water table during mining activities, this paper proposes an improved method and puts forward a concept of dynamic virtual large diameter well (DVLDWM) and establishes a theoretical model of the central position and influence radius of the “mining large diameter well” moving forward. The first (periodic) caving step is taken as the calculation unit and generalized as the “dynamic large diameter well,” which is used to calculate the dynamic water inflow in the process of mine advancing. Taking the No.7208 mining panel in Zhangshuanglou Coalmine in Xuzhou City, Jiangsu Province, as the study area, the mine water inflow was calculated dynamically by using the DVLDWM. The results show that the mine water inflow calculated is similar to the actual mine water inflow of the No.7208 mining panel observed, thus proving the reliability and credibility of the DVLDWM.

Prediction of mining-induced subsidence at Barapukuria longwall coal mine, Bangladesh

It is essential to predict the mining-induced subsidence for sustainable mine management. The maximum observed subsidence having a noticeable areal extent due to Northern Upper Panels (NUP) and Southern Lower Panels (SLP) at the Barapukuria longwall coal mine is 5.8 m and 4.2 m, respectively, after the extraction of a 10 m thick coal seam. The mining-induced subsidence was simulated by the Displacement Discontinuity Method. The numerical model considered the effects of the ground surface, mining panels, faults, and the dyke. The predicted and the observed subsidence due to the mining of NUP and SLP were compared by varying Young's modulus, and the 0.10 GPa Young's modulus was found to be the best match in the geo-environmental condition. The effects of the faults and the dyke in the calculation were negligible. Future subsidence was predicted by considering 30 m extraction of the thick coal seam as 15.7–17.5 m in NUP and 8.7–10.5 m in SLP. The vulnerable areas demarcated considering the tilt angle and extensile strain might extend up to the coal mine office area and some villages.

Calibration of Water Inrush Channel and Numerical Simulation of Water Inrush Process in Coal Mine Roof

The surrounding rock of a coal mine roof fractures with the excavation of the underground working face in coal mining. These mining-induced fractures are connected and extended upward to form water inrush channels. A water inrush accident may occur when there is a sufficiently large water source. To elucidate the formation mechanisms of the roof water inrush channel and the characteristics of water inrush in goafs, we performed a case study of No.18401 Panel of Xiqu Coal Mine in China and determined whether the roof water inrush channel is connected by theoretical calculation and microseismic monitoring. The modified mechanical parameters of rock masses were embedded into the numerical model based on microseismic data. Microseismic monitoring and numerical simulation were organically combined to analyze the connection process of the water inrush channel, after which the roof water inrush channel is calibrated on the No.18401 Panel. We established a non-Darcy flow model for water inrush in the water-conducting fractured zone of mines by coupling the Darcy, Forchheimer, and Navier–Stokes equations. Finite element language and its compiler (FELAC) was used to study the water inrush mechanism of non-Darcy seepage. The results show that the pressure, velocity, and porosity in the water-conducting fractured zone are non-uniform in water inrush occurrence and development, and the mixed fluid mainly passes through the “dominant channel.” The development of water inrush is accompanied by the release of the hydrostatic pressure in the aquifer, the sudden increase of the velocity at the water inrush position, and the increase in fluid concentration. Hence, the underground water inrush can be predicted and prevented by monitoring the aforementioned indicators. This research is of great significance for the calibration of the water inrush channel of the roof and the prediction of water inrush disasters.

Study on the Mechanism of Weakening Thick and Hard Roof by Deep-Hole Blasting in Deep Coal Mines

In the mining process of deep coal mines with a thick and hard roof, it is easy to form a large overhanging roof and accumulate a lot of strain energy. The sudden breaking of the suspended roof may induce seisms, which seriously threaten the safety of underground miners and equipment. To reveal the mechanism of weakening the thick and hard roof by blasting in deep mining, the four times deep-hole blasting in 63upper06 panel of Dongtan coal mine are considered. First, the temporal and spatial distribution of seismicity events monitored before and after blasting is investigated. Second, the process of deep-hole blasting is simulated using finite element and discrete element methods. After blasting, the small-energy mining-induced seismicities within 20 m of the roof suddenly increase and gradually transfer to the mined-out area and the front of the working face. Meanwhile, the high rock stratum is broken and a large amount of strain energy is released, which causes the range of fall zone enlarge a lot, and the stress in the roof is decreased obviously. With the increase in the number of deep-hole blasting, the pressure relief effect becomes more obvious, and the newly developed fracture is mainly located in the low strata. Microseismic monitoring results agree with the calculated results. Moreover, the rock caving steps are easily formed after deep-hole blasting, and the collapse is more sufficient. Furthermore, blasting cracks are most restrained in the vertical direction of the maximum principal stress. Moreover, the delayed blasting method is more conducive to the expansion and penetration of blasting cracks. Results show that the deep-hole blasting technology has a significant effect on weakening the roof of coal seam and preventing and controlling large-energy mining-induced seismicities.

4D gas geological research on coal seam with gas hazard potential in mining panel

According to regulations of the mining industry in China, it is necessary to carry out gas hazard prevention projects in advance when mining coal seams with gas hazard potential, and gas geological research should be taken as the basic work for optimal design and effective construction of gas hazard prevention projects. Research on coal seam with gas hazard potential have shown that anomalous geological area could be the gas hazard potential area as well, where superimposed tectonic and mining stress field usually results in tectonically disturbed coal and pressured gas. A 4D gas geological research method is used to find out the anomalous geological area and assess its gas hazard potential. The method covers two ranges of gas geological research: fine geological survey and 4D analysis. The former includes a comprehensive prospect of concealed small geological anomalies (such as small fault, small fold and coal thickness variation) by use of gas extraction projects; The latter includes a dynamic forecast of gas hazard potential from space-time perspective based on numerical simulation analysis on additional stress fields around small geological structures beyond coal mining face. Its research benefit the optimal design and effective implementation of gas hazard prevention measures in coal mining panel with high coal and gas outburst potential.

Unearthing Underground Mining–Induced Strata Disturbance by Electrical Resistivity Tomography Interpretation

ABSTRACT The focus of the study was to evaluate the rock strata transformation above an underground mine panel during pre-and-post mining based on an electrical resistivity tomography (ERT) geophysical technique. The data were acquired using two electrode arrays (i.e., pole-dipole and Wenner-Schlumberger [WS]) with electrode spacing of 6 m up to 570 m in length. The resistivity data were digitally processed through RES2DINV software. The formation of fractured rock in the overburden caused by underground mining operations was clearly distinguished by resistivity anomalies observed using the pole-dipole array. Variation in the hydrogeological condition in the strata was also assessed during the pre-and-post mining conditions. The impact of compression and tension generated in the strata as a result of extraction of coal and subsidence in the overburden rock was observed through prominent resistivity variations observed in an inversion modelling of the WS true resistivity profile. The influence of surface topography in the near surface top weathered rock was also distinctly outlined by the resistivity measurements. ERT is a strong tool capable of providing valuable information regarding strata deformation caused by mining.

Stress environment around head entries with pillarless gobside entry retaining through numerical simulation incorporating the two type of filling wall

Longwall mining is the most productive system for underground extraction of coal. Many coal mines use a pillarless mining. Reserving a gateroad for the usage of next panel mining is a popular gob-side entry retaining. Thus, the conventional entry retaining method requires an installation of filling walls. The mechanical properties of filling materials largely determine the quality of job-side entry retaining. Stress field evolution study around head entries when main roof console length increase with two variants of filling wall. Ansys code was used to analyze the stress evolution law under different mining conditions. As a result of numerical simulation, it was found that in the case of gob-side entry retaining, the localization of maximum stresses in surrounding rock is determined by the length console of the main roof, which hanging on the border with the gob, and the filling walls deformation module. Potential location of roof cutting, stress gradient and extremum stress in the main roof define the stability of entries. Main roof console length and filling material parameters control can help to the formation of a stable structure around the entry to meet the requirements of the next working face.

Comprehensive Monitoring Research on the Effect of Roof Cutting and Pressure Release: A Case Study of the Jiulishan Coal Mine in China

The longwall panel of the Jiulishan coal mine is affected by floor-confined water, while the roof rock weighting makes the production management of some longwall panels difficult. This has caused engineering methods of roof cutting and pressure release to be considered. To explore the dynamic effects of roof cutting and pressure release method, the 14141 longwall panel was taken as the test point, and a variety of monitoring methods were used to comprehensively analyze the characteristics of roof rock weighting, front abutment pressure, and floor mining failure. The main results are as follows: first, the weighting interval, the weighting intensity distribution, and the gateway deformation are asymmetrical. Second, the peak point of the front abutment pressure is approximately 6 m away from the coal wall, the peak stress is 7.02 MPa, the concentration coefficient is 1.54, the range of the pressure increasing area is approximately 16.4 m, and the farthest end of the front abutment pressure effect area is 22.4 m away from the coal wall. Furthermore, the maximum depth of the floor failure is at the No.17 measuring point (A117) position under the condition of one electrode distance. The maximum damage depth is 9.8 m, and the horizontal distance between the location of the maximum failure depth and the working face is 4.1~10.3 m. Finally, compared with the formula calculation value without considering the effect of roof cutting and pressure release or the adjacent 14121 longwall panel, the weighting interval and the weighting intensity, the gateway deformation, the degree of coal wall spalling, the influence range of the front abutment pressure, and the degree of floor mining failure are significantly reduced. The research results provide scientific and technological support for roof cutting and pressure release as a technical method to prevent floor water inrush and reduce the roof rock weighting intensity on the longwall panel.

Resources Optimization in Underground Gold Mining Case Study the Kubang Cicau Gold Vein in Pongkor Area, West Java, Indonesia

Mining activities are typically controlled by the smallest mining units (SMU). These SMUs comprise mining blocks with dimensions that are generally adjusted to the mining equipment used as well as various geotechnical factors. In addition to SMUs, the smallest mining decision unit (SMDU), which is a collection of several SMU blocks, is usually established. In this paper, the SMDU is represented by an underground (UG) mining panel. This paper presents the results of a study on the optimization of gold resource in SMU blocks within SMDU and cut-off grade (CoG) variations. The study focuses on how to design a panel as an SMDU that is based on a weekly production quota that defines an optimum weekly rate of production that meets processing and milling capacities. The UG mining scheme in this paper is realized using a level, a panel, and SMU blocks. The level represents the progress of the mining in a vertical direction, while the panel represents the progress of the mining in a horizontal direction. Acting as the objective functions are the ore tonnage and gold mass. In relation to the gold mass, the goal is to reach the optimum level within the SMDU and fulfill the constraint function through the number of SMU blocks within the SMDU and the range of CoG variations. The optimization process was conducted using a genetic algorithm scheme. Kubang Cicau Vein B at Pongkor Gold Mine Business Unit was selected for the case study.

Bed Separation Characteristics of an LTCC Panel and Subsidence Controlling Grouting: Case Study of Longquan Coal Mine, China

The bed separation backfill grouting (BSBG) is commonly used to mitigate the surface subsidence caused by coal mining. The distribution characteristics of bed separation and its dynamic evolving process are crucial for BSBG design. This paper utilizes the continuum-discontinuum element method (CDEM) to study the distribution characteristics of bed separation for a longwall top coal caving (LTCC) panel of Longquan coal mine. Numerical results indicate that in addition to the bed separation below the primary key stratum, several small bed separations may also occurred in the strata between the primary key stratum and the subordinate key stratum. The bed separations in the overburden could be classified into three classes: the upper bed separation, the middle bed separation, and the lower bed separation. The upper bed separation has the longest duration time, and the middle bed separation has the shortest duration time. And the BSBG should be started before the closure of the middle bed separation. Based on the actual geological information, the BSBG scheme for 4203 LTCC panel is proposed to mitigate the surface subsidence by taken the results of numerical simulation into consideration. In addition, the case study of the BSBG is introduced in detail. By using gangue power slurry, BSBG could not only effectively mitigate the surface subsidence but also solve the problems of environmental pollution and land occupation caused by traditional gangue stacking. The present study could provide technical support for surface subsidence mitigation and coal gangue disposal for LTCC mining with similar conditions.

Failure Mechanism of Gob-Side Roadway under Overlying Coal Pillar Multiseam Mining

Roadway deformation and rock burst are the two key challenges faced by the safe operation of coal mines. Aiming at the issue of large deformation of the gob-side roadway under coal pillars in multiseam mining, this study has considered the case of the 8308 panel of Xinzhouyao coal mine in China. Based upon a combination of theoretical analysis, numerical simulations, and engineering practices, the mechanical model of “stress and deformation quantitative calculation of gob-side roadway under overlying coal pillars” was established in this study. The analytical solutions of the vertical stress distribution and the plastic zone of the gob-side roadway under overlying coal pillars were obtained. Finally, the accuracy of the mechanical model was verified using numerical simulations. The results showed that the coal pillar, upright above the gob-side roadway, and the cantilever roof around the gob-side roadway were the main factors leading to stress concentration and deformation around the gob-side roadway. For the particular cases considered in this study, the peak stress of the gob-side roadway could reach 1.8 times of the self-weight stress of overlying strata. The rates of the contribution of the gob-side roadway’s overlying pillar and the cantilever roof around the gob-side roadway to peak stress were 78.3% and 16%, respectively. The obtained results have an essential reference significance for stress calculations and rock burst prevention design of gob-side roadway under overlying coal pillars in multiseam mining.

Study of Ground Movement in a Mining Area with Geological Faults Using FDM Analysis and a Stacking InSAR Method

Underground coal mining activities and ground movement are directly correlated, and coal mining-induced ground movement can cause damage to property and resources, thus its monitoring is essential for the safety and economics of a city. Fangezhuang coal mine is one of the largest coalfields in operation in Tangshan, China. The enormous amount of coal extraction has resulted in significant ground movement over the years. These phenomena have produced severe damages to the local infrastructure. This paper uses the finite difference method (FDM) 3D model and the stacking interferometric synthetic aperture radar (InSAR) method to monitor the ground movement in Fangezhuang coalfield during 2016. The FDM 3D model used calibrated Fangezhuang geological parameters and the satellite InSAR analysis involved the use of ascending C-band Sentinel-1A interferometric wide (IW) data for 2016. The results show that the most prominent subsidence signal occurs in mining panel 2553N and the area between panel 2553N and fault F0 with subsidence up to 57 cm. The subsidence observed for the FDM 3D model and stacking InSAR to monitor land deformation under the influence of fault are in close agreement and were verified using a two-sample t-test. It was observed that the maximum subsidence point shifted towards the fault location from the centre of the mining panel. The tectonic fault F0 was found to be reactivated by the coal mining and controls the spatial extent of the observed ground movement. The impact of dominant geological faults on local subsidence boundaries is investigated in details. It is concluded that ground movement in the study area was mainly induced by mining activities, with its spatial pattern being controlled by geological faults. These results highlight that the two methods are capable of measuring mining induced ground movement in fault dominated areas. The study will improve the understanding of subsidence control, and aid in developing preventive measures in Fangezhuang coalfield with fault reactivation.

Slow surface subsidence and its impact on shallow loess landslides in a coal mining area

Surface subsidence caused by underground coal mining affects the hillslope stability conditions. However, few studies have focused on the coupling relationship between slow surface subsidence and landslide occurrences. A detailed landslide and fissure inventory in a coal mining area in Shaanxi Province, China, was produced based on interpretation of multitemporal satellite images and unmanned aerial vehicle (UAV) surveys. We used the interferometric synthetic aperture radar (InSAR) technique and landslide and fissure spatiotemporal statistics to investigate the spreading process of the slow subsidence caused by underground mining and examined its impact on the occurrence of shallow landslides. The InSAR results indicate that the actual extent of the subsidence zone is larger than the range of underground mining, which formed a subsidence basin along the coal mining panels. The subsidence curves go through initial, accelerative, and slow subsidence stages and characterized by S-shaped, which can be adequately fitted with logistic regression. Moreover, subsidence does not cease after the end of coal exploitation. Logistic models predicted that the duration of residual subsidence reached about 2–3 years. Subsidence significantly increased the likelihood of landslide occurrences. The spatial pattern of landslides is associated with the actual coal mining. We also investigated the clustering phenomenon of landslides and fissures under the impacts of subsidence. The frequency ratio of landslides and fissures increased with the cumulative subsidence. Finally, we propose a schematic view for landslides caused by coal mining and precipitation. This study will be helpful for elucidating the spatial–temporal evolution of slow subsidence and its impact on loess landslides in coal mining area.

Investigation on the Movement and Fracture Characteristics of an Extra-Thick Hard Roof during Longwall Panel Extraction in the Yima Mining Area, China

As an extra-thick hard roof is a significant contributing factor to frequently induced sudden roof collapse accidents and coal bursts, this study investigates the relationship between extra-thick hard roof movement and mining-induced stress using physical experiments and numerical simulation methods based on mining activities in a longwall panel in the Yima mining area, Henan province, China. The results suggested that the movement and failure processes of the extra-thick roof could be divided into three main periods: the undisturbed, movement stabilization, and sudden collapse periods. The roof displacement remained essentially unchanged during the undisturbed period. During the movement stabilization period, the displacement gradually increased into the upper roof. However, the extra-thick main roof remained undisturbed until the immediate roof experienced its fourth periodic caving in the physical model. Consequently, the displacement expanded rapidly into the extra-thick main roof during the sudden collapse period and the strain energy was violently released when it accumulated in the extra-thick main roof. Additionally, the mining-induced stress was characterized by a sudden decrease in the gradual increase trend when the extra-thick roof instantly collapsed. The deformation and fracture of the extra-thick roof could cause a sudden decrease in the mining-induced stress and lead to continuous and unstable subsidence pressure exerted on the mining panel and roadway. This significantly contributes to the occurrence of coal bursts.

A new model for the identification of subcritical surface subsidence in deep pillarless mining

The identification of the subsidence stage is vital for the surface infrastructure protection above underground mining panels, while prior studies have only focused on shallow mining with large interpanel pillars. In this study, we aimed to develop a new model to identify the initiation of subcritical subsidence in deep pillarless mining. The key stratum theory was used to transform the problem of stage identification for surface subsidence into the primary key stratum (PKS) failure. The findings show that the PKS in deep mining can remain stable after a single panel is extracted. The narrow pillar gradually loses its structural integrity and fails to isolate the movement of PKS above two panels as the second panel passes it. Consequently, the PKS above two panels integrally fails as an L-shaped plate, causing the transition from super-subcritical to subcritical subsidence stage. According to these findings, the L-shaped PKS model was developed using the theory of elastic plates to determine the critical span of PKS failure and identify the occurrence of subcritical subsidence in pillarless mining. The model was validated using a three-year field measurement data on surface subsidence in Longtan coal mine. This study contributes to the understanding of subsidence mechanism in deep pillarless mining and provides new insight into designing pillarless mining with surface subsidence control.

Mineral and rare earth element distribution in the Tunçbilek coal seam, Kütahya, Turkey

The mineral and rare earth element distributions of Tunçbilek coal, Turkey were studied and their potential to be a source for REY was investigated. The studied samples were taken from the BYJ, BYL, 48P open-pit mine panels and Ömerler and İğdekuzu underground mines. In order to observe the mineral and REE element distributions along the coal seam profile, samples were taken by using channel sampling method from the BYJ, BYL and 48P open-pit mine panels. On the other hand, representative samples which represent the whole coal seam including partings and clayey layers were taken from the same open-pit mine panels, İğdekuzu and Ömerler undergroud mines to investigate the REE distributions in the coalfield. The proximate, ICP-OES, XRF, SEM and XRD analyses were performed on the samples. Quartz, kaolinite and dolomite are the most abundant minerals in the samples. Smectite, mica, illite, pyrite and siderite are the second common minerals. In a few samples, alkali feldspar, chlorite, gypsum, jarosite, magnetite, feldspar, vermiculite and zeolite minerals are identified. In addition, monazite, florencite, baryte and thorite were detected in minor amounts using SEM analyses. The most abundant major oxides are SiO2, Al2O3, MgO, Fe2O3, CaO and SO3 respectively. The K2O, MnO, Na2O, P2O5 and TiO2 major oxides are occur in lesser amounts. Kaolinite and quartz minerals might be the main sources of Al2O3 and SiO2 in the samples. The MgO, CaO, Fe2O3 and SO3 major oxides can be derived from mainly dolomite, siderite, feldspar, smectite, montmorillonite, serpentine and pyrite. The P2O5 and TiO2 are derived from the apatite, monazite, florencite, clay and mica minerals. The La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Ho, Tm and Lu elements in the samples have higher concentrations than the World brown coal averages. The total REY and LREY concentrations show similar distributions and reach high values at the south of the coal basin. However, the HREY and MREY concentrations are high at the Ömerler underground mine. The coal layers show HREY enrichment whereas the clayey coal and clayey layers indicate LREY type enrichment. The Ce, Eu, La, Nd and Sm elements are associated with the clay and phosphate minerals. Moreover, the Dy, Er, Gd, Ho, Lu, Pr, Tb, Tm and Yb are related to the pyrite, siderite and dolomite. The REY concentration in the Tunçbilek Basin is probably related to the terrigenous, tuffaceous and hydrothermal types of accumulations. The total REY concentration of the samples is below the cut-off grade (1000 μg/g) although the concentration coefficients of the Tunçbilek coal samples indicate slight enrichment. Based on the relation between cut-off grade and Coutl values, the Tunçbilek coal cannot be a potential source of REY.

How to Assess the Moment Tensor Inversion Resolution for Mining Induced Seismicity: A Case Study for the Rudna Mine, Poland

Underground exploitation of georesources can be highly correlated with induced seismic activity. In order to reduce the risk and improve the mining operations safety, the mining activity is monitored by a dedicated seismic network. Moment tensor inversion is a powerful method to investigate the rupture process of earthquakes in mines, providing information on the geometry of the earthquake source and the moment release. Different approaches have been proposed to estimate the source mechanisms, with some advantages and limitations. One of the simplest and most used methods rely on the fit of the polarity and amplitude of first P wave onsets. More advanced techniques fit the full waveforms and their spectra. Here, we test and compare moment tensor and focal mechanism estimations for both inversion techniques. In order to assess the inversion resolution, we built realistic synthetic data, accounting for real seismic noise conditions and network geometry for the Rudna copper mine, SW Poland. The Rudna mine pertains to the Legnica-Glógow Copper District, where thousands of mining induced earthquakes are detected yearly, representing a serious hazard for miners and mining infrastructures. We simulate a range of different processes and locations, considering pure double couple, deviatoric and full moment tensors with different magnitudes and located in different mining panels. Results show that the P-wave first onset inversion is very sensitive to the geometry of the seismic network, which is limited by the existing underground infrastructure. On the other hand, the quality of the moment tensor solutions for the full waveform inversion is mainly determined by the strength of mining tremor and the signal-to-noize ratio. We discuss the performance of both inversion techniques and provide recommendations toward a reliable moment tensor analysis in mines.

Resultant axial stresses in instrumented rockbolts induced by dynamic effects occurred due to multi-face blasting in the working areas

Multi-face blasting is one of the most frequently used active rockburst prevention methods in the Polish copper mines. Simultaneous firing of a group of faces generates vibrations which, propagating in the form of para-seismic waves, affect the condition of the rock mass structure and allow to trigger high-energy tremors during the production process. However, the simultaneous firing of explosives in several mining faces may have the negative impact on the condition of the rockbolt support system in the roof strata and stability of the roof rocks located in the vicinity of the mining front. Therefore, this impact under the conditions of selected mining panels of the Lubin mine was examined by measuring the axial stresses in instrumented rockbolts. The statistical correlation between the measured axial stresses and the estimated para-seismic peak particle velocity has been analysed to determine the potential dependence between these quantities. The obtained results have shown that in the geologic and mining conditions of the analysed mining panels, simultaneous firing of explosives in a number of mining faces did not induce significant permanent changes in values of the measured axial stresses within the instrumented resin anchored rockbolts. In result, further development of multi-face blasting in terms of seismic wave amplification may be proceeded without risk of significant damaging of the immediate roof strata.

Analysis of the Geomechanical Phenomena That Led to the Appearance of Sinkholes at the Lupeni Mine, Romania, in the Conditions of Thick Coal Seams Mining with Longwall Top Coal Caving

Thick coal seam no. 3, block V, Lupeni mine was mined by longwall top coal caving (LTCC). After the coal mining, the ground surface underwent continuous subsidence, but since 2008, three sinkholes have appeared on the surface with important dimensions, atypical for the geo-mining conditions in this coal basin. This article is a synthesis of the study meant to decipher the geo-mechanical phenomenon that led to the emergence of these sinkholes and highlighting the main factors that contributed to the development of this phenomenon. For this purpose, measurements were made on the terrain deformations using photogrammetric methods and aerial laser scanning, when modeling with 3D finite elements, in elasto-plasticity and with the help of the Knothe–Budrik influence function. The factors that contributed to the occurrence of discontinuous subsidence phenomena are shallow mining depth, the LTCC mining method, and the presence of faults in the vicinity of the mining panels. Additionally, the geo-mechanical phenomena of subsidence terrace development and sinkholes in the mining subsidence troughs at the Lupeni mine were described.