Search Results (37)

As metal mines advance into deep mining, the increase in tectonic stress and horizontal stress leads to a higher degree of joint and fissure development in roadway surrounding rocks, along with a significant rise in both the fragmentation degree of the rock mass and the support cost. This paper adopts field monitoring and numerical simulation methods to analyze the characteristics of mining-induced stress rotation after unloading due to deep roadway excavation in the Jinchuan mining area, and proposes corresponding surrounding rock control countermeasures and optimized schemes for the original support. The research results show that after the unloading caused by the excavation of deep roadway surrounding rock, the magnitudes and directions of the maximum, intermediate, and minimum principal stresses all exhibit a trend of slow change, followed by drastic change, and finally gradual stabilization. When the roadway advances to 4 m in front of the monitor section, the adjustment of the magnitude of principal stress of the surrounding rock is the most drastic. Moreover, as the working face moves away from the monitor section, the principal stress gradually stabilizes and becomes lower than the initial stress value. When the roadway advances to 6 m in front of the monitor section, the adjustment of the direction of the principal stress of the surrounding rock is the most drastic. The rotation angle of the maximum principal stress shows a trend of first increasing and then decreasing with the increase in the excavation step, while the rotation angles of the intermediate and minimum principal stresses show a trend of first decreasing and then increasing as the excavation step increases. Based on the spatial distribution characteristics of joints and fissures in the roadway surrounding rock, the sensitive area for the rotation of mining-induced stress direction is defined. By changing the advancing direction of the roadway, the rotation trajectory of the principal stress can be deviated from the sensitive area, thereby improving the self-stabilization ability of the roadway surrounding rock. It is proposed that asymmetric coupling support be adopted to reinforce the positions where the principal stress rotation of the rock mass around the anchorage is severe, which can effectively reduce the range of the plastic zone in the roadway surrounding rock. The research results provide new ideas for the surrounding rock control of deep roadways, as well as a theoretical basis for the design and optimization of roadway support parameters in similar mines. Full article

To address the challenges associated with deep ground pressure control at the Sanshandao Gold Mine, a pre-controlled top-to-middle and deep-hole upper and lower-wall goaf subsequent filling mining method was proposed. Three distinct downward mining schemes were designed, the excavation procedure is systematically designed with 18 steps, and the temporal and spatial evolution characteristics of stress and displacement were analyzed using FLAC3D. The results revealed that stress concentration occurred during excavation steps 1–3. As excavation progressed to steps 4–9, the stress concentration area shifted primarily to the filling zones of partially excavated and filled sections. By steps 10–12, the stress concentration in these areas was alleviated. Upon completion of all excavation and filling steps, a small plastic zone was observed, accompanied by an alternating distribution of high and low stress within the backfill. Throughout the excavation process, vertical displacement ranged from 4.42 to 22.73 mm, while horizontal displacement ranged from 1.72 to 3.69 mm, indicating that vertical displacement had a more significant impact on stope stability than horizontal displacement. Furthermore, the fuzzy comprehensive evaluation method was applied to optimize the selection among the three schemes, with Scheme 2 identified as the optimal. Field industrial trials subsequently confirmed the technical rationality and practical applicability of Scheme 2 under actual mining conditions. Full article

As resources are extracted from the deeper sections of a mine, the ventilation network becomes increasingly complex. Consequently, determining the optimal installation location for speed-measuring equipment that accurately reflects the average wind speed along the roadway remains a challenging task. In this study, two three-dimensional geometric models, smooth and rough, were developed based on field conditions. The cross-sectional widths, heights, and flow velocities of the model channels were processed dimensionlessly. The dimensionless velocity distributions of the smooth and rough models were then analyzed for different Reynolds numbers. It was observed that the dimensionless average velocity ring distributions for the rough model were smaller than those for the smooth model. Additionally, the maximum values of dimensionless flow velocities were negatively correlated with the flow velocities under laminar flow conditions, whereas they largely overlapped under turbulent flow. The dimensionless distances of the average velocity rings from the top and sidewalls of the channel were studied and determined for both models across different flow regimes. Specifically, the dimensionless distance values $d(-)$ were found to be 0.111 for the smooth model and 0.101 for the rough model under the laminar regime. Under the turbulence regime, the corresponding values were 0.106 and 0.108. Likewise, the values of $h(-)$ were 0.135 and 0.135 for the smooth and rough models in the laminar flow regime, while under turbulent flow, the values were 0.131 and 0.162, respectively. The largest dimensionless velocity value was identified at the center of the velocity distribution circle. For corners that did not maintain simple parallelism with the walls, these regions were incorporated into the circle equation using the Least Squares Method, providing a theoretical basis for the placement of velocity-measuring equipment in practical applications. By using the sidewall as the reference coordinate, an appropriate mathematical model was employed to establish the functional relationship between the centerline velocity of the roadway and the dimensionless horizontal coordinate. The fitting results showed good agreement, and this model can be used to back-calculate and expand the potential installation locations for a mine anemometer. Full article

The Maoniuping Rare Earth Elements (REE) deposit, the second largest light REE deposit in the world, has been mined for decades, with serious impacts on the surrounding environment. However, the impact of mining on heavy metals in the downstream area (Nanhe River Basin) has not been systematically documented. To address this issue, this study explored the extent, transport, and accumulation of heavy metal contamination in the Nanhe River Basin through field surveys (2946 topsoil samples and four vertical soil sections) and regional geographic attributes (e.g., mining area, river, and elevation) combined with a variety of methods such as statistics, geostatistics, spatial analysis, geo-accumulation index, and potential ecological risk index. The results showed that soils in the Nanhe River Basin presented different degrees of heavy metal pollution, with Pb and Cd being the most abundant, and the soils as a whole showed moderate-heavy ecological risks. The spatial distribution and correlation of heavy metals exhibited similar distribution patterns and sources. Further analyses revealed that mining of REE in Maoniuping was the main source of heavy metal pollution in the Nanhe River Basin, with heavy metals entering the soil through runoffs. At the same time, mining activities led to the migration of heavy metals in different directions in the Nanhe watershed, i.e., about 1.3 km horizontally, 16 km longitudinally, and more than 1 m vertically. In addition, about 38.1 km² of the watershed is contaminated by mine wastes, which is 6.6 times the size of the mining area. In order to mitigate the threat of heavy metals, the local government has implemented water diversion projects and crop conversion in the Nanhe River Basin. This study provides a reference for research on the environmental problems caused by the exploitation of REE mines and other mineral resources. Full article

To investigate the reasonable width of a coal pillar in the downward mining section of close-distance coal seams, the stress state of any point below the residual coal pillar in the overlying goaf and the width of a small coal pillar were studied by theoretical calculation, numerical simulation, similar simulation and field monitoring. The findings indicate that the width range of the small coal pillar is 7.92~11.42 m. The 4-1 coal seam is in the stress reduction zone when it is more than 16.6 m horizontally from the border of the residual coal pillar above it. In addition, the peak stress is situated inside the elastic zone of the coal pillar and is lower than the coal pillar’s bearing limit when a small coal pillar of 8 m is maintained. With the help of distributed optical fiber monitoring to model the coal pillars’ stress distribution, it is found that 8 m simulated coal pillars have a certain bearing capacity. The practical findings demonstrate that the 8 m small coal pillar that was left on the site satisfies the demand, and the convergence of the roadway’s floor and roof, and its two sides fall within the controllable range. The findings of the study offer a reference for the location of a return air roadway and the width of section coal pillars in the downward mining of close-distance coal seams. Full article

The dipping dike model has shown to be a useful approximation for mineral deposits. To make this model more realistic, we include the thickness, which yields the depth to the bottom, as an additional parameter. The magnetic anomaly is obtained by combining the anomalies of two infinite dikes, so that the resulting expression is simpler than the classical prismatic models with polygonal cross section. We employ a Metropolis-Hasting (MH) algorithm coupled with the Levenberg-Marquardt (LM) method to invert magnetic profiles assuming a model of multiple dike-like sources. We use a few iterations of the LM method to improve the candidate solutions at the end of each random walk generated by MH. The following parameters are obtained: depth to the top, thickness, half-width, horizontal location of the top center, geological dip, in addition to two effective parameters that depend on the intensity of magnetization and the directions of the induced and remanent fields. For synthetic anomalies, both noise-free and noisy magnetic data are considered, with examples presented for each scenario. These examples highlight the discrepancy between models with finite and infinite sources. They also illustrate the higher accuracy of the hybrid MH-LM method over the pure MH approach. Moreover, two field examples related to mineral exploration have been considered: the Pima copper mine, United States, where the relative differences between the parameters obtained by our algorithm and those known from drilling are not higher than 10%, and a magnetic profile over iron ore deposits located in Laje, northeast Brazil, where the inverted parameters were useful for detailing previous studies. Full article

In the process of mining, a large area of hard roof will be exposed above a goaf and may suddenly break. This can easily induce rock burst and has a significant impact on production safety. In this study, based on the engineering background of the hard roof of the 2102 working face in the Balasu coal mine, the spatial and temporal characteristics of the strain energy of the roof during the initial mining process were explored in depth. Based on a theoretical calculation, it is proposed that hydraulic fracturing should be carried out in the medium-grained sandstone layer that is 4.8–22.43 m above the roof, and that the effective fracturing section in the horizontal direction should be within 30.8 m of the cutting hole of the working face. The elastic strain energy fish model was established in FLAC^3D to analyze the strain energy accumulation of the roof during the initial mining process. The simulation and elastic strain energy results show that, as the working face advances to 70–80 m, the hard roof undergoes significant bending deformation. The energy gradient increases with the rapid accumulation of strain energy to a peak value of 140.54 kJ/m³. If the first weighting occurs at this moment in time, the sudden fracture of the roof will be accompanied by the release of elastic energy, which will induce rock burst. Therefore, it is necessary to implement roof cutting and pressure relief before reaching the critical step of 77 m. To this end, the comprehensive hydraulic fracturing technology of ‘conventional short drilling + directional long drilling’ is proposed. A field test shows that the hydraulic fracturing technology effectively weakens the integrity of the rock layer. The first weighting interval is 55 m, and it continues until the end of the pressure at the 70 m position. The roof collapses well, and the mining safety is improved. This study provides an important reference for hard roof control. Full article

In order to mitigate the risk of roof-dominated coal burst in underground coal mining, horizontal long borehole staged hydraulic fracturing technology has been prevailingly employed to facilitate the weakening treatment of the hard roof in advance. Such weakening effect, however, can hardly be evaluated, which leads to a lack of a basis in which to design the schemes and parameters of hydraulic fracturing. In this study, a combined underground–ground integrated microseismic monitoring and transient electromagnetic detection method was utilized to carry out simultaneous evaluations of the seismic responses to each staged fracturing and the apparent resistivity changes before and after all finished fracturing. On this basis, the comparable and applicable fracturing effects on coal burst prevention were evaluated and validated by the distribution of microseismic events and their energy magnitude during the mining process. Results show that the observed mining-induced seismic events are consistent with the evaluation results obtained from the combined seismic-electromagnetic detection method. However, there is a limited reduction effect on resistivity near the fractured section that induces far-field seismic events. Mining-induced seismic events are concentrated primarily within specific areas, while microseismic events in the fractured area exhibit high frequency but low energy overall. This study validates the rationality of combined seismic-electromagnetic detection results and provides valuable insights for optimizing fracturing construction schemes as well as comprehensively evaluating outcomes associated with underground directional long borehole staged hydraulic fracturing. Full article

Geotechnical parameters are crucial for mine planning and operation at different stages of development. However, estimating these parameters requires a large number of boreholes and subsequent detailed analysis of the samples, making it a cumbersome exercise. Moreover, even after conducting these studies, it is not possible to cover the entire operational area. To address this issue, this study presents an indirect method of estimating geotechnical parameters through mathematical relations using resistivity data. The present study incorporated 2D and 3D subsurface imaging techniques for exploring coal reserves and analyzing geotechnical parameters that define subsurface soil properties. Electrical resistivity tomography (ERT) was utilized for data acquisition, employing a Dipole–dipole array with a multielectrode ABEM Terrameter LS instrument. Six parallel profiles were conducted, each 400 m in length, with an inter-electrode spacing of 10 m and a spacing of 50 m between profiles. These profiles were combined into a 3D dataset referred to as quasi-3D ERT. The inversion process for both 2D and 3D data was performed using the Res2dinv and Res3dinv programs, respectively. This study overcame the challenges of 2D resistivity sections by evaluating horizontal depth slices in the x-z plane from layers 1 to 10, reaching a depth of 81.2 m. The geotechnical parameters, including cohesion, friction angle, moisture content, and plastic index, were derived from the resistivity data. The ERT method proved to be cost-effective and efficient in determining soil properties over a large area compared with traditional laboratory analysis of borehole samples. Additionally, the variation of geotechnical parameters with resistivity values exhibited unique characteristics. The results from both the 2D and quasi-3D ERT were well correlated with the borehole data. Such studies are valuable for resource exploration and mine planning purposes. Full article

Historical maps represent a unique and irreplaceable source of information about the history of a country, be it large (historical) regions, individual geomorphological units or specifically defined sites. Using a methodologically correct, critical historical analysis, old maps provide both the horizontal and vertical analysis of a landscape and its transformation in different time periods. These maps represent some of the oldest, but relatively easily accessible, historical pictorial documents (plausibly) depicting historical landscapes. This study provides the methodology for processing and georeferencing old mine maps with the possibility of their further use for the purposes of mining tourism. The 1696 Marsigli mine map has been chosen for the case study in question. It depicts a cross-section of the copper mines in Smolník and shows in detail the process of cementation water mining. Through an analysis and a detailed study, two-dimensional parts of a georeferenced historical map have been plotted in Google Earth’s three-dimensional space. Full article

Shale gas is mostly produced using horizontal wells, since shale gas reservoirs have low porosity and permeability. It is challenging to predict a horizontal well’s critical liquid-carrying gas flow rate because horizontal wells have more complicated well structures and gas–liquid two-phase pipe flows than vertical wells. In addition, there are significant differences between shale gas reservoirs and conventional natural gas reservoirs as well as dynamic changes in the liquid production rate. The majority of critical liquid-carrying models currently in use in engineering are based on the force analysis of droplets in the gas stream or liquid film on the pipe wall in annular-mist flow in the vertical wellbore. However, they do not take into account the impact of changes to the entire wellbore structure and dynamic changes in the liquid production rate on gas–liquid two-phase flow patterns and liquid carrying in the wellbore. In order to perform the critical gas velocity test for liquid carrying in the entire wellbore of horizontal wells, a visual liquid-carrying simulation experimental device for the entire wellbore of horizontal wells and a high-speed camera were used in this study. The onset of liquid accumulation was analyzed comprehensively according to the overall increase of the wellbore liquid and the change of the system pressure. A modified K–H wave theory liquid-carrying model was developed by taking into account the impacts of liquid production rate and well inclination angle based on the experimental data, the K–H wave theory, the cross-section actual gas velocity, and the angle correction correlation formula. The improved liquid-carrying model is in good accordance with the test findings, according to the experimental results. In Shunan Gas Mine, Sichuan, China, there are eight deep shale gas wells, which produced a total of 25 sets of tests. The modified model was used to forecast and diagnose the liquid-carrying capacity in the entire wellbore of these wells. The diagnosis results are in good agreement with the actual production situation, and the coincidence rate is 92%. Full article

In recent years, the water–sand composition of the Yangtze River channel has changed due to the influence of human factors, especially the construction of water reservoirs such as the Three Gorges Project. Changing water–sand conditions have a long-term impact on the shaping of the river channel morphology in the middle and lower reaches of the Yangtze River, and the erosion retreat of local river sections has caused great harm to embankment projects. This paper focuses on the river evolution mechanism of the river channel from Chenglingji to Datong in the middle and lower reaches of the Yangtze River over the past 31 years. Landsat remote sensing images from 1989–2019 were used to extract and interpret water bodies, river shorelines, and central bars in the study area using the Modified Normalized Difference Water Index (MNDWI) combined with visual interpretation. We used near analysis to study the morphological evolution characteristics of the river, the channel, and selected typical river reaches for comparative analysis. We found out that the overall change in river morphology between 1989 and 2019 was small in the horizontal direction, but the local area changed significantly. Considerable scouring occurred in the vertical direction. Combining hydrological and meteorological data, we investigated the effects of the Three Gorges Dam, instream sand mining, boundary conditions, vegetation cover on both sides of the riverbanks, and aspects of storm flooding in the watershed on the evolution of the river. The study indicated that the geological conditions on both sides of the river, the implementation of the bank protection project, and the improvement of vegetation cover on both sides of the river have made the riverbanks more resistant to scouring. However, heavy rainfall floods, the operation of the Three Gorges Reservoir, and sand mining activities in the river channel make the river channel more susceptible to scouring. Based on the calculation of the slope change rate of the accumulated volume, it was found that the runoff is mainly influenced by precipitations, while the sand transport is mainly affected by human activities. This study shows that natural and anthropogenic activities affect the equilibrium state of the river’s water and sediment to varying degree. Full article

The mining-induced ground response (MIGR) has a critical impact on safety management, the mining plan, and entry support. A clear understanding of the characteristics is the foundation of the MIGRs scientific control. This study is the result of the MIGRs development of the non-pillar mining panel with gob-side entry by roof cutting (GSERC). Comprehensive research of the in situ measurements, numerical simulation, and theoretical analysis to determine the ground response characteristics, including mining panel and GSERC, were implemented. The results indicate that the MIGR presents the characteristic of asymmetric development and that the ground response near the non-roof cutting side is more significant than that near the roof cutting side. The development stage of the entry convergence of GESRC can be divided into seven stages; the primary rapid development stage should be paid more attention to in the support process. The entry convergence rapidly increases to 275 mm, 380 mm, 410 mm, and 525 mm, respectively, for the roof cutting rib to the virgin coal rib, the roof near the virgin coal side, the roof of the middle section, and the roof near the cutting side. The hydraulic support end cycle resistance at the roof cutting side and the middle section of the mining panel with the value of more than 30.8 MPa is greater than that at the non-roof cutting side with the value of less than 26 MPa, which presents the asymmetric feature. The numerical simulation results regarding vertical stress development, vertical displacement, and horizontal displacement also presents the asymmetric feature. The MIGR division is divided into five divisions. Division II (the middle section of the panel) and division IV (the entry range near the roof cutting side) should be paid more attention to in the panel mining process. The results of this study can provide technical guidance and theoretical reference for similar engineering practices. Full article

The disturbance depth of traffic load has a direct impact on the stability of a room-and-pillar mining goaf. To quantitatively calculate the relationship between the traffic load disturbance depth and influencing factors, 49 groups of horizontal combinations of different influencing parameters are designed in this study, based on the orthogonal experimental design method. Midas GTS is used to simulate and obtain the corresponding traffic load disturbance depth data. A multivariate linear regression analysis of the traffic load disturbance depth is conducted, and a regression formula for calculating the traffic load disturbance depth is established. According to the traffic load disturbance depth, goaf depth, and the stability of the roof, coal pillar, and base plate under traffic load conditions, a judgment flow of the room-and-pillar mining goaf treatment method under traffic load conditions is established, and it is applied to the reconstruction and expansion project of the Jixi section of the Dan-A national highway. The results show that a geogrid can be used for treatment purposes when the traffic load disturbance depth is 1.5 times lower than the depth of the room-and-pillar mining goaf, or when the traffic load disturbance depth is 1.5 times greater than the depth of the room-and-pillar mining goaf but the roof, coal pillar, and base plate are stable. Additionally, grouting is needed for treatment in other cases. The results of this study can provide a scientific basis for the selection of treatment methods for room-and-pillar mining goafs underlying highways in the future. The results are of great significance in the field of engineering for the safety measures concerning highway room-and-pillar mining goafs. Full article

Trapezoidal roadways in large inclination coal seams show asymmetrical tectonic characteristics, while there is still a lack of theoretical results on stress, deformation, and efficient and effective supporting methods on high walls. In this paper, based on the geological characteristics of a large, inclined coal seam roadway, a mechanical model for stress–deformation analysis of trapezoidal section roadway was established. Complex analysis and a comfort map were employed to investigate the stress and deformation distribution on the roadway surface, and a novel yielding prop with high load capacity and constant working resistance was employed to support a high wall side based on analytical results. The results are as follows: (1) The deformation of the high wall is larger than that of the low wall, and the deformation of the roof is larger than that of the floor. The overall deformation of the surrounding rock shows that the rib closure is larger than the roof-to-floor closure. (2) The stress of the surrounding rock shows that both horizontal and vertical stresses are highest in the upper corner, indicating that the broken zone is most likely to occur at this location. (3) A new support employed with a high-yielding prop and a high-strength cable in a large, inclined angle roadway is proposed. On-site experiments were conducted in a large 5-1081 roadway of a coal mine in Shanxi, China. Under the influence of mining disturbance, the deformations at the top corner decreased by 40% compared with before. The test results show that the new support scheme can effectively control the development of roadway deformation and damage during the mining process. The new support also shows friendly environmental support and fast installation. Full article