Rock Mining Research Articles

Numerical modelling of rock fragmentation under high in-situ stresses and short-delay blast loading

Since the invention of electronic detonators with a delay accuracy within 1 ms, short-delay blasting technology has been used in mining and tunnelling engineering to improve rock fracturing and control blast-caused vibration. However, the fragmentation characteristics of pre-stressed rock under short-delay blast loading have not been studied in detail. In this study, the interaction between the short-delay blast loading and static in-situ stress is investigated using a FEM-based modelling method and image-processing approach. Firstly, single-hole blasting tests were conducted in an underground roadway with a burial depth of 620 m. Subsequently, a single-hole blasting model was developed in LS-DYNA and validated against one of the experimental results, a two-hole delay blasting model was established to simulate rock fracture and fragmentation under different delay times and in-situ stresses. Finally, the underlying mechanism of in-situ stress affecting the optimum delay time was theoretically analyzed and an analytical solution for optimum delay was proposed. The tested results show that under a borehole length and charge weight of 1 m and 1.5 kg, respectively, the average fragment size is approximately 10.5 cm, and the crater radius and depth are 0.67 m and 0.96 m, respectively. The numerical results indicate that both of average fragment size and fragment size distribution range significantly increase with the increase of in-situ stress, while they first decrease and then increase with the increase of short delay times. Moreover, there is a specific delay window ranging from 0.5 to 3 ms where short-delay blasting improves fragmentation performance, and the optimum delay time increases with the increase of in-situ stress. The findings of this study can aid in improving the efficiency and safety of blasting operations in deep hard rock mining.

Monitoring and evaluation of disaster risk caused by linkage failure and instability of residual coal pillar and rock strata in multi-coal seam mining

Comprehensive research methods such as literature research, theoretical analysis, numerical simulations and field monitoring have been used to analyze the disasters and characteristics caused by the linkage failure and instability of the residual coal pillars-rock strata in multi-seam mining. The effective monitoring area and monitoring design method of linkage instability of residual coal pillar-rock strata in multi-seam mining have been identified. The evaluation index and the risk assessment method of disaster risk have been established and the project cases have been applied and validated. The results show that: ①The coal pillar will not only cause disaster in single-seam mining, but also more easily cause disaster in multi-seam mining. The instability of coal pillars can cause not only dynamical disasters such as rock falls and mine earthquakes, but also cause surface subsidence and other disasters. ②When monitoring the linkage instability of residual coal pillar-rock strata, it is not only necessary to consider the monitoring of the apply load body (key block), the transition body (residual coal pillar) and the carrier body (interlayer rock and working face), but also to strengthen the monitoring of the fracture development height (linkage body). ③According to the principles of objectivity, easy access and quantification, combined with investigation, analysis, and production and geological characteristics of this mining area, the main evaluation indexes of the degree of disaster caused by linkage instability of residual coal pillar-rock strata are determined as: microseismic energy, residual coal pillar damage degree, fracture development height. And the evaluation index classification table was also given. ④According to the measured value of the evaluation index, the fuzzy comprehensive evaluation method was used to calculate the disaster risk degree in the studied mine belongs to class III, that is, medium risk level. The corresponding pressure relief technology was adopted on site, which achieved a good control effect, and also verified the accuracy and effectiveness of the risk evaluation results.

Extra‐terrestrial resources: A potential solution for securing the supply of rare metals for the coming decades?

The forthcoming energy transition driven by the need to reduce CO2 emissions requires large amounts of critical elements to construct renewable energy devices such as car batteries, wind turbines and solar panels. For many elements such as Li, Co, REEs and Ti, the production sources are located in countries with poor social and environmental standards, prone to political destabilization such as military conflicts, or vulnerable to strained relationships with consumer countries. Lately, the volatile geopolitical context has further demonstrated the high dependency of Europe and other developed countries in terms of raw material supply. In addition, there is a debate about the Earth's potential to sustain the transition toward a green society by using conventional resources from mining of terrestrial rocks. As nature conservation and climate mitigation are now priorities for the majority of governments, and since conventional mining on Earth suffers from a growing social resistance, humankind may need to look toward new frontier resources for supplying the mineral needs of the coming decades. Here, we explore the use of extra‐terrestrial resources as a potential source to feed the future supply of critical metals. Extra‐terrestrial mining may be an opportunity for wealth creation and an option for critical metal resource supply when mining on Earth becomes increasingly untenable. We conclude that the potential impacts of extraction and exploitation of space resources, both good and bad, could be societally profound.

Comparison of circulating and excreted metals and of autoimmunity between two Great Plains Tribal communities

Metals contaminants of the environment from mine waste have been implicated as contributing agents in autoimmune disease. The current study compares metals and autoimmunity in two Tribal communities residing in the Black Hills and the Bighorn Mountains geographical regions that are scattered with extant hard rock mines. With documented drinking water contamination in both communities, in vivo levels of more than half of the measured serum and urine metals differed between the two communities and were substantially different from their national median values. Serum autoantibodies associated with systemic autoimmune disease were rare or at low-level, but antibodies to denatured (single-stranded) DNA and thyroid-specific autoantibodies were commonly elevated, especially in women. A three-tier statistical modeling process was carried out to examine individual metals exposure as predictors of autoantibody levels. For the most part only weak positive associations between individual metals and systemic autoantibodies were found, although univariate quantile regression analysis showed positive statistical associations of serum lead and antimony with anti-chromatin and anti-histone autoantibodies. Using age and gender-adjusted multivariable statistical models, metals did not predict anti-thyroglobulin or -thyroid peroxidase significantly and metals were generally negative predictors of the other autoantibodies. Overall these results suggest that elevated levels of environmental metals and metalloids in these communities may result in suppression of autoantibodies associated with systemic autoimmune disease.

Life on the edge-a changing genetic landscape within an iconic American pika metapopulation over the last half century.

Declines and extirpations of American pika (Ochotona princeps) populations at historically occupied sites started being documented in the literature during the early 2000s. Commensurate with global climate change, many of these losses at peripheral and lower elevation sites have been associated with changes in ambient air temperature and precipitation regimes. Here, we report on a decline in available genetic resources for an iconic American pika metapopulation, located at the southwestern edge of the species distribution in the Bodie Hills of eastern California, USA. Composed of highly fragmented habitat created by hard rock mining, the ore dumps at this site were likely colonized by pikas around the end of the 19th century from nearby natural talus outcrops. Genetic data extracted from both contemporary samples and archived natural history collections allowed us to track population and patch-level genetic diversity for Bodie pikas across three distinct sampling points during the last half- century (1948-1949, 1988-1991, 2013-2015). Reductions in within-population allelic diversity and expected heterozygosity were observed across the full time period. More extensive sampling of extant patches during the 1988-1991 and 2013-2015 periods revealed an increase in population structure and a reduction in effective population size. Furthermore, census records from the last 51 years as well as archived museum samples collected in 1947 from a nearby pika population in the Wassuk range (Nevada, USA) provide further support of the increasing isolation and genetic coalescence occurring in this region. This study highlights the importance of museum samples and long-term monitoring in contextualizing our understanding of population viability.

Modelling the loosening of rock in the experimental rock mining method

Analytical description of the process of rock discontinuity caused by the operation of an experimental cutting head, in which a combination of cutting and loosening methods was used, is presented. Loosening of the rock fragment takes place after reaching the tensile or shear strength of the rock, what is more favourable compared to the classical mining methods. An analytical model of the stress in the crack initiation plane was developed using the models of rock loosening using the disc tools and relationships formulated in fracture mechanism. The special integral of the differential equation of the loosening line was determined by geometric integration. Numerical simulations of the chip loosening were also carried out using the model of the solid rock built using the Finite Element Method. The developed models of losing the rock continuity were used in numerical simulations of loosening the rock fragment to analyze the impact of the selected parameters of the mining technology, of the rock properties and geometrical features of the experimental cutting head, on the shape of the loosening line and its extend. Using the stand test results, the qualitative compliance of the shape of the loosening line, determined using the analytical model and the numerical model, with the geometrical features of the rock chips obtained in the laboratory, was confirmed. It was found that the proper selection of the design features of the cutting head, such as: a small angle of the loosening disc and a small angle of inclination of the head axis, cause a qualitative increase in the loosening range.

Present Situation and Research Progress of Comprehensive Utilization of Antimony Tailings and Smelting Slag

The production process of antimony produces a large amount of solid waste, such as waste rock in mining, tailings in the beneficiation, metallurgical slag in the smelting, and so on. At present, most of these solid wastes are currently in storage, and the storage of a large amount of solid wastes is not only harmful to the local ecological environment but also a waste of resources. In view of this situation, this paper will take antimony tailings and metallurgical slag as examples and summarize them according to their different treatment methods. The comprehensive utilization of antimony tailings is mainly recovering metals by beneficiation and metallurgy and using antimony tailings as building materials and underground filling materials, while the comprehensive utilization method of antimony metallurgical slag is mainly the recovery of valuable metals by pyrometallurgy or hydrometallurgy or the stabilization technology. This paper summarizes the advantages and disadvantages of different treatment methods and puts forward the prospect of future research directions for the treatment of different metallurgical slags and tailings.

Study of the Failure Mechanism of Soft Rock Mining Roadways Based on Limit Analysis Theory

To study the deformation and failure mechanisms of soft rock mining roadways, the 1506 return airway of Anyang Coal Mine is taken as the engineering background. Based on limit analysis theory, a failure model based on a rigid slider system is constructed to assess the failure of the soft rock surrounding a roadway. The formulas for calculating the self-weight power of the slider in the velocity discontinuity line of the rock surrounding the roadway, the work power of the surrounding rock pressure, and the energy dissipation rate of the velocity discontinuity line are derived, and the upper limit objective function of the velocity discontinuity line height is obtained. The failure characteristics and fracture evolution process of the surrounding rock under different mining stresses are analyzed by means of physical similarity simulations. The simulation results show that shear failure occurs first on the roadway side due to stress concentration. The fissures expand along the bottom angle of the roadway to the blind support area and the low-intensity support area. The cracks weaken the support strength of the angled anchor cable and bolt in the roadway shoulder. Under the action of roof pressure, the status of the rock mass inside and outside the shear slip zone changes from static to dynamic. This causes deformation and failure of the roadway roof, side, and floor.

Study on segmentation of blasting fragment images from open-pit mine based on U-CARFnet.

Bench blasting is the primary means of production in open-pit metal mines. The size of the resulting rock mass after blasting has a significant impact on production cost. Currently, the ore fragment size is obtained mainly through manual measurement or estimation with the naked eye, which is inefficient and inaccurate. This study proposes the U-CARFnet and U-Net models for segmenting blasting fragment images from open-pit mines based on an attention mechanism, residual learning module, and focal loss function. It compares this technique with traditional image segmentation ones and a variety of deep learning models to verify the efficacy of the proposed model. Experimental results show that the accuracy of the U-CARFnet model proposed in this paper reaches 97.11% in the performance evaluation, which shows better performance than the traditional image segmentation method. In this study, the U-CARFnet model is used in the application, and a superior performance is obtained, with an average segmentation error of 5.46%. The proposed approach provides an effective technique for statistically analyzing images of mine rock.

Bibliometric Analysis of Research Progress and Perspectives of Deep Underground Rockburst Using Knowledge Mapping Method

In order to ensure the successful construction and stable operation of deep engineering projects, significant progress has been made in researching deep underground rockburst issues from various perspectives. However, there have been few systematic analyses of the overall research status of deep rockburst to date. In this study, a bibliometric approach using CiteSpace software (version 6.2.R3) was employed to visualize and analyze knowledge maps of 353 research articles on deep rockburst collected from the Web of Science core database from 1996 to 2022. The results show that the number of publications experienced exponential growth after an initial stage of budding and peaked in 2016. In terms of collaboration, China plays an absolute central role. The top three highly cited journals were the International Journal of Rock Mechanics and Mining Sciences, Rock Mechanics and Rock Engineering, and Tunneling and Underground Space Technology. In the keyword co-occurrence analysis, the keyword “prediction” had the highest frequency of occurrence in the past two decades, indicating it as the major research focus in deep rockburst studies. The keyword co-occurrence clustering analysis revealed eight clusters, including conventional criteria, acoustic emission, geology, seismic velocity tomography, dynamic disturbance, and others, representing the primary research topics. This study provides a comprehensive analysis of the current research progress and development trends of deep underground rockburst, helping to understand the key areas of focus in this field and providing potential prospects for future investigations for researchers and practitioners.

Stability mechanisms of soft rock mining roadways through roof cutting and pressure relief: an exploratory model experiment

IntroductionSoft rock mining roadways are severely deformed and damaged during coal mining. Blindly increasing the support strength not only has little effect but also wastes material resources.MethodsMaintaining the original support parameters, model experiments were conducted to investigate the mechanism of pressure relief protection of the front soft rock mining roadway by cutting the roof behind the longwall face. The roof-cutting height was 2.5 times the coal thickness, the angle was 10°, and the advance distance is 0. ResultsThe study found that the abutment stress borne by the roof of the original roadway was transferred to the coal seams to be mined. The average stress of the coal seams increased by 10%, while the average stress of the surrounding rock in the front roadway decreased by 12.57%. The roof cutting weakened the influence of the overlying strata in the gob on the rear roadway. The stability of the rear roadway also weakened the traction effect on the front roadway. The vertical convergence of the front roadway decreased by 27.3%, and the deformation of the coal pillars decreased by 15.7%.DiscussionThe roof cutting reduced the stress of the front roadway to the peak failure stress, fundamentally weakening the main factor that induced the deformation of the front roadway. Numerical simulations were performed to research the deformation and stress distribution properties of the surrounding rock after roof cutting, and the model experimental results were validated. Finally, engineering recommendations are presented, which are expected to provide a reference for controlling the roadway stability of soft rock masses.

Assessment of Rock Engineering Risk Management Frameworks Used in Underground Mines

Over 40% percent of the accidents encountered at Unki Mines are related to ground failure and other geotechnical complications. This research sought to address the monetary losses incurred in revenue and productivity through absenteeism and injury. With the development of mine production in Zimbabwe, the depth of mines gradually increased, and the ecological environment developed complex conditions. Deep mining unlike shallow mining is characterized by extra ground pressure, more gas, and faster deformation rates. These factors affect the safety of mining production. Therefore, as the mining depth and breadth increase, the difficulty of mine rock engineering is also increasing. The deepening of mining depth and the improvement of the mechanization level have brought increasing difficulties regarding the stability of surrounding rock hence risk issues arise. The ultimate objective of this study was to ensure a robust design of support systems at Unki Mine that would eventually reduce the risks associated with rock engineering excavations. Findings from the study and its analysis established the following conclusions. On the fore is the fact that hanging wall instability at Unki Mine are predominantly governed by geological and span attributes. The computed k value is 7% less the k value of 57.33 MPa used for existing pillars. An analysis of FOS and its relationship with recovery and Pillar W/H ratio shows that over-break has a huge impact on the span stability hence the effect of the ANFO need to be reviewed for an alternative explosive that ensures recovery within 80% range to ensure that the FOS is maintained above 1.6. A decrease in FoS increases the probability of failure, hence it is also important to device a pillar support system that is less prone to effects of over-break since the ground conditions are poor.

Lead isotopes and rare earth elements geochemistry of global phosphate rocks: Insights into depositional conditions and environmental tracing

Phosphate rock bears both geologically and environmentally significant information. Rare earth elements and yttrium (i.e., REY) characteristics have been commonly used for reconstructing the redox conditions of depositional environments and the effects of post-depositional diagenetic alteration on phosphate rock. In addition, phosphate rock is typically enriched in a range of trace elements such as uranium (U) and cadium (Cd) that can be dispersed as contaminants into the environment with phosphate mining and phosphate fertilizer application. Here we report the lead (Pb) isotope compositions combined with Pb and REY concentrations of both global sedimentary and igneous phosphate rocks, aiming to evalute the geological origin of phosphate rocks over time and the potential of using them for environmental tracing. Phopshate rock samples analyzed in this study were sourced from major economic phosphate deposits in the world, including China, Southern Tethys (e.g., Morocco, Tunisia, Israel), the U.S., India, South Africa and Russia. Our results show a wide range of 208Pb/204Pb (35.70 to 60.58), 207Pb/204Pb (15.20 to 18.25), and 206Pb/204Pb (16.369 to 71.806) ratios in the phosphate rocks, with sedimentary phosphate rocks being significantly more radiogenic than igneous rocks. The majority of sedimentray phosphate rocks show a notable isotopic overprinting by non-radiogenic terrestrial Pb, except for those from Israel and Morocco that have the most radiogenic Pb isotope compositions. Correspondingly, phosphate rocks with more radiogenic Pb isotope ratios show relatively pristine seawater REY features, likely suggesting their preservation of the original oxic seawater conditions and/or minimal diagenetic alteration. In contrast, phosphate rocks with less radiogenic Pb isotope compositions show REY indications for more anoxic seawater redox conditions and/or greater diagenetic alteration. We further evaluate the potential utility of Pb isotopes for tracing the associated contamination with phosphate rock mining and fertilizer application in the environment. In most cases, the radiogenic Pb isotope composition of phosphate rocks and corresponding P-fertilizers is distinctive from both natural crustal Pb and major anthropogenic Pb sources (e.g., Pb ore deposits and pesticides), which provides a great advantage for applying Pb isotopes as an environmental tracer for metal(loid) contamination from phosphate sources. The combination of Pb isotope ratios and REY proxies could further constrain the Pb source discrimination. Overall, this study provides new Pb isotopic and REY geochemical data on global phosphate rocks and fertilizers, which lays the groundwork for future regional and local studies on both their geological and environmental implications.

Cadmium accumulation in paddy soils affected by geological weathering and mining: Spatial distribution patterns, bioaccumulation prediction, and safe land usage

The abnormal enrichment of cadmium (Cd) in soil caused by rock weathering and mining activities is an issue in southern China. Although the soil Cd content in these regions is extremely high, the bioavailability of Cd in the soils differs significantly. The carbonate area (CBA) and tin-mining area (TIA) in Hezhou City were investigated to determine the primary features of soil Cd mobility in these regions and improve environmental management. Lateral and vertical spatial distributions revealed different accumulation and migration mechanisms of soil Cd in the CBA and TIA. Further analyses revealed that mining activities and geological weathering resulted in different soil geochemical parameters, thus yielding significantly lower levels of Cd in rice grains in the CBA than in the TIA. The random forest (RF) model predicted the bioaccumulation factor (BAF) (R2 = 0.69) better than the support vector machine (SVM) model (R2 = 0.68). Subsequently, a novel land management scheme was proposed based on soil Cd and the prediction of Cd in rice to optimize the spatial resources of agricultural land and ensure the safety of rice for consumption. This study provides a novel approach for land management in Cd-contaminated areas.

Coal Mine Rock Burst and Coal and Gas Outburst Perception Alarm Method Based on Visible Light Imagery

To solve the current reliance of coal mine rock burst and coal and gas outburst detection on mainly manual methods and the problem wherein it is still difficult to ensure disaster warning required to meet the needs of coal mine safety production, a coal mine rock burst and coal and gas outburst perception alarm method based on visible light imagery is proposed. Real-time video images were collected by color cameras in key areas of underground coal mines; the occurrence of disasters was determined by noting when the black area of a video image increases greatly, when the average brightness is less than the set brightness threshold, and when the moving speed of an object resulting in a large increase in the black area is greater than the set speed threshold (V > 13 m/s); methane concentration characteristics were used to distinguish rock burst and coal and gas outburst accidents, and an alarm was created. A set of disaster-characteristic simulation devices was designed. A Φ315 mm white PVC pipe was used to simulate the roadway and background equipment; Φ10 mm rubber balls were used to replace crushed coal rocks; a color camera with a 2.8 mm focal length, 30 FPS, and 110° field angle was used for image acquisition. The results of our study show that the recognition effect is good, which verifies the feasibility and effectiveness of the method.

Evaluating Fractal Damage and Acoustic Emissions of Soft Rock–Coal Combinations in a Deep Mining Area

Weakly cemented soft rock mines in the Ordos Basin are susceptible to mining disasters, including roof collapse and substantial deformation of surrounding rocks, during coal mining operations. Researching the damage characteristics of structures composed of low-strength “soft rock–coal” combinations is crucial for effectively preventing and controlling disasters in deep soft rock mining. To investigate the fractal damage characteristics of soft rock–coal combinations with different height ratios, uniaxial compression tests were conducted on specimens containing soft rock percentages of 20%, 40%, 50%, 60%, and 80%. The results show that the uniaxial compressive strength and modulus of elasticity of the soft rock–coal combinations increased with increasing proportions of soft rock. The soft rock–coal combination was clearly segmented, and the 40%, 50%, and 60% soft rock–coal combinations had good self-similarity. The fractal dimensions were 2.374, 2.508 and 2.586, which are all within the interval [2, 3]. When the percentage of soft rock was 20%, the specimen damage yielded flaky coal bodies with smaller grain size, whereas the coal–rock interface was spalled by small conical rock bodies. As the soft rock proportion increased, the percentage mass of fragments with particle size greater than 20 mm increased from 83.34% to 94.15%. The failure mode in soft rock–coal combinations is primarily attributed to the partial tensile splitting of the coal body. As the proportion of soft rock increased, there was a gradual reduction in the extent of coal body damage. Moreover, the acoustic emission absolute energies and counts decreased as the proportion of soft rock increased. The acoustic emission energy was reduced from 2.46 × 109 attoJ to 3.41 × 108 attoJ, and the acoustic emission counts were reduced from 18,276 to 7852.

Creep properties and constitutive model of salt rocks under a slow cyclic loading path

The construction of compressed-air energy storage (CAES) plants using the huge space created by salt rock mining is a key means of optimizing China's energy structure. The creep properties of salt rock are vital parameters for ensuring the long-term, stable operation of CAES plants. According to the operation mode of CAES plants, creep tests were conducted on salt rock under the influence of slow loading and unloading. The results indicated that the slow loading and unloading history locally changed the creep development process but did not affect the overall creep process. Additionally, the steady state creep rate of the salt rock depended mainly on the magnitude of external stress. Moreover, the creep test was monitored simultaneously using acoustic emission (AE) technology, and the distribution of the AE absolute energy during the initial loading phase and steady state creep phase satisfied the power law. To more accurately describe the creep characteristics of the salt rock under the influence of slow loading and unloading, a full-process creep constitutive model of salt rock was constructed using state variable, fracture expansion factor, and unloading factor.

Underground Development of Mineral Subsoil Using Microorganisms: A Mini-Review

This mini-review is devoted to the analysis of the current state of the relatively rarely used underground bio-mining of natural minerals. On the basis of this analysis, it is substantiated that bacterial leaching technology has no alternative for environmentally safe and economically break-even mining of ore-bearing rocks and off -balance metal-bearing formations that are difficult to access, or unprofitable for traditional methods. It is emphasized that the efficiency of biotechnology depends on the accuracy of modeling and operational control of the working parameters of the process of biological extraction of metals, for which it is necessary to develop a new combined hydro-technical system with the possibility of the reverse technological influence on the regimes of leaching. Such controlled modes of the process are the intensity of forced aeration, pH level of the bacterial solution, amount of nutrient medium, and duration of leaching. To improve the accuracy of prediction and control of underground microbiological development, the use of a control method based on an adaptive-network-based fuzzy inference system (ANFIS) is recommended.

Triaxial Compression Strength Prediction of Fissured Rocks in Deep-Buried Coal Mines Based on an Improved Back Propagation Neural Network Model

In deep coal mine strata, characterized by high ground stress and extensive fracturing, predicting the strength of fractured rock masses is crucial for stability analysis of the surrounding rock in coal mine strata. In this study, rock samples were obtained from construction sites in deep coal mine strata and intact, as well as fissured, rock specimens were prepared and subjected to triaxial compression tests. A numerical model based on the discrete element method was then established and the micro-parameters were calibrated. A total of 288 triaxial compression tests on the rock specimens under different conditions of confining pressure, loading rate, fissure dip angle, and fissure length, were conducted to obtain the triaxial compressive strength of the fractured rock specimens under different conditions. To address the limitations of traditional back propagation (BP) neural networks in solving stochastic problems, a modified BP neural network model was developed using a random factor and an interlayer mean square error corrected network model evaluation function. The traditional and modified BP neural network models were then employed to predict the triaxial compressive strength of the fractured rock specimens. Through comparative analysis, it was found that the modified BP neural network prediction model exhibited smaller errors and significantly reduced overfitting, making it an effective tool for predicting the strength of fractured rocks in deep coal mine strata.

The concept of forecasting the reclamation costin rock mining

The concept of forecasting the reclamation costin rock mining