Mechanism of Rockburst Prevention in Deep Thick Coal Seams with Cemented Paste Backfill: A Case Study

The aim of this study is to explore a safe mining method to effectively excavate the deep thick coal seams in rockburst-prone mines. Based on the theory of elastic foundation and geological conditions of the Xinhe Coal Mine, the cemented paste backfill (CPB) is proposed to prevent rockburst. In this study, the roof fracture mechanism of block caving mining (BCM) and CPB methods are established. Then, the stress evolution of the surrounding rock and the subsidence of roof strata with these two methods are compared. The results show that the maximum bending moment appears in the middle of the roof, and the value is far below the critical bending moment of the roof by using the CBP. While using the BCM, this value exceeds the critical bending moment of the roof, which may trigger rockburst-related problems. In addition, there is no first weighting and periodic weighting phenomena by using the CPB method as the overburden pressure is gradually transferred to the backfill body, resulting in a safer mining condition. Furthermore, the engineering application indicates that the frequency of daily microseismic events and the burst energy are significantly reduced by using the CPB.

Research on the Mechanism of Main Roof Advanced Breaking and Supporting Technology When Long-wall Face Passing Through Abandoned Roadways

Unlike general long-wall mining, the roof activity is more intense when long-wall face passes through the abandoned roadway. Technically, the coal pillar between the abandoned roadway and the long-wall face will suddenly fail with a certain critical value of its width, leading to the roof breaks in advance and other production-restricted problems because of the support loss, which will be a great threat to underground mining activities. In order to guarantee a safe mining condition, therefore, it is greatly necessary to uncover how the roof breaks in advance and how to cope with it. From the stability maintaining of the key block perspective, this paper took for research that the 12404-1 long-wall face of Wulanmulun coal mine, China. The critical value of the coal pillar’s width was determined to be about 5m by theoretical analysis, likely, the appropriate support force of the abandoned roadway’s roof is about 4020KN per meter. Meanwhile, a numerical simulation method was adopted to study the ground pressure when the long-wall face passing through the abandoned roadway. Correspondingly, a compound supporting technology involving the roof presplit technique, anchor cable supporting and pumping pillar supporting were proposed for the roof of the abandoned roadway, and it practically worked well.

Research on Optimization of a Solid Filling Mining Face Layout Based on a Combined Clamped Beam Model

Optimizing the mining scheme is an essential work for improving recovery efficiency of filling mining. An optimization equation of mining face width under a gangue mining condition is derived firstly. Then, analysis of the optimization equation of the mining face width is carried out based on the measure data of the F5001 mining face in the Tangshan Coal Mine. At last, the reasonable mining face width is determined combined with numerical simulation. Results show that mining face width and roof subsidence increase with the increase of unit weight and mining depth, but decrease with the increase of the elastic modulus of roof. The maximum width of the mining face is 105 m in Tangshan Coal Mine. When the mining width increases from 66 to 105 m, the increasing percentage of roof subsidence is 15–18%. Roof subsidence is controlled less than 30% of the mining height. The variation range of the maximum roof subsidence is small, which means the mining face width can be designed reasonably through the proposed equation.

Applications of Geophysical Logs to Coal Mining—Some Illustrative Examples

Geophysical logs can be used not only for qualitative interpretation such as strata correlation but also for geotechnical assessment through quantitative data analysis. In an emerging digital mining age, such a use of geophysical logs helps to establish reliable geological and geotechnical models, which reduces safety and financial risks due to geological and geotechnical uncertainty for new and existing coal mining projects. This paper presents some examples of geological and geotechnical characterizations from geophysical logs at various coal mines in Australia and India. The applications include rock strength and coal quality estimations, automated lithological/geotechnical interpretation and geophysical strata rating, all based on geophysical logs. These derived parameters could provide input to modelling, control, even ‘digital twin’ generation in a form of geological and geotechnical models as part of the future digital mining. The outcomes can be visualized in 3D space and used for identifying the key geotechnical strata units that are responsible for caving behaviors during longwall mining. This could assist site geologists and planning and production engineers predict and manage mining conditions on an ongoing basis. Both conventional logs such as density, natural gamma and sonic and less common logging data, such as full waveform sonic, televiewer and SIROLOG spectrometric natural gamma logging data are examined for their potential applications. The geotechnical strata classification and rock strengths predicted from the geophysical logs match the laboratory tests, drill core geotechnical strata classification, core photos and the mining condition/behavior observed. These illustrate the usefulness and effectiveness of using geophysical logs for geological and geotechnical characterizations.

Performance evaluation of continuous miner based underground mine operation system: An OEE based approach

CM is a globally renowned machine, designed to work as a mass production technology for underground coal. Different major coal producers across the globe are using this technology for decades to produce underground coal efficiently. India is also one of the major players globally in the arena of coal production and adopted this cutting edge technology since last decade by implementing at. few of the selective underground coal mining projects. Performance of CM technology is influenced by the geo-mining condition, fleets of other ancillary units and reliability of subsystems while implementation of this system depends largely on the extent of reserve. These aspects generate a scope of large scale research and development in this field. Overall Equipment Effectiveness (OEE) is the parameter to benchmark the equipment performance globally. OEE is the product of equipment availability, performance and product quality. This mining machine based paper focuses on the Overall Equipment Effectiveness (OEE) of the complete CM based operation to identify the vulnerable systems, which helps to design proper preventive maintenance programme. The CM based system is divided into few subsystems, such as; electrical, cutter, gathering arrangement, traction, hydraulic, chassis, feeder breaker, shuttle car, CM conveyor and out-bye conveyor. The downtime data used for this analysis is collected from an underground coal mine situated in the central part of India, belongs to one leading coal producing company of the country. From analysis it was found that, electrical systems and conveyors are among most vulnerable systems and deserves more care during maintenance. On the basis of these results recommendations are made to redesign the Preventive Maintenance Programme, in order to avoid the lower availability as well as lower OEE.

Lifi Based Audio Communication for Coal Mine Parameter Monitoring and Automatic Control System

Li-Fi (Light Fidelity) is a quick and shoddy optical rendition of correspondence. The principle segments of this correspondence framework are a high power white LED which goes about as a correspondence source and a silicon Photo diode which demonstrates great reaction to noticeable wavelength locale filling in as the getting component. An essential factor while planning Li-Fi is Line of Sight (LoS). The LED can be turned on and off to create advanced series of 0s. Information is coded in the light which changes into new information by shifting the glinting rate of the LED. Since the speed of the light is exceptionally quick, the transmitted yield is gotten as voice signs to the specialists at the coal mineshaft. Coal mining and oring includes the disclosure of coal and its troublesome works of extraction, notwithstanding its evacuation and deal in the generation of concrete industry. Most wounds occurring in the underground mines incorporates the falling of rocks, slips and blasts. Harmful gas is produced amid the season of mining and oring forms. The mining laborers are influenced by lung illness by breathing in residue and lethal gas in Coal mining condition. This data is implied to the specialists at the coal mineshaft from the higher authorities through Li-Fi as a voice motions in this work

Surface Subsidence Prediction Method for Coal Mines with Ultrathick and Hard Stratum

Overburden conditions consisting of ultrathick and hard stratum (UTHS) are widespread in China and other countries, but existing surface subsidence prediction methods ignore the strong impact of UTHS on surface subsidence. They are thus not applicable for surface subsidence prediction for coal mining with the presence of UTHS. We conducted actual measurements of surface and UTHS subsidence in the Tingnan Coal Mine. The results showed that under the UTHS mining condition, the required gob dimension is much larger than the empirical value when the surface reaches sufficient mining and that the actual measured maximum value of surface subsidence is much smaller than the empirical value. The UTHS subsidence is approximately equal to the surface subsidence. The movement of UTHS has a strong impact on surface subsidence and has a controlling function for it. It was proposed that surface subsidence could be approximately predicted by calculating the UTHS subsidence. The UTHS movement characteristics were studied using Winkler’s theory of beams on an elastic foundation, the subsidence prediction equation of the main sections in the strike and dip directions was obtained under different mining dimensions, and the subsidence prediction equation of any arbitrary cross section parallel to the two main sections was established. Then, the surface subsidence prediction method for coal mining with the presence of UTHS was developed, and the influences of UTHS thickness, strength, and layer position on the surface subsidence were discussed. The Tingnan Coal Mine was taken as an example, and the subsidence curves of the strike and dip main sections were calculated using different mining dimensions. Subsequently, the surface subsidence after the mining of working faces 204, 205, 206, and 207, respectively, was predicted, and the prediction method was verified by comparing the results with the measured surface subsidence results of working faces 204, 205, and 206.

Evolution Characteristics of Composite Pressure-Arch in Thin Bedrock of Overlying Strata During Shallow Coal Mining

Under the shallow coal mining condition and based on the cracking and movement rules of the roof in different mining stages, the mechanical models of symmetrical pressure-arch, stepped pressure-arch, rotating-squeezed pressure-arch in the mining field were established. Then, the instability criterion of each pressure-arch structure was derived. Through the similarity material experiment and numerical simulation, the evolution characteristics of the composite pressure-arches in the near- and far-field were revealed. Results show that the stepped pressure-arch in broken blocks of the basic roof was formed when the horizontal principal stress was greater than the in-situ stress. The broken blocks’ sliding could induce roof cutting off and strong weighting load. The structural characteristics of the overlying strata were determined by the thickness of the bedrock. The upper broken rocks formed a symmetrical pressure-arch in the near- and a far-field pressure-arch formed in the mining field. The median periodic broken rocks formed the rotating-squeezed pressure-arch, bearing the load of the loose layers and protecting the mining panel. After all bedrocks breaking, the latter arch foot of the far-field pressure-arch was transferred to the compacted caving zone. This study can provide a theoretical reference for the similar mining engineering.