Underground Coal Mining Systems Research Articles

A novel index for shearer system resilience in underground coal mines based on the operational environment

The use of resilience during the mining period by guaranteeing the safety and performance of the systems greatly helps the managers and engineers with their decision-making and designing different systems. During the last two decades, various studies have been conducted in this regard. However, the analysis of underground coal mining systems’ resilience has been rarely addressed by these studies. The present study aims to provide a quantitative index for resilience in the environment of underground coal mining operations based on the risk factors. To do so, in a case study of Tabas Mechanized Coal Mine, the Failure of shearer data and the stoppages caused by it (for 2 years and a half, from March 2017 to June 2019) were studied to analyze the system’s resilience. Then, the experts were surveyed. After collecting and categorizing the data, the data analysis calculations were done for indicators of reliability, maintainability, supportability, organizational resilience, PHM system efficiency, and economic resilience. Finally, a new quantitative index named the “Shearer System Resilience Index” was introduced. The results indicated that resilience is reduced over time. They also shows that in order to improve resilience, project managers should pay more attention to these indicators, especially the indicators of maintainability, and organizational resilience. Therefore, regarding the scope of the data investigated in the current study, the use of Failure of Shearer data-based risk factors and experts’ opinions for the analysis of resilience in the case study is strongly recommended.

Experimental and numerical study of coal-rock bimaterial composite bodies under triaxial compression

To accurately predict coal burst hazards and estimate the failure of coal pillars in underground coal mining systems, it is of great significance to understand the mechanical behavior of coal-rock bimaterial composite structures. This paper presents experimental and numerical investigations on the response of rock-coal, coal-rock, and rock-coal-rock bimaterial composite structures under triaxial compression. The triaxial compression experiments are conducted under confining pressures in the range of 0–20 MPa. The resulting inside fracture networks are detected using X-ray-based computed tomography (CT). The experimentally observed data indicate that the mechanical parameters of the rock-coal-rock composites are superior to those of the rock-coal and coal-rock combinations. After compression failure, the coal-rock combination specimens are analyzed via X-ray CT. The results display that the failure of the coal-rock composite bodies primarily takes place within the coal. Further, the bursting proneness is reduced by increasing confining pressure. Subsequently, the corresponding numerical simulations of the experiments are carried out by using the particle flow code. The numerical results reveal that coal is vulnerable with regard to energy storage and accumulation.

A Tightly Coupled GIS and Spatiotemporal Modeling for Methane Emission Simulation in the Underground Coal Mine System

Mine safety is of primary concern in the underground coal mining system. At present, there is a lack of an efficient platform to manage the numerical simulation procedure and inherent spatiotemporal data for coal mine disasters. This necessitates the coupling of spatiotemporal model with geographic information system (GIS) in practical application. Here, a novel spatiotemporal model tightly coupled with GIS is presented to improve the model-data integration. Such tight coupling is achieved by developing a lattice Boltzmann method (LBM) based turbulent model with an underlying shared FluentEntity model within the LongRuanGIS platform. The case study and comparison with the traditional computational fluid dynamics (CFD) method demonstrated that the platform is capable and effective in providing functionalities for lattice domain decomposition, simulation, visualization and analyses, as well as improving the computational efficiency. The proposed approach and platform, promising for the disaster prevention, offer a template for future GIS-Model integration and also applicable for other underground coal mine disasters.

A Case Study of an Optimized Intermittent Ventilation Strategy Based on CFD Modeling and the Concept of FCT

With the increasing operation costs and implementation of carbon tax in the underground coal mining systems, a cost-effective ventilation system with well methane removal efficiency becomes highly required. Since the intermittent ventilation provides a novel approach in energy saving, there still exists some scientific issues. This paper adopts the design concept of frequency conversion technology (FCT) to the ventilation pattern design for the first time, and an optimized intermittent ventilation strategy is proposed. Specifically, a real excavation laneway of a coal mine in China is established as the physical model, and computational fluid dynamic (CFD) approaches are utilized to investigate the spatiotemporal characteristics of airflow behavior and methane distribution. Plus, the period of intermittency and appropriate air velocity are scientifically defined based on the conception of FCT by conducting the parametric studies. Therefore, an optimized case is brought out with well methane removal efficiency and remarkable energy reduction of 39.2% in a ventilation period. Furthermore, the simulation result is verified to be reliable by comparing with field measurements. The result demonstrates that a balance of significant energy saving and the methane removal requirement based on the concept of FTC is possible, which could in turn provide good operational support for FTC.

Stability control of narrow coal pillars in gob-side entry driving for the LTCC with unstable overlying strata: a case study

In underground coal mining systems, the subsidence of unstable overlying strata (UOS) has a key effect on the deformation of narrow coal pillars that are contiguous to the caved zone. This paper investigated the failure mechanism of coal pillars by combining the in situ testing and numerical modeling methods. Several striking findings can be drawn. (1) Six fracture patterns exist in the in situ pillar, and their distribution divides the coal pillar into three zones, namely, the fracture zone, stable zone, and collapsed zone. (2) The stable zone, which has a width that accounts for one third of the pillar, is decisive to pillar failures. (3) The deformation of the contiguous pillar can be divided into two stages. Prior to the excavation of mining entry under the UOS, the pillar moves towards the caved zone. After the excavation, a reversed area (0 to 1.8 m) of the pillar moves back to the current panel, while the remaining area (1.8 m to 3.0 m) moves continuously to the caved zone. Consequently, a pillar-reinforcement method was proposed. It is concluded that the method and experience successfully practiced in the Baodian coal mine can be applied in other coal mine systems.

Mechanical Properties and Failure Behavior of Composite Samples

In underground coal mining systems, the occurrences of coal burst hazards and pillar failures relate not only to the condition of stress distribution but also the geometry of roof-coal-floor structures. To study the failure response of these structures, the rock-coal-rock (RCR) sample, in which a coal component is sandwiched between rocks, is always employed as the experimental subject. In this study, the effect of height ratio (a ratio represents the height percentage of coal component in an RCR sample) on the mechanical properties and deformation behavior of RCR samples was numerically investigated by using the distinct element model (DEM). The results reveal the following. (1) The uniaxial compression strength (UCS) of the RCR sample decreases with increasing height ratio as an inverse proportional function. (2) With increasing height ratio, the elastic modulus of the RCR sample decreases exponentially, while the postpeak modulus is strengthened in an inverse proportional manner. (3) Microcracking activity of the RCR sample is different from that of the pure sample during loading. Specifically, a reactive period always occurs after the quiet and active periods in the RCR sample. (4) The RCR sample fails in a progressive manner, in which cracking bands develop preferentially in coal and then extend to rocks. Expectably, the mechanical properties and failure behavior of RCR samples are height ratio dependent, which may contribute to predicting the hazard of coal bursts and estimating the failure of rock-coal-floor structures.

Failure response of composite rock-coal samples

To accurately predict coal burst hazards and estimate the failure of coal pillars in underground coal mining systems, it is of great significance to understand the static and dynamic mechanical behavior of rock-coal structures. In experimental scale modeling, rock-coal structures are usually considered as samples (typically φ50 mm × 100 mm) composed of rock or coal components. This work examines the coupled effects of height ratio (a ratio of the height of coal to the height of whole sample) and loading rate on the mechanical interactions of composite samples using granular dynamic models. Results show that: (1) The peak strength of the composite sample decreases with increasing height ratio, while the peak strength increases linearly with loading rate under uniaxial compression. (2) Both the height ratio and loading rate have a significant effect on the micro-cracking in the composite sample. Micro-cracking evolves with strain and this rate increases first slowly and then advances rapidly. (3) Composite samples fail in a progressive manner, and the failure of the coal components controls the collapse of the ensemble sample. Specifically, cracks develop preferentially in the coal and then propagate into the rock.

Coupled Effects of Moisture Content and Inherent Clay Minerals on the Cohesive Strength of Remodelled Coal

Injecting water into a coal seam to enhance the cohesive strength of coal and thus minimize and reduce the coal wall spalling risk must be considered in underground coal mining systems. In general, coal with low cohesive strength contains clay minerals which may affect the stability of coal by interacting with water. Therefore, the coupled effects of moisture content and inherent clay minerals on the physical properties (i.e., cohesive strength and internal friction angle) of coal samples should be addressed. In this paper, direct shear tests were conducted by remodelling the Yiluo coal with various moisture contents ranging from 6.6% to 20.7%. According to Mohr–Coulomb failure criterion, cohesive strength and internal friction angle of coal were obtained. Afterwards, effects of moisture content and clay minerals (i.e., Kaolinite, Smectite and Illite) on the cohesive strength of coal were analysed using X-ray diffraction (XRD) method. The results show that cohesive strength increases when the moisture content rises from 6.6% to 17.6%, after which it decreases with increasing moisture content. This trend can be well illustrated by the relationship between typical water retention curve (WRC) and suction stress of soil. Therefore, a moisture content of 17.6% would be an optimal value to enhance the stability of the Yiluo coal seam.

Categorization and standardization of accidental risk-criticality levels of human error to develop risk and safety management policy

In addition to increasing mechanization, technology upgradation and process automation, safety enhancement in systems operation is one of the key parameters of productivity improvement. Now, it is an established fact that human error plays a crucial role in accidents and needs to be addressed adequately in risk and safety management. This paper aims at assessing, categorizing and setting standards for human error risk and criticality of system activities. Based on the classification and standardizations of human error rate, consequences of human error and criticality index of errors, different policy decisions for risk and safety management are suggested. The proposed methodology has been demonstrated with reference to the system activities of an underground coal mining system. However developed method can be equally adapted to other systems.

AVAILABILITY AND RELIABILITY MODELING OF AN INTEGRATED UNDERGROUND COAL MINING SYSTEM

This paper presents a systematic approach to evaluation of the availability of an automated underground coal mining system, the longwall system. Five analytical models are developed by applying the techniques of reliability modeling and stochastic systems analysis. Each model is formulated to evaluate the availability of a longwall system with unique longwall operating logic. The application of these models is illustrated with a case study and the uses of the results are discussed.