Coal Goaf Research Articles

Mechanical Parameters of Deep‐Buried Coal Goaf Rock Mass Based on Optimized GSI Quantitative Analysis

In order to obtain the accurate mechanical parameters of deep‐buried coal goaf rock mass, the limitation of geological strength index (GSI) in concealed rock mass is analyzed. Based on the test result and analysis of the current normative standards, the classification indexes of rock mass structural are optimized based on discontinuity distance d and rock mass integrity index Kv. The ratio of rock mass saturated strength to dry strength, η, is introduced, quantization formula of structural surface conditions is proposed, and the influence of groundwater and rock types is included in structural surface condition classification. The GSI system is improved to better suit all types of deep‐buried and water‐rich rock masses. Furthermore, the rock mass disturbance factor D’s quantitative formula is listed according to the Hoek–Brown (HB) criterion. Taking the goaf roof under railway as an example, the parameters of deep‐buried rock mass are obtained based on the improved quantitative GSI system and HB criterion. This research provides a scientific reference for achieving geological parameters and engineering designing in goaf areas.

One-dimensional constrained inversion study of TEM and application in coal goafs’ detection

Abstract Transient electromagnetic method (TEM) is often used in urban underground space exploration and field geological resource detection. Inversion is the most important step in data interpretation. Because of the volume effect of the TEM, the inversion results are usually multi-solvable. To reduce the multi-solvability of inversion, the constrained inversion of TEM has been studied using the least squares method. The inversion trials were performed using two three-layer theoretical geological models and one four-layer theoretical geological model. The results show that one-dimensional least squares constrained inversion is faster and more effective than unconstrained inversion. The induced electromotive force attenuation curves of the inversion model indicate that the same attenuation curve may be used for different geological conditions. Therefore, constrained inversion using known geological information can more accurately reflect the underground geological information.

Research on failure characteristics of goaf floor in the inclined coal seam based on the fracture mechanics

Floor failure is the leading cause of mine water inrush after coal mining above the confined aquifer. Therefore, the prediction of floor failure depth is an important content of mine water prevention. The mining-induced failure depth and goaf floor characteristics are researched to grasp the goaf failure condition after the inclined coal seam mining with the theoretical analysis method. The inclined coal goaf floor's stress solving mechanics mode is set up based on the fracture mechanics theories. According to the Mohr–Coulomb criterion, the floor failure depth solving the equation is derived. With the theoretical analysis of the floor failure characteristics during the inclined coal seam mining, (1) the maximum failure depth of floor is nonlinear to the coal seam dip and the lateral pressure coefficient; the working face length, mining depth and floor cohesion positively correlate with the failure range; the floor cohesion is reversely proportional to the failure range. (2) There appears asymmetry in the layout of stress and plastic zones in the inclined coal goaf floor. Failure range and depth in-floor plastic zone increasingly enlarge when the coal face advances.

Using an Azimuth Electromagnetic Wave Imaging Method to Detect and Characterize Coal-seam Interfaces and Low-resistivity Anomalies

It has been found that the traditionally used electromagnetic wave instruments have limitations in detection depths, as well as a lack of directionality. Therefore, those types of instruments cannot meet the needs of geo-steering applications. However, azimuth electromagnetic wave instruments have shown the ability to quickly acquire effective geo-steering information using a tilt coil design method, which can potentially provide accurate guidance for decision-making in drilling direction adjustments. In this study, a design method for an azimuth electromagnetic wave detection instrument for underground coal mining was proposed. The relationships between the structural parameters of the instrument and installation angles of the coils and the response signals were obtained in this study using simulations. Then, by choosing reasonable instrument spacings, coil installation angles, and transmitting frequencies, the detection performances of the instrument were successfully improved. Also, the basic parameter selections of the proposed logging-while-drilling azimuth electromagnetic wave logging instrument were determined to be suitable for underground coal-mining purposes. It was also found that the symmetric compensation of the instrument was sensitive to the interface responses, and the anti-symmetric compensation was sensitive to the anisotropic responses. In addition, a method of detecting the interface positions and azimuth of coal-seam interfaces using azimuth electromagnetic waves, as well as the potential for the application of the instrument for the detection of low-resistivity anomalies in coal goafs, were effectively demonstrated. The results of this study provided theoretical references for future coal-seam boundary detections and explorations, and also added insight into the development processes of coal-seam bedding.

Research on Reducing Mining-Induced Disasters by Filling in Steeply Inclined Thick Coal Seams

Surface filling during the mining of steeply inclined thick coal seams is an efficient method for restraining disasters caused by the cascading movement of overburden rocks. This study aims to control rock damage during the mining of thick coal seams steeply inclined at typically more than 45° in fully mechanized coal caving work surfaces with high section heights. Based on the green mining concept, we analyzed the movement of roof strata after filling using multiple methods, including field investigation, theoretical analysis, numerical calculation, and field monitoring. Results show that, in dynamic mine disasters caused mainly by complex coal conditions and strong disturbances in fully mechanized coal caving in large sections, the strength of the filling material is dependent on the features of the surrounding rock and burial depth. Also, the mining-induced peak stress shows a linear increase after filling, with the goafs in stress-free conditions, and failure zones occur in the roof and floor strata after mining. The stability of the rock pillars and overburden strata are better, and there are no large-scale tensile fissures in the ground surface. We adopted an intelligent underground radar detection technique that can reflect the rock-failure characteristics through the propagation characteristics of the electromagnetic spectrum. The detection results show that the coal goafs were filled properly as they were matched with the caving roof, which will collapse along with the release of the top coal, with the filling body able to move downward along with the discharge of top coal. The use of surface filling can restrain the dynamic disaster induced by a fully mechanized coal caving surface with a large section when mining steeply inclined thick coal seams, thereby ensuring safety and promoting the use of green mining practices.

Monitoring Land Surface Displacement over Xuzhou (China) in 2015–2018 through PCA-Based Correction Applied to SAR Interferometry

Land surface deformation in metropolitan areas, which can cause varying degrees of hazard to both human lives and to properties, has been documented for decades in cities worldwide. Xuzhou, is one of the most important energy and industrial bases in eastern China, and has experienced significant land subsidence due to both excessive extraction of karst underground water and exploitation of mineral resources in recent decades. Furthermore, Xuzhou has recently undergone rapid urbanization in terms of urban expansion and underground construction, which could induce additional pressure on the urban land surface. However, most previous research on land surface deformation in the Xuzhou urban areas has been conducted based on traditional ground-based deformation monitoring techniques with sparse measurements. Little is known about the regional spatiotemporal behavior of land surface displacement in Xuzhou. In this study, a detailed interferometric synthetic aperture radar (InSAR) time series analysis was performed to characterize the spatial pattern and temporal evolution of land surface deformation in central areas of Xuzhou during 2015–2018. A method based on principal component analysis was adopted to correct artifacts in the InSAR signal. Results showed the correction strategy markedly reduced the discrepancy between global navigation satellite systems and InSAR measurements. Noticeable land subsidence (−5 to −41 mm/yr) was revealed widely within the Xuzhou urban areas, particularly along subway lines under construction, newly developed districts, and in old coal goafs. Remarkable consistent land uplift (up to +25 mm/yr) was found to have significantly affected two long narrow areas within the old goafs since 2015. The possible principal influencing factors contributing to the land surface displacements such as subway tunneling, building construction, mining, underground water levels and geological conditions are then discussed.

Numerical Analysis of Air Leakage Characteristics of Coal Seam Goaf Close to Thin Band

This paper aims to research the air leakage of coal goaf near to thin band in Nantun Coal Mine. With using PFC3D numerical simulation software and establishing close distance coal seams mining numerical model, it analyzes roof migration characteristics of lower coal seam during mining and researches the law of development of roof air leakage passage in goaf; It also analyzes the changing situation of porosity of goaf in upper coal seam and researches the law of leaking oxygen expansion of goaf in upper coal seam. It is indicated from the research results that the curve and subsidence of main roof on working face forms fractures and cracks in its interior causing the air leakage passage between upper coal seam and lower coal seam. With the fracture of lower coal seam roof, the range of air leakage passage of goaf expands rapidly. And with the periodic fracture of roof, the air leakage passage moves forward continuously to prompt the leaking oxygen of lower coal seam to go into the upper coal seam goaf, and this is good for the spontaneous combustion of remaining coal body. Before the first weighting of main roof, the porosity of No. 3 upper coal seam goaf almost has no change; during the period of the first weighting of main roof, the porosity in No. 3 upper coal seam goaf close to palisades becomes big; with the periodic caving, the porosity of No. 3 upper coal seam goaf appears periodic enlargement and movement, and this is good for the diffusion of leaking oxygen in upper coal seam goaf and intensifies the spontaneous combustion of remaining coal in upper coal seam goaf.

Construction risks of Huaying mount tunnel and countermeasures

The Chongqing-Guang’an motorway is planned to cross Huaying mount at Jingguan town of Chongqing city. The whole mount is a colossal anticline whose core is consisted of coal measure strata (upper Permian Longtan formation P2l) and the limbs are limestone strata (middle Triassic Leikoupo formation T2l and lower Triassic Jialingjiang formation T1j). The tunneling is full of risks of collapse, gas explosion or gas outburst, water (mud) inrush, gas inrush because of existence of faults, high pressure gas, karst tectonics and coal goafs around the tunnel. In order to cope with the high risk, two main countermeasures were taken to ensure security of construction. One is geology prediction, and the other is automatic wireless real-time monitoring system, which contains monitoring of video, wind speed, poisonous gas (CH4, CO, H2S, SO2), people location, and automatic power-off equipment while gas contents being more than warning threshold. These ascertained the engineering safety effectively.

Goaf Temperature Monitoring System Based on ZigBee Revised Routing Algorithm

In the process of coal-mine production, the self-ignition of left coal in goaf area has always been major disasters, and spawns amount of economic loss. As a consequence, it is necessary and essential to monitor the self-ignition of left coal in goaf. In consideration of the complex and poor environment of the goaf area, this thesis adopts ZigBee wireless sensor network instead of traditional fixed cable sensor network to monitor the self-ignition of coal goaf area. It has the advantages of wild covering, convenient layout and easy adapting to environment. In addition, counting on the revised routing algorithm, the whole wireless sensor network has obvious advantages of its network performance and low consumption, which makes the whole system monitor the self-ignition of left coal steadily and permanently.

The Research of Gas Drainage Technology in Daning Coal Mine

3# coal seam of Daning coal mine is outburst,thus severely restricting the safe production. Based on the analysis of gas emission sources and the logical drainage parameters, firstly, Daning coal mine arranged some drilling fields, then utilized the VLD-1000-type rig to drill boreholes, achieving the integrated gas drainage of the coal seam and goaf. Finally, there is a test on the drainage result. The results showed that, through this kind of integrated gas drainage technology, the highest value of gas pressure in the coal seam reduced to 0.63MPa from 1.95MPa after twelve months’ drainage, and the gas drainage rate of the whole mine reached 77.6%, achieving efficient use of gas clean energy.

A Data Transmission Algorithm Based on Dynamic Grid Division for Coal Goaf Temperature Monitoring

WSN (wireless sensor network) is a perfect tool of temperature monitoring in coal goaf. Based on the three-zone theory of goaf, the GtmWSN model is proposed, and its dynamic features are analyzed. Accordingly, a data transmission scheme, named DTDGD, is worked out. Firstly, sink nodes conduct dynamic grid division on the GtmWSN according to virtual semicircle. Secondly, each node will confirm to which grid it belongs based on grid number. Finally, data will be delivered to sink nodes with greedy forward and hole avoidance. Simulation results and field data showed that the GtmWSN and DTDGD satisfied the lifetime need of goaf temperature monitoring.

Application of the Least Squares Fitting in Mine Optical Fiber Carbon Dioxide Monitoring System

Carbon dioxide is one of the important signature gases in spontaneous combustion forecasting of coal goaf area. In the mine limited ventilation environment, concentration of CO2 directly affects the health of coal mines. So a new application of the least squares fitting method in Coal Mine gas monitoring was introduced. The optical fiber CO2 monitoring system which based on this method and tunable diode laser absorption spectroscopy (TDLAS) technology was used in Coal Mine beam tube system, and selected a near-infrared wavelength 1609.117nm fiber-coupled distributed feedback laser (DFB) as light source. Goaf area gas concentrations were directly calculated by the least squares fitting method which also simplified the calibration operation that used only one point to calibrate. Compared to electronic CO2 detector, this improved system has very high detection accuracy and stability. In the condition of 1.4m gas cell, the minimum detectable concentration is 0.05%, and the minimum detectable spectral absorption rate can up to , response time≤60s.

Study on the Deformation and Stability of Building Foundations in Mining Subsidence Areas

To enhance the effective of the land in mining subsidence areas, realize the development of new rural construction and urbanization. According to the geological and mining conditions, the scale, shape and regularity of the potential crack areas in the coal goafs, separated overburden strata, and the influencing factors which affect the deformation foundation of architecture and stability are studied. Probability integral method is used to establish the further deformations formula of the building foundations in mining subsidence areas. The monitoring data from the ground observation stations are used to invert the further deformation predicting parameters, the surface further deformations of each coal goafs, and the whole surface’s further deformations are calculated by the superposition method. The foundation further deformations, geological structures, etc, are comprehensively taken into consideration. The stability of the building foundations in mining subsidence area are analyzed and evaluated. Research results are very valuable to process, design, and plan the foundations of the buildings in coal mining subsidence areas.

Relationship between Methane Emission and Strata Behavior at Island Coal Face

According to the practical conditions of the island coal face in No.2 Coal Mine of Pingdingshan Coal Company Ltd., China, the strata behaviors and methane emission were monitored and their two relationships were analyzed. The results indicate that strata behavior at coal face affects its methane emission rates at coal wall and goaf，which the quantity of methane emission rate at coal face is largely increasing after main roof weighting. So through the monitor of periodic roof weighting time, larger methane emission rate at coal face can be predicted. Then the related methane control measures can be taken timely.

Fiber Optic Temperature and Gas Concentration Sensor for Mine Goaf Area Inner Detecting

Spontaneous combustion in coal goaf area is one of major disasters in coal mines. Detection technology based on signature Gas and Temperature is the primary means of spontaneous combustion forecasting of coal goaf area. A real-time remote fire detection system is proposed based on tunable diode laser absorption spectroscopy technology and FBG temperature sensing technology, to achieve valid detect of gas concentration and temperature. The System include fiber mathen concentration sensor and fiber temperature sensor based FBG. The system achieved remote on-line monitoring of gas concentration and temperature in mine goaf, meet the fire forecast need for Coal goaf area. There are obvious advantages Compared with the existing beam tube monitoring system in coal mine.

Study on Eco-Planning of Coal Town Special Land Based on Extenics

At present, the coal town special land mainly includes subsided, goaf and gangue etc, these lands for ecological restoration and reconstruction is coal town planning research hot spot. The article based on the Extenics method, with the resource exhaustion town theory as a foundation, to coal town special land as empirical research object, through the depth of coal town of space development trends and development orientation, puts forward the gangue land ecological adjustment mode, coal goaf and subsided development countermeasures. Through to the coal town special land ecological adjustment of spatial structure of towns thinking clarify coal optimization idea the feasibility, for cold to coal town of land development to provide certain reference.

DETERMINATION OF SPONTANEOUS COMBUSTION “THREE ZONES” IN GOAF OF NO.713 FULLY MECHANIZED LONGWALL OF QINAN COAL MINE

Mine fire is one of the major disasters in coal mine. In our country 56% coal mine exists spontaneous combustion problem, among them, the goaf spontaneous combustion take up subject status. The research of spontaneous combustion in the goaf is mainly about heat dissipation zone, oxidation zone and suffocation zone. The distribution condition and the range of the “three zones” spontaneous combustion in goaf is one of important basis of the parameters which are the prevention and control of the spontaneous combustion. For these hold the balance to nitrogen injection of mined-out area, grouting, face mining sequence and mining strength and so on, the scope of the working face spontaneous combustion “three zones” directly decides the position of nitrogen injection, nitrogen injection quantity, nitrogen injection intensity and other technological parameter, and decided the grouting time, grouting quantity, drawing speed of working face and so forth. So, experts and scholars throughout home and overseas have made a lot of research and have acquired some achievements. And the division of coal goaf spontaneous combustion “three zones” is mainly based on the change of oxygen concentration, change of temperature and air leakage speed, etc. How to obtain these parameters? By coal bed itself conditions which include geological conditions, mining technology and ventilation mode is different, and the research approach we adopt is different, the results are quite different. This paper is based on the essence of “three zones”, the factors are comprehensive considered which consist of air leakage speeds, oxygen concentration and temperature to study the coal goaf spontaneous combustion “three zones” distribution laws.

The Study of Event-Driven Clustering Routing Algorithm for WSN in the Coal Mine Goaf

Monitoring coal goaf mainly is arrangement of the wireless sensor network node in goaf to monitor the change of gas concentration and environmental temperature. This paper presents a clustering routing algorithm based on event-driven. In conventional circumstances, we adopt an improved LEACH algorithm. In the case of an event occurs, the nodes within the event region form a sub-cluster automatically, electing a cluster head node in cluster center. Cluster head after fusion data, in the direction of the shortest distance with the sink node forms a series of dynamic clustering and transmits the data to the sink node. Through MATLAB simulation studies show that the improved LEACH prolongs network life cycle efficaciously, clustering routing algorithm based on event-driven will transmits the data to the sink node reliably and in real time.