Stability evaluation of highwall slope in an opencast coal mine – a case study

Apr 2018 / by I. Satyanarayana, G. Budi, Phalguni Sen and A. K. Sinha

The stability analysis of slopes is an integral part of the opencast and highwall mining operations during the entire life cycle of the project. In India, fast increase in output of various minerals can be largely attributed to rapid increase in opencast mining activities and intensified mechanization. This has resulted in the opencast mines going deeper day by day with the maximum stripping ratio being planned currently looking up to 1:15, at a depth of about 500 m. As a direct consequence, the amount of waste mining and dumping will also be commensurately very high thereby increasing the risks of highwall, slope and dump failures tremendously. Safe, properly designed, and scientifically engineered slope is essential for economic, safe and successful operation of opencast mine. Engineering of safe and stable slopes is of significant importance and is normally carried out by empirical, observational or analytical techniques. While less than 3% of mine accidents are associated with slope stability problems, slope failure accidents were responsible for more unproductive work, loss of equipment and poor economic performance. Massive highwall failures containing a million cubic metres of material or more can be dangerous for heavy-equipment and persons working over there. Several remote sensing technologies are being evaluated as tools to monitor slope stability to assess hazards in advance. This paper makes an attempt to review the important factors affecting slope stability and analyze stability of slopes with a case study from the Singareni Collieries Company Limited (SCCL).
Keywords: Shear strength, slope failure, failure analysis, numerical modelling, monitoring, safety factor

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Experimental study of wettability alteration to gas wetness method to enhance coal bed methane production

Apr 2018 / by Ma Dong and Zhang Peng

It is of great importance and significance to study the production improvement technology for coal bed methane. Wettability alteration technology has been successfully applied to enhance oil production and recovery. However, literature on wettability technology used to enhance production of coal bed methane has not been reported. In this paper, a physical model was developed to describe the mechanism of wettability alteration technology to enhance coal bed methane. Gas-water displacement test was conducted in coal samples with and without the wettability alteration to gas wetness. Comparison of gas-water relative permeability curve before and after wettability alteration showed that wettability alteration technology could increase gas phase relative permeability, and reduce water residual water saturation in the gas-water displacement. The experimental results demonstrated that the wettability alteration to gas wetness technology can enhance the production of coal bed methane.
Keywords: Coal bed methane, enhance production, wettability alteration

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Experimental study on conductivity of hydraulic fracture in coal bed

Apr 2018 / by Dong Guang, Deng Jingen and Zhu Haiyan

Hydraulic fracturing is an important stimulation technology of coal bed methane well. It is different between CBM reservoirs and conventional oil and gas reservoirs. The research conclusion of coal bed hydraulic fracture conductivity is different from that of conventional oil and gas reservoir. It is necessary to carry out the research of coal bed hydraulic fracture conductivity. In this paper, fracture conductivity of coal rock is evaluated by FCES-100 fracture conductometer. The effect of closure pressure, sand concentration, time, the natural fractures of coal rock as well as proppant type on fracture conductivity are studied. The study shows that as the closure pressure increases, there is a decline of more than 50% about coal bed fracture conductivity. The conductivity under high sand concentration is significantly higher than that under single layer sand concentration. Thereby, increasing the concentration of sand is conducive to the formation of high conductivity fracture. With the time increase, fracture conductivity is decreased with a decline of 20%~35%. Natural fracture has a direct impact on conductivity, and this impact is performed particularly evidently in the case of a higher closure pressure. Meanwhile proppant type is also an important factor in affecting the fracture conductivity.
Keywords: Coal bed; hydraulic fracture; proppant; conductivity

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Characteristics of hydraulic fracture surface based on 3D scanning technology

Apr 2018 / by Fan Zhang, Geng Ma, Yunqi Tao, Xiao Liu, Yixin Liu and Rui Li

The surface characteristics of fractured specimens are important in hydraulic fracturing laboratory experiments. In this paper we present a three-dimensional (3D) scanning device assembled to study these surface characteristics. Cubeshaped coal rock specimens were produced in the laboratory and subjected to triaxial loading until the specimen split in two in a hydraulic fracturing experiment. Each fractured specimen was placed on a rotating platform and scanned to produce 3D surface coordinates of the surface of the fractured coal specimen. The scanned data was processed to produce high-precision digital images of the fractured model, a surface contour map, and accurate values of the surface area and specimen volume. The images produced by processing the 3D scanner data provided detailed information on the morphology of the fractured surface and the mechanism of fracture propagation. High-precision 3D mapping of the fractured surfaces is essential for quantitative analysis of fractured specimens. The 3D scanning technology presented here is an important tool for the study of fracture characteristics in hydraulic fracturing experiments.
Keywords: Surface characteristic; hydraulic fracturing; 3D scanning; 3D coordinates; surface area

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Evaluation on floor water inrush danger of Weibei during mining over pressurized water and prevention countermeasures to the water disaster

Apr 2018 / by Li Ang, Ma Qiang, Kang Li, Li Liang, Cai Lei and Wang Wei

With increasingly high comprehensive mining intensity to the coal resources and wider mining width of the mining area, the mines of Chenghe No.2 mineral are getting deeper and deeper and the hazard from the high pressure water of Ordovician limestone of #5 coal bed bottom is getting increasingly intense, which will seriously influence safety production of the mines. Therefore, how to liberate the under draught coal reserves of #5 water body is a difficult problem as well as the key issue to ensure safety production of the mines. As for this, the first author will combine with the hydrogeological condition of Chenghe No.2 mineral in this article, and adopt standardized water bursting coefficient method to evaluate the water insulation capability of Taiyuan formation #5 coal floor upon comprehensive analysis on influencing factors of floor water inrush, to consider whether to divide #5 coal floor under waterdiversion failing zone thickness into different compensated mining areas, having predicted water inrush probability of the mining area in the future, and to release the coal reserves threatened by Ordovician water disaster. The result shows: (1) Among the factors that influence #5 coal floor water inrush of Chenghe No.2 mineral, head pressure of the aquifer is motive power of water inrush, the floor strata lithology and its combination feature are safety barrier for confined water extraction, and geological structure is in most cases the channel of floor water inrush; in accordance with the latest stipulations on mine water prevention and control and design specifications on coal mine water prevention, the first author takes 0.06MPa/m and 0.1MPa/ m as boundary conditions of critical water inrush coefficient, divides #5 coal floor water-resisting layer into compensated mining extremely dangerous zone, dangerous zone and exploitable zone; (2) As to areas that mining above the pressured water are inapplicable in consideration of the coal floor water-diversion failing zone, latest water bursting coefficient formula can be adopted to realize safe compensated mining, which has reduced danger of floor water inrush, and satisfied the requirements of safe compensated mining of this mining area; (3) Without considering condition of the water-diversion failing zone, it can liberate compressed coal reserves of #5 coal floor that are threatened by Ordovician limestone water disaster and enhance the recovery ratio of coal resources; (4) Based on the evaluation results of floor water inrush danger, the author has proposed major water disasters to the coal floor and prevention countermeasures, which has provided valuable reference for safety compensated coal mining above seam floor pressure-bearing water body of Chenghe minerals and even Weibei coalfield, brought tremendous social and economic benefits, is of practical significance for realization of green coal mining, and will drive local economic development, thus worth being generalized and applied.
Keywords: Water inrush; evaluation; prevention; confined aquifer

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Coal seam fire area determination using pixel values of the satellite data

Apr 2018 / by Vikas Srivastava, Sanjay K. Sharma and G. S. P. Singh

A large amount of coal is locked up in coal seams worldwide, every year, due to uncontrolled coal seam fires (CSF). China and India are most affected due to these fires. Mapping an quantification of these fires requires the spectral characterisation of land use and land cover (LULC) from the satellite imagery. Remote sensing (RS) and Geographic information system (GIS) are useful tools for the assessment of the underground CSF. This paper reports the experiences obtained from the experiments on spectral band of satellite imageries in delineating the thermal regimes of CSF in a coalfield in India. The steps involved in the coal fire data analysis are preprocessing, processing and post processing. The data analyses have been carried out on the satellite data. The changes in LULC have been detected by visual interpretation, image differencing, band rationing and level slicing. The field observations were incorporated in analysis to identify the scope for further improvement in LULC simulations for the reliable modelling, delineation, mapping and monitoring of the CSF. The results obtained from the study depict that shallow depth workings, contiguous panel multi seam workings and the thick seam mining had created directly or indirectly very complex situations in thermal regimes of CSF. The province ratification of the CSF surveillance by LULC depicts that the propagation of the fire is higher in the lateral direction i:e in perpendicular direction of the fire heading.

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Layout of buried pipe drainage in the goaf under Y-type ventilation

Apr 2018 / by Haidong Chen, Fenghua An Zhaofeng Wang and Hongmin Yang

Y-type ventilation is commonly used in coal mines of many countries in recent years. Due to the lack of leakage airflow return roadway in the deep part of the goaf under Y-type ventilation, gas with high concentration would appear behind the hydraulic supports, which is easily to cause gas overrun accidents. Drainage pipes buried inside the goafside roadway retained can change the flow filed in the goaf and is commonly used to reduce the danger of gas overrun behind the hydraulic supports of the workface with a high gas emission. Based on the engineering practice of Xingwu coal mine in China, Fluent numerical simulation software was used to determine the reasonable mixed gas drainage volume of drainage pipes buried inside the goaf-side roadway retained. Then, taking into account the use of a single drainage pipe required larger diameter, and easy deformation, affecting the gas drainage effect; three drainage pipes instead of a single drainage pipe are arranged into the goaf-side roadway retained. Finally, through the field test, the rationality of the gas drainage volume and the layout of drainage pipes being selected are verified.
Keywords: Y-type ventilation; gas overrun; gas drainage; numerical simulation

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Beneficiation of goethite-laterite ore – an alternative

Apr 2018 / by Nirlipta. P. Nayak, B. K. Pal and Gyana P. Paul

Depleting iron ore reserves coupled with increasing demand for low-alumina iron ore fines to improve blast furnace performance in terms of productivity and reduced slag rate necessitate intensive beneficiation of iron ore. The sample was collected from Barsua iron ore mine assaying 40% Fe, 9.48% SiO2 and 19.97% Al2O3. In order to produce the pellet grade concentrate multiple stages of beneficiation were opted for. Detailed characterization of the iron ore revealed that most of the impurities in the form of alumina and silica are concentrated in the finer size fractions while iron is concentrated in the coarser size fractions. Therefore, it is imperative that removal of ultrafines using a desliming operation would improve the grade. A beneficiation scheme was chosen involving desliming by simple washing, jigging followed by gravity separation. To study the beneficiation prospects of coarse particles a first stage of gravity separation by jigging is carried out. Finally, further comminution and a second stage of tabling out of all the techniques, reduction roasting was found to be the most suitable one.
Keywords: Laterite, goethite, beneficiation, roasting

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Effect of coating thickness on SI engine performance

Apr 2018 / by Tanweer Alam and Birendra Kumar

Present work is intended to investigate the stress and temperature distribution for a partially coated spark ignition (SI) engine piston. For comparison purpose analysis was also made on uncoated piston and results were compared to the temperature and stress distribution obtained from the application of different coating thickness and width on the piston. It is found that increase in coating surface temperature with coating thickness is in a decreasing rate. From the analysis of bond coat surface, it is found that with the increase in coating thickness decrease in normal stress is steady while rise of maximum shear stress is in decreasing rate.
Keywords: Ceramic coating; spalling; bond coat; piston; coating thickness, crevices

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