Image analyser measurements of coal reflectance

The application of an image analyser to the rapid measurement of coal reflectance histograms is described. The ability of an image analyser to utilize a two-dimensional image allows the coal only to be represented in the reflectance histogram, with contribution from the resin used in particulate block specimens eliminated. While the accuracy of reflectance measurement with an image analyser is not as great as can be obtained with a spot photometer system, sufficient accuracy is obtainable for rank determination.     

Coal pillar design when considered a reinforcement problem rather than a suspension problem

Current coal pillar design is the epitome of suspension design.A defined weight of unstable overburden material is estimated, and the dimensions of the pillars left behind are based on holding up that material to a prescribed factor of safety.In principle, this is no different to early roadway roof support design.However, for the most part, roadway roof stabilisation has progressed to reinforcement, whereby the roof strata is assisted in supporting itself.This is now the mainstay of efficient and effective underground coal production.Suspension and reinforcement are fundamentally different in roadway roof stabilisation and lead to substantially different requirements in terms of support hardware characteristics and their application.In suspension, the primary focus is the total load-bearing capacity of the installed support and ensuring that it is securely anchored outside of the unstable roof mass.In contrast, reinforcement recognises that roof de-stabilisation is a gradational process with ever-increasing roof displacement magnitude leading to ever-reducing stability.Key roof support characteristics relate to such issues as system stiffness, the location and pattern of support elements and mobilising a defined thickness of the immediate roof to create(or build) a stabilising strata beam.The objective is to ensure that horizontal stress is maintained at a level that prevents mass roof collapse.This paper presents a prototype coal pillar and overburden system representation where reinforcement, rather than suspension, of the overburden is the stabilising mechanism via the action of in situ horizontal stresses.Established roadway roof reinforcement principles can potentially be applied to coal pillar design under this representation.The merit of this is evaluated according to failed pillar cases as found in a series of published databases.Based on the findings, a series of coal pillar system design considerations for bord and pillar type mine workings are provided.This potentially allows a more flexible approach to coal pillar sizing within workable mining layouts, as compared to common industry practice of a single design factor of safety(Fo S) under defined overburden dead-loading to the exclusion of other relevant overburden stabilising influences.     

Development of a new algorithm for implementing the edge effect offset for subsidence calculations

The surface deformation prediction system(SDPS) program has been developed as an engineering tool for the calculation of subsidence deformation indices through the implementation of various prediction methods.From basic user-defined input parameters, SDPS can determine subsidence indices, such as mining induced displacements, strains, tilt, etc., at any elevation between the seam and the horizontal or varying surface topography.A fundamental parameter in obtaining reliable ground deformation results is the determination of the edge effect offset.The value assigned to the edge effect offset corresponds to a virtual offsetting of boundary lines delineating the extracted panel to allow for roof cantilevering over the mined-out area.The objective of this paper is to describe the methods implemented in updating the edge effect offset algorithm within SDPS.Using proven geometric equations, the newly developed algorithm provides a more robust calculation of the offset boundary of the extracted panel for simplistic as well as more complex mining geometries.Given that an extracted panel is represented by a closed polyline, the new edge offset algorithm calculates a polyline offset into the extracted panel with respect to the user defined edge effect offset distance.Surface deformations are then calculated using this adjusted panel geometry.The Matlab program was utilized for development and testing of the new edge effect offset algorithm.After completing rigorous testing regimes, the new offset algorithm will be integrated into SDPS further increasing the speed and reliability of the program resulting in a retrospective increase in capability and flexibility.     

Analysis on the multi-phase flow characterization in cross-measure borehole during coal hydraulic slotting

Hydraulic slotting in a gas drainage borehole is an effective method of enhancing gas drainage performance. However, it frequently occurs that a large amount of slotting products(mainly the coal slurry and gas) intensely spurt out of the borehole during the slotting, which adversely affects the slotting efficiency. Despite extensive previous investigations on the mechanism and prevention-device design of the spurt during ordinary borehole drilling, a very few studies has focused on the spurt in the slotting process. The slotting spurt is mainly caused by two reasons: the coal and gas outburst in the borehole and the borehole deslagging blockage. This paper focuses on the second reason, and investigates the hydraulic deslagging flow patterns in the annular space between the drill pipe and borehole wall.Results show that there are six deslagging flow patterns when the drill pipe is still: pure slurry flow, pure gas flow, bubble flow, intermittent flow, layering flow and annular flow. When the drill pipe rotates, each of those six flow patterns changes due to the Taylor vortex effect. Outcomes of this study could help to better understand the slotting-spurt mechanism and provide guidance on the anti-spurt strategies through eliminating the borehole deslagging blockage.     

Using LaModel to analyze coal bumps

Coal bumps have long been a safety hazard in coal mines, and even after decades of research, the exact mechanics that cause coal bumps are still not well understood. Therefore, coal bumps are still difficult to predict and control. The LaModel program has a long history of being used to effectively analyze displacements and stresses in coal mines, and with the recent addition of energy release and local mine stiffness calculations, the LaModel program now has greatly increased capabilities for evaluating coal bump potential. This paper presents three recent case histories where coal stress, pillar safety factor, energy release rate and local mine stiffness calculations in LaModel were used to evaluate the pillar plan and cut sequencing that were associated with a number of bumps. The first case history is a longwall mine where a simple stress analysis was used to help determine the limiting depth for safely mining in bump-prone ground. The second case history is a room-and-pillar retreat mine where the LaModel analysis is used to help optimize the pillar extraction sequencing in order to minimize the frequent pillar line bumps. The third case history is the Crandall Canyon mine where an initial bump and then a massive pillar collapse/bump which killed 6 miners is extensively back-analyzed. In these case histories, the calculation tools in LaModel are ultimately shown to be very effective for analyzing various aspects of the bump problem, and in the conclusions, a number of critical insights into the practical calculation of mine failure and stability developed as a result of this research are presented.     

Micro shape of coal particle and crushing energy

A large amount of energy is consumed in a coal and gas outburst since a mass of coal is pulverized and ejected, accompanying a great quantity of gas emitted, resulting in a major mining hazard in underground coal mining around the world. Understanding how potential energy stored in gassy coal seams dissipates in the process of outbursting may possibly be a key to clarify the mechanisms responsible for coal and gas outburst. The present study was aimed to evaluate energy for crushing coal to various size fractions in coal and gas outbursts through theoretical and experimental investigation into the shape of fine coal particles and their equivalent diameter. Theoretical analysis indicates that the shape of a particle has a significant impact both on its equivalent diameter and hence on its outer surface area.Microscopic observations demonstrate the particle fraction with diameters less than 0.075 mm, produced from crushing coal samples, mostly takes on a spherical or ellipsoidal shape, and experimental data also show this part of particles consists of 30%–50% surface area newly generated from crushing operation,though these fine coal accounts for only less than ten percentages by weight. Further, analysis of experimental data indicates that the total surface area of this particle size fraction varies exponentially with input crushing energy, and the specific area energy is not a constant but probably in association with physical properties and textures of material.     

地球物理勘探技术在煤炭勘探领域中的应用

地球物理勘探技术中包含了很多物理勘探方法,根据不同的勘探条件和目的,选择相适应的勘探方法。由于我国的经济水平不断发展,煤炭的开发与利用逐渐增大,地球物理勘探技术在煤炭勘探领域中的应用也越来越多,并为煤炭勘探领域带来了更多的方便与利益。试行分析目前地球物理勘探技术在煤炭勘探领域中的应用。     

煤层底板岩体阻水能力原位测试研究

介绍了煤层底板岩体阻水能力的测试原理、测试方法和测试过程 ,分析了测试成果的可靠性 ,并对杨庄煤矿六煤底板岩体的阻水能力进行了评价 ,为煤矿底板突水防治提供了一条新途径。     

Investigations of groundwater bursting into coal mine seam floors from fault zones

This paper presents a case study of investigations into retarded groundwater bursting along the fault zones in the seam floors in coal mines. In addition to in situ measurements of ground stresses, a number of rock samples from the fault zones at the site of the case study were taken, and laboratory tests were performed for conventional and special rheological rock mechanics properties. The effects of different parameters on deformation and failure of the fault zone materials were analyzed, and the mechanism of retarded groundwater bursting along fault zones was further revealed. In the case study, different scenarios accounting for the different development phases of the fault weakness zone and groundwater bursting as well as different groundwater pressures were considered, and each of them was simulated using the 3D visual elastic–plastic numerical mechanics model FLAC^3D (Fast Lagrangian Analysis of Continua in 3 Dimensions). Through the case study, the applicability of rock mechanics modeling software for studying retarded groundwater bursting along a fault zone was examined. Several issues are discussed regarding the investigations of retarded groundwater bursting and a general structured approach to investigate and control this geological hazardous event is presented.     

Effect of seepage force on tunnel face stability reinforced with multi-step pipe grouting

Tunneling in difficult geological conditions is often inevitable especially in urban areas. Ground improvement and reinforcement techniques are required to guarantee safe tunnel excavations and/or to prevent damage to adjacent structures. The steel pipe-reinforced multi-step grouting method has been recently applied to tunnel sites as an auxiliary technique in Korea for impermeabilization in underwater tunnels as well as for reinforcement. However, this technique has been usually employed empirically without much understanding with regard to its effect on the tunnel safety. In this study, the face stability with steel pipe-reinforced multi-step grouting in underwater tunnels was evaluated by simultaneously considering two factors: one is the effective stress acting on the tunnel face calculated by limit theorem and limit equilibrium method; the other is the seepage force obtained by means of numerical analysis. This study revealed that the influence of the steel pipe-reinforced multi-step grouting on the support pressure required for the stability of the tunnel face in dry condition is not significant while there is relatively a significant reduction in seepage forces by adopting the technique in the underwater tunnel. The effect of permeability anisotropy on the seepage force acting on the tunnel face was also assessed by conducting a coupled analysis.