Energy-limiting factor for coal and gas outburst occurrence in intact coal seam

This research reviewed the mechanics and gas desorption properties of intact coal,and tested the crushing work ratios of different intact coals,and then,studied the stress conditions for the failure or crushing of intact coal and the gas demand for the pulverization of intact coal particles.When a real-life outburst case is examined,the required minimum stress for intact coal outburst is estimated.The study concludes that the crushing work ratios of three intact coal samples vary from 294.3732 to 945.8048 J/m^(2).For the real-life case,more than 2300 MJ of transport work is needed,and 10062.09,7046.57 and 5895.47 m^(3) of gas is required when the gas pressure is 1,2 and 3 MPa,respectively.The crushing work exceeds the transport work and even reaches 13.96 times of the transport work.How to provide such an enormous crushing work is an energy-limiting factor for the outburst in intact coal.The strain energy is needed for the crushing work,and the required minimum stress is over 54.35 MPa,even reaching 300.44 MPa.These minimum stresses far exceed the in-situ vertical and horizontal stresses that can be provided at the 300–700 m mining depth range.

Multi-scale pore fractal characteristics of differently ranked coal and its impact on gas adsorption

Well-developed pores and cracks in coal reservoirs are the main venues for gas storage and migration.To investigate the multi-scale pore fractal characteristics,six coal samples of different rankings were studied using high-pressure mercury injection(HPMI),low-pressure nitrogen adsorption(LPGA-N2),and scanning electron microscopy(SEM)test methods.Based on the Frankel,Halsey and Hill(FHH)fractal theory,the Menger sponge model,Pores and Cracks Analysis System(PCAS),pore volume complexity(D_(v)),coal surface irregularity(Ds)and pore distribution heterogeneity(D_(p))were studied and evaluated,respectively.The effect of three fractal dimensions on the gas adsorption ability was also analyzed with high-pressure isothermal gas adsorption experiments.Results show that pore structures within these coal samples have obvious fractal characteristics.A noticeable segmentation effect appears in the Dv1and Dv2fitting process,with the boundary size ranging from 36.00 to 182.95 nm,which helps differentiate diffusion pores and seepage fractures.The D values show an asymmetric U-shaped trend as the coal metamorphism increases,demonstrating that coalification greatly affects the pore fractal dimensions.The three fractal dimensions can characterize the difference in coal microstructure and reflect their influence on gas adsorption ability.Langmuir volume(V_(L))has an evident and positive correlation with Dsvalues,whereas Langmuir pressure(P_(L))is mainly affected by the combined action of Dvand Dp.This study will provide valuable knowledge for the appraisal of coal seam gas reservoirs of differently ranked coals.

碎软煤层双管定向钻具自动加卸系统关键技术与应用

为提高双管定向钻进钻孔施工时钻具加装和拆卸的自动化水平,提高装卸效率,开发一种双管自动加卸装置,实现不同工况下钻具的全自动装卸,解决双管定向钻进过程中钻杆和套管的同时加装和拆卸的技术难题,完成装置结构和控制系统的设计,运用末端柔顺技术,限制施工过程中装置承受的载荷,明确控制程序关键边界条件,制定不同工况下钻具自动装卸施工工艺流程。在安徽淮北矿业祁南煤矿展开工业性试验,试验顺利完成4个钻孔的施工,共进尺1170 m。试验过程中双管自动加卸装置运行平稳,能够满足不同工况下钻具组合的加装和拆卸需求。将原本需要2~3人密切配合才能完成的钻具组合自动装卸工作,变为依靠程序控制自动完成,钻杆和套管同时装卸和单独装卸平均效率较人工装卸分别提高了350%和110%,保证了双管定向钻进综合施工效率,减少了作业工人数量,降低了工人劳动强度,保障了施工安全。试验结果表明:双管自动加卸装置运行稳定可靠,施工工艺流程合理,装置各项性能满足双管定向钻进需求。研究成果为双管定向钻孔施工钻具的自动装卸提供了技术和装备支撑,为双管定向钻进技术在煤层气开采相关领域的推广应用奠定了基础。

Study of methane and carbon dioxide adsorption-desorption hysteresis in coals from Sydney Basin:A theoretical and experimental approach

Methane(CH_(4))and carbon dioxide(CO_(2))are primary components of coal seam gas(CSG).Understanding their adsorption-desorption hysteresis characteristics,along with the fundamental mechanism,is crucial for CSG exploitation and related hazards mitigation.This research focused on the representative Bulli coal seam in the Sydney Basin,Australia.Through the purpose-built indirect gravimetric high-pressure isothermal adsorption-desorption hysteresis experiment,a novel Langmuir-based desorption model,incorporating hysteresis effect and residual gas,was proposed.Quantitative characterization of the adsorption-desorption hysteresis degrees of CO_(2)and CH_(4)i n coal particles of various sizes and inΦ50mm 100 mm intact coal samples were achieved using the improved hysteresis index(IHI).The experimental findings validated that the proposed desorption model accurately describes the desorption behavior of CO_(2)and CH_(4)in coal(R^(2)>0.99).Based on the adsorption-desorption properties of inkbottle-shaped micropores and pore deformation caused by gas adsorption-induced coal expansion,the occurrence mechanism of adsorption–desorption hysteresis and the fundamental reasons for the presence of residual gas were elucidated.Furthermore,the study explored the impact of CO_(2)and CH_(4)adsorption-desorption hysteresis effects on coal and gas outbursts,suggesting that coal seams rich in CO_(2)do not have a higher propensity for outbursts than those rich in CH_(4).

A numerical simulation study on mechanical behaviour of coal with bedding planes under coupled static and dynamic load

To investigate the bedding influence on coal mechanical behaviour in underground environments such as coal or rock burst, simulations of dynamic SHPB tests of pre-stressed coal specimens with different bedding angles were carried out using a particle flow code 2-dimensional(PFC2D). Three impact velocities of 4, 8 and 12 m/s were selected to study dynamic behaviours of coal containing bedding planes under different dynamic loads. The simulation results showed that the existence of bedding planes leads to the degradation of the mechanical properties and their weakening effect significantly depends on the angle h between the bedding planes and load direction. With h increaseing from 0° to 90°, the strength first decreased and subsequently increased and specimens became most vulnerable when h was 30° or 45°.Five failure modes were observed in the specimens in the context of macro-cracks. Furthermore, energy characteristics combined with ultimate failure patterns revealed that maximum accumulated energy and failure intensity have a positive relation with the strength of specimen. When bedding planes were parallel or perpendicular to loading direction, specimens absorbed more energy and experienced more violent failure with increased number of cracks. In contrast, bedding planes with h of 30° or 45° reduced the specimens' ability of storing strain energy to the lowest with fewer cracks observed after failure.

Groundwater impact of open cut coal mine and an assessment methodology:A case study in NSW

Large scale open cut coal mining operations have significant impacts to groundwater in surrounding areas in both active and post-mining phases. The prediction of water inflows into a surface mine excavation is one of the many components involved in mine design phase. Groundwater performance also reacts to mining activities from the operational, economic and safety implications perspective. Under NSW planning legislation, as part of the comprehensive risk assessment, a groundwater impact assessment has to be conducted for a coal project to predict and mitigate the impacts in consideration of the government requirements. In this paper, the groundwater assessment modelling of mine pits was discussed in predicting of groundwater inflows and reviewing analytical and numerical approaches. A methodology of groundwater impact assessment for an open cut mine in NSW with a three-dimensional groundwater flow model Modflow Surfact demonstrated its functions in simulating the project's impacts on the groundwater regime. The key findings with mitigations are discussed and recommended in the paper to reduce impacts on groundwater and fulfil regulation requirements in NSW.

A hybrid tubular standing support for underground mines:Compressive behaviour

This paper presents the development of an innovative standing support for underground mines.The main feature of this standing support is its exterior container,a combination of polyvinyl chloride(PVC)with large rupture strain and fibre-reinforced polymer(FRP)with high strength-to-weight ratio.To demonstrate the advantages of this cementitious grout filled PVC-FRP tubular(PFT)standing support,a series of compression tests were conducted.Test variables included the strength of cementitious grout infill material and the thickness of FRP jacket.Compression tests were also conducted on cementitious grout-filled PVC tubular(PT)support and cementitious grout-filled FRP tubular(FT)support.These tests showed that PFT support presents a typical strain-hardening behaviour together with an outstanding axial deformation ability(>20%of the overall height of the support).In addition,the maximum compressive strength of PFT support is much higher than that of the corresponding PT support and FT support.Furthermore,using thicker FRP jacket or high strength cementitious grout material can enhance the load carrying capacity of PFT support.These comparative results indicated that the high performance of PFT support is mainly attributed to the combination of confining constituents(i.e.PVC and FRP)and infill material.

Evolution and application of in-seam drilling for gas drainage

The presence of seam gas in the form of methane or carbon dioxide presents a hazard to underground coal mining operations.In-seam drilling has been undertaken for the past three decades for gas drainage to reduce the risk of gas outburst and lower the concentrations of seam gas in the underground ventilation.The drilling practices have reflected the standards of the times and have evolved with the development of technology and equipment and the needs to provide a safe mining environment underground.Early practice was to adapt equipment from other felds,with rotary drilling being the only form of drilling available.This form of drainage allowed various levels of gas drainage coverage but with changing emphasis,research and development within the coal industry has created specifc equipment,technology and practices to accurately place in-seam boreholes to provide effcient and effective gas drainage.Research into gas content determination established a standard for the process and safe levels for mining operations to continue.Surveying technology improved from the wire-line,single-shot Eastman survey instruments which was time-dependent on borehole depth to electronic instruments located in the drill string which transmitted accurate survey data to the drilling crew without time delays.This allowed improved directional control and increased drilling rates.Directional drilling technology has now been established as the industry standard to provide effective gas drainage drilling.Exploration was identifed as an additional beneft with directional drilling as it has the ability to provide exploration data from long boreholes.The ability of the technology to provide safe and reliable means to investigate the need for inrush protection and water drainage ahead of mining has been established.Directional drilling technology has now been introduced to the Chinese coal industry for gas drainage through a practice of auditing,design,supply,training and ongoing support.Experienced drilling crews can offer site specifc gas drainage drilling services utilising the latest equipment and technology.

Developing coal burst propensity index method for Australian coal mines

Coal burst is the violent failure of overstressed coal, and it is often accompanied by sound, coal ejection and seismic events. It is subsequently recognized as a serious safety risk of Australia after double fatalities coal burst happened at Austar Coal Mine. Considering the increasing trend of coal burst severity and frequency with mining depth, it is an urgent task to develop the coal burst risk assessment methods for Australia underground coal mines. Coal burst propensity index method is a widely used method of burst risk evaluation of coal as it is summed up from the coal burst research and practice of many countries.This paper presents the experimental and theoretical research of coal burst propensity index method for coal burst risk assessment in Australia. The definition of four indexes including elastic strain energy index(W_(ET)), bursting energy index(K_E), dynamic failure time(DT) and uniaxial compression strength(RC)is introduced in the first part. Then, the standard laboratory test process and test parameter of coal burst propensity index is presented. DT test is conducted with 0.3 mm/min displacement control loading rate while other test is with 0.5 mm/min. Besides, modified data processing and risk classification method of test are proposed. Differentiate analysis of stress-strain curve is adopted in the data processing of DT and KEindex. A four level risk classification form of burst risk is recommended for Australian underground coal mines. Finally, two likely improvement methods of W_(ET) test, including volumetric strain indicator method and theoretical calculation method, are discussed.

In-situ gas contents of a multi-section coal seam in Sydney basin for coal and gas outburst management

The gas content is crucial for evaluating coal and gas outburst potential in underground coal mining. This study focuses on investigating the in-situ coal seam gas content and gas sorption capacity in a representative coal seam with multiple sections (A1, A2, and A3) in the Sydney basin, where the CO_(2) composition exceeds 90%. The fast direct desorption method and associated devices were described in detail and employed to measure the in-situ gas components (Q_(1), Q_(2), and Q_(3)) of the coal seam. The results show that in-situ total gas content (Q_(T)) ranges from 9.48 m^(3)/t for the A2 section to 14.80 m^(3)/t for the A3 section, surpassing the Level 2 outburst threshold limit value, thereby necessitating gas drainage measures. Among the gas components, Q_(2) demonstrates the highest contribution to Q_(T), ranging between 55% and 70%. Furthermore, high-pressure isothermal gas sorption experiments were conducted on coal samples from each seam section to explore their gas sorption capacity. The Langmuir model accurately characterizes CO_(2) sorption behavior, with ft coefcients (R^(2)) greater than 0.99. Strong positive correlations are observed between in-situ gas content and Langmuir volume, as well as between residual gas content (Q_(3)) and sorption hysteresis. Notably, the A3 seam section is proved to have a higher outburst propensity due to its higher Q_(1) and Q_(2) gas contents, lower sorption hysteresis, and reduced coal toughness f value. The insights derived from the study can contribute to the development of efective gas management strategies and enhance the safety and efciency of coal mining operations.

Inertisation options for BG method and optimisation using CFD modelling

Spontaneous combustion(sponcom) is one of the issues of concern with the blasting gallery(BG) method of coal mining and has the potential to cause fires, and impact on production and safety, greenhouse gas(GHG) emissions and huge costs involved in controlling the aftermath situations. Some of the research attempts made to prevent and control coal mine fires and spontaneous combustion in thick seams worked with bord and pillar mining methods are presented in this paper. In the study, computational fluid dynamics(CFD) modelling techniques were used to simulate and assess the effects of various mining methods, layouts, designs, and different operational and ventilation parameters on the flow of goaf gases in BG panels. A wide range of parametric studies were conducted to develop proactive strategies to control and prevent ingress of oxygen into the goaf area preventing spontaneous combustion and mine fires.

Guest Editorial-Special Issue on Green Mining

The 6th International Symposium on Green Mining(6th ISGM)was co-hosted by the University of Wollongong(UOW)and China University of Mining and Technology(CUMT),Australia,24–26th November 2013.The symposium attracted more than 150 dele-

Fracture features of brittle coal under uniaxial and cyclic compression loads

Under the efects of complex geological and stress environments,burst hazards continue to be a major challenge for underground space utilization and deep resources exploration as its occurrence can lead to personnel causalities,equipment damage and structural collapse.Considering the stress path experienced by in-situ coal body,cyclic loading appears in quite various forms for instance shearer cutting,overlying strata breakage,hydro-fracturing and blasting,during tunnel,mining and underground space utilizing process.The stability of the underground coal body subject to periodic loading/unloading stress is extremely important for maintain the function of designed engineering structure for waste storage,safe mining,roadway development,gas recovery,carbon sequestration and so on.The mechanical properties of hard rock subject to cyclic fatigue loads has been intensively investigated by many researchers as the rock burst induced by supercritical loads has long been a safety risk and engineering problems for civil and tunneling engineering under deep overburden.More recently,the mechanical properties of coal samples under cyclic fatigue loads is investigated from the aspect of hysteresis,energy dissipation and irreversible damage as the burst hazards of brittle coal is rising in many countries.However,the crack propagation and fracture pattern of brittle coal need more research to understand the micro mechanism of burst incubation subject to cyclic fatigue loads as brittle coal can store more elastic strain energy and rapidly release the energy when its ultimate strength once reached.This research studied the internal crack status corresponding to diferent cyclic fatigue loading stage of brittle coal samples.The AE monitoring was applied during the uniaxial and cyclic loading process of brittle coal samples to record the crack intensity of samples at diferent loading stages.The damage evolution curve corresponding to loading status was then determined.The fracture pattern of coal samples determined by micro-CT scan was observed and discussed.It has been found by this paper that brittle coal of uniaxial compression tests demonstrated sudden failure caused by major splitting fracture while that of cyclic fatigue tests experienced progressive failure with mixture fracture network.

Uniaxial compressive behaviour of a FRP standing support made of mine wastes

Twenty-seven specimens were tested to investigate the uniaxial compression behaviour of an innovative standing support for underground space applications.The innovative standing support consisted of an external fibre reinforced polymer(FRP)jacket and the infill column made of cementitious grout,tailings and coal wash rejects.Effects of the FRP layers number and water to the cementitious grout(w/g)ratio were evaluated.Test results indicated that lower w/g ratios produced stronger infill columns.With FRP confinement,the standing support demonstrated strain-hardening loading characteristics with a significant improvement in both strength and ductility.The highest strength and strain of the specimens achieved was 58.4 MPa and 11.8%respectively.Compared with the unconfined specimens,the confinement with four FRP layers increased the specimen strength and associated strain up to 3.6 and 27.0 times respectively.A correlation between the compressive strength of the infill material and the ultrasonic pulse velocity was also investigated.Furthermore,a simple design-oriented model was proposed to predict the peak strength and the corresponding strain of the innovative standing support.

A new scientific explanation to rock fracture-induced electromagnetic radiation process

The electromagnetic radiation(EMR)monitoring and early warning technology has experienced decades of successful applications for worldwide coal and rock dynamic disasters,yet a fundamental model unifying physical mechanism and generation process for EMR is still lacking.The effective revealing of EMR's mechanism is crucial for dynamic disaster control and management.With this motive,a multi-scale experimental study was conducted in the earlier stage.At the micro-scale,the charge's existence and non-uniform distribution on rock's micro-surface were confirmed by atomic force microscope(AFM),and deduced the relationship with load changes.At the meso-scale,the time sequence synchronization and frequency domain consistency of EMR and micro-vibration(MV)in the rock fracture under load have been confirmed.Therefore,it is inferred that the vibration of the crack surface acts as the power source of rock fracture-induced EMR,and the original charge on the crack surface and the charge generated by the new crack surface are the electrical basis of EMR.Based on the above two experimental findings,this paper proposes a new mechanism of rock fracture-induced EMR defined as the electricity-vibration coupling mechanism,stating that,the vibrating charged crack generates the EMR.Subsequently,a generation model was constructed based on vibrating charged crack clusters to elucidate this mechanism.The experimental results demonstrated that the EMR waveform calculated by the model and measured by antenna exhibited good correspondence,thereby verifying the effectiveness of the constructed EMR model.The proposal of this new mechanism and the model further clarified the EMR's mechanism induced by rock fracture.Moreover,the inter-relationship among crack propagation,vibration,and EMR was developed by this model,which could be immensely beneficial in EMR-based identification and prediction of dynamic disasters in complex mining environments worldwide.

澳大利亚采矿工程教学方案制定与课程体系结构

在介绍澳大利亚采矿工程教育的基本情况、分析澳大利亚采矿工程专业教学方案的制定方式以及对澳大利亚8所主要开设采矿工程专业的大学的课程设置进行了详细的对比之后,归纳出澳大利亚采矿工程专业教学方案制定和课程体系结构设置的五个特点,即充分重视专业认证、多方面参与共同确定课程方案、系统全面的工程基础课程以及内容丰富的选修课程、注重实践环节的特点。

混合所有制企业在金融危机中的绩效表现与恢复能力研究

本文以2008年国际金融危机为背景,通过比较不同所有制结构的上市公司在金融危机期间的绩效表现及恢复能力,探究我国混合所有制企业的国有股成分与股权制衡类型对公司绩效的影响,以及非国有股东引入的优序选择问题。利用我国2005—2011年上市公司面板数据,本文通过Probit模型回归等实证分析发现:(1)在国际金融危机期间,国有股比例越高的上市公司绩效越好;(2)国有股比例越高的公司越不容易发生业绩下降问题;(3)后金融危机阶段,国有股比例越高的公司并不一定更易恢复,相反,当其作为民营企业的制衡股东时,国有股东更能帮助企业提升危机恢复能力。除国有股东外,混合所有制类型也会对企业的绩效产生影响,概言之:(1)金融危机发生时,有制衡股东的企业比无制衡股东的企业更易从危机中恢复;(2)在国有和民营资本组成的混合所有制企业中,民营控股型企业业绩明显好于国有控股型企业。本文从实证角度为国有企业改革中控制权的适时转移提供了有力支持,当前国有股减持并积极引入非国有股东的做法是提升国有企业绩效的有效途径,但在混合所有制改革中还需特别注重国有及非国有资本间的股权配置问题,以充分发挥股东间的制衡与协同效应。

Experimental Study of the Adsorption-Induced Coal Matrix Swelling and Its Impact on ECBM

Carbon dioxide （CO2） enhanced coalbed methane （ECBM） is an effective method to im- prove methane （CH4） production and this technology has already been used to increase gas production in several field trials worldwide. One major problem is the injection drop in the later period due to permeability decrease caused by coal matrix swelling induced by CO2 injection. In order to quantify the swelling effect, in this work, coal samples were collected from the Bulli coal seam, Sydney Basin and adsorption tests with simultaneous matrix swelling measurement were conducted. The adsorption and swelling characteristics were analyzed by measuring the adsorption mass simultaneously with the strain measurement. Then experiments were conducted to replicate the ECBM process using the indi- rect gravity method to obtain the swelfing strain change with CO2 injection. The results show that the coal adsorption capacity in CO2 is almost two times greater than that in CH4, and nitrogen adsorption is the least among these gases. A Langmuir-fike model can be used to describe the strain with the gas pressure and the swelling strain induced by gas adsorption has a Hnear relationship with gas adsorp- tion quantity. Moreover, swelling strain increase was observed when CO2 was injected into the sample cell and the swelling strain was almost the sum of the strains induced by different gases at correspond- ing partial gas pressure.

Resignation of officials as independent directors and firm performance

In 2013,the Chinese government implemented Rule No.18,which suspended the directorships of incumbent government officials and precluded those who retired within the past three years from serving as independent directors for listed firms.The surprise implementation of Rule No.18 triggered a wave of resignations among official independent directors(OIDs).The event provided a unique opportunity to examine the impacts of the political connections of board members on firm performance.We applied a difference-in-difference technique to empirically investigate the effect of OID resignations on firm performance from the perspectives of resource dependence theory and social capital theory.The results indicate that the resignation of OIDs had a significantly negative effect on firm performance,as measured by Tobin's 0 and firm leverage.This also confirmed the importance of independent directors'political connection on firm performance,as discovered in prior research.However,this influence varied across OIDs'heterogeneity,external environment and firm ownership.The results indicate that political connections may not be necessary channels for firms to achieve success.

Stabilized oil production conditions in the development equilibrium of a water-flooding reservoir

Water injection can compensate for pressure depletion of production.This paper firstly investigated into the equilibrium issue among water influx,water injection and production.Equilibrium principle was elaborated through deduction of equilibrium equation and presentation of equilibrium curves with an“equilibrium point”.Influences of artificial controllable factors(e.g.well ratio of injection to production and total well number)on equilibrium were particularly analyzed using field data.It was found that the influences were mainly reflected as the location move of equilibrium point with factor change.Then reservoir pressure maintenance level was especially introduced to reveal the variation law of liquid rate and oil rate with the rising of water cut.It was also found that,even if reservoir pressure kept constant,oil rate still inevitably declined.However,in the field,a stabilized oil rate was always pursued for development efficiency.Therefore,the equilibrium issue of stabilized oil production was studied deeply through probing into some effective measures to realize oil rate stability after the increase of water cut for the example reservoir.Successful example application indicated that the integrated approach was very practical and feasible,and hence could be used to the other similar reservoir.