Size distribution measurement of coal fragments using digital imaging processing

This paper focuses on the size distribution measurement of coal fragments by digital imaging processing. The fast and precise measurement of coal fragments, which is important to understand the crack propagation and energy dissipation process of coal failure, has not been achieved by previous research. In this paper, an image analysis method using MATLAB is proposed to measure fragment size distribution of coal fragments. The acquisition setup, analysis step and coding process for fragment size distribution measurement by digital imaging processing are introduced in detail. The statistical size distribution of coal fragments measured by image processing is compared with the theoretical distribution function and manual sieving results. This paper provides an innovative and efficient method for size distribution measurement in the study of coal failure process

A review of energy sources of coal burst in Australian coal mines

Abstract: Coal burst, which refers to the violent and catastrophic failure of coal, is a serious safety hazard for underground coalmines. Coal burst has attracted intensive research interest from mining and geological scholars. Due to the shallow mining depth, simple geological condition, advanced mining technology and reasonable geotechnical design, coal bursts has not been identified as a safety hazard in Australia coalmines as there are no documented coal bursts cases in Australia before 2014. However, more recently, the coal burst risk in Australian coalmines was highlighted by coal burst accidents in some coalmines. This paper reviewed the potential energy sources and their influence on past coal burst accidents in Australia. It is believed that the previous coal burst accidents in Australia are more likely to be the dynamic failure of highly stressed coal triggered by small-scale dynamic disturbance. Coal burst propensity index method and micro seismic monitoring technic are recommended to indicate coal burst risk before and during mining activities

Coupled cfd-dem modelling of mine dust dispersion in underground roadway

Dust particles floating inside roadways are characterized by various sizes. However, it is difficult to replicate the dust environment with such factors taken into consideration in laboratory experiments. Fortunately, computational technology provides an alternative way for that. In this study, in order to investigate the movement mechanism of dust with different diameters from heading face in the underground roadway, a three-dimensional CFD-DEM coupling numerical model is presented using the Eulerian-Lagrangian method. A numerical roadway model based on a practical engineering case has been established for the purpose of studying the dust diffusion under single-forced ventilation condition in roadway underground. The study suggests that particle size has a significant effect on dust dispersion. The results demonstrate that CFD-DEM coupling computational simulation can be an effective approach for the investigation of dust issues in underground engineering

The development of a novel backfilling technology: concept and behaviour

A novel backfilling method for underground coal mines has been recently proposed at the University of Wollongong. Different from traditional backfilling technology (i.e. solid backfilling and paste backfilling), the main feature of this technology is that cementitious material with high water-to-solid ratio is directly pumped into the gob filled with coal reject aiming to fill the large number of voids. To verify the feasibility and potential advantages of this new technology compared to its counterparts, a series of compression tests have been conducted. A total of four cubic samples with the dimension of 300 mm and the height of 150 mm have been tested to better understand the effect of cementitious material on the compressive behaviour of the combined backfill. The experiment results show that the strength of combined material with confinement is significantly affected by the coal reject filling coefficient. Based on the experimental observations, the compressive behaviour of the combined backfilling consisting of three typical stages, namely initial compacting stage, support improving stage and stable sedimentation stage has been determined

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 θ between the bedding planes and load direction. With θ increaseing from 0° to 90°, the strength first decreased and subsequently increased and specimens became most vulnerable when θ 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 θ of 30° or 45° reduced the specimens\u27 ability of storing strain energy to the lowest with fewer cracks observed after failure

Influence of human body size on lower limb injury parameters in car-pedestrian collisions

Lower extremities are the most vulnerable parts in vehicle-pedestrian traffic accident. At present, EC78/2009 (European Community.No78/2009) and GTR9 (Global Technical Regulation.No.9) are the major regulations of pedestrian protection. A fixed mass and length of lower leg impact or is applied to predict the lower limb injuries in these regulations. But, in the real world, the pedestrian\u27s body characteristics, such as height and weight, are significantly different, therefore there may exist certain limitations in the present regulations for testing the injury parameters of lower limbs. In current study, three typical car models and three different percentile pedestrian models were established using multi-body dynamics method. Then the influence of pedestrian weight and height on lower limbs injuries were thoroughly investigated by comparing the tibia acceleration, shear displacement and bending angle of the knee. The results showed that the maximum knee shear displacement rose up as the height and weight of pedestrian models increased. While the knee bending angle was greatly affected by the collision location of the vehicle to pedestrian, the collision position was closer to the knee joint, the bending angle was bigger. The maximum tibia acceleration illustrated different variation tendency with the change of vehicle front structure

Estimation of average ejection velocity generated by rib burst under compression load

The ejection velocity associated with coal burst is an important parameter for support and protection structure design against coal ejection, as the support or protection design rationale is to dissipate or absorb the kinetic energy carried by ejected coal. This paper provides a novel method to estimate the average particle ejection velocity of rib burst based on the energy dissipation and coal fragmentation of coal brittle failure. This research shows that the scale of kinetic energy released by coal burst in underground roadways can reach over 107 J, which can offer ejected coal with an over 26 m/s initial velocity and cause serious even fatal injury to miners without sufficient protection

Analysis of energy accumulation and dissipation of coal bursts

Coal bursts are a serious dynamic hazard for underground coalmines, and they attract the extensive interest of studies from mining and geotechnical researchers worldwide. More recently, coal-burst incidents were reported in some Australian coalmines as a result of inadequate geological assessment of coal-burst hazards. The coal-burst process is closely associated with the accumulation of elastic energy and the rapid dissipation of kinetic energy. This paper introduces the essential geological conditions for energy accumulation, and the likely precursors for rapid energy dissipation leading to coal burst, which can be used by Australian coalmines to determine their coal-burst risk accordingly. Different energy forms and their transformations during the coal-burst process are introduced in detail in this paper. The dominant geological factors resulting in the accumulation of massive energy are analyzed, and the likely precursors associated with the instant release of elastic energy are discussed

Numerical study on the fracture characteristics and failure mode of hard coal under coupled static and dynamic loads

It has been well accepted by mining researchers that coal tends to undergo abrupt fracture under the coupling effect of dynamic and static loads. Hence, the study of influence of coupled static and dynamic loads on coal failure behaviour is meaningful for the understanding of coal burst. In this paper, PFC modelling of SHPB test is adopted to investigate the fracture mode and energy evolution of Australian hard coal under different combinations of pre-stress levels and impact velocities. Results have shown that high dynamic load will make the fracture mode and energy release of coal samples more violent even the static load is low. Although the strain energy increases with pre-stress level, the kinetic energy remains on a low level with the increase of pre-stress level when the impact velocity is 4 m/s