Sudden Gas Research Articles

Gas-dynamic roof fall during the potash deposits development

In the development of practically all potash salt deposits, the study of gas-dynamic phenomena (GDP) is one of the most difficult tasks to ensure mining safety. Sudden salt and gas outbursts, dynamic breakdown, which are accompanied by intense gas release and possible broken rock carry-over into the mine workings, are associated with GDP. Geological preconditions for the GDP development are often the layered structure of the salt rock mass, the presence of interlayers and layers of salt clays.
 For the conditions of the Usolsky potash plant mine, complex studies of factors that characterize the possibility of gas-dynamic roof fall of the stoping rooms were carried out. In mine studies, free gases pressure and the initial velocity of gas release in the rocks of the roof workings were determined. The obtained experimental estimations were used as a parametric basis for mathematical modeling of geomechanical processes under conditions of a near-contact accumulation of free gas.
 The deformation of a layered salt mass produced by a room development system was described by the model of an ideal elastic-plastic medium with internal friction. The parabolic envelope of Mohr circles was used as a plasticity criterion in the compression area. In the numerical implementation, the deformation of clay contacts was modeled by Goodman contact elements. Based on the results of multivariate numerical calculations, it is established that the main factors determining the possibility of implementing GDP are the additional gas pressure at the contact, the width of the workingspan, and the distance from the roof to the first gas-containing contact. With multi-level lamination of roof rocks, there is a danger of large sources of GDP formation and the mechanism of successive fall of layers in an instant mode is implemented.

Mechanical behaviour and seepage characteristics of coal under the loading path of roadway excavation and coal mining

The mechanical behaviour and seepage characteristics of coal under the mining engineering disturbance are of great significance to prevent gas disasters. Based on the geological conditions of the No. 12 mine of the China Pingdingshan Mining Group, the mechanical seepage experiments of coal under the stress path of roadway excavation and coal mining were carried out. The experimental result shows that: The coal in fracture zone is most strongly affected by the roadway excavation. The samples showed obvious expansion phenomenon, and their cracks were the most complex. They formed effective permeability before the peak strength, and their permeability was the largest; the coal in disturbance zone is less affected by roadway excavation, and the coal samples formed effective permeability after the peak strength. Their permeability was smaller than the samples in fracture zone; the coal in original rock stress zone is only affected by coal mining, and its crack growth degree is the lowest. The coal samples formed stable permeability in the residual strength stage, and their permeability was the smallest. In practical engineering, special attention should be paid to the sudden gas gushing caused by the sudden increase of coal seam permeability, which will cause gas disaster.

Transition processes in coal field development in the light of intelligent control

Relevance of the work. The problem of sudden outbursts of coal and gas has been studied for more than a century and a half using various approaches to study this process. In order to prevent accidents and conduct safe mining operations. Today this problem remains relevant in the territory of the Russian Federation. In connection with the changed external and internal challenges of the development of coal mining at Russian mining enterprises, it is proposed to consider the problem in the light of two aspects, one of which is the geographical location of subsoil use objects and intelligent control. Objective. The work is devoted to the study of the development of transient processes at a coal mining enterprise from the standpoint of intellectual management. The task of the work is to create in the first approximation an industrial knowledge graph. Method and methodology of the work. The study is based on a problem-oriented approach to solving the issue of safe mining, namely, to thoroughly study the problem of sudden emissions of coal and gas before the release occurs. To solve the existing problem, it is proposed to create an industrial graph of knowledge, taking into account the peculiarities of geomechanical processes occurring in the mountain range. In the created industrial knowledge graph, the main classes are shown that contribute to the presentation and structuring of knowledge about the causes of sudden coal and gas outbursts for a particular coal seam being put into production. Results. Because of the study, based on the construction of an industrial knowledge graph, we can conclude that it is necessary to create a classification with geomechanically specific phenomena and their features. Study of normative and reference information and identification of semantic patterns in them. All these studies are complicated by the large volumes of data, their fragmentation, and in some cases the unreliability and inconsistency of information. When obtaining a semantically non-contradictory industrial graph of knowledge, knowledge can be “useful” for constructing a mathematical model for predicting sudden coal and gas emissions.

Approach to creating an integrated model for research forecast of extraordinary emissions of coal and gas

The article sets out an approach to the study and creation of a comprehensive model of sudden coal and gas emissions, from the standpoint of applying the theory of creating expert systems and the theory of intelligent control, based on the idea of studying the emission before it occurred, taking into account classification genetically specific phenomena and their signs, allowing to consider the sudden release of coal and gas not in general, but under specific conditions. The objectives of this work are to provide an overview of the existing mining, technological and geophysical methods used to forecast sudden coal and gas emissions, as well as to propose intelligent control methods for the process of studying the occurrence of sudden coal and gas emissions, with a view to further forecasting. The paper proposes an algorithm for studying the occurrence and forecast of sudden coal and gas emissions within the framework of the idea of an interdisciplinary approach. Research methods are proposed, such as fuzzy logic methods, decision-making methods in conditions of risk, decision-making methods in conditions of uncertainty, methods of variable states. The main recommendations for the construction of an integrated model of sudden emissions of coal and gas are given. If it is impossible or difficult to build a model, a recommendation is given on the decomposition of the model using causality logic, namely with the use of ontologies, that is, the creation of industrial knowledge graphs.

Collinear dual-pulse laser optical breakdown and energy deposition

A non-equilibrium model for laser-generated plasmas is used to represent collinear dual nano-second-pulse interactions. In the specific case considered, the breakdown is initiated with an ultraviolet (UV) laser pulse at 266 nm, which pre-ionizes the gas, and it is followed by a near-infrared (NIR) pulse at 1064 nm, which deposits significant energy into the ionized mixture. The model is validated against corresponding experiments, and simulation results are interrogated to understand key features of the plasma-kernel dynamics and the post-discharge hydrodynamics. The hydrodynamics of the non-equilibrium plasma is governed by the two-temperature Navier–Stokes equations accounting for both multiphoton ionization and inverse bremsstrahlung. The interaction between the laser beam and the plasma is modeled based on the radiative transfer equation. The temporal and spatial offsets of the two pulses can generate ionization kernels with different topology and dynamics. It is shown that the UV pre-ionization pulse can tailor the plasma region, leading to a larger ionized volume than would occur for a single-pulse breakdown, and it increases the efficiency of the energy deposition for the following NIR discharge. Vorticity in the early post-discharge phase is generated via baroclinic torque from the misalignment of the radial gradient of density (sudden gas expansion) and the strong pressure gradient (initiated by energy deposition from the laser beam). It is predicted that the collinear dual pulse can be designed to specify the plasma kernel size, shape, and maximum temperature in the breakdown phase, and the initial post-breakdown vorticity and plasma-core decay.

Corrosion behaviours of Ti6Al4V-Mg/Mg-Alloy composites

The effect of coupling of unalloyed Mg and Mg-alloys (AZ91 and WE43) with Ti6Al4V alloy on corrosion and degradation behaviours of produced composites has been investigated in simulated body fluid (SBF) by hydrogen evolution, and surface and electrochemical characterization techniques. Combining of unalloyed Mg with Ti6Al4V intensified galvanic corrosion and catastrophic failure occurred by initiation of microcracks formed by sudden hydrogen gas evolution. In contrast to other composites, Ti6Al4V-AZ91 composites, containing new TiAl3 interface layer formed during composite production, preserved their mechanical integrities due to lowest corrosion and degradation rate of AZ91 alloy.

Methane gas hydrates influence on sudden coal and gas outbursts during underground mining of coal deposits

The mechanism of gas hydrates formation in coal seams is studied in the paper, as well as their involvement is hypothesized in the sudden outbursts of coal and gas during underground mining of coal deposits. It has been substantiated and proved that one of the real reasons for subsequent outbursts is the formation of gas hydrates in coal as a type of secondary gas hydrate deposits. It has been also substantiated that, as a result of coal metamorphism, a large amount of gaseous hydrocarbons, mainly methane, is formed in the seam, which under certain thermobaric conditions leads to the gas hydrates formation. It has been experimentally proved that the mechanism of such inclusions formation between gas hydrate and coal is a result of strong chemisorption, which, when disturbing thermobaric conditions, leads to gas-dynamic activity of coal seams. It has been revealed that during the dissociation of gas hydrates, obtained in a medium of activated coals, twice as much gaseous methane is released. The research analysis indicates that the formation of natural gas solid solutions in coal pores under certain thermodynamic conditions and the natural humidity, characteristic of coal seams, is one of the causes of sudden coal and gas outbursts. The gas hydrates dissociation influences on the gas-dynamic activity of a coal seam and the formation of an outburst hazardous situation.

Representation of the process of sudden outbursts of coal and gas using a knowledge graph

In the process of developing a coal deposit, significant amounts of data and extensive knowledge about the object of operation are accumulated. This data and knowledge may not be structured, not reliable, contradictory. In turn, for the further conduct of the entire complex of mining operations and the development of a coal mining enterprise, structured and reliable data and knowledge are needed. The aim of the study is to propose structuring knowledge about the process of sudden outbursts of coal and gas by presenting knowledge about the subject of research in the form of an elementary knowledge graph. The study is based on an ontological approach to solving the issue of safe mining, namely, to study the problem of sudden emissions of coal and gas from the standpoint of the fact that the release is considered before it has occurred. To solve the existing problem, it is proposed to create an elementary knowledge graph that takes into account geological, hydrogeological, geophysical, mining information about the subsoil use object, as well as geomechanical and geodynamic processes, and physicochemical mass transfer processes occurring in the coal seam and the accumulated experience and knowledge of miners using methods Data mining. As a result of the study, we can conclude that it is necessary to create a network of elementary knowledge graphs, and use other methods of knowledge extraction. For further analysis and refinement of data and knowledge about the process of sudden coal and gas emissions.

Simulation of dynamic phenomena in the ventilation network due to sudden gas outburst

An increase in the pace of cleaning and preparatory work, a transition to deeper horizons, a high concentration of machines and mechanisms in places where minerals are excavated and transported increase the likelihood of one of the most difficult and dangerous types of underground accidents - sudden outbursts of coal, rock and gas. In the event of a sudden outburst, the air distribution existing in the ventilation network experiences a sharp dynamic effect, leading to a violation of the stability of the ventilation of the workings close to the center of the outburst and the overturning of the air flow in them. The methane released in this case forms an atmosphere dangerous for humans in the adjacent workings. The size of the gas contamination zone depends on many factors: the intensity of the outburst, the ventilation scheme of the mine, the presence of ventilation facilities, their number, and others, and can become the object of special studies, including the study of the outburst process itself and its interaction with the ventilation network. The specificity of the occurrence of an oytburst as a type of accidents does not allow obtaining statistical and experimental results directly during its course, which greatly complicates the study of this process. In this regard, the most acceptable research method that allows assessing the results of the interaction of the outburst with the ventilation network and, guided by them, to develop effective measures to eliminate its consequences and restore the normal functioning of the mine, is the simulation method using a PC. The article analyzes the stages of changes in the mining-geological and mining-technical conditions preceding the occurrence of the outburst, the stage of the outburst, the calculation formulas are given, by which it is possible to evaluate the configuration and dynamics of the development of the zone polluted with methane as a result of the outburst. The results of modeling the gas-dynamic manifestations of the outburst and its effect on the state of mine ventilation are of great importance in ventilation calculations in emergency modes in order to use the possibilities of ventilation effects on an emergency, limit emergency zones and increase the effectiveness of eliminating the consequences of an accident.

ДО ПИТАННЯ ПРОГНОЗУ ВИКИДОНЕБЕЗПЕЧНОСТІ ВУГІЛЬНИХ ПЛАСТІВ ЛЬВІВСЬКО-ВОЛИНСЬКОГО БАСЕЙНУ

Sudden coal and gas outbursts in coal mines are one of the most harmful and at the same time, dangerous gas-dynamic phenomena faced when coal producting. The sudden coal and gas outbursts is the evanescent destruction of the bottom-hole area in the coal bed, which develops from the bottom into the depth of a massif, and the crushed coal with gas is thrown to a long distance from the bottom into the mine, destroying everything in its way, creating the conditions for explosion and fire breaking-out. Sudden outbursts lead to significant material losses for the recovery from an accident and in some cases injuries and human losses. The problem of reliable prediction, prevention, and control of sudden coal and gas outbursts at coal mines remains extremely urgent, due to the constant increase in the depth of mining operations. The analysis of the experience of predicting and preventing the outburst hazard in coal beds of Donets and Lviv-Volyn coal basins is analyzed. At Donbas mines since 1906, there have been more than 7.5 thousand sudden outbursts. Although mining had now reached considerable depths (from 300 to 600 m), the emergence of coal and gas outbursts have not been recorded. The purpose of the research is to determine the depth of the possible emergence of sudden coal and gas outbursts in the LVB, with regard to the peculiarities of the geological structure of the coal-bearing strata in the Lviv-Volyn coal basin. The comparative possible depth estimation in the manifestation of the outburst hazard of the coal beds in the LVB is given. It is calculated according to the normative technique and performed according to the formulas obtained by the statistical analysis for the actual position of the minimum depth of coal and gas outbursts at the Donbas mines. The absence of sudden coal and gas outbursts at LVB mines on the coal beds, which are hazardous according to the prediction data, is performed according to the methods regulated by the normative documents and compiled by the experience of studying the outbursts in Donbas, is explained by the differences in the geological structure of the LVB, the main of which is the presence of thick mass of covering deposits and a significantly greater depth of the methane gas zone. The application of the empirical formulas prediction, which includes the methane gas zone depth index, allows us to account for these differences and it is much more reliable to determine the possible depths of sudden outbursts for LVB, which, all other things being equal, should be greater than in the Donbas. In particular, according to the performed calculations, the outburst hazard situation at the “Stepova” mine is predicted at depths of more than 700 m. As prediction indices for the calculations, values of methane gas zone depths of 450 m were adopted, and the minimum value of volatile-matter yield was 33.3%. This approach can be proposed for predicting the coal and gas outbursts hazard in other Lviv-Volyn basin mines. To determine the predicted depth of the possible emergence of sudden coal and gas outbursts, it is advisable to take into account the depth of the methane gas zone in the prediction calculations.

Numerical simulation for three-dimensional flow in a vortex tube with different turbulence models

Three-dimensional flow in a vortex tube with straight nozzle was investigated numerically. Four different turbulence models, Spalart-Allmaras, standard SST and realizable were proposed to replicate the flow in the vortex tube. The simulation results of pressure, temperature and velocity field were compared with the experimental data based on dimensionless analysis. It was found that the sudden gas expansion in the vortex chamber causes a pressure drop. The secondary circulations phenomena were observed and identified. Furthermore, the friction between the gas and wall surface and the energy transfer between different laminar flows are the main factors of energy separation in the vortex tube. The realizable model predicts energy separation better than other models studied in this research.

Modification of a wideband spectral-acoustic method for controlling stress state of a face space

To control and manage a stress state of an underground working face space it is important to measure the components of actual stresses. Traditional method for relieving a core-sample with central drill is time and labour consuming and is characterized by a lack of accuracy. To improve these issues geophysical methods which do not interfere with mining are to be used for controlling stress state. Acoustic methods are less time and labour consuming. Justification of spectral-acoustic method modification for controlling stress state of a face space is introduced. It is done on the basis of the dependence of the acoustic signal of the operating equipment amplitude-frequency response median on average stresses. The acoustic signal is recorded in the entire sensitivity band of the geophone. The description of a flow chart and operating principle of intrinsically safe portable device for implementing the modification in mines on the seams dangerous on gas and dust and prone to sudden coal and gas outbursts and rock bursts are given. The device operates in three modes: determining amplitudes of background noise and setting signal amplification coefficient; controlling stress state while generating continuous acoustic signal produced by operating mining equipment (combined machine, drilling device, plough-type machine) into the massif; control of stress state during generation a discrete acoustic signal produced by artificial source (heavy hammer strokes) into a massif.

Correlations between quality parameters of some types of unpasteurized beer and consumers safety

Most microalgae cells are very resistant to mechanical and chemical stresses. Because target products are mainly located inside the cells, disruption of the cell wall is an essential step in downstream processing to recover the microalgae ingredients. This study is focused on the development of a mild cell disruption method based on explosive CO2 decompression to allow the recovery of multiple sensitive products.The principle behind cell rupture via explosive decompression is the uptake of a gas under elevated pressure into the microalgae cells, where after a sudden depressurization gas expansion causes rupture of the cells. Conventional explosive decompression uses stirred tank reactors wherein, because of inefficient mixing, the gas/liquid interfacial area is minimal, resulting in long contact times, inefficient gas uptake and inefficient cell rupture. To increase the mixing yield and the formation of a gas-liquid micro-emulsion, a new continuous apparatus and a method were developed to process microalgae biomass by CO2 based explosive decompression. The final design consisted of 2 pumps, a tubing system, a sparger, a hydrodynamic agitation zone and a heated relief valve. Experimental comparison of the conventional batch and the new continuous devices showed that process time was reduced 3.2–9.6 fold, the biomass and biochemical release efficiency increased more than 2 fold, and CO2 consumption reduced 2–4 fold. The method can be considered as mild, since it can operate at room temperature without addition of chemicals. Moreover, the calculated shear rate on the algae cells is only 0.33% of the shear rate recorded during bead milling, while depending on the process parameters releasing a similar amount of biomass components from the cells into the supernatant. The article describes the development of the explosive decompression systems supported by computational fluid dynamics simulations and experimental data on algae cell disruption, complemented with a first techno-economic assessment.

Disruption of microalgae with a novel continuous explosive decompression device

Most microalgae cells are very resistant to mechanical and chemical stresses. Because target products are mainly located inside the cells, disruption of the cell wall is an essential step in downstream processing to recover the microalgae ingredients. This study is focused on the development of a mild cell disruption method based on explosive CO2 decompression to allow the recovery of multiple sensitive products.The principle behind cell rupture via explosive decompression is the uptake of a gas under elevated pressure into the microalgae cells, where after a sudden depressurization gas expansion causes rupture of the cells. Conventional explosive decompression uses stirred tank reactors wherein, because of inefficient mixing, the gas/liquid interfacial area is minimal, resulting in long contact times, inefficient gas uptake and inefficient cell rupture. To increase the mixing yield and the formation of a gas-liquid micro-emulsion, a new continuous apparatus and a method were developed to process microalgae biomass by CO2 based explosive decompression. The final design consisted of 2 pumps, a tubing system, a sparger, a hydrodynamic agitation zone and a heated relief valve. Experimental comparison of the conventional batch and the new continuous devices showed that process time was reduced 3.2–9.6 fold, the biomass and biochemical release efficiency increased more than 2 fold, and CO2 consumption reduced 2–4 fold. The method can be considered as mild, since it can operate at room temperature without addition of chemicals. Moreover, the calculated shear rate on the algae cells is only 0.33% of the shear rate recorded during bead milling, while depending on the process parameters releasing a similar amount of biomass components from the cells into the supernatant. The article describes the development of the explosive decompression systems supported by computational fluid dynamics simulations and experimental data on algae cell disruption, complemented with a first techno-economic assessment.

Toxic gas dispersion prediction for point source emission using deep learning method

Accurate and rapid toxic gas concentration prediction model plays an important role in emergency aid of sudden gas leak. However, it is difficult for existing dispersion model to achieve accuracy and efficiency requirements at the same time. Although some researchers have considered developing new forecasting models with traditional machine learning, such as back propagation (BP) neural network, support vector machine (SVM), the prediction results obtained from such models need to be improved still in terms of accuracy. Then new prediction models based on deep learning are proposed in this paper. Deep learning has obvious advantages over traditional machine learning in prediction and classification. Deep belief networks (DBNs) as well as convolution neural networks (CNNs) are used to build new dispersion models here. Both models are compared with Gaussian plume model, computation fluid dynamics (CFD) model and models based on traditional machine learning in terms of accuracy, prediction time, and computation time. The experimental results turn out that CNNs model performs better considering all evaluation indexes.

RESEARCH CONCERNING OF THE ATTRIBUTION TO THE CONCEPT OF "WORK WITH INCREASED RISK" TRANSFER OF EMPLOYEES IN MINES TO THE PLACE OF PERFORMING WORK

Development of coal deposits in Ukraine is carried out in complicated mining and geological conditions in the presence of high parameters of gas formation, mountain pressure, temperature of enclosing rocks, danger of appearance of sudden coal emissions, rock and gas and the ability of minerals to spontaneous combustion. Being found in mining work places (permanent or temporary stay), as well as while moving to the place of performing work, there is an influence possibility on an employee of hazardous and harmful production factors that by their origin can be of industrial or natural nature. The analysis of accidents in the mining industry demonstrates that accidents occur with the miners who are in the mine, not only while performing a task at the work place, as well as during a descent into the mine leaving the cage on the working horizon, during the movement of mine workings on foot or underground transport to the work place. The research concerning of the attribution to the concept of "work with high risk "of stay of the workers in mine workings while of moving to the place of performing works during carrying out forensic engineering and technical examinations regarding investigation on causes and consequences of emergencies in the mining and underground conditions is carried out. Investigating normative documents and regulations and other sources regarding the regulation of underground works, it possible to conclude that underground staying, namely moving to a workplace by mine working is an operational need, when the worker is located in a dangerous area where he can be exposed to action of hazardous and/or a harmful production factor of natural or anthropogenic origin, therefore the movement of workers in mine workings to the place of performing works is classified as "work with increased danger".

Variations in CO2 emissions at a mud volcano at the southern base of Mt Etna: are they due to volcanic activity interference or a geyser-like mechanism?

Mud volcanoes are often associated with large areas of CO2 and CH4 emission that are potentially dangerous due to sudden paroxysmal gas and mud eruptions. Despite the interest in understanding such natural environments, they have not yet been thoroughly investigated and a single interpretative framework remains to be elaborated. This lack of knowledge may be due to the difficulty in measuring in-plume CO2 as there is very little contrast with atmospheric CO2, coupled with the complex organizational strategies required for long-term monitoring. This work features three different methods that were used to evaluate the CO2 flux at the Salinelle mud volcano in the foothills of Mt Etna (Italy), carried out periodically from December 2013 to April 2018. We computed in-plume CO2 flux indirectly using a tunable laser and a portable MultiGAS and, directly, measuring the gas volumetric flux from bubbling pools. The morphological variations of the mud field were recorded using unmanned aerial vehicle (UAV) imagery, which provided information on the migration of vents in relation to the observed variations in measured gas output. Our analysis shows that the three methods gave comparable values, indicating the feasibility of this approach. Our findings suggest a pseudo-cyclical pattern in the bulk CO2 emitted at Salinelle, introducing a new interpretation of the processes involved in mud volcano dynamics. We theorize that the periodic variation of the gas emitted at the Salinelle may be attributed to a “geyser-like” mechanism that may be subject to interruption or changes in magnitude by volcanic or seismic events.

Hazardous manifestation of gas-dynamic phenomena in the faces of coal mines

The statistics of coal and gas outbursts in the faces of the Russian coal mines is provided. The mining-geological and mining-engineering conditions for the occurrence of sudden outbursts during the coal mining are considered, and the distinctive features in the factors of their occurrence and behavior are discussed. The criteria for identifying the potentially hazardous zones with the help of geophysical measurements are given. It is shown that it is important to take into account the data on the actual occurrence of outburst hazard in overlying and underlying longwall faces and development workings, as well as the results of the current forecast when preparing the extraction area for mining, as it follows from the results of underground investigations. The features are noted and the concept of the mechanism causing sudden coal and gas outbursts of faces is formulated. According to this concept, the probability of a hazardous situation is minimal at the beginning of the face advancement before the primary roof collapse. After the primary caving, the outburst hazard increases with the face advancement from the place of caving due to increased stresses in the bearing pressure zone, strengthening of the restraint of the nearest roof support, and the formation of a low permeable bridge in the coal seam near the exposed surface of the coal massif, which increases the pressure and free gas volume behind this bridge. The maximum degree of outburst hazard in the cleaning face is reached at the time of secondary roof collapses.

Using hydraulic fracturing to control caving of the hanging roof during the initial mining stages in a longwall coal mine: a case study

Hanging roofs can occur on a very large scale (generally can reach 15,000 m2) during the initial mining stages in longwall coal mining operations and are often a result of hard roof at the active mining face. Besides, when it suddenly fractures and caves, some risks and disasters would occur such as shock loading, wind blasts, and sudden gas extrusion from gob to working face. To control the size and competency of the hanging roof, Φ32-mm fracturing drills can create holes in the roof near the front and back coal walls, and Φ32-mm linear fracturing drills can be used to create holes in the roof at the face ends. The length of these drill holes is 3 to 5 times the height of the mining face and is based upon the principle that the gob should be fully filled with a caved roof to support vertical stresses, as well as the assumption that the broken-expansion coefficient of the rock is given as an empirical value. Considering the fracture propagation range and the support form of the cut, the drill-hole spacing is set to be between 1 and 2 times the single-hole crack propagation range. Hydraulic fracturing can generate main fractures and wing-shaped branching cracks inside the roof rock and can transform and weaken the roof structure, forming weak fracture plane favorable to roof caving. These fractures cause the roof to cave in a timely and adequate manner under in situ ground pressures. Successful field test in the no. 2 mine of Cuncaota, Shendong group indicated that the propagation range of hydraulic fractures is approximately 4–8 m. When the active face advanced 22.5 m, the roof beyond the hydraulic supports caves entirely, and gradually, the gob is fully filled with the caved roof and is absent of large voids. Thus, hazards such as shock loading, wind blasts, and sudden gas extrusion can be reduced or eliminated.

Spatial context in the calculation of gas emissions for underground coal mines

The prediction of gas emissions arising from underground coal mining has been the subject of extensive research for several decades, however calculation techniques remain empirically based and are hence limited to the origin of calculation in both application and resolution. Quantification and management of risk associated with sudden gas release during mining (outbursts) and accumulation of noxious or combustible gases within the mining environment is reliant on such predictions, and unexplained variation correctly requires conservative management practices in response to risk. Over 2500 gas core samples from two southern Sydney basin mines producing metallurgical coal from the Bulli seam have been analysed in various geospatial context including relationships to hydrological features and geological structures. The results suggest variability and limitations associated with the present traditional approaches to gas emission prediction and design of gas management practices may be addressed using predictions derived from improved spatial datasets, and analysis techniques incorporating fundamental physical and energy related principles.