Experimental and numerical modelling investigations into coal mine rockbursts and gas outbursts

Rockbursts and gas outbursts are a longstanding hazard in underground coal mining due to their sudden occurrences and high consequences. These hazards are becoming prominent due to the increase in mining depth, difficult mining conditions, and adverse gas pressure conditions. Several researchers have proposed different theories, mechanisms, and indices to determine the rockbursts and gas outbursts liability but most of them focus on only some aspects of the complex engineering system for the ease to represent them using partial differential equations. They have often ignored the dynamics of changing mining environment, coal seam heterogeneity and stochastic variations in the rock properties. Most of the indices proposed were empirical and their suitability to different mining conditions is largely debated. To overcome the limitations of previous theories, mechanisms and indices, a probabilistic risk assessment framework was developed in this research to mathematically represent the complex engineering phenomena of rockbursts and gas outbursts for a heterogeneous coal seam. An innovative object-based non-conditional simulation approach was used to distribute lithological heterogeneity occurring in the coal seam to respect their geological origin. The dynamically changing mining conditions during a longwall top coal caving mining (LTCC) was extracted from a coupled numerical model to provide statistically sufficient data for probabilistic analysis. The complex interdependencies among several parameters, their stochastic variations and uncertainty were realistically implemented in the GoldSim software, and 100,000 equally likely scenarios were simulated using the Monte Carlo method to determine the probability of rockbursts and gas outbursts. The results obtained from the probabilistic risk assessment analysis incorporate the variations occurring due to lithological heterogeneity and give a probability for the occurrence of rockbursts, coal and gas outbursts, and safe mining conditions. The framework realistically represents the complex mining environment, is resilient and results are reliable. The framework is generic and can be suitably modified to be used in different underground mining scenarios, overcoming the limitations of earlier empirical indices used.Open Acces

Rockburst in underground excavations: A review of mechanism, classification, and prediction methods

Technical challenges have always been part of underground mining activities, however, some of these challenges grow in complexity as mining occurs in deeper and deeper settings. One such challenge is rock mass stability and the risk of rockburst events. To overcome these challenges, and to limit the risks and impacts of events such as rockbursts, advanced solutions must be developed and best practices implemented. Rockbursts are common in underground mines and substantially threaten the safety of personnel and equipment, and can cause major disruptions in mine development and operations. Rockbursts consist of violent wall rock failures associated with high energy rock projections in response to the instantaneous stress release in rock mass under high strain conditions. Therefore, it is necessary to develop a good understanding of the conditions and mechanisms leading to a rockburst, and to improve risk assessment methods. The capacity to properly estimate the risks of rockburst occurrence is essential in underground operations. However, a limited number of studies have examined and compared yet different empirical methods of rockburst. The current understanding of this important hazard in the mining industry is summarized in this paper to provide the necessary perspective or tools to best assess the risks of rockburst occurrence in deep mines. The various classifications of rockbursts and their mechanisms are discussed. The paper also reviews the current empirical methods of rockburst prediction, which are mostly dependent on geomechanical parameters of the rock such as uniaxial compressive strength of the rock, as well as its tensile strength and elasticity modulus. At the end of this paper, some current achievements and limitations of empirical methods are discussed

Mathematical Problems in Rock Mechanics and Rock Engineering

With increasing requirements for energy, resources and space, rock engineering projects are being constructed more often and are operated in large-scale environments with complex geology. Meanwhile, rock failures and rock instabilities occur more frequently, and severely threaten the safety and stability of rock engineering projects. It is well-recognized that rock has multi-scale structures and involves multi-scale fracture processes. Meanwhile, rocks are commonly subjected simultaneously to complex static stress and strong dynamic disturbance, providing a hotbed for the occurrence of rock failures. In addition, there are many multi-physics coupling processes in a rock mass. It is still difficult to understand these rock mechanics and characterize rock behavior during complex stress conditions, multi-physics processes, and multi-scale changes. Therefore, our understanding of rock mechanics and the prevention and control of failure and instability in rock engineering needs to be furthered. The primary aim of this Special Issue “Mathematical Problems in Rock Mechanics and Rock Engineering” is to bring together original research discussing innovative efforts regarding in situ observations, laboratory experiments and theoretical, numerical, and big-data-based methods to overcome the mathematical problems related to rock mechanics and rock engineering. It includes 12 manuscripts that illustrate the valuable efforts for addressing mathematical problems in rock mechanics and rock engineering

An investigation into gas emission and outburst control in thick seam coal mining

Nowadays, coal mining is extending to deeper and deeper levels, facing ever increasing coal seam gas contents, much higher gas emissions and outburst risks. Capturing coal seam gas before it migrates into atmosphere has been seen as an effective approach to simultaneously improve mining safety, reduce greenhouse gas emissions, and produce clean energy. Thick seams account for a considerable share of global coal reserve. The application of longwall top coal caving (LTCC) method to extract thick seams generally yields a much higher productivity and is more efficient in comparison to a mechanised single-slice longwall panel. However, the greater productivity achieved by LTCC may further exacerbate the gas emission problems often faced in longwall mining. Geomechanical response of the strata and associated gas emission patterns around thick seam layouts are significantly different from coal mining under thinner multi-seam mining conditions, which is not well understood. This thesis focuses on establishing an understanding of the stresses, pressure regimes, and gas emission patterns around advancing LTCC faces. During the PhD research, gas pressure and gas concentration were measured in a large number of boreholes in and around an advancing LTCC face at a coal mine. These data are complemented with ventilation and seismic monitoring programmes at the same LTCC district. An integrated analysis of the monitoring data has been carried out and conceptual models for gas emission and drainage for LTCC faces have been developed. These were later used as the basis for numerical modelling research. A two-way sequential coupling of a geomechanical simulator with a reservoir simulator has been achieved, whereby mining induced stresses and pressures are linked by two coupling parameters: permeability and pore pressure. By applying this approach, gas emission during coal extraction at a LTCC panel in the study coal mine has been successfully modelled and history matched with field data. Recognising that coal and gas outbursts are the most serious and violent gas emissions in both thick and thin seam mining, the application of the coupled modelling approach has been further extended to model two common types of outbursts experienced in an outburst-prone coalfield. Gas drainage before mining is a standard gas emission control technique, however, its application is largely limited to high permeability coal seams and roof/floor source seams undermined/overmined by single level longwall mining. The feasibility of utilising mining induced permeability enhancement zones to drain gas at thick and tight seams mined by multi-level LTCC method was studied via field trials and numerical models. Building upon the gas emission model developed earlier, a parametric study was carried out to assess different borehole layouts in order to optimise gas drainage designs. It is believed that the findings of this research and gas drainage methods developed for thick seam mining will create a safer underground environment for miners at high productivity LTCC panels.Open Acces

Modern Observational Techniques for Comets

Techniques are discussed in the following areas: astrometry, photometry, infrared observations, radio observations, spectroscopy, imaging of coma and tail, image processing of observation. The determination of the chemical composition and physical structure of comets is highlighted

Advances in Unconventional Oil and Gas

This book focuses on the latest progress in unconventional oil and gas (such as coalbed methane, shale gas, tight gas, heavy oil, hydrate, etc.) exploration and development, including reservoir characterization, gas origin and storage, accumulation geology, hydrocarbon generation evolution, fracturing technology, enhanced oil recovery, etc. Some new methods are proposed to improve the gas extraction in coal seams, characterize the relative permeability of reservoirs, improve the heat control effect of hydrate-bearing sediment, improve the development efficiency of heavy oil, increase fracturing effectiveness in tight reservoirs, etc

Design and Implementation of Coal Mine Physiological Parameters Monitoring Protocol

Modernization in the industries also concerns with the safety of workers especially for underground mining?s. This paper mainly deals with surveillance and safety measures for mine workers, which is most essential in underground mining areas. Here, a concept of wireless sensors network is used to monitor the environment parameters of underground mine area and all sensed parameters are sent to host computer. Arduino Microcontroller is a heart of a system used to build a fully automated measuring system with reliability, high accuracy and smooth control. Upon detecting critical conditions, alert system starts and the same information is transmitted to remote location by ZigBee Communication. The observed changes in the parameters will also be displayed on the host computer at base station which makes it easier for the underground control center to monitor and to take necessary immediate action to avoid damages

Against the Tide. A Critical Review by Scientists of How Physics and Astronomy Get Done

Nobody should have a monopoly of the truth in this universe. The censorship and suppression of challenging ideas against the tide of mainstream research, the blacklisting of scientists, for instance, is neither the best way to do and filter science, nor to promote progress in the human knowledge. The removal of good and novel ideas from the scientific stage is very detrimental to the pursuit of the truth. There are instances in which a mere unqualified belief can occasionally be converted into a generally accepted scientific theory through the screening action of refereed literature and meetings planned by the scientific organizing committees and through the distribution of funds controlled by "club opinions". It leads to unitary paradigms and unitary thinking not necessarily associated to the unique truth. This is the topic of this book: to critically analyze the problems of the official (and sometimes illicit) mechanisms under which current science (physics and astronomy in particular) is being administered and filtered today, along with the onerous consequences these mechanisms have on all of us.\ud \ud The authors, all of them professional researchers, reveal a pessimistic view of the miseries of the actual system, while a glimmer of hope remains in the "leitmotiv" claim towards the freedom in doing research and attaining an acceptable level of ethics in science

Study on Energy Accumulation and Dissipation Associated with Coal Burst

Coal burst, which refers to the brittle failure of coal, has been a serious hazard for underground coal mining, particularly at greater depth. Massive energy accumulated in coal could be dissipated almost instantaneously in the form of kinetic energy when the loading stress exceeding the ultimate strength of coal. This thesis qualitatively and quantitatively examines the energy accumulation and dissipation process associated with coal burst through a comprehensive research program of literature review, theoretical analysis and experimental studies. The energy accumulation sources, dissipation forms and its influencing factors of coal burst are reviewed based on the energy conservation law and the static-dynamic loads superposition theory. The burst energy is provided by static loads including gravitational and abutment stress, and dynamic loads including fault slipping and roof weighting. Studies indicated that the main driving energy source of coal burst occurred in Australian coal mines resulted from elastic energy storage that has been accumulated during the loading process of coal