nach oben

2016 | Buch

Ground Engineering - Principles and Practices for Underground Coal Mining

verfasst von: J.M. Galvin

Verlag: Springer International Publishing

Enthalten in: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik" , Springer Professional "Wirtschaft"

Einloggen, um Zugang zu erhalten

Über dieses Buch

This book teaches readers ground engineering principles and related mining and risk management practices associated with underground coal mining. It establishes the basic elements of risk management and the fundamental principles of ground behaviour and then applies these to the essential building blocks of any underground coal mining system, comprising excavations, pillars, and interactions between workings.

Readers will also learn about types of ground support and reinforcement systems and their operating mechanisms. These elements provide the platform whereby the principles can be applied to mining practice and risk management, directed primarily to bord and pillar mining, pillar extraction, longwall mining, and sub-surface and surface subsidence.

The text concludes by presenting a framework of risk-based ground control management systems for achieving safe workplaces and efficient mining operations. In addition, a comprehensive reference list provides additional sources of information on the subject. Throughout, a large variety of examples show good and bad mining situations in order to demonstrate the application, or absence, of the established principles in practice.

Written by an expert in underground coal mining and risk management, this book will help students and practitioners gain a deep understanding of the basic principles behind designing and conducting mining operations that are safe, efficient, and economically viable.

Provides a comprehensive coverage of ground engineering principles within a risk management framework

Features a large variety of examples that show good and bad mining situations in order to demonstrate the application of the established principles in practice

Ideal for students and practitioners

About the author

Emeritus Professor Jim Galvin has a relatively unique combination of industrial, research and academic experience in the mining industry that spans specialist research and applied knowledge in ground engineering, mine management and risk management. His career encompasses directing ground engineering research groups in South Africa and Australia; practical mining experience, including active participation in the mines rescue service and responsibility for the design, operation, and management of large underground coal mines and for the consequences of loss of ground control as a mine manager; appointments as Professor and Head of the School of Mining Engineering at the University of New South Wales; and safety advisor to a number of Boards of Directors of organisations associated with mining.

Inhaltsverzeichnis

Frontmatter

1. Scope of Ground Engineering

Abstract

Ground engineering is concerned with the design, construction, operation, maintenance and, ultimately, the closure of safe, serviceable, durable, environmentally sustainable and economic structures built on or within geological materials. It is characterised by pervasive uncertainty and, therefore, needs to be practiced within a risk management framework.

This first chapter notes the wide range of professional competencies involved in ground engineering and some of the models proposed in attempting to clarify interactions between the underpinning and, sometimes, competing disciplines. The three geo-engineering triangles of the practice are defined, being engineering geology; geomechanics; and geotechnical engineering. It is shown how these provide a basis for developing geological models, turning them into ground models and, ultimately, geotechnical models.

The design process in ground engineering is quite different to that in most other branches of engineering. Factors that contribute to this situation in general practice and, more specifically, in an underground environment are presented. The state of the art is reviewed and supported by an appendix that provides a brief history of key developments in ground engineering relevant to underground coal mining.

The chapter concludes by presenting the basic framework for managing risk as a basis for discussing ground engineering in a risk management context in subsequent chapters, with the final chapter dealing with risk based ground management systems in more detail. Evidence is presented of the positive impact that a risk management approach supported by technological innovation has had on the safety and productivity performance of the underground coal mining sector in Australia.

J. M. Galvin

2. Fundamental Principles for Ground Engineering

Abstract

In essence, all underground mining methods are the same, comprising one or more excavations separated by pillars of rock sandwiched at some orientation between the hanging wall and the footwall. The progressive removal of rock to form an underground excavation results in a decrease in the load carrying capacity of the immediate surrounding rock mass, the creation of a void into which the rock mass can displace, and stress changes in a rock mass that is weakened by the removal of confinement. The resulting rock deformation is governed by both the structural and the mechanical properties of the rock mass and the surrounding stress environment.

This chapter commences with an overview of the geological settings of underground coal mines and of the generic types of mining techniques and mine layouts utilised in the given conditions. This provides context to the basic concepts of physics and applied mechanics that control rock deformation and underpin ground engineering. The more fundamental of these are developed from first principles in the remainder of the chapter under the headings of rock mass fabric; physical parameters; material properties; rock mechanics; analysis techniques; and statics. This provides a foundation for developing the principles in more detail and applying them to mine design, stability analysis, operational practices and risk management in later chapters. Their application is not confined to underground coal mining, with many being applicable to any form of excavation made in a geological setting.

J. M. Galvin

3. Excavation Mechanics

Abstract

A mine structure is comprised of three basic building blocks, of which the starting block is an excavation. The development of two separate adjacent excavations results in the formation of the second kind of building block, namely a pillar. The formation of many excavations and pillars requires consideration of a third type of building block, being the surrounding strata. This chapter presents the basic principles of how the rock mass responds to the formation of single and multiple excavations in the same mining horizon.

The changes that take place in the rock mass in the immediate vicinity of an excavation are conceptualised using a number of simple two-dimensional models. The width of an excavation is progressively increased in order to induce caving of the immediate roof strata that, with further increases in excavation span, ultimately result in subsidence of the surface over and outside of the footprint of the excavation. The basic physical and mechanical principles established in Chap. 2 are applied and further developed to account for how mining span, mining depth and the structural and mechanical properties of the superincumbent strata affect the stability of this strata and the maintenance of ground control in the vicinity of active mining faces.

These principles provide the basis for considering three situations where risk may be elevated when employing high percentage extraction mining methods. The situations relate to mining under strong massive strata; to mining in environments subjected to elevated horizontal stress; and to mining at shallow depth. Theoretical and practical aspects associated with each circumstance are discussed. This provides insight into the type of controls required to effectively manage risk.

J. M. Galvin

4. Pillar Systems

Abstract

Underground coal mining is characterised by the formation of extensive areas of pillars. The history of mining continues to be blemished by the failure of pillar systems, often with catastrophic consequences. Examples and their underpinning causes are presented throughout the chapter. Most incidents reflect that pillar system design is deceptively complex, with behaviour and stability governed by both the regional environment, which determines the load acting on the pillars, and the local environment, which determines the strength of the pillars. There is a range of pillar system design methodologies, all having limitations and none being applicable to all circumstances.

This chapter presents the structure for a functional, risk based approach to pillar design. It then builds on the fundamental physical and mechanical principles established in Chaps. 2 and 3, supported by a comprehensive review of historical and contemporary research outcomes, in presenting methodologies for estimating pillar system loads and strengths. Typical factors of safety for pillar systems are noted, with a strong emphasis placed on proceeding to probabilistic based design approaches. An example is provided of one such approach that has proved to be very successful.

Thereafter, types of coal pillar failure modes are reviewed. All of this information provides the basis for then discussing the complexity of coal pillar system behaviour and for signalling out specific critical and practical aspects of coal pillar design for more in-depth discussion. The chapter is supported by an appendix that discusses the application of civil engineering bearing capacity theory to coal pillar foundation performance.

J. M. Galvin

5. Interaction Between Workings

Abstract

Except in some very shallow situations, mining effects on the rock mass extend laterally beyond the boundaries of mine workings, decaying with distance. In all cases, mining effects also extend vertically into the roof and floor strata and, similarly, decay with distance. Hence, mining panels in the same seam and in different seams interact if they are sufficiently close. Assessment of this interaction requires consideration of the behaviour of excavations and pillar systems and of the properties of the surrounding strata.

This chapter applies the basic physical and mechanical principles of rock behaviour established in preceding chapters to consider firstly, interaction between workings in the same seam and, secondly, interaction between workings in multiseam situations. It has a particular focus on understanding and conceptualising how stress and deformation are distributed about mine workings. This forms the basis for designing mine workings in manners that not only avoid exposure to excessively high stress concentrations but also provide opportunities to exploit stress relief methods on both a local and regional scale.

Issues examined in this chapter include chain pillar design; stress notching in longwall gate-roads; stress notching between mining panels; optimising extraction direction in both single seam and multiseam mining situations; exploitation of sacrificial roadways and goaves to create stress relieved zones; superpositioning of bord and pillar workings; superpositioning of total extraction panels and panel entries in multiseam mining situations; optimising the sequence of extracting multiple seams; the impact of remnant pillars; and the potential for inrushes in multiseam mining situations.

J. M. Galvin

6. Support and Reinforcement Systems

Abstract

Once an excavation is formed, it must be ventilated and made secure before persons can venture through it. A wide range of ground support and reinforcement systems are available for securing the surfaces of underground excavations in coal mines. This chapter is focussed on identifying these systems and providing a mechanistic understanding of how they function. This provides an engineering basis for selecting suitable support and reinforcement systems, installing them in an effective manner, and appropriately monitoring the resulting ground response.

The chapter commences by identifying the primary characteristics of any ground support system, being initial stiffness, load capacity, yield capacity and, where appropriate, stability. The distinction is made between the function of a support element and that of a reinforcing element. It then goes on to evaluate support and reinforcement systems under the headings of standing support; tendon support and reinforcing elements; surface restraint systems; spiling; strata binders; and void fillers.

A considerable portion of the chapter is devoted to the anchorage methods for tendon support systems as these play a critical role in tendon performance. The principles of classical beam theory presented in Chap. 2 are then invoked and developed further to provide direction as the type, location, density and timing of installation of ground support systems. The chapter is supported with an extensive selection of photographic illustrations of these systems installed in coal mines along with other figures to help the reader visualise and better understand the underpinning engineering principles.

J. M. Galvin

7. Ground Support Design

Abstract

This chapter is concerned with assisting practitioners in evaluating and responding to their local ground conditions and site-specific behaviours and in drawing better informed conclusions as to the merits, limitations and reliability associated with support system designs. This approach also provides clarity to some contentious aspects of support system design. Support design considerations specific to pillar extraction and longwall mining are dealt with in Chaps. 8 and 9.

The five basic modes of roof failure in underground coal mining are identified. These may be interactive and some, in turn, may initiate a secondary mode of failure. A series of tables covering these failure modes is presented to provide guidance on identifying and responding to some of the more common types of roof behaviour in underground coal mines. The tables are supported with graphics of potential failure modes and photographs of these in underground coal mines.

Consideration is then given to a range of theoretical and operational aspects relating to roof support and reinforcement. These include the applicability and scope of classical beam theory; the role and timing of the installation of long centre tendons; aspects of some empirical based design methodologies; the effectiveness of pretensioning; the merits of numerical modelling; and stress relief.

Next, consideration is given to loss of rib control which in some countries such as Australia, accounts for the majority of serious and fatal falls of ground. Rib composition and behaviour are discussed along with a range of design considerations. The chapter concludes with a review of operational factors specific to coal ribs.

J. M. Galvin

8. Pillar Extraction

Abstract

Pillar extraction, (also referred to as retreat mining; pillar recovery; stooping; pillar robbing; and bord and pillar second workings) is the practice of forming a series of pillars and then partially or totally extracting some or all of the pillars, usually with mining operations retreating out of a panel. There are a number of basic pillar extraction methods, with numerous permutations being associated with some of these methods. The practice has a history of being the most hazardous form of underground coal mining and a reputation for being an art as much as a science. However, since the mid 1990s, research into coal pillar mechanics in combination with new technology, education and a risk management approach to design and operation, have resulted in substantial improvements in the safety of pillar extraction.

This chapter commences with defining terminology specific to pillar extraction and reviewing attributes of the mining system that account for it being such a hazardous form of secondary coal extraction. It then presents a range of mining layouts and extraction sequences that have been developed in endeavours to reduce risk related to loss of ground control. This forms the foundation for evaluating ground control under the headings of global stability; panel stability; and workplace stability. Consideration is given to factors such as panel width to depth ratio; shape and age of pillars; goaf edge behaviour; goaf edge support systems; the design and impact of remnant pillars; and the significance of speed of extraction. It concludes by emphasising the importance of having operational discipline.

J. M. Galvin

9. Longwall Mining

Abstract

Since the early 1980s, the longwall method has developed into the safest, highest producing and most productive form of underground coal mining, rivalling the performance of many surface mining operations. This is due in large part to the rapid uptake of computer based technologies for automation and monitoring; improved reliability and performance of longwall mining equipment; and the adoption of plant management and loss control principles. This situation has many important implications for the geoscience and geotechnical engineering professions. For example, lost opportunity costs associated with loss of ground control are now so high that many of the simple observational and empirical approaches traditionally applied to geotechnical designs and operational aspects in longwall mining are no longer commensurate with the business risks that have to be managed. There is an increased need for geotechnical input to be based on sound engineering principles that encapsulate measured ground behaviour, applied mechanics, and numerical modelling. Ongoing research is important to support this need.

This chapter addresses geotechnical principles and practices relevant to satisfying these engineering requirements, making extensive use of figures and photographs to illustrate important concepts. It considers panel layout options and associated chain pillar design; traces the history of powered support design to draw learnings about their static and kinematic requirements; identifies and assesses operational variables, including cutting and support techniques, powered support maintenance, and face operational practices. It then reviews face behaviour and ground control requirements and practices; and evaluates the design and support of installation roadways and longwall recovery roadways, including pre-driven roadways.

J. M. Galvin

10. Overburden Subsidence

Abstract

The term subsidence has two meanings in ground engineering. It can encapsulate all mining-induced movements of the overburden and the ground surface above, as it does in this text, or it can refer specifically to vertical displacement of the ground. In this chapter, the significance of subsidence is discussed in terms of effects, impacts, and consequences, with these terms ascribed the following meanings:

Effect – the nature of a particular mining-induced ground movement.
Impact – any physical change to the fabric of the ground, its surface, or a man-made feature resulting from a subsidence effect.
Consequence – any change in the amenity, function or risk profile of a natural or man-made feature due to a subsidence impact.

Subsidence behaviour associated with secondary extraction systems is classified under one of three headings, recognising that in practice there will be transitional states between these scenarios. Consideration is then given to the behaviour of the superincumbent strata between the mining horizon and the surface and to a number of models that have been proposed to represent this behaviour. This forms the basis for considering subsurface effects and impacts, including those on groundwater.

Consideration is then given to subsidence effects, impacts and consequences at the surface. Subsidence is classified under the headings of Sinkhole and Plug Subsidence; Classical Surface Subsidence; and Site-centric Subsidence. Research findings in relation to Valley Closure, Upsidence and Far-field Movements are presented. Prediction methodologies are discussed along with subsidence impacts and consequences and measures to mitigate and remediate these. Photographs are used to illustrate a variety of related field experiences.

J. M. Galvin

11. Operational Hazards

Abstract

Ground engineering is a risk control measure for a considerable number of operational hazards in underground coal mining. Effective management of these hazards requires consultation and collaboration across a range of disciplines and skill sets. In some cases, the knowledge base concerning the nature of the hazards and their effective control is still evolving and, therefore, it is important that risk management includes provision for monitoring and responding to research and technological developments.

This chapter addresses the operational hazards associated with Windblast; Feather Edging; Top and Bottom Coaling; Inclined Workings; Inrush; Flooding of Mine Workings in the Long Term; Bumps and Pressure Bursts; Gas Outbursts; Mining through Faults and Dykes; Frictional Ignition Involving Rock; Backfilling of Bord and Pillar Workings; Effect of Roof Falls on Pillar Strength; Recovering Roof Falls; Experimental Panels; Alternative Applications for Rock Bolts; and Mining in the Vicinity of Convergence Channels and Paleochannels.

J. M. Galvin

12. Managing Risk in Ground Engineering

Abstract

All stages in the life cycle of a construction in geological materials are characterised by uncertainty. This is because it is neither practical nor economically feasible to fully identify the composition and properties of ground engineering materials. The geological, geomechanical and geotechnical engineering knowledge bases that underpin stability assessment and design are still evolving. Moreover, there is a range of design approaches, each of which has its strengths and its weaknesses, and ground conditions can change over time. A Ground Control Management Plan (GCMP) that is consistent with ISO 31000, the international standard for risk management, provides a basis for safely and effectively managing geotechnical uncertainty.

The philosophy behind a GCMP and the generic structure for a GCMP are presented. A distinction is drawn between the concepts of reducing risk to ‘as low as reasonably practicable’ and reducing risk to ‘so far as is reasonably practical’. Matters considered include Risk Assessment Techniques and Processes; Hazard Plans; Trigger Action Response Plans (TARPs); Professional Competencies; Change Management; Auditing of Risk Assessments; Residual Risk; and Monitoring Devices and Strategies. Extracts from a range of GCMPs are presented in the chapter and associated appendices to illustrated aspects of these elements.

Monitoring is integral to the effectiveness of a GCMP, both for avoiding an unwanted event and in managing the consequences of such an event occurring. The chapter concludes with a discussion of instrumentation options and monitoring strategies and a reminder that the most important consideration in ground engineering must always be the safeguarding of health and safety.

J. M. Galvin

Backmatter

Titel: Ground Engineering - Principles and Practices for Underground Coal Mining
verfasst von: J.M. Galvin
Verlag: Springer International Publishing
Electronic ISBN: 978-3-319-25005-2
Print ISBN: 978-3-319-25003-8
DOI: https://doi.org/10.1007/978-3-319-25005-2