Coal Operators' Conference

Hybrid double-skin tubular members for sustainable mining infrastructure

Tao Yu — Thu, 21 Feb 2013 20:39:18 PST

Hybrid FRP-concrete-steel double-skin tubular members (hybrid DSTMs) are a new form of hybrid structural members. A hybrid DSTM consists of an outer tube made of fibre reinforced polymer (FRP) and an inner tube made of steel, with the space between filled with concrete. The two tubes may be concentrically placed to produce a section form more suitable for compression members, or eccentrically placed to produce a section form more suitable for flexural members. In hybrid DSTMs, the three constituent materials are optimally combined to achieve several advantages not available with existing structural members, including their excellent corrosion resistance and energy-dissipation capacity. Hybrid DSTMs are therefore a sustainable alternative to existing structural components, especially for use in structures which are likely to be exposed to a harsh environment. This paper explains the rationale and advantages of this new form of structural members, presents an overview of existing and ongoing research on their structural behaviour and design, and discusses their potential applications in mining infrastructure.

Modelling and design of pentice protective structures to resist high-speed projectile impacts

Alex Remennikov — Thu, 21 Feb 2013 20:35:36 PST

This paper presents the results of a research study carried out to investigate the performance of the pentice structure at an underground mine in NSW during the extension and equipping of a haulage shaft by Macmahon under high-speed impact loading caused by the potential projectiles falling from the surface. This assessment will allow the structure to comply with AS 3785.5 for “Headframes” (Australian Standard, 1998). The pentice structure is installed 1000 m below the surface in a 4.268 m diameter shaft at the considered underground mine. The objective of the pentice is to allow Macmahon construction and shaft sinking crews to work in the shaft without any risk to their safety. The pentice structure includes a number of steel boxes 1-m high that are filled with high yielding foaming grout Tekseal from Minova Australia Pty Ltd. The major aim of this investigation is to evaluate the capacity of the existing pentice to resist high-velocity impacts and to develop a high-performance protective system which is capable of absorbing energy and terminating large projectiles falling from a height of 1000 m. High-fidelity physics based finite element models for the mine pentice were developed to find a satisfactory solution to protect workers 1000 m below the surface from potential falling projectiles. It is established that the existing level 11 pentice structure is not capable of stopping the projectiles dropping from a height of 1000 m. Several high-performance protective solutions for strengthening the pentice against impact loads were proposed and evaluated numerically. As the final design, two-level protection is designed that includes the 9 level and 11 level pentice protective structures. The models of the 9 level pentice and the 11 level pentice are evaluated for the relevant impact loads. It is found that the new 9 level pentice requires an additional layer of the railway concrete sleepers along with the high-strength steel cover plate to provide adequate protection and terminate the falling projectiles. The supporting frames for the 9 level and 11 level pentice structures are designed using the dynamic reaction forces transferred from the pentice boxes. The developed two-level pentice protective system has proven to provide high level of protection against high-speed falling projectiles for workers performing shaft sinking duties in the shaft below.

Effect of dynamic elastic properties of rock on fragmentation in Choghart Ironore Mine, Central Iran

Mohammad Farouq Hossaini — Thu, 21 Feb 2013 20:31:25 PST

Blast fragmentation is a measure of efficiency in an open cast blast operation. Specific Charge (SC) plays an influential role on the fragmentation distribution, the quality of product and the production cost. Dynamic properties of rocks can be used for estimation of rock fragmentation and specific charge. Fragmentation analysis by digital image processing is a low cost and quick method. In this paper, the results of the seismic refraction technique are presented for Choghart Iron ore mine in central Iran. The P-wave velocity of the ore body has been measured at the site. The source of vibration generation was by hammering. The fragmentation resulting from blasting was monitored using a digital camera. Split Desktop software was used to quantify fragmentation size distribution. The mean fragmentation size of P50 was obtained as representative of the average fragmentation size. SC of ANFO was calculated. The relationship between SC with P50, Vp and Dynamic Elasticity Modulus (Edyn) were obtained. It was found that P50 and SC are increased with increased Vp and Edyn. P50, increases with increase of SC. These results can be utilised in blasting design in order to optimise fragmentation and SC for improvement in t the blast operation efficiency.

Numerical modelling of cyclic shear behaviour of rock joints under constant normal stiffness condition

Ali Mirzaghorbanali — Thu, 21 Feb 2013 20:24:51 PST

The cyclic shear behaviour of rock joints was investigated in the laboratory under constant normal stiffness condition for low and high values of initial normal stress and asperity angle. The Universal Distinct Element Code was applied (UDEC) to simulate the laboratory behaviour using two available models. The predicted shear stress, normal stress, and dilation with shear displacement were compared with experimental results. It was observed that the change in the shear strength and recovery of dilation upon load reversal are simulated using the Coulomb Slip model for low values of initial normal stress and asperity angle when the shearing mechanism was sliding over asperities. However, the Continuously Yielding model replicated better cyclic shear behaviour of rock joints under breaking mechanism (i.e. high levels of initial normal stress and asperity angle), as this model represents progressive damage of asperities during shearing and approaching to the residual friction angle when asperities are fully degraded.

Changes in rock properties following immersion in various chemimcal solutions

Luke Summersby — Thu, 21 Feb 2013 20:20:27 PST

Many clay-bearing rocks will undergo changes in material properties after immersion in water. This is often accompanied by a reduction in strength and cuttability properties associated with increased degradation. In extreme cases such as with water active shales, it can lead to complete collapse or sloughing of the material. This can have important implications for Australian coal mining operations in terms of maintaining ground stability where clay-bearing rocks are in close proximity to coal formations. Previous research has examined whether chemical solutions containing potassium chloride and copper sulphate could arrest these changes in rock properties. While they provided encouraging results, they did not fully explore the effects of altering the exposure times or concentrations of chemical solutions. The purpose of this paper is to outline the effect of changes in the concentration and exposure times of potassium chloride, magnesium chloride and copper sulphate solutions on clay-bearing rock. The Slake Durability Index Test was used to examine the degradation of a claystone after immersion in a range of chemical solutions at different concentrations. There was little quantitative change due in part to the low permeability of the rock. Qualitatively it was found however that degradation was exacerbated following immersion in a copper sulphate solution and to a lesser extent with magnesium chloride. Conversely, potassium chloride at all concentrations was found to reduce the degradation effects of water. Immersion of the test specimen in each of the solutions of potassium chloride, magnesium chloride and copper sulphate improved rock cuttability relative to dry, untreated rock.

Mega project development: optimising current practices and strategies

Richard Wittig — Thu, 21 Feb 2013 20:13:45 PST

The forecast capital cost for the 295 Australian projects that are in the project development phase (Evaluation) is approximately A$245 billion. With average prices for projects increasing, the project development phases have never been more critical (Australian Government, Bureau of Resources and Energy Economics 2012). Project development in the Australian mining community is generally undertaken in four separate stage-gated study phases Resource Planning, Concept, Pre-feasibility and Feasibility. Each phase further defines the level of maturity required for investment, risk and project portfolio evaluation purposes. However, even with this mature project development approach, the vast majority of mining mega projects has experienced cost and schedule overruns. Current industry practices are outlined, which suggests a vertically integrated framework for the four study phases through project development. This approach is focused on increasing the links between project development and program and project portfolio management and presents a new vertically integrated model in an optimised project development life cycle, adapted from current standard linear.

Evaluation of structural component design in life-of-mine planning

Greg Kay — Thu, 21 Feb 2013 20:10:11 PST

Industry practice around structural component design has progressed significantly in recent years with a key result being the application of known engineering principles to the design of ventilation control devices and bulkheads. The properties of shot blast products are now well understood with computer modelling and full-scale live blast test analysis having aided the selection of the most effective type of device for specific site conditions. However, as underground mines increasingly focus on life-of-mine planning, understanding the long-term behaviour of installations plays an increasingly important role in structural system design. As many structural components found in underground mines have been designed and certified at time of installation, the review of these installations, specifically the impact of environmental and other factors, provides the opportunity for continued learning and development in this area. Studies conducted at underground mines where structural components have undergone long term testing and monitoring are discussed. The impact of key environmental conditions on the behaviour of structural components in underground mines is described. The limitations of current testing and monitoring processes as well as opportunities for long term mine planning are assessed.

Issues related to stability design of very high spoil dumps

Leonie Bradfield — Thu, 21 Feb 2013 20:05:52 PST

As spoil dumps get higher, particularly in strip mining where most overburden is placed in-pit, consequences of slope failure become disproportionately greater. Current understanding of the shearing behaviour of spoil for stability design has involved a combination of laboratory-scale diagnostic testing and engineering judgment. This is a relatively empirical approach that provides a linear shear strength envelope for materials known to exhibit non-linear behaviour, particularly under high confining stresses. A shortcoming to the diagnostic testing is that oversize particles are usually scalped to accommodate the device capacity. The influence of prototype-size particles on the geomechanical behaviour of mine spoil is not truly captured. In response to concerns about overestimating the shear strength and stability of high spoil dumps, and current plans for coal mine dumps to exceed 400 m in height, there is a need to rationally define the stress-strain behaviour of more characteristic spoil masses under representative compressive and shearing loads. A Large Direct Shear Machine (LDSM) has been designed at The University of Newcastle to generate reliable stress-strain data on large samples of coal measures spoil (0.72 m x 0.72 m x 0.6 m) subjected to loads representative of very high dumps (~3.5 MPa). This paper reviews current methods for predicting shear strength parameters in the context of very high spoil dumps, and presents an overview of the design considerations of the DSM.

Improvements in truck requirement estimations using detailed haulage analysis

Patrick Doig — Thu, 21 Feb 2013 20:00:29 PST

Accuracy in haulage analysis is fundamental for reliable cost and productivity estimation. The level of detail to which haulage analysis is conducted can significantly influence these estimations. The recent advancement of computer processing has enabled a range of software to manage large datasets and run multiple and complex haulage scenarios, thus increasing the level of detail. Substantial evidence is available to affirm the benefits of detail in haulage analysis through the scope of truck cycle time and truck prediction methods. However, due to the novelty of advanced software, no literature that documents the level of detail and frequency of haul roads required for haulage analysis was found. It was therefore, the objective of ongoing work for this research project to quantify the value added through additional detail in haulage analysis, specifically, the benefit of frequently changing haul roads. To facilitate this process, nineteen haulage scenarios were analysed with varying detail. In addition, a geological model and topography was created. From the analysis conducted, a clear relationship was identified between decreasing haul road calculation frequency and inverse variance error from the mean cycle time. The research showed that performing two as opposed to a single haulage analyses for a strip can affect the calculated truck cycle times from 6% to 14%. Additionally, it was found that changes in horizontal distance from the endwall were more significant than the vertical change for the analysed strip.

The economics of extended pre-strip stripping

Retief Nel — Thu, 21 Feb 2013 19:55:45 PST

Waste stripping involves the most costly processes for any given open cut coal mining operation, As such, it is fundamentally important to optimise material scheduling and the sequences involved in excavating and hauling waste material. In situations constrained by fleet capacity and productivity. The only viable option to potentially yield further cost gains is to modify current mining methods. In the case of many Australian coal mines, truck-shovel systems excavate the initial overlying waste, known as pre-strip, down to a predetermined level known as the pre-strip horizon. This paper provides and analyses a simulation model to derive the optimal strip width for pre-strip activities. Case study data obtained from an established leading coal producer in the Bowen Basin was implemented into a pit simulation model to assess the effect of pre-strip width on the overall pit economics. Pre-strip widths of 60 to 120 m in 10 m increments were assessed whilst keeping dragline and coal stripping widths constant at 60 m. The simulation revealed the potential for cost reductions to be significant when a 90 m pre-strip case is adopted as opposed to the base case of 60 m. The paper presents the simulation findings for each case and discusses the key drivers behind the cost variations for each case.

Comparison of photogrammetry and survey laser scanning output data for use in mapping joints in open cut highwalls

Alison McQuillan — Thu, 21 Feb 2013 19:51:42 PST

The Anglo American open-cut coal mines in Australia routinely obtain structural data from exposed highwalls to determine the potential for instability caused by joint orientation, joint dip, and joint persistence. Three methods are currently available to obtain this data: direct in-pit measurements with a geological compass, photogrammetry, and laser scanning. Direct measurements are often very time-consuming and can lack the precision of other methods due to the inability to perform proper line surveys where mandatory safety stand-off distances are enforced at the toe of each highwall. For this reason, photogrammetry has been the method of choice for many years, where stereo pairs are used to create a 3D image of the highwall. In recent years however, laser scanners now appear to be the preferred method of data acquisition due to their faster capturing and processing time, as well as their user-friendly CAD processing functionality. Concerns however have been raised over the accuracy of laser scanner data as examples to date have lacked the point cloud density necessary for picking representative joint planes. To resolve this issue, both methods were applied on the same highwall and the outputs compared. From this comparison, it was concluded that accuracy is not compromised with laser scanner acquisition methods as long as the correct intensity is selected prior to capturing the scan. Discrepancies were however identified between the joint orientation outputs of Sirovision and I-site mapping technologies. These discrepancies are attributed to the different algorithms each program uses, as well as the survey control and density of data points produced and required by each method.

Carbon sequestration in coal measures rocks

Ian Porter — Thu, 21 Feb 2013 19:47:50 PST

It is a widely held belief that anthropogenic addition of greenhouse gases to the atmosphere will lead to rapid climate change. It is also a widely held belief that the burning of fossil fuels for power generation is a major contributor to these anthropogenic additions, predominantly the emission of carbon dioxide and the consequential increase in carbon dioxide levels in the atmosphere. Irrespective of the cause and effect of the increased carbon dioxide levels it is in the interest of the coal mining industry to work with various partners to develop methods of reducing the rate of emission of carbon dioxide to the atmosphere. Carbon capture and sequestration has the potential to meet that objective. This paper looks at the various methods of carbon sequestration and presents the published results from various laboratory and theoretical studies to determine the potential for carbon sequestration in coal measures rocks.

International experience of gas emission and gas outburst prevention in underground coal mines

Thomas Imgrund — Thu, 21 Feb 2013 19:42:54 PST

With increasing depth of cover, control of gas emissions and prevention of gas outbursts has become a more and more important issue in mine design and mine operation. Long term experience in these fields exists, especially in Australia, Germany, China, Kazakhstan and Ukraine. Based on local conditions including geology, market conditions and mining regulations, different approaches have been developed in these countries. Changes in these parameters have however exposed the limitations of traditional solutions. While the Australian approach is based on the premise that gas content will be reduced below specific threshold values ahead of mining, opportunities of pre-drainage are limited in low permeability coal such as that encountered e.g. in Germany and China. In the case of multi seam mining, a highly effective increase in permeability can however be achieved through pressure relief by unconventional mining sequences. Although practiced at several mines in Europe and Asia, realising this in open market conditions requires a high quality of planning in regard to mine layout, mine development and gas drainage as well as the appropriate geotechnical assessments. A key factor is access and extraction of the first seam at or near to virgin gas contents. Mining at high gas contents by applying local exploration and pressure relief drilling has been practiced in a successful and safe way in several European mines. This has to be connected with a proper management system and safety system, allowing efficient reactions to identified hazards. Apart from international experience and development, the paper will also discuss current and future approaches of technology transfer. Merging the future development in gas drainage with unconventional approaches is therefore an opportunity for accessing deep and difficult deposits.

A study of coal swelling-controlled CO2 diffusion processes

Wei Li — Thu, 21 Feb 2013 19:36:06 PST

CO₂ sequestration in deep and unmineable coalbeds is regarded as a viable option for carbon storage. CO₂ diffusion is a key assessment parameter to effectively seal CO₂ in the coal seam. By conducting laboratory tests of coal CO₂ desorption and unsteady gas diffusion theory model calculation, the desorption dynamic characteristics of Yaojie coal was studied under the condition of constant temperature and different balance pressure, and the CO₂ diffusion coefficient was obtained through the non-steady diffusion model at different time. The results show that the higher the balance pressure, the greater the diffusion coefficient under the same condition. As the pressure drops, the CO₂ diffusion coefficient gradually decreases as time increases, and the CO₂ desorption mass fraction has a linear relationship with the diffusion coefficient. It is observed that under high pressures, the diffusion coefficient initially increases, then gently decreases. The non-steady CO₂ diffusion in Yaojie coal relates to the CO₂ swelling effect of the coal, especially in high pressure condition, the glass transition of coal with CO₂ maybe the governing factor leading to the nonlinear diffusion of CO₂ in coal.

A fractal theory based Fractional diffusion model of methane in coal and experimental verification

Haina Jiang — Thu, 21 Feb 2013 19:23:56 PST

Structure parameter θ that reflects the dynamic character of methane in coal and fractal dimension d_f that reflects the static structure of coal were introduced into Fick’s model, and based on the assumption that the diffusion is memorable by introducing a parameter v, a Fractional order of diffusion model was established (the FFD Model). Several adsorption and desorption experiments on anthracite coal with different grain sizes (0.2-0.25 mm, 1-3 mm) were performed under different equilibrium pressures (1 MPa, 4 MPa) to determine the parameters and to confirm the validity of the FFD Model. On that basis, further desorption experiment of pulverized coal was conducted to validate the applicability of the FFD Model on pulverised coal. The results showed that the desorption rate of the 0.045-0.075 mm grain size coal is seven times of the 0.106-0.25 mm grain size coal. The implications of the study are for the pulverising phenomenon during the coal and gas outburst. The desorption velocity will increase rapidly, resulting in the dramatic increase of expansion energy of methane, and this further accelerates the pulverising process - a positive feedback effect between desorption velocity and dusting process. This can be used to explain the phenomenon of the gas-solid two phases flow and the piston effect during the coal and gas outburst.

Estimation of fugitive emissions from open cut coal mining and measurable gas content

Abouna Saghafi — Thu, 21 Feb 2013 19:14:41 PST

To evaluate fugitive emissions from open cut coal mines, emission factor values of 3.2 m3/t and 1.2 m3/t have been used for the two main Australian coal-producing states of New South Wales and Queensland, respectively. CSIRO developed these values in the early 1990s. They were meant for use as average regional values (Tier 2 method), but were subsequently used for all mines, irrespective of the level of ‘gassiness’ of specific coal seams and strata. Over the past decade, A new method has been developed for Australian open cut mining that is specific to each mine site (Tier 3 method). The proposed method has been adopted by National Greenhouse and Energy Reporting and is the basis of Method 2 or 3 for calculation of emissions. The new method is based on an emission model, which considers the coal seams and sedimentary gas-bearing horizons (layers) as individual gas reservoir units. These units release part or all of their gas during mining. The main data required are in situ gas content, gas composition and thickness of the gas-bearing horizons within the column of strata above and below the mine base. In this method, drilling can be reduced by partitioning the mine site into ‘gas zones’ in which similar patterns of gas distribution are expected. Two to three core drillings are required to characterise a gas zone and to provide the main input of the model. Routine geophysical log data can also provide the thickness of gas-bearing layers. Because of the limitations of the standard gas content measuring method, different commercial laboratories claim various limits of detection (i.e. measurability). However, in view of the very different global warming potential values of coal seam gas components, different limits of measurability can lead to significant differences in the estimation of fugitive emissions.

A critical analysis of gas data in relation to gas drainability in the Bulli seam

Lei Zhang — Thu, 21 Feb 2013 19:10:48 PST

To prevent the outburst fatality, outburst threshold limits was established. It is the stipulation of limits on seam gas content prior to mining. The outburst threshold limits varied linearly based on gas composition, increasing from a minimum in CO2 rich conditions to a maximum in CH4 rich conditions. It is believed that the gas data of the drainage boreholes are closely related to the gas drainability in Bulli Seam. A total of 519 sample results from Metropolitan mine has been examined. It was found that Q1, Q2 and Q3 components increased in response to increasing measured total gas content QM. Statistical analysis also shows an increasing trend in the Q1:QM and Q2:QM ratio corresponding to increased QM, but there was a decrease in trend in the Q3:QM ratio corresponding to increased QM. A power relationship was considered to more accurately represent the average of each gas content component relative to QM, especially for “Fail” samples. The average value of CO2 composition of “Pass” samples is 73.5 % and it was 82.6 % for “Fail” samples. The zone with CH4/ (CH4+CO2) ratio of less than 0.2 includes 171 “Fail” samples, accounting for 88.1 % of total “Fail” samples.

Cyclic inert gas injection - an alternative approach to stimulate gas drainage from tight coal zones

Dennis J. Black1 — Thu, 21 Feb 2013 19:02:12 PST

Traditional methods of coal seam gas drainage depend on reducing the reservoir pressure to enable gas desorption from the coal matrix. Studies in coal mine gas drainage, particularly in coal seams that are deeply undersaturated and have low permeability, found the rate of reservoir pressure reduction was prohibitively slow. In such conditions, lengthy production delays were experienced while additional gas drainage drilling was undertaken in an attempt to reduce seam gas content below specified threshold limits. Such additional drilling represents a high additional operating cost and typically yields low total gas production whilst adversely impacting the mine’s gas drainage drilling schedule and potentially leading to coal production delays. kA novel method to enhance gas drainage from tight coal zones, known as cyclic inert gas injection, which does not rely on reservoir pressure reduction to stimulate gas flow is proposed.

A new in-situ method for measuring simultaneously coal seam gas content and permeability

John Pope — Thu, 21 Feb 2013 18:58:05 PST

This paper will describe a new method for measuring simultaneously coal seam gas content and permeability that can be performed on existing coal quality holes. The goal of the work was to provide an operational expedient and cost effective method for achieving these simultaneous measurements reliably and accurately. This reported method involves combining an established gas testing technique, based on downhole Raman spectroscopy, with an established permeability testing technique, based on open hole inflate straddle packer technology. This paper describes these two key enabling technology platforms and the means developed to facilitate simultaneous operations of both. A standard test program is also described, encompassing a review of test planning, test methods, and operational considerations required to successfully combine these measurement methods. In addition, the steps required to validate data integrity and ensure accuracy while optimising operational efficiencies are discussed. The conclusions of the work indicated that proper selection of equipment options and careful coordination of the test plans typically used for the two methods results in successful integration of the testing methods and simultaneous measurement of gas content and permeability in coal seams.

Cross-measure directional drilling

Frank Hungerford — Thu, 21 Feb 2013 18:53:05 PST

The development of directional drilling in the coal industry has been driven by the need to provide reliable in-seam gas drainage ahead of development. The same technology has been utilised for cross-measure drilling in adjacent seams other than the working seam and also in surrounding strata. The equipment and technology utilised for the applications of directional drilling in cross-measure applications is identified. The process of designing both lateral and vertical aspects of the drilling is explained with specific reference to the limitations and practices of directional control during the inter-burden section of each borehole. Cross-measure drilling applications of in-seam pre and post gas drainage, goaf gas drainage, water management and in-rush protection as well as exploration are described to explain the ways the technology has been utilised.

An engineered approach to bushfire management

Frank Mendham — Thu, 21 Feb 2013 18:48:24 PST

In the summer of 2010 to 2011, enhanced levels of vegetation occurred across Queensland due to a number of major rainfall events. New mining operations, as well as significant coal seam gas gathering developments, were considered to be under threat from bushfire hazards during the impending dry season due to abnormal natural fuel loads. This paper outlines a risk based fire management strategy using high level multi-discipline systematic risk analysis tools, including fault tree analysis, to develop controls that were viable in terms of implementation and cost. A quantitative approach to the designation of fire risk zones was applied through the calculation of thermal radiation caused by potential fire in vegetation surrounding exposed areas. The methods used to perform these calculations were derived from the Australian Standard AS 3959:2009 - construction of buildings in bushfire prone areas. Bushfires are a significant risk in Australian conditions. Putting in place measures to protect local worker communities, process assets, cultural heritage values and the environment, was seen as essential under current and impending climatic and ecological conditions. The use of a risk based approach offered an effective, quantifiable and reproducible system to meet this challenge.

Early fire detection in underground coalmines

Frank Mendham — Thu, 21 Feb 2013 18:45:02 PST

Analysis of mine fire growth and spread is important for improving safe emergency egress for mine workers in fires. In fire engineering, a ‘design fire’ is the term that describes the characterisation of a fire in relation to its growth and decay. Defining the design fire is the starting point for managing the fire risk of a mine and is the basis for further analysis of emergency response. A current Minerals Industry Safety and Health Centre (MISHC) PhD project is researching methods of improving fire life safety and asset loss control in mining using Video Based Fire Detection (VBFD) in the context of fixed plant fires. Experiments were carried out at Safety in Mines Testing and Research Station (SIMTARS) facilities. This research was part of the MISHC project to better understand the detection capabilities of VBFD in relation to weak plumes from the early combustion of coal associated with fixed plant. This part of the research specifically deals with assessing the physical dimensions and shape of the low energy, non-flaming weak plumes formed from smouldering coal fires. It demonstrates how experimental methods were used to successfully validate the corresponding numerical simulation of the design fire so it can be used for further research.

Ensuring the survival of critical information sources after an underground incident - can it be achieved?

Darren Brady — Thu, 21 Feb 2013 18:03:40 PST

Through a risk management process ACARP Project C19010 (Emergency Response: Mine Entry Data Management) identified critical information decision makers required to make informed, risk based decisions on whether mines rescue teams could enter or remain in a mine in response to an incident. The project also developed a proof of concept software tool to assist making informed and considered, risked based decisions founded on predetermined relevant and reliable information. One of the questions that presented most commonly throughout this project was how can operations effectively sustain the systems which could provide this required information once an incident occurs. This leads to other questions such as; what level and type of incident could render our existing systems obsolete in an emergency? And what contingencies do operations have in place or available to them to counter this risk? To assist address these issues an extension to ACARP Project C19010 was sought and successful, allowing a scoping study to research and identify existing and future strategies, systems and hardware which have the potential to support and provide the information requirements of decision makers during or after an incident at an underground coal mine. This paper outlines findings to date, of the ACARP Project C19010 extension.

Pike River Royal Commission outcomes

Stewart Bell — Thu, 21 Feb 2013 17:52:30 PST

On the 19th November 2010 29 men died when a methane explosion ripped through the Pike River coal mine near Greymouth on the South Island of New Zealand. Two survivors staggered out of the mine one hour after the initial explosion but the mine remains a tomb for the Pike 29. Over the next few weeks three further explosions occurred until the mine was inerted using the GAG jet inertisation device and then sealed. This paper summarises the finding of the Royal Commission of Inquiry that was convened in December 2010 by the New Zealand Government, to address the questions of: What went wrong at Pike. Why were the previous lessons from mine disasters in developed countries around the world not learned and what is the potential to learn from this event. The report from the Royal Commission was provided to the Governor General of New Zealand on the 30th October 2012. Pike was a coal mine with difficult geological and topographical conditions. This mine needed the best of everything but this didn’t happen and 29 people paid the ultimate price. This presentation will set the context of Pike, look at the rescue recovery operation and cover the Royal Commission report and what the future holds for the New Zealand coal mining industry. The paper extensively references the information contained within the report of the Royal Commission. The bodies have not been recovered and the definitive cause of the disaster has not been determined but the Royal Commission uncovered a litany of problems that lead to the explosion on the 19th November. These problems should have been addressed. This disaster was avoidable.

Prediction and control of spontaneous combustion in thick coal seams

Ramakrishna Morla — Thu, 21 Feb 2013 17:34:19 PST

Spontaneous combustion is one of the causes of fire in underground coal mines especially in thick coal seams, which may cause loss of working personnel, production, valuable reserves, and damage or loss of expensive mining equipment. The blasting gallery method in an 11 m thick seam in Indian geological conditions was considered to model prediction and control of spontaneous combustion (sponcom) in thick coal seams. To find sponcom properties of the coal, gas evolution test, sponcom propensity test, differential scanning calorimetry and crossing point temperature tests were conducted for the specified thick seam. The knowledge of goaf gas behaviour in the blasting gallery extraction method during sponcom can be useful in controlling and minimizing the effects of fire. The paper discusses the application of computational fluid dynamic simulations to investigate the goaf gas behaviour at the time of sponcom in the blasting gallery panels. Computational fluid dynamic simulations studies were also conducted with ascentional and descentional ventilation systems with inert gas injection at a single injection point, multiple injection points and at various inert gas flow rates. The results indicate that the descentional ventilation system is useful for goaf inertisation and multiple inert gas injection points are more effective than the single point injection. The paper also presents the effect of sealing of bottom rooms by inertisation.

Remote monitoring of subsurface heatings in opencut coal mines

John Malos — Thu, 21 Feb 2013 14:50:11 PST

The detection and monitoring of spontaneous combustion (sponcom) events in opencut coal mines are significant hazard management issues. Currently, the only way of locating sponcom incidents is by manual inspection, whether by visual examination or by use of hand-held thermal cameras, often putting personnel at risk. These inspections are also limited in terms of access and coverage. Therefore, there is a need to implement a convenient remote means to detect and monitor the state of subsurface heatings in opencut coal mines over extended areas for significant periods of time. A versatile self-contained imaging system has been developed that is deployed using an unmanned aerial vehicle. The system eliminates the safety hazard of personnel accidentally entering hot ground and being exposed to toxic gases often associated with heatings. Results obtained from the imaging system is presented, which generates thermal and visible geo-referenced images that can be overlaid onto a digital map of the surveyed area. The data allow rapid detection and accurate localisation of anomalous heat levels within target areas that can be updated on the mine plan for management purposes, and thus enables mitigation strategies to be monitored for effectiveness.

Delaying spontaneous combustion of reactive coals through inhibition

Basil Beamish — Thu, 21 Feb 2013 14:43:15 PST

A moist coal adiabatic oven test has been used to quantify the effect of applying an anti-oxidant agent to reactive coals from Australia and the US. For the dosage rate applied, the anti-oxidant significantly reduces the coal self-heating rate and extends the time taken to reach thermal runaway by a factor of three for sub-bituminous coal and by a factor of two for the same application to high volatile C bituminous coal. The laboratory result obtained for sub-bituminous coal from Powder River Basin is in direct agreement with the practical site experience of applying the anti-oxidant product as a spontaneous combustion management control. Consequently, it is now possible to benchmark the application of the anti-oxidant to any reactive coal prior to mining as part of developing a leading practice spontaneous combustion management plan.

Design and field trials of water-mist based venturi systems for dust mitigation on longwall faces

Ting Ren — Thu, 21 Feb 2013 14:32:05 PST

Dust generation from longwall chock movement and the Beam Stage Loader/crusher (BSL) is a major source of air contamination on modern longwall faces. If not controlled effectively, much of these respirable dust particles would disperse quickly into the longwall due to high face ventilation velocities, contributing significantly to higher dust levels. A new water mist based venturi system has been developed for the purpose of suppressing respirable dust from longwall chock movements close to the maingate (MG). The unit is powered by compressed air and water using an ultrasonic nozzle embedded in a venturi body. The ultrasonic nozzle is capable of producing ultra fine water mist with droplet sizes ranging from 1 to 100 μm. Laboratory tests indicate that the ultrasonic nozzle (MAL-1300-B), when combined with a 70 mm (diameter) x 143 mm (length) venturi body, was can produce an optimum spray covering a distance over 10 m. Further tests show that a combination of air supply at 6 bar and water at 4 bar produces the optimum water mist thrust with inducted air velocity over 8 m/s. The venturi system was built as a stand alone unit using fire resistant and antistatic materials and can be easily hooked under the chock canopy with a magnetic base. The system can be powered by compressed air and water supplied to the longwall face and adjusted with the spray angle to achieve the droplet size and velocity needed for dust suppression and diversion. Computational Fluid Dynamics (CFD) modelling was undertaken to gain a better understanding of face ventilation and dust flow patterns to optimise the spray orientation of the venturi system for field trial installation. CFD modelling results show that the operating conditions of sprays with the best mitigation performance vary according to the source of dust, a better dust mitigation effect can be achieved when the venturi units on longwall chock are installed at 20^o down towards the floor and tilted 45^o along the face. Field trials were conducted at two underground longwall mines in QLD and NSW. Three venturi units were installed on Chock No 6 on the longwall with an additional unit trialled at the BSL to mitigate dust from longwall outbye. Dust measurements with real time monitoring Personal Dust Monitor (PDM) and gravimetric samplers indicate dust mitigation efficiency up to 30% has been achieved in both trials.

Full scale explosion testing and design of gypsum plaster ventilation seals

Verne Mutton — Thu, 21 Feb 2013 14:19:37 PST

This paper describes recent research to evaluate Gypsum plaster seal designs in the full-scale pressure test facility at Londonderry, NSW. After the Moura Number 2 Mine explosion a review of the safety of coal mine operations resulted in changes to mining legislation where ventilation control devices (VCDs) were required to be tested in an internationally recognised mine testing explosion gallery to achieve over pressure ratings of 14, 35, 70, 140 or 345 kPa. Since this disaster, Minova has live tested all VCD designs to provide validation test data for design purposes. In recent years validation and certification of seal designs has been undertaken by Queensland Registered Professional Engineers (RPEQs) using laboratory measured seal material properties as input to 3-dimensional numerical models. As an engineering material, mining plaster has properties that approximate to those of a low-strength concrete. Unlike concrete, mining plaster gains strength extremely rapidly and this makes it ideal for constructing seals where downtime while waiting for material strength literally costs money. As a result of these properties, Sprayplast UW VCDs can be rapidly brought into service as explosion rated and/or water holding seals and stoppings. Previous full-scale explosion testing carried out in Australia at Testsafe’s Londonderry Explosion Gallery (Pearson, 1999) has shown that mining plaster stoppings can resist significant blast pressures. This paper describes a recent series of full-scale explosion tests carried out at the Londonderry Testing facility in NSW, which were intended to build on experience gained from earlier tests carried out at the Lake Lynn experimental mine in the USA and at Londonderry, NSW in 1999. The testing process and instrumentation layout will be described in which each seal design was subjected to a series of explosions progressively increasing in intensity until seal failure resulted. Two seal designs at 100 and 150 mm nominal thickness were constructed and instrumented to provide time-related overpressure and wall deflection response during the controlled series of explosions in separate test programs. Suppliers worked to develop reliable engineering designs, with results of the testing used to calibrate a numerical engineering model for Sprayplast UW mining plaster that can be used to design seals for overpressures up to the maximum currently legislated in Australia. The model can also be used to design bulkhead thicknesses for water retention. In addition to theoretical analysis, this paper also considers some of the practicalities of seal location, design, construction and maintenance.

Real-time air velocity monitoring in mines - a quintessential design parameter for managing major mine health and safety hazards

Bharath Belle — Thu, 21 Feb 2013 14:07:47 PST

Mines should be safe places in which to work. These safe places are achieved by means of natural and mechanical means of ventilation. Air velocity is a quintessential ventilation design parameter in diagnosing and ascertaining the adequacy of ventilation for managing mine health and safety hazards. Although Australian coal mines are recognized as being the safest mines in the world using both real-time and tube bundle monitoring systems, monitoring of airflow at critical locations in real-time is glaringly deficient and poor ventilation monitoring practice. This paper discusses the needs for real-time velocity monitoring and the implementation benefits of it in mines. What is an acceptable velocity measurement error in the carbon era? Current carbon emission guidelines do not clarify the measurement challenges associated with air velocities, let alone air velocity accuracy. Historically, there are references to acceptable measurement errors ranging from ± 5 % to ± 20 %. Measured differences in monthly ventilation surveys against the real-time airflow monitoring were found to be 13.3 % resulting in annual carbon costs of A$580 000 for a CH4 level of 0.2%. It is considered that, it is never too late to implement real-time velocity monitors in Australian mines, a safety enabler and a leading practice in the mature mining world.

Australian longwall panel ventilation practices

Stewart Gillies — Thu, 21 Feb 2013 14:02:57 PST

A study has been undertaken into mine ventilation systems currently in use within Australian modern coal Longwall (LW) extraction mines. It reviews systems and discusses evolving changes being adopted to address the more complex challenges. There is a strong move to longer panels, wider faces, greater extraction heights, increased production rates, more efficient ventilation and decreased personnel. In addition mine workings are moving deeper which results in increased ventilation control issues such as higher total and respirable dust levels, greater seam gas contents in parallel with lower in situ permeabilities, spontaneous combustion and heat management issues. Currently there are a variety of LW panel ventilation circuits used in Australian underground coal mines due to various combinations of seam characteristics, gas emission rates, spontaneous combustion, geological features and surface constraints. The main issues usually addressed in the designing and planning of ventilation circuits for LW panels are airway velocity, gas concentrations, LW cutting methods (e.g. Bi-di, Uni-di or half web), ventilation of control devices, pressure differentials and leakage paths and understanding gas concentrations across the length and width of the goaf. If the ventilation circuit can manage the applied contaminant load (gases, heat and dust) at an acceptable cost and circuit duty, then supplementary controls, such as gas drainage, refrigeration and dust sprays and scrubbers, may not be required. The study has been undertaken based on reviews of LW mining operational practices in Australia.

Tear tests of glass fibre reinforced polymer skin spray-on liner

Jan Nemcik — Wed, 20 Feb 2013 21:44:42 PST

Current research into strata support automation in coal mine roadways requires development of a strong, tough and effective skin support that can be applied remotely. To investigate suitability of a glass fibre reinforced polymeric thin Spray-On Liner (TSL) numerous small and large scale samples were tested. These tests include; the tear load due to the lateral movement of TSL to fail in tear through the bolts installed in underground roadway roof, and the ‘truser tear’ due to the differential movement of the supported strata. The laboratory experiments suggested that a polymer based TSL can withstand substantial tear loads and despite the tear failure, the remaining TSL sheet can maintain strata support effectively. The tear strength tests were conducted using a standard 22 mm diameter steel bolt tearing the 5 mm thick polymer sheets reinforced with two or three glass fibre layers. The trouser tear tests were conducted with two and three layers of glass fibre reinforcement. The bolt tear tests indicated load bearing capacities in the range of 7.4 to 13.8 kN depending on the amount of reinforcement, while the trousers tear strength ranged from approximately 0.4 to 1.1 kN.

Study on the bolt-mesh-anchor support technology for mining roadway in complex coal seam

Ying Chen — Wed, 20 Feb 2013 21:40:36 PST

The stability of mining roadway is affected significantly by the condition of the surrounding rock and stress regime, which is the key factor for determining the roadway support program. Located in syncline axis, the No.15 seam is a steep seam at - 230 m level in Changgouyu coal mine, the original flexible shield cannot meet the safety and production requirement. The No.15 seam is classified as unstable and relatively complex according to the analytic hierarchy process (AHP). The distribution characteristics of stress in the seam around the synclinal axis before and after mining are analysed by use of FLAC2D. According to the complexity of the coal seam and the stress distribution characteristics, the supporting parameters using bolt-mesh-anchor were selected and implemented successfully in an underground roadway, which can be referred to as in the design of roadway support in similar complicated coal seams.

Dilatational slip angle of rebar bolts under axial loading

Chen Cao — Wed, 20 Feb 2013 21:35:26 PST

Mechanical interlock is an important component in load transfer capacity in the rockbolting system. It is in turn dominated by the rebar bolt profile configuration. To gain a deeper understanding of their interactions, rebar bolt units under axial loading were studied. Two kinds of failure mode have been identified, namely parallel shear and dilational slip failures. Based on some assumptions made, a universal upper limit of slipping angle of dilation slip failure can be found as the complementary angle of the grout material internal friction angle, which is also the minimum value of the bolt rib face angle. This theory can explain similar performances of rock bolts in pull-out tests while their face angles are large. In addition, once the geometric parameters of a rebar bolt profile are provided, more narrow slip angles range can be figured out via simple plots. As a result, the grout between the bolt profiles can be recognised as three sections, one works as part of the bolt profile, one carries out shear failure and the bottom part keeps intact.

New approach to resin sample preparation for strength testing

Naj Aziz — Wed, 20 Feb 2013 21:26:37 PST

A new method of preparing multiple samples, from one resin mix portion, for strength testing is presented. The method is based on rapid mixing of the resin mechanically and forcing a select number of seven specially prepared moulds into the mixed resin. The system is applicable for both cylindrical and cube/prisms particularly suited for fast setting resin. The study demonstrated that the samples are easily prepared, uniform in composition, with little or no entrapped air. It was found that the samples yielded consistent uniaxial compressive strength values with a standard deviation of 0.47 and a coefficient of variation of 0.88%. The methods can be used for different sample sizes.

Rock bolt corrosion - an experimental study

Naj Aziz — Wed, 20 Feb 2013 21:20:12 PST

The effect of long term exposure of full size bolts to corrosive environments is presented. A special test rig was used to test four bolts under different loading conditions. Four, X-grade identical profile bolts, each of 21.7 mm core diameter (23.7 mm full diameter) were subjected to prolong corrosion testing using acid sulphate water. The pH value of the circulated water varied between 3.4 and 4.3. The corrosion exposure test period lasted three and half years. Two bolts were axially loaded to 10 and 20 t force respectively, the third bolt was subjected to a 360 Nm torsion load and the fourth bolt was left unstressed to act as a reference bolt. After the test period ended, the bolts were stripped of their corroded coatings and weighted for weight loss. The diameter of each bolt was subsequently measured, and the loaded bolt samples were first tested non-destructively for tensile cracks and then tested for tensile failure. No cracks were found on post corrosion bolts tested non-destructively. The failure strength reduction on all four post-corroded bolts was significant, varying between 21% and 39%. The onset of corrosion was not confined to the targeted mid-section length of the bolt, however, the severest corrosion occurred at the anchored ends of the bolts.

Variation in load transfer along the length of fully encapsulated rock bolts, based on the installation mixing parameters

James Hillyer — Wed, 20 Feb 2013 21:13:05 PST

The reinforcement quality of the fully resin encapsulated bolt depends on several factors, which are a combination of the bolt design configuration, bolt/hole diameter ratio and installation procedure. Gloving in bolt installation constitutes a challenging problem for effective strata reinforcement and the stability of gate roads and tunnels. A total of ten bolts were installed into ten 1.7 m long threaded steel pipes with different resin spin times, the pipes were retrieved from the installed holes in an underground mine road way roof and then cut into 100 mm long sections. The encapsulated bolts in the tube sections were then push tested. Significant variations were found in bond strength along the installed bolt length in the whole tube, with typically the top 200 mm of bolt being significantly lower (50%) in most cases due to gloving and unmixed resin components.

In-situ pull testing of cable bolts encapsulated with injection polyurethane

Peter Craig — Wed, 20 Feb 2013 21:06:27 PST

Polyurethane (PUR) injection into underground coal mine strata has been practiced in Australia as early as 1985. The ACARP report C100019 discussed several case studies of which one included PUR injection into resin anchored, pre-tensioned hollow central tube cable bolts. In cases of rapid response to accelerating strata movement it is the preference of site geotechnical personnel to install immediate pre-tensioned cable support, followed by re-consolidation of the strata through injection of grout or PUR. Cementitious grouting of cable bolts has two operational time restrictions; 1) 24-48 h restrictions can be placed on roadway widening or longwall chock removal while waiting for the grout to achieve adequate strength and 2) a 24 h restriction being placed on PUR injection after grouting has taken place to avoid unwanted chemical reactions and heat generation. In the last few years, more mines, faced with time critical ground support, have been utilising hollow cable bolts as the support and the means of injecting PUR into the strata. The main reason is time, 24 h lost to cementitious grout curing could be used in stabilising the strata by PUR injection into distant fractures, and operationally 24 h gained on a longwall move represents a large financial advantage. It has been considered that foregoing cementitious grouting of cables and replacing it with PUR will reduce the load transfer of the cable bolt, but no readily available data exists on how much reduction in bond strength occurs. Underground short encapsulation cable pull tests were conducted at Springvale Colliery comparing cementitious grout against PUR at both 24 h and nine days cure time.

Improvements in long tendon support with pumpable resin

Tom Meikle — Wed, 20 Feb 2013 20:59:29 PST

Long tendon support systems provide several challenges when used as part of the secondary or primary support cycle. A two-component pumpable resin, Carbothix, has been in development for use with self-drilling rock bolts. Many of the attributes of this new resin system make it ideal for grouting long tendon support systems. While neat Portland cement grouts or polyester resin capsules have been used with long tendon support systems for many years, two-component pumpable resin systems overcome many of the shortcomings in these systems. The two-component systems dramatically improve the set-time to enable mining face advance with fewer delays, enable longer pumping distances, improve quality control, and enhance load transfer mechanisms. This paper describes the key benefits associated with a new pumpable resin and details the Coal Services Health/Workcover atmospheric testing results and cable load testing completed to date. It also details the results of the Australian mine site trials and the introduction of these systems into production use.

Experimental approach to measure stress and stress changes in rock ahead of longwall mining faces in Czech coal mines

Kamil Soucek — Wed, 20 Feb 2013 20:52:07 PST

The measurement and monitoring of stress in rock mass are very important tasks in mining geomechanics. With increasing mining depth and worsening of the geological and mining conditions, a suitable method to determine and monitor rock stress and stress changes due to longwall coal mining is needed. Detailed knowledge of the stress state in rock mass is very useful when designing safe mining activity, especially in rockburst areas. The paper presents a brief description of the Compact Conical-ended Borehole Monitoring (CCBM) method for rock stress evaluation and the technical details of this innovative technology. The second part of the contribution evaluates and discusses initial results and experience obtained from the use of CCBM equipment for determination and observation of mining-induced stresses during mining of selected longwall panels in the conditions of the deep coal mines of the Upper Silesian Coal Basin.

Tectonic stress environment of coal-rock dynamic hazard in Kailuan mining area, China

Jun Han — Wed, 20 Feb 2013 20:42:59 PST

Using HI (Hollow Inclusion) method, the in-situ stress of Kailuan mining area was measured in the field. The characteristics of the in-situ stress field and the relationship to regional structures are analysed systematically. Then the relationship between in-situ stress field coal-rock dynamic hazard, include coal and gas outburst, rockburst and water inrush, is analysed. Studies show that in-situ stress field in Kailuan mining area is a high stress zone of Earth dynamical field, with the horizontal tectonic stress being dominant. The magnitude and azimuth of the stress regime is controlled by Kaiping syncline. In-situ stress is the highest in Kaiping synclinal axis section, and as far away from the axis, the stress decreases gradually. The orientation of the maximum principal stress is approximate perpendicular to the axis of Kaiping syncline. The tectonic stress field also controls coal structure, gas content, coal permeability and other parameters. In the Kailuan mining area, coal and gas outburst and rock burst occurred in synclinal axis section of Kaiping syncline where in-situ stress is the highest, whilst water inrush occurred in the wing of Kaiping syncline where in-situ stress is the lowest. Coal-rock dynamic hazard in Kailuan mining area has almost identical tectonic stress environment.

Application of advanced InSAR techniques for the measurement of vertical and horizontal ground motion in longwall minings

Javier Duro — Wed, 20 Feb 2013 20:28:23 PST

Synthetic aperture radar interferometry technology detects ground motion with millimetric precision. The measurements are taken remotely from space and represent a very efficient tool for ground motion measurement even in large and remote areas where land-based measurement techniques are inconvenient and costly. Furthermore and due to the availability of archive radar images, InSAR technology is the only technology able to provide measurements of ground deformations that occurred in the past. Past data allow the establishment of early baselines before any coal production starts and before any subsidence induced by previous production activities. This allows the total levels of subsidence to be identified and allows mine decision-makers to determine the vulnerable zones that could be affected by subsidence. Results of a recent ground motion study on a longwall mine in the Southern Coalfields of NSW, Australia are discussed. The results were obtained using an advanced differential interferometric chain, Stable Point Network, (SPN) which is capable of processing radar images at millimetric precision and very high density of measurements. The paper aims to compare the advanced InSAR retrieved motion with surveying data and to show that InSAR can retrieve the vertical and the horizontal motion that can be present in this type of mining.

Management of subsidence at the Tasman and Abel Mines - issues and outcomes

Steve Ditton — Wed, 20 Feb 2013 20:22:35 PST

Tasman and Abel Mines are underground pillar extraction coal mines located to the west of Newcastle, NSW. Tasman mine extracts coal from the Fassifern Seam in the Upper Newcastle Coal Measures and Abel Mine operates in the Upper Donaldson Seam to the north in the Tomago Coal Measures. Each mine apply a range of partial to total pillar extraction techniques depending on allowable impact limits to a broad range of sensitive surface features such as cliff lines, Schedule 2 creeks, Hunter Water lines, public recreation areas and walking tracks, broadcasting and 132/330 kV transmission towers, highly significant aboriginal heritage sites and an operating cattle agistment business. This paper will discuss the mine management responses required to deal with delayed softening of claystone floors, optic fibre cable relocation, irregular surface cracking and how surface and subsurface monitoring techniques were applied to validate subsidence predictions and modify mine design layouts to meet the required performance measures.

Analysis and design of faceroad roof support (ADFRS)

Mark Colwell — Wed, 20 Feb 2013 20:18:12 PST

This paper summarises the results of a research project whose goal was to provide the Australian coal industry with a longwall installation roadway design methodology that could be utilised by suitably qualified colliery staff. This goal has been achieved and the design methodology (and software package) is referred to as Analysis and Design of Faceroad Roof Support (ADFRS). The intended benefits to underground operations, in the provision of this information and resource, are a safer and more productive workplace. ADFRS now fills the gaping void that existed in the Australian underground coal industry with respect to the geotechnical design and management of longwall installation roadways. In addition to the standard two-pass widening, ADFRS deals with all other aspects of installation roadway design, including faceroad intersections, stables and adjacent maingate and tailgate intersections. ADFRS is based on a sound mechanistic understanding of the roadway development and widening process and the design equations (with strong to very strong correlations) are fully consistent with measured roof behaviour. To the best of the authors’ knowledge ADFRS is the first systematic faceroad design technique to be developed for any country’s underground coal industry.

Estimation of rock cavability in jointed roof in longwall mining

Alireza Jabinpoor — Wed, 20 Feb 2013 20:04:44 PST

Longwall mining is one of the major methods in the coal mining industry. A main concern in this method is roof cavability and caving step or required advance length to make the roof to cave; this is specifically important when roof is relatively hard and caving is controlled by discontinuities within the roof rock. In this research roof caving is studied for different advances and various specifications of discontinuities. A rating method is suggested to characterize the rock mass based on the developed models. A graph has been constructed using the proposed rating system, which can be utilised to predict necessary caving step for the roof.

Prediction of damaged zone in longwall working panels

Hamid Mohammadi — Wed, 20 Feb 2013 19:56:21 PST

In longwall mining, the instability of roadways can affect the mine safety, production rate and consequently the economic condition of mine. Therefore their stability analysis is one the most important technical problems in underground mining. The stability analysis and the design of support systems have to be investigated from two points of view; 1) the pressure and displacements of damaged zone around gate roadways due to the construction process and stress redistribution and 2) the working loading due to coal seam extraction and overburden caving that extends the damaged zone size. The aim of this research is the calculation of working effect on the damaged zone around gate roadway considering geomechincal properties of medium and the geometric characteristic of the roads and working. Therefore, a method has been obtained to calculate the total damaged zone area and working influence coefficient using geometric concepts and mathematical relations, then a design algorithm has been suggested based on the obtained method.

Monitoring longwall weighting at Austar Mine using microseismic systems and stressmeters

Baotang Shen — Wed, 20 Feb 2013 19:43:45 PST

Cyclic weighting is a major hazard for longwall operations in many deep mines with strong roof strata. Significant cyclic weighting events had been experienced at Austar Mine, resulting in production delays. Early warning of imminent weighting events by means of geotechnical monitoring will help to minimise the risk associated and to develop preventative solutions. This paper describes a study undertaken by CSIRO and Austar Mine in which an integrated stress and microseismic monitoring system was trialled to detect strata responses to the mining processes. The main objectives of this study were to understand the caving mechanics and develop an effective early warning system for roof weighting management. The field monitoring results clearly demonstrated the effectiveness of using both stress and seismic signatures to infer longwall caving and weighting events. Stress changes recorded by stressmeters in shallow surface strata and underground roadway roofs showed a strong correlation with the chock pressure increase at the longwall face. The same phenomenon had also been observed from the recorded microseismic events. In order to develop an automated early warning system for longwall weighting, a trigger index method, which integrates the warning signs from different sensors, was developed and tested against the mine weighting observations and chock pressure data. A remarkably good agreement was achieved. For a limited number of cases examined, the warning signs from the monitoring system mostly occurred at least several hours before the roof weighting events and the major increase in chock pressure. This has demonstrated that the integrated stress and microseismic monitoring system, together with the analysis method developed, is capable of providing sufficient early warning for imminent underground weighting events.

A holistic examination of the geotechnical design of longwall shields and associated mining risks

Russell Frith — Wed, 20 Feb 2013 19:34:33 PST

This paper examines the design of longwall shields, focusing on those geotechnical aspects that are critical to either their success or failure during longwall extraction. The driver for the paper is the recognition that in many instances, longwall shields are assessed and designed along similar lines to that of roadway ground support systems, namely according to typical or normal geotechnical conditions. However the paper will contend that for longwall shields, this is inappropriate as unlike roadway ground support systems, longwall shields cannot be supplemented with additional or secondary support in localised areas of adverse geotechnical conditions. In other words, the longwall shield needs to be designed according to what are judged to be worst case or adverse geotechnical conditions, the outcome being that a well-designed shield will be significantly over-rated for the majority of its working life. However it will be argued that the additional capital cost of such shield design can be readily justified as a prudent risk-based outcome that is essential to minimising future business risks due to strata instability on the longwall face. Shield geometry is discussed including such relevant factors as leg angle, inclination of the top caving shield, canopy ratio, operating height range and tip to face distance, these all being well established longwall shield design considerations and most importantly, areas whereby inadequate design can render a longwall shield highly ineffective. The issue of tip to face distance is considered in detail, in particular the extent by which it is an important geotechnical design consideration. The critical importance of maximising set to yield ratio within practical operating limits is discussed. Overall the aim of the paper is to provide industry with a set of suggested guidelines for future use when designing longwall shields and hopefully to initiate discussion on a subject that unlike roadway ground support design is not well covered in its entirety in the published technical literature.

Development of a method for layout selection using analytical hierarchy process

Shaima Abdalla — Wed, 20 Feb 2013 19:30:04 PST

One of the most critical and complicated steps in mine planning is the selection of a suitable layout based on geological, geographical, geotechnical and economical parameters. These parameters influence the choice of different layouts of coal mine workings and normally examined on the basis of experience gained in the coalfields. The wide ranging combinations of geological, geotechnical and mining conditions make the selection of the optimum design and layout for a particular situation a difficult task. Variations in these parameters result in multiple feasible mine layouts; where each layout entails some inherent problems and the optimal layout is the one that offers the lowest problems. These variations in designs result in complex multi-decision situations that cannot be solved by a simple technique. This paper develops a method based on an analytical hierarchy process to select the most viable panel orientation for longwall operation. A back analysis of this technique was conducted at a mine located in central Queensland. The geological and geotechnical aspects of the mine resulted in variations in the recommended panel orientations. Three different mine layouts with variable geological and geotechnical impacts were evaluated and the optimum mine layout was determined. This paper also challenged the viability of the obtained results by performing a consistency check at every critical stage of the project.

Geotechnical modelling based on geophysical logging data

Peter Hatherly — Wed, 20 Feb 2013 19:15:55 PST

Computer modelling of coal seams and their properties is standard geological practice for both underground and open cut mining. It is based on correlations of coal seams made between boreholes and the interpolation of relevant coal seam properties on the basis of the inferred coal seam boundaries. In the case of geotechnical studies, this same approach is not followed because there are insufficient geotechnical test results to form a basis for modelling and the geological models do not typically create boundaries for interburden rock types. Instead, geotechnical models tend to be based on coal seam geological models with test results shown as point data in the interburden intervals. This situation can be improved if geophysical logging data are used as the basis for geotechnical modelling. Appropriately analysed, these logs provide continuous measurements of lithological and geotechnical properties. In the case of natural gamma data, an analysis to show the variations in clay content allows sandstones to be separated from finer grained siltstones. If geophysical strata rating values are determined from the geophysical logs, they provide a measure of rock quality. From these analyses, 3D models showing interburden properties as well as boundaries of the relevant rock types can be created and used as a basis for mine design and control of geotechnical hazards.

Geotechnical roof classification for an underground coal mine from borehole data

William Lawrence — Wed, 20 Feb 2013 19:10:34 PST

It is standard and critical practice in the majority of geotechnical engineering applications to use a rock mass classification system to evaluate the condition of rock in mine planning and operations. The use of geotechnical classification schemes for rock mass characterisation in underground coal mines is well established. Several rock mass classification systems have been developed and used in civil engineering design and for underground mining operations. In the past, these rock mass classification systems were modified and used in the coal mining industry to quantify descriptive geological information for use in coal mine design and roof support selection. To facilitate geotechnical evaluations, mining companies in the Bowen Basin of central Queensland put considerable effort into obtaining geomechanical data from surface exploration boreholes and borecore. The advance or innovation in the proposed method is not in doing the characterisations, but the method of evaluating the required parameters from available borehole geophysics and geomechanical test data. Evaluating radial point-load strength from geophysical correlations is dependent on collating a large comprehensive database of actual point-load test data across the range of lithological types.

CoalLog: the standard for collection recording storage and transfer of geological and geotechnical data for the Australian coal industry

John Simmons — Wed, 20 Feb 2013 19:03:38 PST

A standard has been developed to improve and upgrade the collection and coding of geotechnical data as part of geological exploration activity. CoalLog was developed by industry-based geoscientists and geotechnical specialists in response to outdated terminologies, non-translatable data coding, and con-conformances with relevant Australian and international standards for geotechnical investigation, testing, and reporting. The new standard will allow the industry to use geotechnical information efficiently and accurately, thereby minimising potential legal liabilities associated with non-conformance to recognised standards that are already in-place in the non-coal geotechnical sector. Adoption of this standard will also promote opportunities for a wider range of geotechnical specialists to provide services to the coal industry.