Making effectiveness audits truly effective
Paul Harrison and Phil Goode
The Queensland Coal Mining Safety and Health Act 1999 and the Mining and Quarrying Safety and Health Act 1999 require a mine to have a Safety and Health Management System (SHMS) in place to manage the risk to safety and health of persons at the mine. The legislation assigns the obligation to the site senior executive to develop and implement the mine’s SHMS. It assigns a further obligation to the mine operator to audit the effectiveness of the system put in place by the site senior executive.
What is exactly meant in the legislation by the term ‘effectiveness,’ and how to go about assessing effectiveness has been the topic of much debate since the legislation was enacted. In 2008, the Queensland Mines Inspectorate attempted to provide clarification on the issue, when it published Queensland Guidance Note QGN09 Reviewing the Effectiveness of Safety and Health Management Systems. While providing some additional guidance, QGN09 fell well short of resolving the issue and debate continues.
In this paper, former Queensland Commissioner for Mine Safety and Health, Paul Harrison, and former Queensland Chief Inspector of Mines, Phil Goode, discuss what effectiveness means from a regulator’s perspective. They also discuss how, in their experiences as former regulators, many effectiveness audits generally fail to assess effectiveness. The paper goes on to describe a methodology for properly assessing effectiveness. The methodology uses a quantitative tool to measure and score effectiveness that can be used to compare the current state of a mine’s SHMS with the required state. The tool, which has been honed and calibrated over more than 100 audits, can be used to rate and benchmark the performance of an SHMS against what is currently required, over time as improvements are made, and against management systems at other mines.
Geotechnical aspects of Longwall pre-driven recovery roads including developing cuttable grout pillars
Robert Thomas, Matthew Johnson and Verne Mutton
Longwall face recovery is a complex geotechnical challenge faced by most coal mine operators with high potential for losses due to the occurrence of ground support problems. In recent times, the use of pre-driven recovery roads has improved the overall efficiency and safety of moving longwall equipment from panel to panel.
In 2015 Dendrobium Mine and Golder Associates developed a grout pillar design that could be constructed within the pre-driven recovery road before longwall recovery. The longwall pre-driven recovery road geotechnical environment and support design in weak ground conditions provide background for the decision to construct large yieldable grout pillars that provide additional roadway stability with a yielding fender and cantilevered roof. Due to the resulting increase in support density, recovery road conditions have improved as shown by roadway monitoring data. Longwall operators have considerably less exposure to potential hazards during bolting operations with reduced bolt up time resulting in increased longwall productivity.
All elements of support including 46 grout pillars had to be safe to cut and remove via the mine conveyor system. Due to lack of surface access, all materials to construct the grout pillars were transported up to 14 km from the mine portals. Grout pillar formwork design initially incorporating fabric bladders and steel formwork has been replaced with a lattice of fibreglass (FG) dowels and hessian coated FG mesh, sprayed with a Gypsum based plaster. Air-driven placer pumps were replaced by electric placers with greater reliability and grout quality control procedures ensured that the target pillar strength was reached before holing of the longwall.
Pre-driven recovery road support design incorporating cuttable grout pillars has been combined with the development of a grout delivery system and containing formwork to delivery key productivity and safety improvements during longwall recovery.
Characterisation of weak roof strata at Oaky North Mine
Medhurst, T., Vorster, B., Huey, A. and Davies, A.
Oaky North Mine has experienced some difficulties in predicting areas of “micaceous roof”. These areas often require additional support and can be prone to stress related damage and/or time dependent degradation. To help alleviate this situation, a study was initiated to investigate methods for roof characterisation using geophysical logs. This involved the use of neutron log data to provide an indirect measure of the proportion of carbonaceous/micaceous laminae present in the immediate roof strata. Detailed analysis of the clay – porosity inter-relationships arising from this analysis provided a means to estimate the proportion of laminations in a given roof interval. This paper outlines the process and how it was used to improve the current GSR modelling and hazard mapping process.
A case for harmonised performance based respirable dust sampler for personal exposure assessment in Australia.
The period between the previous (Y2015) and the current (Y2017) brought about the alarming news of re-identification of coal worker’s pneumoconiosis (CWP) or commonly known as ‘black lung” in Australia, after nearly over five decades of lack of such reports. While, in South Africa, the statistics on CWP are unverifiable, certainly the CWP cases are not eliminated. These events have re-kindled the need for better understanding of personal respirable dust monitoring, compliance determination, and performance of sampling devices. In this light, the review of currently used sampling devices over the last two decades was carried out. Dust sampling is pivotal in estimating the ‘dose’ of dust exposure and in deriving dose-response curves in epidemiological studies. Over the last half century, gravimetric sampling has been the fundamental means for dust exposure monitoring using recognized respirable size-selective standards. In South Africa, a gravimetric sampling technique in coal mines has been followed since 1990s using various cyclones, which were later termed as the Higgins-Dewell (HD) type cyclones.
With a revision of US respirable coal mine dust standard of 1.5 mg/m3, it is equally important to understand the sampling tools used for compliance determination purposes. This paper provides the results of a performance evaluation of currently used Australian gravimetric sampler and the original Higgins-Dewell Type cyclone under controlled environment. The results consistently suggest that the currently used cyclones do not conform to the required BMRC or ISO 1995 curve. The results show that the currently used cyclone measurements are significantly higher than the original HD cyclone at the current compliance limit of 3 mg/m3. Based on a laboratory evaluation of three used and three newly manufactured local cyclones, the differences can in part be attributed to the ‘non-auditable’ inherent design and manufacturing quality, collecting more of larger sized particles (D90 of 15 µm). This finding has significant consequences for historic personal exposure results and their use in medical surveillance programmes, as well as the current approach to non-compliance determination. In this context, the new real-time mass based dust monitor using the Tapered Element Oscillating Microbalance (TEOM) principle that conforms to the original HD cyclone is a superior mass based sampling device for use in the mining industry. Alternatively, a single correct HD cyclone that meets the size-selective performance criteria must be used uniformly across the country for sampling harmonisation purposes as practiced historically in the USA.
Coal petrography and associated stratigraphy in the central part of Mae Moh Basin, Changwat Lampang, Thailand.
Kunwatoo Rittidate, Punya Charusiri, Benjavun Ratanasthien and Nattapol Srinak
35 coal samples from 3 drilllholes in the central part of Mae Moh basin have been investigated for stratigraphy, petrography, and geochemical analyses. Lithostratigraphic of studied drillholes is Na Kheam formation in Mae Moh group, characterized by fine-grained sediments with thin to thick coals from bottom to top as Q-, K- and J seam.
The Na Kheam formation has been formed by the sedimentation under the alternation of lacustrine and swamp. Na kheam formation is overlaid by Huai Luang formation mainly of fine to coarse-grained sediments with thin coal as I seam interbedded, indicated fluviatile environment. Detailed petrographic of individual seam reveals the studied coals consist largely of macerals >70% with small amount of inorganic materials <30%. Huminite group (43-68%) is characterized by gelinite, densinite, and some texto-ulminite. Liptinite group (5-30%) is composed of liptodetrinite, sporinite, cutinite, alginite, and exsudatinite. Inertinite group (4-15%) is fusinite, semifusinite and sclerotinite. The inorganic material (8-30%) is characterized by diatomite, clay mineral, framboidal pyrite, silicate, carbonate, and some volcanic ash in place. Mae Moh coals were plotted in the Diessel's diagram (1986) with TPI (Tissue Preservation Index) and GI (Gelification Index) base on maceral assemblage.
The results are low TPI values (0.11-0.52) and moderate to high GI value (3.67-13.50); suggesting coals have originated under limnic condition (lacustrine) of peat formation with vegetation characteristics of marsh and wet forest swamp. Based upon the geochemical analyses, the studied coals can be classified as low rank (lignite A to subbituminous B) and low quality due to high ash and sulphur content.
The enhancement of 3D seismic data for the identification of significant geological features to mine planning.
James Dirstein, Gary Fallon, Michael Angel and Steven Winter
Many advances have evolved into each aspect of designing, acquiring, processing and interpreting 3D seismic data since the method was first applied to coal delineation in Australia in the early 1990’s. The primary aim for applying the method of developing a reliable structural model has not really deviated. While it is recognised that incremental improvements at every stage throughout the process will improve the reliability of the final interpretation. This paper presents examples of how greater detail on structure and other geological features can be delineated within a 3D seismic volume.
A seismic signal can be considered to contain a combination of signal, plus random and coherent noise. The frequency content of the signal is a strong determinant of the ultimate resolution capability of the data. It can be difficult to recognise all forms of noise and verify they have been effectively removed from the data before any interpretation can commence. Established techniques can then be used to enhance the frequency content of the signal. At this point the data processing workflow will deviate depending on the aim or requirement of the interpretation. For example, preferential attenuation of higher seismic frequencies can provide an indication of changing pore fluid content. Therefore, localised changes and ratios of the seismic frequencies in the vicinity of the coal seam, can provide indications of changing gas content and rock petrophysics. Moreover, the estimation of geotechnical parameters may be further enhanced by judicial selection of a non-model based inversion process to reduce any likely bias in the final data volume. This inversion process converts a rock interface response into a rock volume response. This seismic data driven model can then be used to better understand complex fault zones and estimate rock strength. The paper presents geological examples and mine reconciled evidence from two different geological and mining environments. The first from a thicker, single seam environment within the Rangals coal measures and the second from a thinner multiseam environment of the Moranbah coal measures.
Underground coal mine gas monitoring emergency preparation.
The gas monitoring system in an underground coal mine is an integral part in creating a safe work environment for the coal mine workers. The gas monitoring system provides feedback on the effectiveness of the ventilation system, gas drainage system, seal integrity in goafs and gas make on the active face/development panel.
The aim of this paper is to provide a number of examples, where possible improvements can be made to tube bundle and real-time system gas monitoring systems. Two of the tube bundle systems biggest limitations are slow response times to changing gas conditions underground and the high cost of tube installation underground. This paper will discuss two possible step change improvements with the aim to address these limitations to make the tube bundle system more responsive and provide greater coverage underground for lower cost outlay.
This paper will explore the use of automation to reduce the cost of tube bundle system maintenance while improving reliability.
The effect of nut length on rock bolt pretension.
Recent studies into rock bolting parameters have suggested that increasing nut length has a positive influence on the pretension achieved during rockbolt installation. A literature survey on bolts and fasteners was undertaken, as well as a laboratory testing program to examine this suggestion. The testing program examined M24 nuts ranging from 1.0d to 1.5d (24mm – 36mm).
These nuts were used to tension a rockbolt using an instrumented drill rig to measure torque, and a through hole load cell to measure pretension. It was found that nut length has no impact on the pretension values achieved during rockbolt installation. The largest factor affecting pretension values was found to be the levels of friction acting between bearing surfaces. Overcoming this friction is estimated to account for 85-90% of the applied torque from the drill motor.
Indented and plain strand cable combined stress relationships.
Kent McTyer and David William Evans
Cables are routinely used for roof support in Australian underground coal mines. Cables resist the vertical displacement and horizontal displacement that occurs in the rock mass surrounding mine excavations. Ground support designers select cables based on laboratory test performance. Commonly, mechanical tensile tests are the only performance measure reported. The laboratory-derived mechanical tensile test methods are both well understood and accepted.
Tensile properties are used to evaluate the expected cable performance when subject to vertical loading in the mine. However, no accepted laboratory test method exists to assess cable performance when subject to a combination of both axial and shear load. Despite both axial and shear deformation frequently going hand in hand the information gap still exists. The current paper pursues further research into the combined stress relationships of cables. Specifically, the peak shear load for the full elastic range of axial load up to 500 kilonewtons.
Testing was performed on both indented and plain strand cable. Outcomes of the testing will improve the understanding of combined stress relationships for cable and allow for better application of cables in underground mines.
Development, trials and testing of a two component rapid set cement grouting system.
In unfavourable strata conditions, it is sometimes necessary to install additional long tendon support as part of a primary support cycle. Although these support systems provide the required additional stability to the roadway, installation does have a significant effect on the rates of development. To overcome the slow cure time of Portland cement type grouts the use of two component resin systems such as Polyurethanes and Urea Silicates have become favourable but concerns over creep properties has led to the development of the new two component grouting medium which displays the properties of traditional cable grouting materials with the rapid reaction times of pump able resin systems.
The objective of the study is to define the properties of new two component cement grout materials and field trial experience. Two component grout affective in providing early load transfer capacity to long tendon support systems. Two component grout has equivalent mechanical properties to existing cement cable bolt grouts whilst achieving rapid cure time and overcoming the issues of limited pot life associated with rapid cure single component grouts.
Changes in the three dimensional stressfield around long wall panels.
Recent work examining stress redistributions have only invoked isotropic rock mass properties and have substantially under-estimated the impact. By invoking the transverse isotropic parameters derived from stress relieving roadways it is argued that there may be stress modifications extending at least 500m from a longwall goal. Implications to maingate roof support and initial mining in new districts will be discussed.
Improvements in longwall technology and performance in Kuzbass mines of Siberian Coal Energy Company (SUEK).
Vladimir Borisovich Artemyev and Peter McInally
SUEK operates nine longwalls in its Kuzbass mines. The area is highly gassy, with low gas permeability that effectively precludes pre-drainage, it has gradients from 5 to 25 degrees, weak roof and floor, and can suffer massive inflows of water into the longwall areas. SUEK has been steadily developing technological solutions, improving equipment, extending face lengths and developing longer panels over the last five years. This is now paying off with extremely high levels of output.
In May 2017 one face produced 1.407 Mt saleable, and in July 2017 the same face produced 1.567 Mt. However, this is only half the problem. The mines are all 4500 km from the ocean, and access to ports in Russia is problematic, so SUEK has had to develop holistic solutions to become the leading coal mining company in Russia.
Analysis of breakages of longwall powered supports - why cycle testing does not guarantee happiness.
In recent years SUEK has suffered serious breakages of four sets of powered supports, including caving shields and the attachment of the powered supports to the AFC. All of these supports had undergone prototype testing prior to manufacture, but the design errors were not manifested under conventional test conditions. Breakages occurred underground where it was not possible to instrument the equipment, and where data is hard to obtain.
This paper describes the "forensic engineering" that led to identification of the root cause of the damage, and the ways in which this was rectified. Two new sets of supports have also undergone design changes to prevent the same risk of damage. The solutions are simple, but developing this knowledge has cost us dearly.
A comparison of performance between resin and cementitious grouting medium for cable bolts.
Edward Pullen, Danqi Li and Paul Hagan
A detailed comparison of the performance between Jennmar ‘standard single speed’ oil-based resin and Minova ‘Stratabinder HS’ cementitious grout was undertaken using a Megabolt MW9S (spiral) cable bolt in standard (42 mm) and oversized (52 mm) borehole diameters in both weak and moderate strength confining mediums of 14 MPa and 60 MPa respectively. The UNSW modified Laboratory Short Encapsulation Pull-out Test (LSEPT) was utilised to determine the axial load and displacement of the cable bolt. It is expected to observe the failure of all samples to occur at the grout/rock interface, and that varying the borehole diameter will yield minimal deviation in the performance of the MW9S (spiral) cable bolt although the moderate strength samples will achieve a higher peak axial load before failure. The results of this study will be beneficial to the mining industry as a whole by providing the necessary insight when deciding on cable bolting as a roof support system in underground mines.
An overview of in-situ stress measurement techniques and experimental study on borehole breakout.
Huasheng Lin, Joung Oh Hossein Masoumi, Ismet Canbulat, Chengguo Zhang and Linming Dou
Changes in stress orientations and magnitudes can have a significant adverse impact on mining conditions such as increasing the risk of violent failures. Knowledge of these changes will indicate the high risk zones within a mine sites, which will enable mine operators to implement appropriate controls. At deep underground excavations, there are some difficulties in collecting reliable data at reasonable costs. Thus, the utilisation of borehole techniques has received a significant attention. In this paper, traditional stress measurement techniques are reviewed, including their pros and cons.
Following the illustration of common shortcomings of these techniques, the development potential of a reliable and cost effective in situ stress measurement technique based on borehole breakout is addressed. To demonstrate the correlation between borehole breakout dimensions and in situ stress magnitudes, true triaxial tests are conducted on pre-drilled rectangular prismatic sandstone samples (75 × 75 × 100 mm3). Experimental results are analysed and discussed in this paper.
Practical use of the underground borehole scanner for geotechnical characterisation and failure pathway quantification.
Richard Campbell and Andrew Seccombe
Geotechnical characterisation of mine roof strata and failure pathways is a vital tool for site engineers to gain the required understanding of the geotechnical environment. Strata monitoring and inspection via borescopes and similar tools has been routinely undertaken for generations. With each tool having its limitations in terms of reliability, data repeatability and analysis subjectivity.
New technologies have been developed by DMT in Germany over the past eight years to provide the industry with the intrinsically safe Underground Borehole Scanner (UBS). The UBS provides optical scanning and digital imaging of 30 to 40mm boreholes upto 12m deep and can be used in any zone of a coal mine as it has full Australian ExIA certification.
The key features of the of the UBS are:
- Is used in holes drilled with standard UG drilling equipment – simple to do;
- 360 degrees optical image in a depth correct and orientated digital format;
- Data storage and analysis using standard equipment;
- Data interpretation and analysis using industry standard WellCadTM software allows for detailed geological/geotechnical logging and characterisation, defect orientation and quantitative fracture aperture analysis that can be simply viewed, stored and peer reviewed.
- Repeated scanning over time provides for analysis of failure pathways and quantification of support effectiveness.
Blackrock Mining Solutions (BMS) has been using the UBS for the past two and a half years and has developed a wealth of experience and case studies for the practical use of the UBS in geotechnical characterisation and quantification of strata deformation in Queensland Mines. This paper presents selected case studies of the application of the tool.
Insights into the energy sources of the burst in coal mines and effectiveness of the preventing and controlling measures.
Mahdi Zoorabadi and Winton Gale
Coalburst is a general term which is commonly being used in industry for the violent failures of the coal in ribs and face of roadways and panels in underground coal mines. Due to lack of interest for industry to reveal the causing source of the event or they might are not sure about the source, they happily use this term. The term by its own does not reveal the source of the energy which causes the event. There are three sources of energy that can cause a burst event in underground coal mines: 1) store elastic strain energy; 2) seismic events and 3) gas expansion energy.
This paper presents the fundamentals about these sources of energy and discusses our knowns and unknowns about the mechanisms. Additionally, it discusses the reliability and effectiveness of the currently used preventing and controlling measures such as stress relief holes, gas relief holes, and high strength reinforcements.
Emerging trends in injuries in the underground coal sector: An analysis of Queensland data from 2006-2016.
This paper analyses the Queensland Mines Inspectorate’s (QMI) lost time injury (LTI) historical data set for underground coal mines. LTI data is reported to the QMI by mine operators on Form 5A as required by legislation. Data discussed includes: injury, body location, worksite location, occurrence class, mechanism of injury, and major equipment involved.
Results are presented along with a discussion of contributing factors. Currently published analysis of these injuries only includes the number of injuries of each type while this analysis expands that to include the severity of the injury (number of days lost and/or days on alternative duties) and the average days away for each type of incident. This analysis also includes cross references of different data types such as Injury Types by Body Location. The analysis includes severity measures for different types of injuries related to the factors collected and drills down deeper into the data than is currently available in reports. Themes in the results are also discussed including information on how to prevent similar occurrences in the future on your job site and improve health and safety outcomes.
Performance characteristics of gas analysers for tube bundle systems.
Martin Tsai and Lauren Forrester
Tube bundle systems are used for long term monitoring of sealed areas in underground coal mines. The gas analysers used in these systems incorporate infrared detection for the analysis of methane, carbon monoxide and carbon dioxide, and paramagnetic detection for the analysis of oxygen. This paper will examine the performance characteristics of these analysers. The linearity and T90 for each gas will be established, as well as recommendations for the calibration levels used. Paramagnetic oxygen analysers are flow rate dependent; the effect of flow rate on the accuracy will be documented. The degree of drift over a period of time will be determined, and potential cross sensitivities with other gases examined. The feasibility of extending the analytical range of carbon monoxide will be investigated, as well as the requirements for automated calibration of the analyser.
Strand wires profiling of sheared cable.
Guanyu Yang, Naj Aziz, Haleh Rasekh, Saman Khaleghparast and Jan Nemcik
Australian mines rely heavily on the use of tendon technology for strata reinforcement in ground control. For the past few decades significant knowledge has been gained on tendon load transfer mechanisms and strength characterisation by pull testing, however, little is known about their performance under shear. When a cable is sheared to failure in soft medium such as in soft rock and in concrete, there is a little chance of the wires in the cable strand to fail fully in shear instead, the strand wires are likely to fail in a combination of tensile and shear. The dominance of strand wires failure in tension over shear or visa-versa will depend on various factors including the medium and grout strength, applied pretension load, testing method and loading condition. This paper examines the shear failure of various cables under different pretension loads using different shear testing methodologies of single and double shear techniques. All tests were carried out in 40 MPa concrete medium. Both plain and indented cable strand wires failure profiling in both test methods are pictorially illustrated. Higher pretension load causes the cable to stiffen and fail at lower vertical shear load and lower shear displacement. The extent of shear displacement plays a significant role in strand wire failure pattern. Increased sheared cable vertical displacement causes increased percentage of wires failing in tension. Increased effective medium (concrete) confinement reduces medium radial fracture and less cable displacement, leading to an increase in strand wires failure with increased dominance of wires failing in shear /tension combination.
Pull testing of different diameter tendons.
Haleh Rasekh, Guanyu Yang, Naj Aziz and Saman Khaleghparast
The load transfer capacity and strength of cable bolts have been studied over the years using different methodologies. The load transfer strength of cable bolts is usually evaluated by pull-out and shear strength tests, while the tensile strength of tendon can be carried out by tensile failure tests. A new pull-out test tool of 250 mm encapsulation length and a free length was used to allow the cable to be pull tested. This system has been designed to study the load transfer capacity of various tendon diameters of 22, 24, 28, 42 and 55 mm respectively. These tests are normally undertaken using either cementitious or chemical resin grouts. The developed facility can be used for comparison testing of both bulbed and un-bulbed cable bolts. In this paper a comparative study was undertaken to evaluate load transfer capacity of both plain and indented cables currently used in Australian mines. Minova Stratabinder grout was used for cable encapsulation. The effect of bulbing and surface profile type on various cables was evaluated. It was found that the peak pull-out load of spiral wire strand cable bolt was greater in comparison with plain surface wire strand and with minimum displacement. The effectiveness on bulbing and birdcaging was demonstrated by higher pull out. The new tool versatility enables load transfer study of different tendon types to be readily assessed at faster rate and irrespective of their diameter size.
Mechanical properties of coal measure rocks containing fluids at pressure.
Ian Gray, Lucy Liu, Xiaoli Zhao and Ben Seeto
The sedimentary rock that comprises coal measures has quite nonlinear, elastic, stress – strain characteristics. It is also affected by the fluid pressure within it. The fluids act in two quite separate ways. The first way in which fluid acts is in a poroelastic manner while the second is within fractures. These effects are important in rock behaviour extending from the deformation around a roadway to failure within an outburst. This paper presents the results of a detailed laboratory studies into coal and sedimentary rock properties. It relates these to the real situations seen in mining.
Mechanics of rib deformation at moranbah north mine – a case study.
The risk of fatalities from rib failure is still prevalent throughout the coal mining industry which prompted further industry research into understanding rib deformation and rib support interaction. This paper provides the results of a rib deformation monitoring project at Moranbah North Mine as part of ACARP project C25057. Moranbah North Mine provided funding and mine site access to assist this research into the industry risk of rib failure. Two rib monitoring sites were installed to monitor rib and roof deformation and rib bolt loads under both development and retreat stress scenarios. The monitoring highlights the progression of rib deformation from the minor deformation and bolt loads experienced on development, through to the significant deformation observed under longwall abutment loads. The Tonstein Band (10-15cm claystone/siltstone band located approximately 1m above the floor), was highlighted as a key driver for the deformation both on development and retreat. The monitoring provided observation of the progression of deformation and highlighted a step change in rib stability. The rib deformation stepped from near rib deformation to a significant increase in depth of softening for the entire rib under longwall abutment loading. It was inferred from the monitoring data that shear failure along the Tonstein Band resulted in the increased deformation for the entire rib. Computer modelling was also used to support the failure mechanisms.
Mechanical Behaviour of fibreglass rock bolts.
Peter Gregor, Ali Mirzaghornanali, Naj Aziz and Kevin McDougall.
A comprehensive literature review on the mechanical behaviour of fibreglass rock bolts was carried out. The literature review was divided in to two main sections namely, axial and shear load transfer mechanisms. Past studies on both pull out and tensile testing were classified for various fibreglass strength ratings, ranging from 15 to 30 t. In the second part, past research studies using single shear and double shear testing instruments were thoroughly investigated. Finally, the preliminary outcomes of medium scale double shear testing of fibreglass bolts encapsulated on low and medium rock strata were presented and analysed.
Mechanical properties of grout for strata reinforcement.
Ali Mirzaghornanali, Naj Aziz, Hamed Alkandari, Peter Gregor and Kevin McDougall.
Past studies on mechanical properties of grout were critically investigated and classified. Small scale and large scale samples were cast using cube and cylindrical moulds. Samples were left undisturbed to cure for various time intervals ranging from 1 to 21 days. Effects of sample scaling on the Uniaxial Compressive Strength of Orica Stratabinder HS was studied, using a compression testing machine. In addition, rectangular samples were cast to investigate bending resistance of the grout product. Four point bending test was carried out on the samples with curing time ranging from 1 to 14 days. It was found that compression resistance of grout samples decrease with increase in curing time. Initial studies showed that bending resistance decreased when curing time increased.
Determination of gas emission in the mining life cycle using iterative spatial interpolation and energy based fundamental concepts.
Patrick Booth, Heidi Brown, Jan Nemcik and Ting Ren
Design of optimal gas drainage and overarching gas management programs throughout the mining life cycle is contingent upon a thorough understanding of the gas emission mechanisms specific to the geological and operational conditions in a particular location. As mining progresses from exploration, through development and into production, the resolution of data typically used for gas emission prediction improves spatially and with respect to time.
Quantification and management of risk associated with sudden gas release during mining (outbursts) and accumulation of noxious or combustible gases within the mining environment is reliant on gas emission prediction which is spatially relevant and applicable to the mining stage being undertaken. Using iterative spatial interpolation techniques, appropriate resolution gas emission model input data may be used to continually improve both the resolution and accuracy of model outputs and also determine triggers where model recalculation is required.
Proposed techniques are validated through case study of gas core samples obtained from two southern Sydney basin mines producing metallurgical coal from the Bulli seam over a period of 10 years. Alignment of data in various geospatial and extraction time-based context, including relationships to hydrological features and geological structures, combined with experimental results assessing the influences of changes in confining stress and gas pressure, appear to align with modelled outputs and recent historical gas emission data. The results suggest variability and limitations associated with the present traditional approaches to gas emission prediction and design of gas management practices may be addressed using predictions derived from improved spatial datasets, and analysis techniques incorporating fundamental physical and energy related principles.
Coal and rock bursts: similarities and differences.
Using metalliferous terminology the sudden collapses of the sides of coal mine roadways are likely to be strain bursts, plus the possibility of some kinematic failures or slumps. In Australian coal mines potential strain bursts are controlled by the routine rib support that is installed off the continuous miners within about 3 m of the mining face. Brittle failure in coal induces vertical slabs parallel to the excavation boundary and, if unsupported, these can topple or slide into the roadway in response to seismic activity. Coal bursts may be the result of the formation and then buckling of slabs as the vertical stresses are rapidly increased later in the mining process. The association of the term “burst” with violent ejection of coal may be preventing the identification of sudden rib failures which are the simple collapse under gravity of kinematically acceptable wedges that have dimensions greater than the length of the installed bolts.
Primary roof bolt length reduction at Mandalong Mine – Occupational health, geotechnical and operational outcomes.
Nigel Birt, Owen Farrugia, John Turner, Kent McTyer and Luke Gibson
Mandalong Mine is a modern, high volume longwall mine located approximately 25km south west of Newcastle in NSW. The mine sets itself high health and safety goals. A key concern at Mandalong is that mine workers’ may potentially suffer shoulder injuries due to the lifting of large numbers of roof bolts per shift. Use of a shorter roof bolt was identified as a possible solution for this problem. Following an extensive change management process the mine introduced a permanent modification to its primary roof support during 2015. The key change was a reduction in primary roof bolt length from 2.1m to 1.8m. The reduction in roof bolt length reduced the mass of the bolt by nearly 1kg (15%) with an associated benefit for mine workers. This report details the procedure followed by Mandalong to introduce the change to shorter roof bolts, and the safety, geotechnical and operational outcomes observed over a two year period.
Improving respirable coal dust exposure monitoring and control.
David Cliff, Nikky LaBranche, Mark Shepherd and Fritz Djukic
This paper will present the progress results of this research project commissioned by ACARP to establish the state of the art with respect to:
- Current dust suppression and prevention controls and their effectiveness
- The basis for setting an exposure standard for respirable coal dust
- The current trends in exposure data and any underlying points of concern or interest
- The capacity to monitor respirable coal dust in real time – what techniques are available and what are their limitations
- Current research into reducing exposure to respirable coal dust
- Future directions for research into better control of respirable coal dust exposure.
A continuous roof and floor monitoring system for tailgate roadways.
Paul Buddery, Claire Morton, Duncan Scott and Nathan Owen
Moranbah North Mine has employed the use of Remote Reading Tell Tale Systems (RRTT Systems) since 2012 for the purposes of ensuring accurate, continuous and real time roof movement monitoring for critical infrastructure roadways.
Recently an integrated monitoring system was installed in the tailgate roadway of LW112 to monitor and record the continuous ground movement outbye of the retreating longwall face to better understand both the roof and floor movement. Vertical convergence of the tailgate roadway is typically managed by installing standing support at Moranbah North Mine. The data has provided significant insights into the magnitude of both roof and floor movement outbye of the longwall which has enhanced the understanding of the required densities of standing support at various locations throughout the tailgate. Once installed, the monitoring system is entirely automated and the data is automatically collected and transferred to surface via an optical fibre cable. The system and real-time communication systems are flexible and can be tailored to meet the site specific monitoring needs.
The system includes: an RRTT System, real time convergence monitoring probes and a real time data acquisition, communication and reporting system.
The system enables Moranbah North to be able to measure total vertical roadway convergence and roof displacement continuously without having to access the tailgate at regular intervals. The combined data can be used to determine: required standing support density; required standing support capacity; tailgate roadways ‘zones’ of increased vertical loading due to intersections; the influence of strata and structural variation; and the optimum support strategy for ensuring roadway stability outbye of the longwall face. The analysis and results produced indicate that standing support densities exceeded the required support loads and enabled optimised support spacings.
Assessment of coal pillars stability at the great depth
Petr Waclawik, Radovan Kukutsch and Jan Nemcik
The trial operation of room and pillar method has been implemented at the shaft protective pillar of CSM Mine. Mining depth of room and pillar trial ranged from 700 to 900 meters, being perhaps the deepest room and pillar coal mining in the world. An extensive monitoring system was implemented to measure the load profile across the coal pillars and the deformation characteristics in the pillars during mining. Stress-deformation monitoring was essential as this was the first application of the conventional room and pillar mining method within the Upper Silesian Coal Basin mines. The results of stress-deformation monitoring allowed pillar loading and yielding characteristics to be described. This data and other analyses are essential to establishing procedures for a safe room and pillar method of mining within the Upper Silesian Coal Basin. The results are also important for global mining, for the largest coal producers will reach higher mining depth in near future.
The abutment angle model and its appropriate use for longwall tailgate design.
Where total extraction methods such as longwall mining are employed, failure of the rock mass above the extraction horizon typically occurs and goaf is formed. The goaf is of reduced stiffness as compared to the original rock mass resulting in a portion of the overburden load above the extracted panel being distributed to adjacent solid coal away from the goaf edge. The distributed load is referred to as the abutment load. In Australia and the USA the longwall gateroad design methodologies Analysis of Longwall Tailgate Serviceability (ALTS) and Analysis of Pillar Stability (ALPS) were developed to assist in the design of chain pillar systems to satisfy gateroad serviceability requirements. Important to the application of both methods is a reasonably accurate determination of the vertical load carried by the chain pillars at the various stages of the longwall extraction cycles. To calculate the load, use is made of tributary area conceptsand the abutment angle model, which utilises the panel and pillar geometry, overburden density, the abutment angle (f) and analytical functions to describe the distribution and manifestation of the abutment load(s) about the longwall face. In Australiaand the USA the abutment angle and load distribution functions have been determined /calibrated based on industry wide underground investigations (i.e. vertical stress change monitoring of chain pillars).
While Tributary Area Theory and the Abutment Angle Model generally assist in providing a reasonable approximation to a complex issue, chain pillar monitoring studies conducted in Australia over approximately the last 30 years strongly indicate that without the application of prudent engineering judgement significant errors in the calculation of the abutment loads carried by the chain pillar system can be made. This paper explores the appropriate use of the abutment angle model for longwall tailgate design and details a number of case studies to highlight the issue.
An investigation of the coal seam gas content and composition in Soma Coal Basin, Turkey.
Olgun Esen, Anıl Soyl, Samet Can Özer, Ata Ramazani Rend and Abdullah Fisne
The Miocene Soma Basin in Turkey is estimated to contain at the least one billion tons of lignite and about half of this reserve is present at depths greater than 600 m. In the Soma Basin, Turkish Coal Enterprises (TKI) has conducted open cut coal mining and underground coal mining activities for several decades in the Northern and Central part of the basin, respectively. It is known from the mining operations that the Soma coal basin have considerably gassy coal seams, but until now there isn’t any sufficient scientific and technical research about gas content and composition of coal seams in the basin. Recently, coal exploration activities have been extended to the Southern part of the basin by means of exploratory drillings. In this context, 49 coal core samples were collected and were analysed in terms of gas content and composition. The gas content measurements indicate that as much as 4.2 m3/t coal is present in the coal recovered from 1010.50 to 1010.90 m below the surface.
The composition of the gas is dominantly methane with more than 80 %. Considering the chemical composition of the gas and gas indices, the source of the coal gas is biogenic probably generated by bacteria that are introduced to the coal seam by fresh water following mainly the normal faults bordering the graben structure. The possibility of coalbed methane potential of the basin is also investigated with regard to preliminary gas content data.
Gas desportion velocities of coal seams in Zonguldak Coal Basin as an indicator of outburst proneness.
Olgun Esen, Abdullah Fisne, Gündüz Ökten
Coal and gas outbursts can be defined as violent ejections of coal and gas away from the freshly exposed coalface during mining operations, either in breaking into or in development of the seam. It has been a major geological hazard to underground coal mining for over 150 years, and continue to cause serious problems in all over the world. Coal outbursts have occurred in at least 18 nations including Turkey. There have been 90 gas and coal outbursts in Zonguldak Coal Basin between the years of 1969 and 2013 resulting in 374 fatalities. Due to the fact that to protect the mine workings from coal and gas outburst events, gas desorption velocity is one of the most indicator parameter to predict outburst prone areas. A number of sorption/desorption indices have been used to predict the proneness of coal outbursts. These indices quantify the nature of coals and the values of these indices must be related to other factors such as structure of coal, gas content, stress, etc.
In this study, desorption velocity of gas in coal was determined by the indices such as ∆P0-60, ∆Pexpress and KT index. Coal samples were taken from Kozlu and Karadon Collieries in Zonguldak Coal Basin, where most of mine accidents were experienced such as gas and coal outbursts, firedamps etc. In addition, only three coal seams (Acılık, Sulu, Çay) were investigated due to coal and gas outburst events mostly experienced in those coal seams. Results are changed between 0.12-0.76 bar for ∆Pexpress, 4-26 bar for ∆P0-60 and 0.56-0.79 for KT index. These values were compared with their threshold limits and finally outburst prone zones in mines were determined.
Ground trotting the interpretation of acoustic and resistivity image logs.
David Titheridge and Saswata Mukherjee
Resistivity and acoustic scanner image logs, in both the CSG and coal-mining industries, are the predominant means of determining azimuths of joints/cleat in coal. Resistivity images of the bore wall reveal large fractures that intersect the entirety of the bore wall (represented by a sinusoidal traces), and those have low height and intersect one side of the bore wall (represented by lineations). Acoustic image logs often only record the larger-scale features.
The strike of fractures that appear on an image log as a lineation are mostly apparent rather than true. In some instances all lineations are presented on rose diagrams as true azimuths, and lineations are erroneously treated as poles to a fracture. Both produce misleading results. A statistical method that extracts the true azimuths from a weighted mean of apparent azimuths, as well as the mean azimuths of highest apparent dips is presented. This is of value to interpreting local tectonic history and planning gas production.
Petal fractures (PF) in coal, when combined with breakout azimuth, can also be used to determine joint/cleat azimuths of both large and small scale fractures. The PF core-based method can be limited by the presence and abundance of PF, and is dependent on restoring segments of core to their correct relative orientation. Bedding-plane observations of core provide cleat/fracture information not obtainable from an image log. The PF core-based method, in combination with bedding-plane observations of cleat and joints, provides a means to ground truth the results of both acoustic and resistivity image log analysis.
Bulli Seam Benchmark – relevance in defining Outburst Threshold Levels
A relationship between measured gas content (QM) and desorption rate index (DRI), known as the Bulli Seam Benchmark, was presented in the early 1990’s and this relationship was adopted by the Australian underground coal industry as the preferred method used to define appropriate outburst threshold levels for all Australian coal seams, except the Bulli seam.
Significant changes in mining conditions and outburst management have occurred in the Bulli seam mines in the twenty plus years since the Bulli Seam Benchmark was presented. This paper presents the results of analysis of current Bulli seam gas data and the current relationship between QM and DRI, and discusses DRI and its relevance in defining outburst threshold levels. Increased in outburst threshold levels at Bulli seam mines and the impact on defined outburst threshold levels at non-Bulli Seam mines are also discussed.
Coal pillar design when considered as a reinforcement problem rather than a suspension problem
Russell Frith and Guy Reed
Current coal pillar design is the epitome of suspension design. In principle, this is seemingly no different to early roadway roof support design. However, for the most part, roadway roof stabilisation has progressed to reinforcement, whereby the roof strata is assisted in supporting itself. Suspension and reinforcement are fundamentally different and, importantly, lead to substantially different requirements in terms of roof support hardware characteristics and their application.
This paper presents a prototype coal pillar and overburden system representation where reinforcement, rather than suspension, of the overburden is the stabilising mechanism via the action of in situ horizontal stresses within the overburden, the suspension problem potentially being an exception rather than the rule, as is also the case in roadway roof stability. Established principles relating to roadway roof reinforcement can potentially be applied to coal pillar design under this representation. The merit of this assertion is evaluated according to documented failed pillar cases in a range of mining applications and industries found in a series of published databases.
Based on the various findings, a series of coal pillar system design considerations and suggestions for bord and pillar type mine workings are provided. This potentially allows a more flexible and informed approach to coal pillar sizing within workable mining layouts, as compared to common industry practices of a single design Factor of Safety (FOS) under defined overburden dead-loading to the exclusion of other potentially relevant overburden stabilising influences.
Overview of numerical analyses for modelling rock dynamic problems in coal mining
Gaetano Venticinque and Jan Nemcik
The application of numerical analysis towards modelling real world problems requires fundamental understanding of the system behaviour as it occurs in nature. The choices of the numerical models largely rely on the modelled problems that may be; static equilibrium such as the stable mine excavation, continually yielding/caving strata such as the goaf formation or dynamic events to simulate fast propagation of fractures in brittle rock of other dynamic behaviour. In engineering, this often involves simplification of real world situations to reduce complex geometries and properties within a numerical model to a reasonable level. For rock dynamic analyses, numerical simplification namely concerns the properties of rock mass and time dependent material response behaviour. The extent of performed numerical simplification can be traced back to the combined selection of Numerical Scheme, Numerical Method and Constitutive Relationships employed in the design of a numerical model. In this paper, applications of different numerical schemes used in commercial software, numerical methods and constitutive relations are reviewed. A few examples of suitable models for different types of rock dynamic problems commonly encountered in coal mining are presented here.
Two-phase flow-deformation coupled numerical simulation of the infilled joints shear behavior and impacts on mining practice
Libin Gong, Jan Nemcik and Ting Ren
Rock discontinuities filled with soil-like materials commonly exist in rock masses, where the saturation/water condition of the infill material is one of the major factors influencing their shear behaviour and ground stability. Compared with fully saturated conditions, the unsaturated joint infill provides a suction strength increasing the joint shear strength. This may be important when considering slope stability such as in the open cut mines or designing underground excavations where infilled joints are common. However so far, research on the unsaturated infill joint behaviour is rare, especially those carried out in numerical simulation where complex conditions can be investigated. This paper investigates the shear behaviour of unsaturated infill joints in the numerical software FLAC/Two-Phase Flow mode to couple the unsaturated flow-mechanical deformation. The FLAC soil-water retention and permeability models were modified in FISH subroutine to consider infill porosity change. A series of constant water content direct shear tests on infilled joints under various ratio of infill thickness to asperity height (t/a) were numerically conducted. Results highlight the necessity of correcting the intrinsic models in FLAC, and indicate that t/a ratio has a distinct influence on the small-strain shear behaviour up to a critical value. Shear induced variations of fundamental infill parameters (e.g. matric suction, degree of saturation and permeability) and their impact on joint strength and mining practice were emphasised.
Mechanism of face support failure in shallow longwall mining and prevention
Weibing Zhu, Jialin Xu，Jinfeng Ju and Qingdong Qu
When longwalls are operated underneath previously mined-out workings in shallow and close coal seams, face supports become ironbound due roof leading to coal face collapse. This type coal face failure has occurred in a number of times in Shendong Coalfield, China, significantly threatening the safety of mine workers and hindering the coal production. The mechanism of such failure was studied in this paper by field investigations, numerical simulations and integrated analyses. Three abnormal mining conditions were identified that can lead to instability of a much larger area of roof strata than normal, and thus causing significant overload imposed to the face supports. These conditions are associated with longwall face positions; (1) underneath uphill sections of valley terrains; (2) advancing out of the boundary of upper coal pillars; (3) below upper chamber of coal pillars. Several guidelines were thereby proposed for the prevention of roof support failure in the above three conditions. These guidelines have been applied to longwall operations in Shendong coalfield, China and proved to be effective.