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By S. Paul Singh

"The long-term viability of seismically active and/or deep mining operations hinges upon the industry's ability to maintain profitability in a climate of increasingly difficult conditions, escalating operating costs and fluctuating metal prices. Within this context, it is prudent to explore mining techniques that could provide means for safer and more profitable extraction of seismically active and/or deep seated deposits that are vital to the long term survival of the industry.The first step was to examine Penetrating Cone Fracture (PCF) and other relevant concepts with the objective of semi-continuous mining in deep underground hard rock mines. This was followed by an assessment of the current conventional drilling and blasting practice. Thirteen blasts were monitored in five different seismically active workings of an operating deep mine. The main concerns during the current drill and blast practice were identified.On the basis of the literature review, three short round blasting techniques were short listed for further review. These techniques were evaluated based upon the available literature and discussions with the persons associated with their applications. Justification, requirements and major challenges for the application of short round blasting have been discussed in this paper. Suggestions for improving the current drilling and blasting practice have also been outlined.INTRODUCTIONRock fragmentation is the key to mineral excavation and production. Increasing working depths, environmental concerns and trends towards continuous mining necessitate the development of new and improved rock breakage methods.The excavation of hard rocks is still dominated by the sequential routine of face preparation, drilling, charging explosives, blasting, ventilating for fume and dust removal, mucking and roof support. Worse still, drilling and mucking require specialized equipment that fills the end of the heading so that no other operation can be performed and the equipment must be removed from the face to protect it from fly rock."

Jan 1, 2010

By B. Singh

The use of wire ropes has already been tried in a few countries for roof support In mines. But the use of scrap wire ropes, as a method of support on extensive scale has not been reported from anywhere except India. Extensive trials using freshly discarded wire ropes for roof support were undertaken both in the laboratory and field. In laboratory, model beams supported with different reinforcing techniques were tested to evaluate their comparative load bearing capacity vis-a-vis reinforcing factor. Among all the tests, the model supported with wire rope system at 60° angle in combination with two supplementary vertical bolts offered the best result 1.e. about 95% reinforcement. It also accepted post fracture loading of the beam. In statical analysis too, the best result could be obtained with the rope installed across the gallery at 60° angle. All these findings are in conformity with the field observations obtained during roof stitching practices in coal mines. Of late, roof stitching, an effective and economical method of roof support developed at CMRS, India in 1972, found wide application in over 200 coal mines. In this method, a freshly discarded wire rope is grouted across a gallery in two inclined drill holes supplemented with two middle vertical roof bolts at every 1.0 to 1.2 m interval along the gallery. It is tensioned against the roof using wooden sleepers and thus, the whole system functions like a roof truss.

Jan 1, 1990

By G. Herget

To improve quality control of roof conditions, a program was carried out at Elliot Lake uranium nines in Ontario, Canada to test a portable TV camera system. This camera has a 29 mm diameter probe and is capable of identifying crock locations, crack width and approximate dip direction. The extent of fractures to the roof was checked with the aid of a vacuum system by placing packers in various boreholes and checking for communication. The removal of some rock bolts indicated an increase in fracture extent.

Jan 1, 1982

One of the most important parameters in rock/resin/bolt load transfer mechanism is the surface property of the bolt. Although there are various bolt surface configurations available in the market, very little work is reported on the bolt/resin interface failure mechanism. This paper examines the behaviour of bolt surface roughness under constant normal stiffness conditions which is considered as being a realistic way of evaluating bolt surface roughness. A series of shear tests have been conducted on the flattened bolt surface to study the shear behaviour of bolt/resin interface. Based on the experimental results, a mathematical model has been developed to predict the shear resistance of the bolt/resin interface at various normal stress levels for the bolt types used in the study.

Jan 1, 1999

Numerical simulation for microseismicity due to mining at one of the collieries in Australia was carried out and the results were compared to the observed microscismicity. 3-D Stress analysis showed stress concentration on the edges of the mined areas and on the coal pillars- The stress concentration ahead of the coal face was biased to the tailgate. This is similar to the observed distribution of microseismic events. Stress reduction above and below the mined area was seen. Tensile stress was observed mainly above the mined area. It was realized that compressive failure due to nearly vertical maximum principal stress and nearly horizontal minimum principal stress in retreat direction (NS) might occur ahead of the face. Tensile failure due to nearly vertical minimum principal stress above the mined area was expected. Compressive failure due to nearly horizontal maximum principal stress in EW direction and nearly vertical minimum principal stress above and below the mined area were also expected.

Jan 1, 2001

By Zhanjing Yu

Longwall ground behavior in the Illinois Coal Basin was studied in the past (1, 2, 3). Most of the past studies, however, were concentrated on either surface subsidence or underground structural behavior. In this study, both surface and in-mine ground behaviors are considered, which include: 1) stress and deformation characteristics in the chain pillars; 2) roof and floor deformations; 3) surface subsidence characteristics, including time effect; 4) relationship between the surface subsidence and underground strata behavior; and 5) the ultimate hearing capacity underneath the chain pillars. Field measurements and tests were conducted and the data were analyzed using both analytical and statistical methods. The findings in this study can he used by mine operators in the Illinois Coal Basin for longwall ground control planning and design.

Jan 1, 1994

By David Newman

The latest version of the Surface Deformation Prediction Software (SDPS) package is presented through its application to a number of case studies. The package now exploits all the benefits of the Microsoft Windows platform and has a direct interface to CAD software, thus facilitating input and output. Also, the package features advanced calibration routines to handle predictions over specific regions. The case studies presented highlight the features and capabilities of the new package.

Jan 1, 2001

By Marc Arl

Failures of the face and roof above longwall shields have caused days and sometimes weeks of lost production. A common recovery method for these failures has been to pump light weight cementitious grout into the roof and face cavity to stabilize the area This approach while effective is very time consuming and costly. Mines in several coal producing nations have over the past few years been applying phenolic foam grouts in these situations in lieu of cementitious materials. Phenolic foam is a two-component injection product intended for cavity filling, air and gas sealing and the consolidation of highly fractured strata. The properties of phenolic foam; rapid application, quick setting, high expansion rate, high compressive strength and excellent anti-static properties, produce a fast, safe and cost effective cavity filing solution. The product is also classified as fire resistant and so is also suitable for sealing off underground heatings and for aiding fire fighting operations in deep mines. This paper will discuss the application and use of phenolic foam in various underground coal mines in the world over the past few years.

Jan 1, 2005

By S. K. Sharma

The present study attempts to critically review the pillar-design as required by Coal Mines Regulations of India vis-a-vis latest rockmechanics formulae, Equivalent material modelling was the approach adopted for testing the safety and stability of the pillar sizes predicted by various formulae. Two parameters, considered here for calculating pillar sizes was the stresses acting over the pillars and the strength of the pillars. Stresses acting on the pillars were calculated by the tributary area method. Based on the studies of Coates and Hustrulid, the stress obtained was reduced by 40 percent. For calculating the strength of the pillars, three formulae, namely Holland and Gaddy, Salamon and Munro and Central Mining Research Station, India, were used. The pillar widths were then determined by equating the product of recommended factor of safety and pillar stress with the pillar strength.

Jan 1, 1992

By Syd Peng

"As the International Conference on Ground Control in Mining (ICGCM) enters its 35th year in 2015, it is time to look back and identify the areas that need to be emphasized and to look forward to see what areas need to be researched in the future. In the past three decades, ground control has made a tremendous advancement, and many case studies published in the 36 volumes of proceedings have demonstrated its important role in the daily mining operations. However, there is still plenty of room for improvements. This paper discusses the research needs in 12 subject areas, including mine geology, rock property, zones of disturbance in overburden, computer modeling, underground stress measurements, research method, roof bolting, coal pillars, failures, subsidence, shield supports, and coal bumps.INTRODUCTIONThe International Conference on Ground Control in Mining (ICGCM) was founded in 1981. Since then, 1,546 papers have been published in the 36 conference proceedings, including the three surface subsidence workshops held in the 1981, 1986, and 1992. All types of topical areas regarding mining, from geotechnical core loggings in the exploration phase through backfilling after mining to finally spoil piles stability on the surface, have been addressed. A review of these papers, and other related literature as well, indicate that ground control has developed to become an inseparable part of mine design and a problem-solving tool for safe production.After 34 years, it is time to look back and identify the areas that need to be emphasized and to look forward to see what areas need to be researched in the future. There is no doubt that the conference series has achieved the goal for which it was originally designed: to provide an annual forum for the exchange of information among the researchers, government regulators, equipment manufacturers, consultants, service providers, and—above all—mine operators. There have been many papers addressing the application of ground control techniques for successful mine design and safe production, and, without these papers, many projects would have failed. In fact, the conference emphasis on application types of papers may have steered too far toward the application side. A review of the conference papers shows that papers have been leaning mostly toward the applied side, leaving most, if not all, fundamental issues behind in nearly every topical area. This paper addresses research needs in 12 topical areas: mine geology, rock property, zones of disturbance in overburden, computer modeling, underground stress measurements, research method, roof bolting, coal pillars, failures, subsidence, shield supports, and coal bumps."

Jan 1, 2015

By L. A. Sandbak, Yan Xing

"The purpose of this study is to evaluate the rock mass stability around the tunnels by three-dimensional (3-D) numerical modeling. Complex geological and tunnel features have been included in the model using the software package 3DEC™. Based on the available information on stratigraphy, geological structures, and mechanical properties of rock masses and discontinuities from the underground mine, 3-D stress analyses were performed on various cases with different K0 (lateral stress ratio) values, constitutive models, as well as support systems. Relations between these factors and the distributions of stress, displacement, and failure zones around the tunnels were obtained and discussed. Finally, comparisons between the field deformation measurements and numerical simulations are used as validations for the simulations, helping to determine the appropriate K0 value and material constitutive models for the underground mine.INTRODUCTIONThe case study site is an underground mine in the USA with a monthly ore production between 20,000 and 30,000 tons. The regional geology of the mine is structurally and stratigraphically complex. Rocks in the area include carbonaceous mudstone and limestone, tuffaceous mudstone and limestone, polylithic megaclastic debris flows, fine-grained debris flows and basalts, all part of the Cambrian-Ordovician Comus formation and related dikes. Both the mineralization and faults have general orientations striking N-S to NW-SE with high dip angles. The ore body in the mine has an incline of about 25---45 degrees located in relatively low quality rock; hence, cut-and-fill mining has been used.This underground mine has two vertical shafts used for ventilation, ore hoisting, and for personnel and material transportation. Development drifts were designed and driven to extract and transport the ore, as shown in Figure I. Bolts, mesh, and shotcrete have been applied in this mine for ground control. In order to reach various locations, the tunnel system is designed with different heading directions and inclines, which will be described in detail later. The area selected for modeling is a cubic region including all the tunnels inside the black square (Figure 1)."

Jan 1, 2016

By Peter Cain

The Phalen Colliery in the Sydney Coalfield is extracting the 2.6 m thick Phalen Seam by the panel and pillar longwall retreat method. Abandoned workings occur in the Harbour Seam 140 m above and overlie the Phalen Colliery. Parts of these workings are flooded, and pose a number of questions relating to the safety of operations in the Phalen Colliery. In order to answer some of these questions, the Cape Breton Development Corporation re-entered an abandoned non-flooded roadway in the Harbour Seam directly above a retreat panel in the Phalen Seam to allow the deployment of instrumentation to monitor interaction effects. Fifteen monitoring sites, each 4.5 m apart, were installed in the 5 East Top Level after it had been re-entered and made safe. Each monitoring station included a vibrating wire strain gauge piezometer and a potentiometric extensometer. The piezometers were attached to rock bolts anchored into the floor and were connected by a flexible standpipe to a constant head apparatus. Variations in hydraulic head due to subsidence were monitored to determine subsidence. The extensometer units were mounted on rock bolts anchored into the floor of the roadway beneath the ribside and monitored ground strains. The instrumentation was capable of remote reading in the event that access to the site was restricted after installation. This paper describes the instrumentation, the installation programme, and some preliminary results.

Jan 1, 1993

By Bruce K. Hebblewhite

This paper provides an overview of the international ?state of the art? with respect to underground coal mining methods used in seams of thickness greater than 4.5 m, through a review of a selection of high performing thick seam mining operations around the world?both Single Pass Longwall (SPL) and Longwall Top Coal Caving (LTCC). The paper discusses the recent operational experiences from these selected faces, together with the ground control issues faced, and identifies some of the major, inherent geotechnical factors that can influence the mining method selection, design criteria, and ultimate performance, from both an operational and safety perspective. It is clear that both of these methods are developing quickly? not only from an operational and equipment perspective, but also from the understanding of critical geotechnical criteria. There is an increasing role for both methods in thick seam environments, although the higher SPL faces will only be successful in the near to mid-term under benign geotechnical environments. Regardless of the method, a thorough understanding of the critical geotechnical factors is a key to successful implementation of either method.

Jan 1, 2013

By P. M. Lin

The problem of abandoned mine land (AML) subsidence is getting more severe because abandoned mine lands which used to be located in the remote areas have been gradually developed into suburbs or even urban areas. Abandoned mine subsidence is also becoming more common than before because the time-dependent effect of exposed underground materials. These materials will deteriorate gradually and cause subsidence as time passes. Subsurface conditions of abandoned mines are seldom known to the public. Mine maps are not always available. If the mine mans are available, their accuracy are very - often questionable. In addition, the most common damages to surface structure and ground surface due to mine subsidence can also be created by other non-mining related geological hazards. These factors make the study of abandoned mine subsidence significantly complicated, tedious, and inconclusive. For instance, the cause, time, and amount of surface subsidence can be predicted with relative accuracy during active mining. However, it will be a considerable challenge to do so on abandoned mine subsidence. If abandoned mine subsidence can be predicted in advance, then the damages can be held to a minimum. However, this prediction technique is not yet well developed. Therefore, remedial measures require more attention. In order to have effective remedial measures, the real cause of the damage should be determined first. This paper describes the approach which was employed for the determination of abandoned mine subsidence. A site investigation was made first. According to the information obtained from the site investigation, a hypothesis was set up. Then the instrumentation was used to prove the hypothesis. By going through the procedures for several cases, a guideline which can be used by the inspectors to inspect abandoned mine subsidence will be established.

Jan 1, 1987

By M. W. Fabjanczyk

Cement and resin encapsulated tendons are widely used in the stabilisation of mine roadways. One of the main factors in controlling the efficiency of the reinforcement is the ability of the tendon to generate load in response to rock deformation. The analysis of field data from instrumented reinforcing tendons complimented with extensive laboratory investigations have more accurately defined the mechanisms by which load generation occurs. The role of reinforcing tendon profiles, hole geometry and encapsulation medium properties in controlling the reinforcement stiffness and capacity are discussed. The results of the investigation have implications in both the design of rock reinforcing systems and the optimisation of encapsulation mediums and tendons.

Jan 1, 1992

By R. Fraher

Hazard analysis utilizes interaction mechanisms in combination with geologic, structural and mining conditions to delineate areas of potential damage in seams subject to interaction. Using characterizations of conditions peculiar to multi-seam mining, such as innerburden thickness, geology and structures, initial interaction contour maps can be constructed. Geologic hazard analysis is then carried out on roof, pillar and floor conditions in the affected seam using lower seam rock properties and layout geometries in the overlying seam. Either safety factors or damage ratings can then be developed representing degree of hazard in the lower seam. The final hazard map shows both the aerial extent and magnitude of potential damage from interaction.

Jan 1, 1992

By E. Yasar

This paper describes the use of the sand and plaster physical modelling technique to investigate the deformation around mine roadways using a variety of support methods in a particular form of stress field. The characteristics and conditions of coal measures rock were considered prior to the preparation of the models and the insertion of support The investigation has clearly shown how floor lift, roof failure and sidewall movements of mine roadways in laminated weak rock conditions gradually develops as a result of the increase in the stress and, also, how it is related to the level of support used.

Jan 1, 1995

By Michael Kelly

Longwall mining is the principal method of underground coal mining in Australia, with 70 million tonnes being produced by longwall mines in 1999. However, the mechanisms that control longwall geomechanics are still not clearly understood resulting in stoppages costing several hundred million dollars per annum The CSIRO has been investigating longwall geomechanics with consultant groups and minesites through several ACARP supported projects since 1994. The research has aimed to improve longwall support design and control methods by defining strata failure mechanisms and their occurrence about underground extraction panels, It also aimed to develop better predictive tools bur a broad range of underground environments. As a result of site studies at more than 8 locations some of the aspects that have been touted to control longwall geomechanics, especially from a 3D aspect are highlighted. These aspects include stress controls, geometry, faulting, depth. longwall width and changes in lithology.

Jan 1, 2000

By Daniel W. H. Su

Underground roof geology reconnaissance is being conducted by CONSOL Inc. to enhance mine productivity. Often, roof instability within mine entries is the consequence of highly variable geology that cannot always be detected from information provided by widely-spaced surface core holes. Utilizing a combination of roof drilling data, geophysical logs, and borehole camera and fiberscope observations, roof geology mapping is conducted within longwall development entries in areas of specific concern prior to commencement of longwall mining, Depending on the uniformity of the site-specific roof geology, data point spacing along the longwall development generally ranges from one to five crosscuts. Surface core hole data are correlated with the roof geology mapped underground to validate the underground observations. Detailed roof geology maps can then be produced to enable ground control engineers and mine management to select cost-effective ground control techniques. However, this procedure is not necessary or useful in all situations and it is employed only when there is strong geologic evidence to justify a closer inspection.

Jan 1, 1999

By Satyendra K. Singh

If the extraction is beneath massive roof strata, the roof tends to 'bridge' across large spans without failing, the caving behaviour is complex and irregular. Understandably, these give rise to many geotechnical problems with safety implications and involving sometime huge direct and indirect costs. Only two important problems, 'feather-edging' in pillar mining and `severe periodic weighting' in longwalling, are discussed in this paper in the background of geomechanics investigations in Australia at Blue Mountain Colliery and in South Bulga Colliery respectively. `Feather edging'- a major source of injury and fatal accidents in Australia and South Africa in such situations, refers to a phenomenon where the roof, at the goat edge, falls as a thin wafer of rock often suddenly, over-riding conventional timber breakerlines. The results of the first comprehensive, monitored trial in an Australian pillar extraction coal mine, suggests how the roof falls into feather-edging caving (generally) because of multiple shear-planes (interpreted) and how it may be alleviated. Because of complex fracturing behaviour of massive roof strata, periodic weighting at a longwall face is certain to manifest itself as 'yielding supports', heavy conditions', rapid convergence and in the worst case, as a cause of face stoppage. After briefly discussing the programme of instrumentation (in a chain-pillar and over the would-be goal) and results, this paper attempts to improve mechanistic understanding of the related geotechnical issues associated with the weighting behaviour and aims at establishing a 'threshold' value of weighting severity index (suggesting intensity of periodic weighting) with an objective to optimise operational controls before mining through potential (future) weighting areas.

Jan 1, 2000