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By Leigh J. Wardle

Significant coal reserves in New South Wales lie under areas with steep topography such as valley slopes and cliffs. Subsidence predictions are difficult to make for these locations as existing empirical databases cannot cover all permutations of topography and mining geometry. Two dimensional numerical model alternatives are of limited applicability. Consequently a novel three-dimensional numerical model is developed including the detailed panel layout, realistic rock mass properties including the full stratigraphy, goat behaviour and actual surface topography. Model results show the same trends as subsidence measurements from Baal Bone Colliery in the Western Coalfield of New South Wales

Jan 1, 1992

By Charles D. Albright

FMC built its first angle bolter in 1969. This was a single mast unit which could drill holes for conventional bolts or angle holes for installing roof trusses. From this drill we learned very quickie that the mast design was an important factor to the success or failure of any angle bolter. The first mast installed on this machine (EXHIBIT 1) was fixed in length with endless chain and hydraulic motor feed. It took less than a shift underground to determine that the fixed length was not going to work. The undulating top created conditions where the mast was too long to be positioned at a 450 angle. Several mast designs were tried and discarded before we felt we had the answer to our problems. (EXHIBIT 2} We developed a mast that would extend or retract without moving the position of the drill unit. This allowed the operator to "wedge" the mast between the floor and roof before starting his drill feed. This arrangement worked exceptionally well, but unfortunately the demand, as perceived by our Sales Department, for angle bolters did not materialize. This unit became an "orphan" and was used by many coal mines until it died a natural death. FMC did not decide to re-enter this market again until 1979. At this time many coal producers were contacted to determine what features should he incorporated into a dual mast angle bolter. From this information we were able to arrive at three main areas of concern that we should consider when designing a new machine. 1. Eliminate overturning moment on drill unit. 2. Provide some sort of steel support near roof line to aid in starting a 15° hole. 3. Dual mast units need a method of raising center of mast rotation to facilitate various mining heights and still maintain a 45° angle and proper distance from rib. I would now like to discuss each of these individually. EXHIBIT 3 indicates the overturning moment resulting from the feed cylinder thrust and the reaction of the drill hit against the roof. To eliminate this moment a mast was designed using two feed cylinders mounted in the plane of the drill center line, thus removing all overturning moments on the drill unit carriage. This mast has been used extensively in vertical drilling with no downtime attributed to wear on mast guides and drill unit supports. The cylinders are designed to provide uniform thrust and feed speed throughout the total stroke. For manufacturing and economic reasons, the final mast design on the first drill was not used for this new drill. A drill steel support mounted on the mast, and positioned by a hydraulic cylinder provides the needed guidance near the roof for starting a hole at a 45° angle. (EXHIBIT 4) This support does not surround the drill steel but simple cradles the drill steel for "collaring" the hole. Once the hole is started, the support can he lowered. The support plate is hinged to allow the drill mast to pass. The advantage of having vertical motion of the center of rotation on a dual mast drill is shown in EXHIBIT 5. Following the criteria recommended by Birmingham Bolt Company, the truss bolts should he at a 45° angle and one fifth of the width of the entry from the rib. Therefore, in an entry 20 ft. wide, the hole should be drilled 4 ft. from the rib and at the 45° angle previously mentioned. With the limitations inherent to dual boom drills, that is, the masts cannot pass each other nor can one mast pass the center line of the machine even if the other is positioned out of the way, it is impossible to accommodate much variation in seam height and maintain the recommended criteria. As shown in EXHIBIT 5, a center of rotation 17 inches above the floor will start a hole 4 ft. and 45°angle at a height of 67 inches. Any height above 67 inches

Jan 1, 1982

By Peter Griesenbrock

In German underground coal mining mostly arch and some rectangular roadways are used in the development work. Due to its positive results from numerical and physical modeling techniques as well as good underground experiences, the numbers of rectangular roadways has increased significantly. Today the bolt support - independent of its cross-sectional shape - represents an undeniable support element. During the introduction of new bolt techniques a detailed investigation of the rock and support mechanical effectiveness of bolt support in roadways at all operation stages is of basic importance. This effectiveness can be predicted and verified using different simulation techniques. For the planning of rockbolted roadways two supplementary simulation techniques are presented in this paper. By combination of all available planning tools the best result for planning assurance can be achieved. Keywords: numerical modeling, physical modeling, arched roadway, rectangular roadway, roofbolting, advancing longwall.

Jan 1, 2002

By David C. Laurence

in March 1999, the School of Mining Engineering at the University of New South Wales carried out a series of underground trials using " Evermine", a South African developed two-part water based polymer membrane. The aim of the trials was to determine the potential of a spray-on polymer membrane such as Evermine as an alternative to conventional rib support systems The mine selected was Angus Place colliery, reputed to have some of the worst ground conditions of any Australian underground coal mine. Ribs at Angus Place are supported by conventional pattern bolting supplemented by wire mesh. The trials indicate that there is significant potential for the introduction of polymer membranes into the underground coal minim; industry Initial results indicated that ribs that had been sprayed exhibited less displacement and spalling than unsprayed ribs. particularly when subjected to abutment loads from an approaching long-wall Further research will he required to conclusively rate the performance of Evermine in comparison to other products in the market and the long term performance of the product

Jan 1, 2000

By C. J. H. Brest van Kempen

The techniques developed should provide a useful tool, not only during the initial formulation of a suitable bolting plan for a new section, but also for periodic check¬ing on the utilization factor of hardware installed in the roof. Indications are that with present practice, utilization seldom exceeds 507.. Retro-fittable bolter equipment now available (FCBS?) allows doubling of the utilization factor in many cases. We are also introducing a computer pro¬gram based on the material outlined in this paper. This program can save a great deal of time in examining the real effect of implementing alternate bolting plans or using different installation techniques. It allows fine-tuning of bolt lengths, spacing and installation tension to mini¬mize roof support cost, while maximizing safe life of the mine opening. We have developed a procedure which allows easy, site-specific quantification of the need for reinforcement of a mine roof. The concept is based on the forma¬tion of a direct link between theory and empirical data to custom-fit each mine section. In its simplest form, the proce¬dure requires only recording of roof bolt torques in a sample working place (16 to 25 bolts) several times during the first week or so after initial bolting. The way in which the torque pattern changes during this time can reveal whether or not the bolts carry enough tension to maintain stability in that specific roof. From the same data, the nature of the anchorage horizon is derived. Specifically, shale or limestone can be distinguished from sandstone. If the procedure is repeated a few times (within the same mine section) with different bolt installation tensions, we can numerically characterize the roof in terms of one single value: an "effective angle of internal friction". This number can then serve to calculate trade-offs in bolting plan design, such as bolt length, bolt spacing and optimum bolt tension. Additional refinement is possible if a sagmeter is installed in the sample work¬ing place being monitored and if bolt anchorage capacity is determined. The lat¬ter can be done automatically on each bolt as it is being installed, using a system we developed and patented. Alternately, a number of pull tests could be performed. Using the sagmeter, bolt torque and anchor¬age data, it is possible to project the safe life of the supported opening. The details of the procedures described apply specifically to tensioned roof bolting, but a brief discussion paints the way for a similar analysis of full-column resin bolting also.

Jan 1, 1986

By Karl Jr. Zipf

The famous Homestake gold mine in Lead, SD. closed recently alter 125 years of operation. However, the mine may receive a new lease on life as a National Underground Science Laboratory (NUSL) supported by the National Science Foundation (NSF) and dedicated to high-energy physics experiments involving neutrinos. These experiments require the construction of many large underground chambers tells of meters wide at depths of over 21 18 m. Construction of such large openings at such extreme depths has few precedents m civil-engineering-type construction. The Spokane Research Laboratory has a long history of ground control research at the Homestake Mine and has supported NSF and the physics community in their efforts to develop a NUSL at I Homestake or other suitable location. This paper will summarize underground science and describe proposed underground science laboratories ill the United States, in particular tile proposed NUSL at Homestake. Next, the paper describes an empirical design approach using the Q system of rock mass classification for these large Openings. .M initial site investigation that produced three good case histories is described. The actual support system used at the three sites agrees well with support recommendations from current support design charts, giving credibility to estimates of the classification parameters and Q. Feasibility of, and support requirements for, 25-, 50-, and 100-m spans arc estimated in the anticipated rock mass. This analysis indicates that 25- and 50-m spans are probably feasible, but a stable 100-nn span may be unachievable. The empirical predictions are then compared to detailed numerical analyses. The paper concludes with preliminary support recommendations and necessary site investigations needed to make a proposed NUSL a successful reality. These studies have been important input to NSF for their decisions on the technical feasibility of developing the proposed NUSL. If NUSL is developed, it could enable scientific experiments in areas beyond high-energy physics. 'the laboratory could also enable research in rock mechanics. ground water hydrology. mining engineering, nine safety and health, and ground control.

Jan 1, 2002

By Thomas Barczak

A new generation of hydraulic mine support prestressing devices has been developed. These thin-walled steel shells are machine-welded and can be inflated with water or any liquid to provide prestressing for a wide variety of roof support products ranging from Can supports to props and cable bolts. With an expansion capability of several inches, depending on the geometry and size of the unit, they can also establish roof contact eliminating the need for wooden wedges or crib blocks that are commonly employed with several standing roof support products. Capable of withstanding pressures from 1,000 to 6,000 psi, these cells are able to transfer roof loading into the support structure without rupturing. A recent development has been the addition of an inexpensive yield valve that provides control of the maximum pressure and load development on the support. This paper examines the performance capabilities of these inflatable prestressing units and the impact they have on the performance of various support systems, including an evaluation of the overall stiffness of the support system and the load control during yielding of the prestressing unit. Recommendations are made regarding the design requirements of the prestressing unit to optimize the support performance. A summary of mine applications using this technology is provided with general comments regarding their impact on ground control.

Jan 1, 2004

By H. Gene Wilson

Mobile Roof Supports (MRS) look similar to a longwall shield on crawler tracks. The MRS units offer a safe, productive method of extracting the 40% to 60% product left normally unrecovered in room and pillar mining. The units feature radio control, self-contained power units, crawler track drive, and a 600 ton yield. Cribbing and setting posts in retreat mining has been a necessary burden to production. The MRS reduces this burden. Long blocks of coal can be developed to further reduce move and tram time, thus increasing production. The MRS units have successful safety records. The workers are removed from the immediate fall area, and we feel back injuries have been reduced by the workers not setting posts. While MRS units have been damaged in falls, the other capital equipment has been unharmed. The MRS product line has undergone normal product improvement and evolution. Product evolution is seen in our development of machines for particular mine requirements. Through the continuing development of the MRS, Fletcher presents the coal industry with a safe, productive method of retreat mining with potential to develop new mining methods.

Jan 1, 1990

By Michael A. Berdine

In early 1997, Twentymile Coal Company took a dramatic departure from traditional longwall recovery methods. Previously, Twentymile's standard longwall meshing procedure included the use of chain link fencing material. Beginning with the 9-Right to 8-Right longwall recovery operation, Twentymile incorporated a polyester geogrid mesh system supplied by DYWIDAG-Systems International. This paper discusses the subsequent utilization of the polyester geogrid mesh system at Twentymile.

Jan 1, 2001

By K. Itakura

Information about geostructure for effective rock bolting must be obtained before setting the bolt into rock in a coal mine roadway. Especially, rock type variation and distribution of discontinuities such as layer boundaries, and separation of strata and cracks all represent indispensable knowledge. To achieve in-situ evaluation of roof rock, we developed an MWD (measurement while drilling) system using mechanical data from a drilling machine for rockbolt. System hardware detects torque, thrust, revolution, and stroke of the machine, and software analyzes the mechanical data log and displays locations of discontinuities using Neural Network techniques. Also, this system is able to estimate roof rock 3-D geostructure for varied rock types and discontinuity distribution in cases of a drill hole array arrangement in roof rock. We conducted a feasibility study for it using hydraulic drilling at roadways of the Taiheiyo Coal Mine, Japan. Simultaneously, some core drillings were also performed to confirm system analysis data. For core samples, distribution of cracks was observed and the borehole wall was investigated by OFS (optical fiber scope). Must discontinuity locations estimated from roof logging were conformed with data obtained from core inspection. However, the core sample contained a number of cracks which were not found in the mechanical data log. This indicates that additional cracks were generated during and/or after core drilling by the influence of rotational force of the machine and water supply. Furthermore, in comparison with the OFS image, resolution of the discontinuity's log estimated by this system was clarified; that is, it is difficult to detect small size cracks (hairline cracks) from a mechanical data log and the core inspection by OFS. This paper outlines the new hardware system for hydraulic drilling machine and compares the discontinuity map obtained from the software system with drilling core inspection.

Jan 1, 2001

By Syd Peng

It is necessary to fully understand roof geological features in order to design a proper roof support system for underground coal mines. These geological features include: rock type, rock strength. rock layer interfaces, voids, cracks, and bed separations. Traditionally, engineers have relied heavily on the use of surface borehole log data to identify geological features. Since surface boreholes very expensive to be drilled in close spacing, log data are often insufficient to provide detailed information on the roof geology. Recent advances in control technology have made a large amount of roof bolter drilling data available to mine personnel. These data can be obtained during normal roof bolt installation cycle with little or no interruption in mining operations. This research project has developed several methods to identify geological features in a mine roof from measured drilling parameters. Power trend line analysis can be used to locate discontinuities and interfaces in mine roof. Power averaging can be applied to determine the relative strength of roof strata. Thrust trend line analysis can be used to locate fractures in mine roof. The results of these methods are combined to produce a mapped roof geology In a production environment, manually interpreting and managing collected drilling parameters is not practical since hundreds of holes will be drilled during a production day. A new software package, MRGIS, has been developed to allow mine engineers to make use of the large amount of roof drilling parameters for roof support design. An actual underground test site is presented to demonstrate the analysis and display capabilities of MRGIS.

Jan 1, 2003

By Gregory Hinshaw

Underground mine bolting machines have evolved since inception in the 1940's due to the need for increased safety and productivity. However, major design innovations historically came from changes in the mining plan and the mine environment. During the last ten years, productivity needs have outpaced the evolution of existing designs. J. H. Fletcher & Co. has responded with a commitment to research and development which has fostered several new designs. The most recent machine built is a walk through crawler frame powering four drilling units simultaneously with semiautomatic computer control using two operators. This machine utilizes technology to create a safer yet more productive roofbolter for continuous mining sections utilizing place changing methods.

Jan 1, 1998

By John Stankus

Accurate evaluation of stress and geological conditions is critical to ground control design in underground openings. For a mine slope entry, the problem becomes more complicated because a slope transverses through many different types of strata. Mine slope ground control has traditionally been practiced based on trial and error and prior experience. There is currently no well-accepted slope and support design methodology available for an economical and technically sound ground control plan. Over the last few years, Keystone Mining Services, LLC (KMS), the engineering affiliate company of Jennmar Cooperation, has developed a ground support design methodology called the ?Stress, Geologic, and Support design system? (SGSSM). This patent pending method enables accurate analysis of actual geo-technical conditions and stress; identifies strong, fair, and weak sections along the slope; formulates primary and supplemental roof bolting systems, designs optimal long-term steel structure support; and verifies the adequacy of the developed support. The method has been successfully utilized on various new slope projects and has been well received by state and federal regulatory agencies during the approval process. This paper details the concepts of the methodology using an actual case study of a slope project in the Midwest.

Jan 1, 2011

By Hai Rong

EH-4 Electrical conductivity imaging system has been playing an important role in prospecting, looking for water resource, and determining coal mine gob boundary by virtue of its significant advantages such as collection of large volume of data, light weight, fast analysis, high-precision, and low cost. However, it has little application in determining the overburden failure zone and development of water flowing fractured zone and bed separation space in complex extra thick coal seam conditions. In order to confirm the overburden failure range and evolution of water flowing fractured zone and bed separations in complex extra thick coal seam conditions the panel 63005 of Laohutai coal mine in China was selected for study in this paper,. EH-4 magnetotelluric method was used to determine the overburden failure zones and bed separations in the overburden. Theoretical analysis and numerical simulation were employed to verify the EH4 survey results. The results show that the failure height in the overburden of the three coal splits was 120m to 170m before panel mining, and increased to 150m to 220m after panel mining. The overburden failure height was on average 7.4 times the equivalent mining height in complex extra thick coal seam condition of Laohutai coal mine when the sand backfilling and fully mechanized top coal caving methods were employed. After mining of panel 63005 started, bed separations were found on the hanging wall and footwall of the F18 fault where water bodies existed. The results obtained in this research not only provide a theoretical guidance for safe mining at Laohutai coal mine but also serve as a reference for predicting and preventing water inrush accidents for coal mines under similar condition in China.

Jan 1, 2014

By Brian E. Travis

The recent development of polymer grids for the underground coal mining industry has created new alternatives for supplemental ground control practices. The grids utilize strong, lightweight polymers - usually special grades of polypropylene. High tensile strengths and resulting load support characteristics are achieved by molecular orientation of these polymers in the manufacturing process. One of the most important applications of polymer grids as supplemental ground control is in longwall shield recovery. When shields are moved from one face to another, the determining factor in the success of the recovery is the ground control provided by roof support structures along the old face. Whereas primary support is usually provided by roof bolts and cables which run the full width of the panel, supplemental support is often provided by metallic meshes of welded wire or chain-link fence. lightweight, high-strength polymer grids replace these heavy, cumbersome metallic meshes, giving the operation increased productivity by decreasing installation time and reducing injury downtime.

Jan 1, 1990

By Douglas Morrison

Hardrock mines in Ontario generally operate at between 3,000 and 7,500 ft below surface and generally experience significant rockburst activity below 5,000 ft. Since the introduction of bulk mining techniques around 1980, the safety record of Canadian hardrock mines has improved dramatically. However, the process of improvement was not a smooth one and, in the early years, the number of accidents and fatalities actually increased. One incident in 1984 that resulted in 4 fatalities in Ontario initiated a complete re-examination of mining practice and by the mid 1980s many changes had been introduced, driven by new non-prescriptive mining legislation. These changes affected not only the technical discipline of mining engineering but also the management of operational procedures and, together, they resulted in the significant improvements that have continued to this day. The analysis of the rock-fall related fatalities showed 5 major causes (loose, scaling, installing support, collapse and rockburst) and by the mid 1990s fatalities in all of these categories, except rockbursting, had been eliminated and even then, all these rockburst fatalities occurred in one mine which was closed shortly afterward. This paper discusses both the technical and social reasons for the initial failure and the ultimate success in improving the safety of these mines, with implications for mines in other major mining jurisdictions.

Jan 1, 2003

Effective strata control, utilising fully encapsulated roof bolts, is dependent on the installed quality of the reinforcement elements. One mechanism by which fully encapsulated roof bolts may become less than fully effective is by gloving (glove fingering) and un-mixing of the resin. Following some small roof failures containing gloved bolts, investigations have been undertaken in some New Zealand coal mines to determine the extent of, and mechanisms involved in, the gloving of fully encapsulated roof bolts for a range of roof types and installation methods. Gloving, in this context, refers to the resin cartridge partially or completely enveloping a length of the bolt, typically with unmixed resin filler and catalyst/hardener remaining within the cartridge. Results have shown that gloving and un-mixing is a systematic and widespread phenomena, occurring across a range of resin and/or bolt manufacturers, and across a variety of roof types. Gloving was found in bolts installed using: hand held pneumatic and continuous miner mounted hydraulic methods, under run of mine (ROM) conditions by mine workers, and under controlled "best practice" conditions. The roofs bolts investigated are all 1800mm (6ft) long, and have shown that, on average, 485mm (-19") of the bolt length is gloved and/or unmixed. This equates to a 27 percent reduction in effective bolt length. The effected length of bolt is sufficient to impact on the load transfer/reinforcement capabilities of the bolt system, and hence impacts on the design assumptions and subsequent stability assessments. Furthermore, there is a direct relationship between the mechanism for the gloving of bolts and an increased occurrence of resin loss and reduction in encapsulations length in soft (less than 10 MPa) and/or highly fractured rock. Investigations have concentrated on developing an understanding of the mechanisms involved. This has been undertaken using both field installations and recovered bolts, as well as test bench trials. The mechanisms involved have been confirmed as being: the development of a pressure front as the bolt encounters the resin and is spun up the hole, which, in turn, leads to over-pressurisation and radial expansion of the resin cartridge, resulting in an increase in diameter of the plastic resin cartridge, which allows the bolt to be spun up into the cartridge without making sufficient contact to shred the cartridge or the hardener tube, resulting in an unmixed portion of resin.

Jan 1, 2003

By Ryan Garvey

A numerical investigation is made into unstable failures of coal pillars (i.e. coal bumps) using the finite difference software FLAC3D. A static energy balance is first derived to calculate the excess energy released as a consequence of unstable failure in rock. Two- and three-dimensional mining layouts are then assessed on their bump-potential based on the magnitudes of excess energy released during simulated pillar failures. A three dimensional pillar model is developed to represent tributary area loading of an infinite room-and-pillar layout. Pillar strength and brittleness characteristics are calibrated using a Mohr-Coulomb strain-softening constitutive law to simulate width-to-height ratio coal pillars ranging from 1:1 to 5:1. Width-to-height ratio pillars 1:1 to 3:1 release large magnitudes of excess energy as the pillars fail, representing massive collapse of room-and-pillar layouts. The larger pillars maintain their residual strength during failure; however significant excess energy is still released during temporary reductions in pillar strength. A two-dimensional model is then constructed of a gate road pillar failing due to elastic rebound of the surrounding rock mass. Soft loading conditions initiate unstable failure for all pillar widths, while the total magnitudes of excess energy increase with the size of pillar being modeled. The results from these tests indicate that excess energy may be used as a direct assessment of the bump potential of simulated mine layouts.

Jan 1, 2013

By John C. Stankus

The success of cable bolts for mine ground control have been well documented in papers presented at this conference too numerous to reference. Cable bolts have proven effective over the years mainly utilized in the form of supplemental support. Some limited work has been conducted on the use of cable bolts as primary support This work has been mainly confined to the West and the bolts utilized were of a non- tensioned type MSHA requirements for primary support have been that the bolt system he tensioned or if non-tensioned, then fully encapsulated with resin. Many operators are now interested in using cable bolts as primary support Further, despite the enormous success of cable bolts, there have been questions raised about the longevity and corrosion characteristics of the cable itself particularly for long tern applications. To improve the corrosion characteristics of cable bolts, galvanized cable has been used for some applications However. although improving the corrosion resistance of cable, galvanized cable for mine ground control does not provide complete protection under certain types of situations and mine environments. Realizing a need for a cable bolt that can be used for primary support and provides consistent installed tension, complete corrosion protection, and a fast installation, Keystone Mining Services. LLC (KMS), an affiliate of Jennmar Corporation, has developed the INSTáL CableOx system. This paper will detail the development and specifics of this system including two underground case studies

Jan 1, 2000

By Xun Luo

In this paper we report on the use of microseismic monitoring techniques to investigate the fracturing process associated with longwall mining. The study was carried out at three mines in Australia and concentrated on some major concerns of the mines, such as failure patterns and growth rate associated with mining progress, their implications to water ingress and gas emissions, caving processes in the goaf and precursors of roof falls. The results have shown that a zone of shear fracturing has occurred further ahead of the longwall face than predicted using conventional longwall geomechanics theory. Failure patterns in the roof and floor vary from mine to mine and this appears to be dominated by geological structures. The reaction of faults, the formation of fractures which allow gas emissions and precursors roof falls have also observed. Results from this work have opened up new understanding of longwall caving processes and proved that microseismic monitoring is a very useful technique for studies of longwall geomechanics and hazard controls.

Jan 1, 1998