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By Adam Gray, Emery Gray

State-of-the-art seismographs can be employed to assist the blasting engineer in understanding the propagation of vibration waves generated by blasting. Wave traces and frequency plots are used to adjust shot loading and timing, especially around close or near- field structures. Successful close-in blasting vibration monitoring requires careful consideration of the following: Geophone locations Mounting of geophone both on structures and in the ground Differences between ground motion and structural response This presentation will discuss methods used to control and monitor blast-induced ground and structure motions. Case histories are presented to illustrate seismic monitoring used as a tool to control vibrations and guide the blaster in the design process.

Jan 1, 2005

Thank you for the invitation to address The AusIMM Young LeadersÆ Conference here today. When I first saw the conference theme û æadvancing technologies and their future applications in the mining industryÆ û my interest was sparked because there is little doubt that technology and technological advances will determine the relevance of this industry in the future. And the people seated here today are major players in determining the minerals industryÆs destiny.During my 20-year association with the mining industry, I have observed a number of significant changes that have been delivered as a result of the vision of technical specialists. These changes have built a more competitive industry, a more socially acceptable industry and most importantly an industry with ever-improving safety performance. The purpose of my address is to attempt to provide a context and foundation for other presenters over the following two days. Today, I wish to try to answer the question, æWhy do we invest in new technology in the mining industry?Æ, via: a brief history lesson, a review of the needs of the business, a look at the process for improvement, and finally an example from WMC ResourcesÆ current technology portfolio. I would like to take a very brief walk back in time. During the iron and bronze ages, whilst our ancestors IÆm sure never spoke the phrase ænecessity is the mother of inventionÆ, I am sure they lived by it. Undoubtedly more so than we do today. The roots of geology, mining and extractive metallurgy grew out of the need for better tools in order to get access to the basic necessities of life. It was their superior ability to generate and deliver these ætechnologyÆ improvements that underpinned great civilisations such as the Egyptians, Romans and Incas. The application of mineral technology improvements by these civilisations was crucial to their success, it was their competitive advantage at the time. Many historical texts include detailed descriptions of both mining and processing fundamentals that formed the basis of many of todayÆs operations and processes. However, it is technological improvements to these fundamentals, as well as the development of new technologies, that have preserved the fundamentals as viable options for the industry today. Even in my time in the industry, there have been substantial improvements in the way business processes operate. When I first started working in a gold mine in WA in the late 1980s, the office had one PC (a 286 processor). All data was managed by paper and then often re-typed into other databases. Electronic mine design and process control was in its infancy. Today, massive amounts of data are recorded, analysed and acted upon almost without any human interaction. Our industry today has far different challenges than those described by Argricola. These are many and diverse, but new technologies are required to address three distinct classes of need: 1. Societal needs: physical needs for food, shelter, recreation and leisure; community and political needs for less waste, less emissions, better safety and working conditions, less energy consumption and sustainability. 2. Individual needs: intellectual needs to create innovative technical and organisational ideas. 3. Wealth generation needs: investor needs for maximising operating efficiency and value growth. Each new technology, to varying degrees, fulfils one or all of these needs. In many cases, the driver of a technological development was to fulfill only one of these needs, but after it was implemented, the development actually fulfilled each need. I would like to expand on these needs.

Jan 1, 2003

By Brian Stump, David Anderson, D. Craig Pearson, Robert Martin

Mining explosions designed to move, bulk or fracture rock are often composed of a number of explosions arranged in a complex spatial and temporal pattern. The effects of the explosions are strongly dependent upon the design and implementation of this blasting pattern. This paper describes the collection, combination and visual display of multiple types of data from these explosions for the purposes of understanding the relationships between the blast design, implementation, and observations. Data sets consist of three-component ground motion, acoustic, video and high speed film, three-dimensional topography, geological and geophysical properties, design blast pattern and timing, and velocity of detonation in the explosive for individual borehole detonation times. The explosions studied include simple single-fired contained explosions, ones designed to bulk and fracture rocks and those that cast material.

Jan 1, 2000

By M. Rebolledo, N. Mora, G. Zarate

For decades, the mining industry has been focussed to find an efficient and economically attractive process for the leaching of chalcopyrite. Jetti Resources has developed a novel hydrometallurgical alternative to extract metals of value from mineral ores that the mining industry has struggled to process. Jetti’s catalytic technology, whilst being especially advantaged for extracting copper from low-grade and highly refractory minerals, such as chalcopyrite, seamlessly integrates with existing heap leaching methods and downstream processing operations. The technology uses a catalyst which weakens the metal-sulfide bond in the crystalline structure of the chalcopyrite mineral and alters the structure of the passivation layer allowing the leaching process to continue. Metallurgical test work was conducted to examine the effect of ore variability, in terms of grade and copper deportment. The results presented in this study highlight the amenability of the technology and demonstrate that it is possible to enhance leaching performance of copper primary sulfides over a wide range of copper grades, from 0.1 to 2.2%. Further, it is concluded that despite the copper grade, the tests with increasing chalcopyrite content render copper recoveries up to 4 times higher compared to the tests under non-catalyzed conditions. Jetti’s catalytic technology is currently being evaluated at larger scales, namely a commercial dump leach operation and 50-tonne crib tests. The results obtained thus far are compared to the results from conventional sulfide heap leaching tests. INTRODUCTION For decades, the mining industry has been focussed to find an efficient and economically attractive process for the leaching of chalcopyrite. Chalcopyrite (CuFeS2) is the most abundant and recalcitrant of the copper sulfides (Singer, 2017). Owing to its abundance and economic importance, it is the most demandable natural source for copper worldwide. In fact, the projected demand for copper is further expected to rise much higher beyond the current demand by the year 2020 (Panda et al., 2015). Therefore, it becomes imperative to find low intensity hydrometallurgical technologies for the extraction of copper from chalcopyrite in ores of such low-grades that are un-economic to concentrate and to augment the supply by extracting copper from ores with complex mineralogy that cannot be concentrated (Watling, 2013).

Jan 1, 2019

By Yunyan Wang

Diagrams of pc-pH for the complex ions concentration and pH value and -g- for activity coefficient and ionic strength ln±MnSOI4had been drew based on the thermodynamic principle of coordination chemistry and combined with Pitzer theory at 298.15K. The diagram of -g- indicated that -gincreased sharply from 0.0000 up to 1.2147 when I changed from 0.00 ln±MnSOIln4±MnSO4to 0.09; The increase of -gbecame slowly when I was more than 1.00 and less than 1.69; kept still when I ln±MnSOln4-g±MnSO4was more than 2.25 and less than 4.00. Diagrams of pc-pH illustrated that the minimum solubility of Mn(OH)2(s) increased with the increase of I, the pc increased from 6.5 to 5.5 when I increased from 0.00 to 4.00; The pH of the minimum solubility of Mn(OH)2(s) increased with the increase of I, the pH increased from 11.80 to 12.76 when I increased from 0.00 to 2.89, the pH kept still when I (I was less than 4.0) increased. There is single function relationship between the minimum solubility of Mn(OH)2(s) and relevant pH in different I.

Jan 1, 2010

By Gregg Vickell

"High tonnage, low grade gold mines such as Omai’s afford economies of scale that are unto their own insufficient to sustain profitability at today’s depressed gold price. Complimenting profitability objectives is the perpetual challenge to reduce operating costs and optimize unit operating efficiencies while being ever vigilant of issues such as environmental control.Key to achieving these objectives at Omai are throughput and availability gains, gold recovery improvements, cost cutting, a skilled workforce and reliable power generation.This paper attempts a cursory review of startup-to-date plant performance advances and future performance-driven objectives.INTRODUCTIONCommercial gold production at Omai commenced in January 1993 with annual output climbing to 250,000 opy by the end of 1994. A mill expansion completed in August 1996 increased gold production to 340,000 opy by the end of 1997. Current milling capacity is 20,000 in tpd (nom.) with actual capacity exceeding 24,000 mtpd on occasion depending on ore size and competency. Mill feed consists of hardrock (andesite, quartz diorite and rhyolite) and softrock (saprolite, laterite) at a nominal ratio of 70:30, respectively. Present day average weighted grade of the feed is 1.4 g/t gold.PROCESS DESCRIPTIONPrimary crushing, ore handling and the original 12,000 mtpd hard and soft rock SABC mill, hereafter referred to as Mill ‘A’, remains essentially as documented by Konigsmann (1 994) complete with poststartup modifications. The mill expansion, hereafter referred to as Mill ‘B’, features an 8000 mtpd hard rock SABC grinding circuit similar in configuration to Mill ‘A’ and differing only in equipment size. Mill ‘B’ includes a 9000 H.P.,reversible variable speed , single pinion drive, 32 ft. x 15 ft. SAG inill , a 7 ft. short head pebble crusher and two parallel 5400 H.P., 16.5 ft. x 30 ft. ball mills with dedicated cyclone packs consisting of D26 hydrocyclones."

Jan 1, 1999

By Timothy J. Myers

Expansion and the economic growth in the southwestern region of Missouri necessitated the expansion of State Route 249 and the construction of a new interchange to provide service to the Joplin, Missouri area. The project is located above a former lead and zinc mine in Jasper County, Missouri and includes a five bridge interchange connecting State Route 249 and US Route 171. The variable subsurface conditions, both natural and manmade, prompted the design team to use ground improvement via grouting and small diameter micropiles to provide support for several of the bridge foundations on the project. The scope of work included mine shaft closures, 56,000 ft of overburden and rock drilling, 11,139 ft of micropiles, 524 cy of balanced/stabilized high mobility grouts, and over 8,700 cy of low mobility grout. The selection of the grout used was based on the actual subsurface conditions. Low mobility grout (LMG) was used in voided conditions and for closure of the mine shafts encountered during the excavation. High mobility grout (HMG) was used in fractured rock with the goal of improving the mechanical properties of the rock underneath the future bridge footings and controlling grout volumes during micropile installation. The split spacing method was utilized for both LMG and HMG holes. Geology of the project site subsurface consisted of extremely variable bedrock with strong to very strong limestone, chert, breccia, extremely weak shale, and weak to strong sandstone. Previous activities associated with the mining disturbance (such as partial filled vertical mine shafts, shallow and deep mine horizons, modified hydrology including artesian conditions) further complicates the site subsurface conditions. Real time monitoring and recording of all drilling and grouting parameters was conducted to assist in the evaluation of in-situ geological properties of the site in order to modify the ground improvement and micropile program as necessary. This paper will discuss the design and execution of the ground improvement and micropile program. The project is an excellent example of the use of multiple ground improvement and foundation support techniques combined with real time data analysis to provide a foundation support solution for a complex geological environment.

Jan 1, 2009

By G Veillette, B Parker, S Hart

This paper provides a history of the challenges that were experienced while treating both the clayey oxide gold ores and the supergene copper-gold ores at the Boddington Gold Mine during the period 1989 to 2001. However the bigger challenge was to find a process flow sheet that would allow the economic treatment of the large low-grade competent gold-copper resource that underlies the oxide and supergene gold resource. Metallurgical test work and engineering studies on this resource started in the mid 1990s and culminated in the approval in 2006 of the 35 Mtpa Boddington Expansion Project to treat this material. The process flow sheet provides the basis of an energy efficient comminution circuit that includes high pressure grinding rolls and a treatment circuit with gravity separation, flash and conventional flotation to produce a precious metal low-grade copper concentrate followed by cyanide leaching of the rougher-scavenger and cleaner tailings streams. The treatment circuit allows maximum removal of copper minerals prior to cyanide leaching and so provides an environmentally responsible tailings disposal circuit.

Jan 1, 2007

By R. Sullivan, K. Joiner, B. Emery, M. de Vries, F. A. Stober, L. R. Nelson, J. M. A. Geldenhuis

Keywords: Pyrometallurgy, smelting, converting, furnace design, furnace retrofit, high-intensity smelting, copper coolers, plate coolers, waffle coolers, tap-blocks, lower sidewall air-cooling, wall hold-down system, platinum group metals, ferroalloys, ferrochrome, ferrocobalt, ilmenite smelting, ironmaking, operational readiness, operational support The paper describes the development of furnace designs by Hatch in conjunction with the smelting plants in Africa to meet the intense process requirements in certain applications; continued improvement in operating efficiency through increased throughput from existing crucibles; and improvement in campaign life and furnace integrity. The era of Hatch in Africa has seen the doubling of furnace power in retrofit projects using existing crucibles to developing the highest intensity immersed electrode operations in the world. This has resulted in minimized OPEX and CAPEX per unit of production. Through the continued development of its cooling, binding and furnace power supply technologies and working with the experienced and knowledgeable personnel at the smelting facilities in Africa, Hatch has managed to meet the challenges of ever increasing furnace process requirements associated with increased power density and superheats prevalent in the operations. In addition to developing furnace crucible designs, Hatch has also intensified its ?after sales service and support? with the construction, commissioning and start-up technical assistance and operational readiness and operational support for ramp-up to nameplate capacity and beyond. The key areas of furnace risk associated with high superheat molten material tapping has also seen the development of diagnostic systems to mitigate risks and produce early warning signals for the operators.

Jan 1, 2006

By F Gervilla, J Laukkanen

The Kevitsa Ni-Cu-PGE deposit in northern Finland contains disseminated Ni-Cu-Fe sulfides, and platinum-group minerals (PGM). The 2.05 Ga-old ultramafic-mafic, funnel-shaped intrusion is intruded into a volcanosedimentary sequence. The major ore minerals are pentlandite, hexagonal pyrrhotite and troilite, chalcopyrite, cubanite and magnetite. Pyrrhotite and pentlandite are replaced by pyrite, millerite and heazelwoodite near the surface. Nickeline, maucherite and gersdorffite are locally abundant. A pilot feed sample of 575 t of the main orebody at Kevitsa had average grades 0.45 per cent Cu, 0.36 per cent Ni, 1.85 per cent S, 0.33 g/t Pt, 0.34 g/t Pd and 0.19 g/t Au, with 0.06 per cent Ni contained in silicates. Higher PGE contents (2 - 27 ppm) occur in a vertical N-S bearing fault zone. The PGM (n = 6022) mapped in specimens of four drill holes, consist of sperrylite 34.7 vol per cent, braggite and cooperite 18.5 vol per cent, geversite 17.2 vol per cent, moncheite 14.7 vol per cent, merenskyite 6.7 vol per cent, stibiopalladinite 4.3 vol per cent, sobolevskite 1.9 vol per cent, kotulskite 0.7 vol per cent, michenerite 0.6 vol per cent, keithconnite 0.3 vol per cent, rustenburgite 0.1 vol per cent, melonite, froodite, laurite together 0.1 vol per cent and only a few grains of sudburyite, irarsite, vysotskite, erlichmanite, hongishiite, Pt-Cu-alloys, three undefined Pd and Pt bismuthinides and antimonides and a Pd-Cu-bearing Pt-Ni-Fe sulfide. Most of the PGM, 62 per cent, are enclosed in silicates, 29 per cent are intergrown with sulfides, nine per cent are within sulfides. A portion of the PGE occurs in solid solution in sulfides and arsenides. Ni flotation yielded smelter-grade concentrates averaging 12.2 per cent nickel. The average sulfide Ni recovery is 78.8 per cent and total Ni recovery is 65.3 per cent. The average Pt is 10 g/t at 55 per cent recovery, Pd 7.7 g/t at 38 per cent recovery and Au 1.6 g/t at ten per cent recovery. Cu concentrates averaged 28.6 per cent Cu with an average recovery of 78 per cent and further 11 per cent in the nickel concentrate. The copper concentrate contains 4 g/t Au at 24 per cent recovery. The average Fe to MgO ratio 17.9 is well above the targeted minimum of 4.5. The pilot results show that the previously used TETA (triethylene tetramine) can be avoided and good quality, smelter-grade concentrates can be produced from the Kevitsa ore at economical levels of recovery by conventional flotation methods.

Jan 1, 2008

By C. M. F. Vieira

This work has as its objective to characterize ceramic bodies for vitrified tiles elaborated with the mixture of nepheline-syenite flux and kaolinitic clay. Formulations were prepared with 0, 30 and 50 wt.% of nepheline-syenite incorporated in a kaolinitic clay. To determine the physical and mechanical properties such as dry bulk density, linear shrinkage, water absorption and flexural rupture strength, specimens were prepared by 30 MPa uniaxial pressure-molding and then fired in a laboratory furnace at 1150oC. The microstructure of the fired ceramics was evaluated by scanning electron microscopy. The results indicated that the nepheline-syenite improved the evaluated properties of the clay and attended the specifications of vitrified ceramic tiles.

Jan 1, 2010

By T. Chong, R. Pesalj, B. Marchant, Z. Nikic

"The Mount Polley copper/gold project is located in central British Columbia and is currently being developed by Imperial Metals Corporation. Extensive laboratory and pilot plant testing was required to develop acceptable metallurgy for recovery of both sulphide and oxide copper-gold mineralization. Copper recovery is highly sensitive to oxide copper content of the feed whereas gold is primarily associated with the copper sulphide minerals. A conventional flowsheet where sulphide flotation is followed by sulphidization and oxide scavenging is described. The conventional flowsheet was used in a feasibility study which resulted in a favourable production decision at Mount Polley. Detailed engineering and permitting are in progress.More recently, laboratory and pilot testing of a new flotation reagent, S-6493*, an oxide specific collector, has indicated that improved copper recovery can be accomplished with reduced reagent consumption, including elimination of the sulphidization step, using S-6493 compared with the conventional flowsheet. The comparative metallurgical results using S-6493 and conventional sulphidization methods are presented, from both bench scale and pilot testing. Comparative economics of the conventional flowsheet and that using S-6493 are also presented. Advantages of S-6493 include reduced reagent costs, increased revenues from additional copper recovery, and overall reduction in capital and plant operating costs due to the simplified flowsheet. INTRODUCDONThe Mount Polley copper/gold property is located in Central British Columbia, 56 air kilometres northeast of Williams Lake. The first recorded exploration was in 1964. By 1989, a total of 238 diamond drill holes, totalling 27, 522 meters, was completed to detail reserves on the Mount Polley prospect. A number of drill core composites were submitted, containing a variety of oxide copper levels, for metallurgical flowsheet development. Six bulk samples were collected from surface trenches for additional bench scale testing and for pilot plant testing."

Jan 1, 1991

By Andy Alder

The Docklands Light Railway (DLR) Extension to Woolwich Arsenal provides a much-needed public transport link to this area of London. The project includes construction of 5.3mID running tunnels under the River Thames, in ground conditions that proved challenging for the Earth Pressure Balance Tunnel Boring Machine (TBM). The project also includes cut and cover tunnel approaches, an underground station, and an emergency shaft on the bank of the river. Major challenges have included tunneling under sensitive infrastructure, and working adjacent to existing operational railways at Woolwich Arsenal. This paper will describe the design and construction of the project and how these challenges were overcome.

Jan 1, 2008

By Michael J. Pazuchanics

This report documents the current status of the U.S. Bureau of Mines ongoing investigation of the use of adaptive signal discrimination (ASD) systems to distinguish between cutting coal and cutting rock. Cutting-tool forces and vibrations were measured in the laboratory using both conical bits and roller cutters in a linear-cutting apparatus for several material samples and two cutting directions. A number of ASD systems consisting of one or more signal classifiers were trained and tested to study how data window size, type of signal feature, and combining (polling) of classifier results influence system performance. The results show that ASD system recognition rates can be improved by increasing data window size, removing air-cutting portions from the signal data, overlapping data windows, and combining (fusing) information at various levels of ASD system operation.

Jan 1, 2010

By M. Desjardins

The Hoyle Pond underground mine, located in the Porcupine Gold Camp, east of the city of Timmins, Ontario, Canada, is the cornerstone of Goldcorp Canada Ltd?s Porcupine Gold Mines. Cut and fill, shrinkage, longhole and panel mining methods are employed to excavate the narrow gold bearing structures. In order to meet increased flow requirements of 256 m3/s at the mine, a new Fresh Air Raise (FAR) and new surface fans were commissioned in early 2005. The newly acquired fans were capable of supplying the desired volume of air within a range of 1.5 and 2.0 kPa. Upon commissioning of the surface fans the total pressure was found to be exceedingly high; far beyond the design capabilities of the new installation. Consequently only one surface fan could be operated at any given time providing about half the required volume of air. Extensive work was immediately started aimed at reducing the system resistance in order to permit operation of the two fans in parallel and achieve the required mine flows. Larger booster fans were installed in parallel at the 900 m level, a 3 m raise bore linking the 450 and 900 m levels was developed to twin the existing fresh air circuit, and the FAR from surface to the 450 m level was twinned with the original FAR. This strategy, completed in 2012, resulted in a drastic reduction in system resistance and pressures, allowing the two surface fresh air fans to be safely operated in parallel and meeting the flow requirements. This paper describes details of the engineering design work and commissioning of the modified ventilation system, successfully ensuring the long term viability of the project.

Aug 1, 2013

By R. Burger, M. Masukawa

Cato Ridge Alloys (CRA) is a joint venture company between Assmang of South Africa, Mizushima Ferro Alloy Company (MZK) and Sumitomo Corporation from Japan. Negotiations for the formation of the company started in 1992 with the joint venture agreement signed on the 19th September 1996. MZK was to supply the technical know how for the production of Medium and Low Carbon FeMn while Assmang was to manage the day to day activities of the company. Sumitomo Corporation was to act as facilitator between Assmang and MZK and, together with Ore and Metal are responsible for the marketing of the refined products. The conceptual design of the plant started in December 1996 and the first charge of molten high carbon ferromanganese metal was charged on the 19th January 1998. Problems experienced during the initial startup period were addressed resulting in substantial operational improvements. A build-up in the stock of fine metal was addressed through the development of a process to remelt the fine metal, the development of a market for fine metal and the upgrading of the crushing and screening plant to reduce the generation of fine metal. The mass yield from High Carbon Ferromanganese to Refined Ferromanganese was increased through the implementation of statistical process control, changes to the blowing patterns and the development of a sampling device for taking samples during the process. Converter refractory consumption was reduced. This was achieved on the converter by improving the cooling of the converters with the installation of cooling fans and cooling fins. The heating schedule of the converters was changed for improved refractory life. Production schedules were modified to allow cooling of the refractory between low carbon erromanganese charges. Additional changes made to improve operations were: ? Changing from mehanite casting trays to metal fines beds. ? Installation of sonic horns in the baghouse to prevent the bridging of dust. ? Improved welding on the lance tips.

Jan 1, 2004

By Paul Semple

"In 2007, Noront Resources Inc. discovered the high grade nickel copper PGE deposit in northwestern Ontario in a region now known as the Ring of Fire. Since the initial discovery, Noront has advanced the Eagle¹s Nest Project and in September 2012 released a feasibility study for the development of the Eagle¹s Nest Project. This paper summarizes the results of this recent study and outlines additional work planned in the next stages of project development. INTRODUCTIONThe following paper summarizes the findings of the recently completed feasibility study on Noront Resources Ltd.’s Eagle’s Nest Project. The feasibility study was compiled into a NI 43-101 report by Micon International. This paper is intended to summarize the major technical findings and for complete information, interested parties can find the entire NI 43-101 report at www.norontresources.com or on SEDAR.LOCATIONThe McFaulds Lake project area, which includes the Eagle’s Nest deposit, is located at approximately UTM 5844000 N and 547000 E, and between approximately 52º42’ and 52º50’ N latitude and 86º06’ and 86º24’ W longitude, approximately 250 km west of the community of Attawapiskat on James Bay and 575 km northwest of Timmins. The closest all-season accessible community to the McFaulds Lake project area is Nakina, 300 km to the south, where there is a paved airstrip, in addition to all weather road and railroad access (see Figure 1).The First Nations communities of Webequie and Ogoki/Marten Falls are located 90 km west and 120 km south southeast of McFaulds Lake, respectively. Both communities are served by regularly scheduled air service, primarily from Thunder Bay; both Thunder Bay and Timmins serve as support centres for the James Bay communities and the exploration projects in the area."

Jan 1, 2013

By Christopher Mark

A coal burst is defined as the sudden, violent ejection of coal or rock into a mine opening. Coal mines in the North Fork Valley (NFV) of Colorado?s Gunnison River have a long history of coal bursts in a wide variety of settings. These have included longwall and room-and-pillar, development and retreat, and single- and multiple-seam mining. In contrast to other coalfields, where bursts are typically associated with strong, massive sandstone and extremely high stress, many bursts in the NFV have occurred beneath shale roof and some distance from the most highly stressed locations. The goal of this paper is to attempt a systematic study of the entire burst history in the NFV, in order to gain insight into their characteristics and causes. The primary sources of information are the reports of investigations conducted by the Mine Safety and Health Administration (MSHA) Roof Control Division over the past 15 years. This paper provides details on the geologic mapping conducted as part of these investigations, as well as a regional plot of burst locations using a Geographic Information System. The mapping indicates that many of the NFV bursts have been associated with structural features, including low-angled faults and well-defined zones of high-density jointing that exhibit little or no displacement. Some of these features appear to extend for several miles, impacting more than one mine.

Jan 1, 2012

By Donald A. Bruce

The paper reviews aspects of the construction and performance of prestressed ground anchors installed in soils and weak rocks. Attention is focused on good practice for drilling, tendon fabrication and handling, grouting, stressing and testing. Regional variations - not always logically justified - are described. The performance of anchors in a variety of geological conditions is illustrated with reference to recent full scale test programs. 1. Introduction In the United States there has been steady growth in the use of prestressed anchors in materials other than competent or hard rock, in the years since their introduction in the late 1960's. This expansion has to a large extent been driven by specialty geotechnical contractors who both imported foreign developments and conducted their own basic researches, in locally prevailing conditions. With such data and experience, these engineers have had the confidence to promote "alternative solutions" for difficult earth support problems to receptive designers and owners. In turn, being engaged in the details of design and performance monitoring has given these parties the close exposure necessary for the real transfer and understanding of the technological concepts, and this knowledge has generated positive feedback for the contractors.

Jan 1, 1991

By W. G. Pariseau

Conventional barrier pillars in underground coal mines are intended to protect mains and sub-main entries for relatively long periods of time. Inter-panel barrier pillars that may be used in especially deep coal mines, say, below 800 m (2,400 ft), are intended to protect longwall panel faces and adjacent panel entries for the life of nearby panels. Barrier pillar failures have serious consequences, especially when failure is sudden and catastrophic. Design of barrier pillars is thus of considerable importance to safety and efficiency of operations. Locally, failure occurs at the limit to elasticity when stress tends to exceed strength. Strength of rock is stress dependent, so an analysis of stress is central to rational design of barrier pillars. There are several approaches to stress analysis for coal mine pillar design that range from the simplified but popular tributary area method including variations that use empirical definitions of the tributary area (volume) to more sophisticated numerical methods such as the boundary element method and the finite element method. Despite ease of use, empirical methods are limited and always suspect when applied to conditions beyond their scope of definition, while boundary element methods do not generally include pillars in the solution domain. The finite element method is not so restricted and thus is a natural choice for conventional and inter-panel barrier pillar safety analyses. Caving of roof strata certainly affects the distribution of stress about longwall faces and nearby barrier pillars. Conventional wisdom that considers roof strata to respond as cantilever beams indicates the longer the span the greater are loads on longwall faces and face supports. Failure of roof beams, caving, shortens spans and relieves face and support loads. The same view is applicable to barrier pillars in that long roof spans outside of barrier pillars leads to higher pillar loads than short spans. Hence, caving should be beneficial to barrier pillar safety. However, the benefit may be small depending on the extent of caving and only in the form of a slight reduction in overburden weight transmitted to the barrier pillar, especially in case of inter-panel barrier pillars. FINITE ELEMENT MODEL Finite element models for stress analysis in rock mechanics are formulated in consideration of physical laws, kinematics, and material laws. These models meet the essential requirements for equilibrium of stress, satisfy strain displacements relations, and in a general sense, relate stress to strain through material laws, often referred to as constitutive relations. The last may be complex and replete with nonlinearities. A de facto engineering material law is the elastic model in the form of Hooke?s law for linear, homogeneous materials that may be anisotropic. A limit to elasticity is imposed by strength in the form of a failure criterion or yield function that accommodates triaxial stress states. Examples used in rock mechanics are the well-known Mohr-Coulomb (MC)criterion, the popular Hoek-Brown (HB) criterion, and the Drucker-Prager (DP) criterion. The first is linear in stress, while the second is nonlinear. Both do not include any effect of the intermediate principal stress. The last is also linear in stress but includes the intermediate principal stress. All show an increase in the major principal stress at failure with confining pressure. In the UT2/3 finite element programs, the failure criterion Y is a nonlinear, anisotropic form and is also the plastic potential [1]: [YJI=+ 11NYJI=+- (1) ] where N is an exponent, usually 2, and J2 and I1 are nonlinear anisotropic forms of the second invariant of deviatoric stress and the first invariant of principal stress. The form (1) reduces to DP when N=1and isotropy prevails. When Y = 1, the limit to elasticity is reached and plastic deformation is possible. The material constants that enter (1) are all computed from unconfined compressive, tensile, and, in case of anisotropy, shear strengths. These latter strengths may be estimated from conventional laboratory test data. Of course, joints in field-scale rock masses induce different values. How different is often a matter of conjecture. For comparative studies, laboratory rock properties seem adequate. Inelastic, that is, plastic behavior occurs with strain beyond the elastic limit. Strain hardening, ideal plasticity, and strain softening are possibilities. Ideally brittle behavior with complete loss of strength is an extreme form of strain softening [2]. Caving may also be considered as strain softening with a less drastic reduction of material properties. As intact roof strata fail, fall, and form a rubble pile below, a new material is formed with greatly reduced elastic moduli and strengths, say, 1/100th of the original intact moduli and strengths. From another viewpoint, caving is simply a natural cut and fill process. Input for stress analysis by the finite element method includes: 1. Preexcavation stress state 2. Geology (stratigraphic column) 3. Structure (major faults, joint sets) 4. Elastic moduli 5. Strengths, and specific gravities of each rock type 6. Excavation sequence Output from an analysis includes distributions of: 1. Stress 2. Strain 3. Displacement 4. Local factor of safety (element fs) The last is defined as the ratio of strength to stress and in view of the failure criterion (1), is the ratio [fsJstrengthJstress=] where the numerator is the maximum possible value and the denominator is the actual value of the square root of the second invariant of deviatoric stress. This invariant is a measure of shear stress intensity but also reduces to uniaxial tensile and compressive strengths as the case may be. An fs greater than 1 indicates an elastic state of element stress; a value of 1 indicates the limit to

Jan 1, 2009