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By Ray L. Tobie, Douglas E. Julin

GENERAL DESCRIPTION Block caving is a distinct caving method applied mostly to large, massive, ore bodies because of its in¬herent low cost and high production capabilities. Areas of sufficient size are removed by undercutting so that the mass above will cave naturally. Drawing of the caved ore at the bottom of the ore column causes the caving action to continue upward until all of the ore above the undercut level is broken into sizes suitable for handling. When properly applied, block caving results in a lower mining cost per ton than any other under¬ground method. There are three distinct forms: (1) dividing the horizontal area into rectangular or preferably square or nearly square blocks, drawing evenly over the entire area to maintain an approximately horizontal plane of con¬tact between broken ore and caved capping; (2) divid¬ing the horizontal area into panels across the ore body, retreating by undercutting manageable areas from one end of the panel to the other and maintaining an in¬clined plane of contact between the broken ore and caved capping (thus the name panel caving); and (3) no division of horizontal area of the ore body into defi¬nite blocks or panels (this is termed mass caving). Undercutting may be from wall to wall, retreating from one end of the ore body to the other, maintaining an inclined plane of contact between the broken ore and caved capping. The total active caved area is deter¬mined by the size of block that will not produce undue stress on workings below the undercutting level and by total production requirements. This type of operation is also referred to as panel caving at some properties. SUITABLE ORE BODIES Block caving in its various forms is applicable to deposits of various shapes and ores of various strengths. Its success is governed by rigid requirements and limi¬tations. In unsuitable deposits or where improperly em¬ployed, the loss of ore may exceed that of any other mining method. Good planning, systematic work pro¬cedures, careful supervision, and good judgment con¬tribute to its success. Ore Characteristics Included as a necessary characteristic in an ore body suited to a successful block-caving operation is a proper fracture pattern. Ore hardness should be another gov¬erning factor, and the toughness or softness of the ore should be considered. There must be sufficient horizon¬tal area available for expansion of the undercut, if neces¬sary, to start the caving process. Large, massive, ore bodies usually meet these conditions. Veinlike deposits must be wide and dip rather steeply to conform to the block-caving limitations. The capping must be of such a nature as to cave when the underlying ore is being removed since the weight of the overburden aids in crushing the ore. The most favorable capping character¬istic is that it breaks into coarse pieces and resists attrition as the block is drawn. Soft capping, by breaking into fine pieces and sifting into the ore or channeling through the ore to the drawpoints, can seriously dilute the ore and hinder the extraction of clean ore from the blocks. Types of Ore In block caving, a fairly uniform distribution of val¬ues in the ore is necessary. Grade values may range from low grade to high grade, but most often the sys¬tem is applied to low-grade ores. Wide veins, thick beds, or massive deposits of homogeneous ore overlain by ground which will cave constitute suitable ore bodies. The ore must be such that it can be supported while blocks are being developed and undercut but breaks up readily when caved. Some applications include porphyry copper, disseminated molybdenite, hematite in the Lake Superior iron district, limonite deposits in northern Spain, the diamond mines of South Africa, asbestos and nickel in Canada, and massive magnetite in Pennsylvania. Size and Shape Outline of the ore body should be fairly regular, and the sides of the ore body should dip steeply. It may not be economical to mine small portions of ore extending into the walls of the deposit, and low-grade inclusions in the ore cannot be left unmined. Some dilution of the ore, as mining progresses, by low-grade or barren cap¬ping is inevitable and, unavoidably, some clean ore is left between drawpoints. Determining Cavability The use of rock mechanics is sometimes advantageous in helping to determine the cavability of an ore deposit. The US Bureau of Mines has information and testing ability which can assist in determining the cavability of ore types. Several competent consulting orga¬nizations knowledgeable in rock mechanics can also as¬sist in evaluating the cavability of an ore body. Some recent work has been done to better define the cavability index of various ore bodies; an example of how this was determined is discussed by McMahon and Kendrick (1969). The intensity of the fracture pattern is a critical parameter to be analyzed. The question to be answered is, "How intense must the fracture pattern be?" Table 1 is a tabulation of the size of rock fragments that appear at the drawpoint of various block-cave mines around the world. These are indicative of the fracture-pattern spac¬ing and, as can be seen, they vary substantially from the almost sandy material at the Mather mine to fairly sizable blocks at the Grace mine. Several sets of fractures are essential to promote good caving. Ideally, two vertical sets at nearly right angles to each other and a third set nearly horizontal are required to insure a good caving ore body. Since initial caving of an ore mass is almost always by the action of gravity acting on these planes of weakness, it is doubtful

Jan 1, 1982

By R. M. Jara

This work evaluates and characterizes the impact of the support size and mining dilution of a block model in the operation and selection of equipment at an open pit mine. An exploratory analysis and geostatistical modelling of the grades assayed on a set of drill hole samples is performed, which allows constructing a grade model on a dense grid by means of a conditional simulation. The grades are then averaged to greater selective mining unit supports in order to proceed with the study and methodology. First, the metal-tonnage curves are used to analyse the loss of selectivity on the in situ resources caused by a change of support. Concerning the ore reserves and their mining sequence, defined in the pit optimization and analysis process, the same curves prove that the loss of selectivity is more accentuated. Second, the importance of the block boundary dilution produced during mining operations is assessed. Its value depends on the amount of ore in contact with waste, on the loading error of the equipment and on the ore loss/waste dilution criterion assumed by the planner. The dilution percentage and the differences between waste and ore grades become higher when the block size decreases. For these reasons, considering the dilution in the production plans makes mining a small support more constraining. An adequate delimitation of the orebody can improve the mining selectivity, leading to greater income. Finally, a study of the increase in mining cost that provides a zero difference in NPV between the different block size options is carried out, in order to determine the maximum increase in mining costs for which it remains profitable to mine at a smaller block size. Keywords: Mining selectivity, support effect, block boundary dilution, selective mining unit size, block model.

Jan 1, 2006

By S. Fuentes, J. Cáceres

"During the past fifteen years, mines utilizing the block caving method have improved performance and systematically reduced total mining costs.This paper describes improvements in mine design, mine planning, and mine management, including methods enabling the Chilean and international mining industry to ensure cost savings and productivity growth while using the block caving method. These improvements have encouraged the re-evaluation of underground operations at operating and closed open pits, and challenge surface mining applications as the only low-cost mining method. This paper describes a strategy to estimate the optimum open pit to underground transition time during the life of a mine. IntroductionDuring the last fifteen years, block caving mines have experienced huge changes in designs, planning and administration. These changes have permitted operators to drastically reduce costs, improve equipment productivity, and improve overall business performance. As a consequence of this situation, the block/panel caving mining system is challenging actual open pit operations to maximize the net present value (NPV)."

Jan 1, 2004

By R. R. Givler

Since the 1860's the good ole days, oil has been nozzle fed to burners under pressure atomizing the oil into droplets -- 1960's has produced vaporized oil that burns oil with the flame color and consistancy of gas -- If you can tell the difference by looking at the flame, gas or oil I?ll buy the lunch. First, we must ask, "Why all the excitement about Blue Flame?" This question is best answered by you after you have studied the principle of operation and see the result. I will attempt to explain both of these so that you can draw your own conclusions.

Jan 1, 1975

By Angela Binder, Mareike Schubert, Yichen Jiang, Sandra Nowosad, Oliver Langefeld

GermanyINTRODUCTIONThe mining industry is currently characterized by various factors such as environmental impact, resource scarcity, social responsibility and geopolitical uncertainty. The production of minerals required to meet the demand for renewable energy is expected to increase by 500 % by 2050, particularly for critical minerals such as graphite, lithium and cobalt 1. Easily accessible deposits are often depleted, meaning that deeper and more complex deposits need to be developed. Furthermore, investors’ value systems have shifted towards more sustainable practices. Alternative approaches to solving this problem are therefore currently being developed, such as the Modular Mining Systems concept for scalable and adaptable mining projects 2. Many mining companies have also taken important steps to become more sustainable, implementing measures such as proactive closure strategies, restoration programs and the development of renewable energy projects. In the European Union, laws such as the Critical Raw Materials Act and the Net Zero Industry Act support the mining industry 3,4. They see it as important for the energy transition and promote more sustainable ways of working in the industry Particularly negative environmental impacts such as land degradation, scarcity of local water resources, water pollution and greenhouse gas emissions are ingrained in society’s memory. Despite these efforts, the public image has not yet changed. To change this perception, the industry must strive to better communicate its sustainable practices and the steps it is taking towards a more responsible and sustainable future, promote transparency and build trust.Digitalization, automation and electrification are driving the digital transformation in mining. However, their implementation can lead to higher capital expenditure, limiting their adoption across the industry. Furthermore, implementing new technologies can be a daunting task for any organization. Change management comes into play when introducing such disruptive technologies. It involves preparing an organization for change, potential resistance and establishing effective communication. This helps to ensure that the implementation is successful and the benefits of the new technology are maximized. Digital transformation requires well-trained, young mining, electrical, mechatronic and software engineers with a deep understanding of information systems. Unfortunately, the industry faces the enormous challenge of attracting this younger generation, who have little interest in the extraction of raw materials. The need for action is compounded by an aging active workforce heading into retirement and the forecast of increasing demand for critical minerals.In this challenging environment, the concept of Blue Mining with its constant further developments represents a promising approach. This implies a shift from a linear to a sustainably oriented circular economy. For the mining industry, this specifically means the introduction of innovative technologies, the increased recovery of materials from waste and the consistent questioning and application of circular principles along the entire life cycle of a mine. Such a change can not only reduce the environmental impact, but also contribute to economic resilience and increased social acceptance of mining.

Feb 1, 2025

Safety is the No. 1 concern of any drill contractor or mine operator. Everyone in the industry knows a safe site helps stabilize operational costs and enables higher productivity. When it comes to exploration drilling, research has proven a majority of injuries are caused by the mishandling of coring rods. A driller helper will typically handle up to 50 rods per shift or up to 15,000 rods per year. With an annual 340 t (750,000 lb) in rods managed by hand, the risk of serious injury is extremely high. Because of this, the top request from the exploration industry is diamond rod handling. The Boart Longyear 4200 surface exploration drill, slated for release in 2009, will give the industry a hand-free, operationally safe rig.. Developed through the collaboration of its global drilling services and products divisions and targeted at the 1,200-m (3,900-ft) NQ market, the upcoming Boart Longyear 4200 surface exploration drill features the safest and most flexible rod management sys-tem in its class. The rig includes the industry?s first, truly hands-free rod handling system. This increases operator safety on the jobsite. In addition to the rod handler, the rig also features many new innovations that boost productivity and rig efficiency while minimizing the risk of downtime due to component failure or operator error. Boart Longyear has also included an intelligent PC-based operating system designed to allow complete drilling control as well as diagnostics reporting for the rig.

Jan 1, 2009

Using mines in Canada, Boart Longyear, a leading provider of drilling services and products, has put its Stage 3 Coring Bit to the test and each time the bit has passed the test with great success. After more than a year in the field at a major mine operation in Sudbury, Canada, the Stage3 coring bit broke life records to become recognized as the most productive design in the industry. In addition to the proven advantage seen in regular bit life increases of as much as 300 percent in some cases, the design is quickly being recognized for its cost-saving operational impact. In Sudbury, the mine operation realized actual cash savings of more than C$45,000 within an eight-month period by making the switch to Stage3 bits. For years, the Sudbury Basin team has relied on the Alpha Extended Crown bit with the Express Waterway geometry option, ordering approximately 500 units per year. This 07 COM ECEX configuration performed well in medium-hard, non-abrasive to ultra-hard, non-abrasive formations with an average bit life of 150 m (490 ft). While satisfied with the performance of the Alpha Ex-tended Crown, the team agreed to put the new Alpha Stage3 to the test. Boart Longyear?s field engineers supplied five drill sites with Alpha Stage3 bits in a 07 COM configuration. After thoroughly testing the Stage3, the results were clear. Even with the well-known performance and versatility offered by the previously preferred configuration, the Stage3 set a new standard of bit performance. The new bit maintained its cutting edge for up to three times longer than the Alpha Extended Crown, a significant performance increase when compared to the 07 COM ECEX.

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

Construction of the Boddington Mine 130 km (81 miles) southeast of Perth, is about 89 percent complete. When the $2.9-billion development is finished, it will be the largest gold mine in Australia, producing 31 t/a (1 million oz/year), according to project majority owner Newmont Mining. Newmont?s acting regional group executive for Asia Pacific, Philip Stephenson, told a gold conference in Australia that the project would be ?the biggest thing for Newmont this year.? The project has been in the works for more than 10 years, but because of a three-sided ownership and fluctuating gold prices, it struggled to get started. However, Newmont is set to become the full owner of the project and is moving ahead on the low-grade project. ?We are targeting annual production of 31 t/a (1 million oz/year) for each of Boddington?s first five years. When it is in full production, Boddington will be the largest gold mine in Australia,? Stephenson said. ?The mine?s costs applicable to sales will be around US$9.64/g (US$300/oz) and that puts Boddington into the bottom quartile of the global cost curve. ?Strategically for Newmont, Boddington coming on-line will improve Newmont?s overall global geopolitical risk profile as it delivers greater exposure to an AAA-rated country.? Boddington has a projected mine life of 20 plus years. It has current total reserves of 622 t (20 million oz) and rising. Stephenson said Boddington has the largest reserve base of all gold projects in production or those that are about to go into production in A-rated countries or better. And it will be an important asset for many years to come. Newmont will acquire the remaining 33 percent share held by AngloGold Ashanti in a deal that should be concluded in the next two months. Australian miner Newcrest Mining Ltd. had exited the joint venture several years ago. Newmont had come into the project through the take-over of then Australia?s leading gold miner Normandy Mining, while AngloGold Ashanti gained entry through

Jan 1, 2009

By S. J. Parry, D. M. Evans, D. L. Buchanan

The reef is a PGE-enriched sulphidic zone, stratigraphically associated with and overlapping the C1d chromitite layer, that was formed by magmatic processes at the 1e-1d subunit boundary. Two distinct patterns of PGE enrichment are related to the presence or absence of Cr2O3 oversaturation during sulphide liquation that occurred during a complex sequence of changes at this boundary

Apr 1, 1996

By Theo Lehner

"The Boliden Rönnskär Smelter operates in the European Context of tight EH&S limits, with ever increasing regulations and tribulations. The near future promises to bring new burdens in the form of C02 trading, miners and pre-treaters increased appetite for a larger share of contained values, and changing compositions and competition in raw materials. On the other hand, European Smelters such as Rönnskär, Harjavalta have demonstrated an astonishing power of survival. This presentation lists and comments on current challenges but opportunities for increased survival power are also presented. One example of the latter is the ongoing investment into increased treatment capacity for e-scrap.UPDATE ON RÖNNSKÄR OPERATIONSThe Rönnskär Smelter has achieved 80 years of age with no signs of retirement. The smelter is most active in spite of its age! And it has undergone some face lift operations to maintain its attractiveness.Raw material, processing facilities and a market for the products are some essential prerequisites for a viable operation. To justify long term survival, economic terms such as return on investments and positive cash flow need to be considered. Below, we illustrate how the Rönnskär Smelter complies with these terms. To update the reader on current operations, our current flow sheet is depicted in Figure 1. The figure summarizes our current input and output."

Jan 1, 2012

By Rita D. Sylvester

"This compilation lists and summarizes publications by Bureau authors published in the regular Bureau of Mines series, in scientific, technical, or trade journals, or in other media; those available from the Bureau of Mines are indicated. Patents issued to Bureau personnel are also listed, and instructions are given on how to apply for permission to use them. One of the outstanding features of this Special Publication is an exhausive subject and author index. IntroductionThe Bureau of Mines was established in the public interest to conduct inquiries and scientific and technologic investigations concerning mining and the preparation, treatment and utilization of mineral substances; to promote health and safety in the mineral industries; to conserve material resources and present their waste; to further economic development; to increase efficiency in the mining, metallurgical, quarrying, and other mineral industries; and to inquire into the economic conditions affecting those industries, The organic act of the Bureau, as amended by Congress and approved February 25, 1913, made it the province and duty of the Bureau to ""disseminate information concerning these subjects in such manner as will best carry out the purposes of this Act.""In accordance with this directive, the Bureau reports the findings of its research and investigations in its own series of publications and also in articles that appear in scientific, technical, and trade journals; in proceedings of conventions and seminar's; in reference books; and in other non-Bureau publications. The number of these reports, the wide range of subjects they cover, and the variety of mediums in which they appear make the kind of list and index presented in this special publication both necessary and valuable. This issue describes reports and articles published during the period January 1, 1970, to December 31, 1974. It supplements the 50-year list of Bureau publications issued from July 1, 1910, to January 1, 1960;2 the 50-year list of articles by Bureau authors published outside the Bureau from July 1, 1910, to January 1, 1960;3 and the 5-year lists of Bureau publications and articles from January I, 1960, to December 31, 1964,4 and from January I, 1965, to December 31, 1969.5 It includes all the material in the four annual lists of Bureau publications and articles from January 1, 1970, to December 31, 1973."

Jan 1, 1975

By Rita D. Sylvester

"THE BUREAU OF MINES was established in the public interest to conduct inquiries and scientific and technologic investigations concerning mining and the preparation, treatment, and utilization of mineral substances; to promote health and safety in the mineral industries; to conserve mineral resources and prevent their waste; to further economic development; to increase efficiency in the mining, metallurgical, quarrying, and other mineral industries; and to inquire into the economic conditions affecting these industries. The organic act of the Bureau, as amended by Congress and approved February 25, 1913, made it the province and duty of the Bureau to ""disseminate information concerning these subjects in such manner as will best carry out the purposes of this Act.""In accordance with that directive, the Bureau reports the findings of its research and investigations in its own series of publications and also in articles that appear in scientific, technical, and trade journals; in proceedings of conventions and seminars; in reference books; and in other non-Bureau sources. The number of these reports, the wide range of subjects they cover, and the variety of mediums in which they appear make the kind of list and index presented III this special publication both necessary and valuable. This issue describes Bureau reports and articles published during the period January 1, 1960 to December 31, 1964. It supplements the 50-year list of Bureau publications issued from July 1, 1910, to January 1, 1960,2 and the 50-year list of articles by Bureau authors published outside the Bureau from July 1, 1910, to January 1, 1960.3 It supersedes the annual lists of Bureau publications and articles from January 1 to December 31, 1960/ from January 1 to December 31, 1961,5 from January 1 to December 31, 1962,6 and from January 1 to December 31, 1963,1 The leading general and technical libraries of the United States maintain files of the Bureau's publications. A list of these libraries appears immediately following this introduction. BUREAU PUBLICATIONSBecause some series of Bureau reports contain both free and sales publications, and because the cost of sales publications varies, prices are indicated in the individual listings of all publications for which charges are made."

Jan 1, 1964

By Shelby Z. Palya

"INTRODUCTION The Bureau of Mines was established in the public interest to conduct inquiries and scientific and technologic investigations concerning mining and the preparation, treatment, and utilization of mining substances; to promote health and safety in the mineral industries; to conserve material resources and prevent their waste; to further economic development; to increase efficiency in the mining, metallurgical, quarrying, and other mineral industries; and to inquire into the economic conditions affecting those industries. The organic act of the Bureau, as amended by Congress and approved February 25, 1913, made it the province and duty of the Bureau to ""disseminate information concerning these subjects in such manner as will best carry out the purposes of this Act.""In accordance with this directive, the Bureau reports the findings of its research and investigations in its own series of publications and also in articles that appear in scientific, technical, and trade journals; in proceedings of conventions and seminars; in reference books; and in other non Bureau publications. The number of these reports, the wide range of subjects they cover, and the variety of mediums in which they appear make the kind of list and index presented in this special publication both necessary and valuable. This issue describes reports and articles published during the period January 1, 1975, to December 31, 1979. It supplements the 50-year list of Bureau publications issued from July 1, 1910, to January 1, 1960; 2 the 50-year list of articles by Bureau authors published outside the Bureau from July 1, 1910, to January 1, 1960; 3 the 5-year lists of publicatioll3 and articles, from January 1, 1960, to December 31, 1964,4 from January 1, 1965, to December 31, 1969,5 and from January 1, 1970, to December 31, 1974; 6 and the annual lists of Bureau publications and articles from January 1 to December 31, 1975,7 from January 1 to December 31, 1976,8 from January 1 to December 31, 1977,9 and from January 1 to December 31, 1978.10"

Jan 1, 1980

By Herbert Clark Hoover, Lou Henry Hoover

IN the last book I have explained the methods of delimiting- the meers along each kind of vein, and the duties of mine officials. In this book1 I will in like manner explain the principles of underground mining and the art of surveying. First then, I will proceed to deal with those matters which pertain to the former heading, since both the subject and methodical arrangement require it. And so I will describe first of all the digging of shafts, tunnels, and drifts on venae profundae; next I will discuss the good indications shown by canales2, by the materials which are dug out, and by the rocks ; then I will speak of the tools by which veins and rocks are broken down and excavated ; the method by which fire shatters the hard veins ; and further, of the machines with which water is drawn from the shafts and air is forced into deep shafts and long tunnels, for digging is impeded by the inrush of the former or the failure of the latter ; next I will deal with the two kinds of shafts, and with the making of them and of tunnels ; and finally, I will describe the method of mining venae dilatatae, venae cumulatae, and stringers.

Jan 1, 1950

Satisfactory means of managing growth in boom towns is a concern in mineral, energy and other large industrial developments. This session will include examinations of socioeconomic impacts, major issues such as social disruption, case studies, methods of managing growth, and concerns involving Indian lands. Innovative methods will be offered to assist the public, government, and industry in finding solutions to managing growth in rapidly growing communities.

Jan 1, 1979

By S. J. Lefond

Most people, when Borates are mentioned, mentally visualize the famous twenty mule team (really eighteen mules and two horses), trudging across the Mojave Desert or "she burns green Rosie, we are rich." Actually, however, the first use of borax was prior to Babylonian times. Their emissaries had orders to bring borax Iron the Gobi desert for use as a flux by the Babylonian goldsmiths. The borate mineral imported for this is not known but probably was borax. The ancient Persians and Arabians knew about borax and the Arabic word "Baurach" appears in a two thousand year old manuscript. The Sanscrit word for borax was tincana which has been corrupted to tincal. The Chinese were using borax as a glaze in three-hundred B.C. Marco Polo brought the first borax, along with gunpowder and spaghetti, from Mongolia to Europe in the late 1300's. Borax from Tibet was imported to Europe for nearly 500 years. In 1772 boric acid (sassolite) was discovered around Tuscany, Italy as a precipitant from volcanic steam vents. Production of boric acid started there about 1815 and provided the sole competition to the borax from Tibet. Borate deposits in Turkey have been known and exploited on a small scale since the 13th century. It is only recently that the operations are being modernized and production increased. About 1836, borax minerals were found in Chile and Argentina with borax production starting in 1852 in Chile and in Argentina in 1886. During the latter half of the 19th Century, Chile was the principle world producer of borax.

Jan 1, 1980

By C. C. Oosthuizen

Paper written on project work carried out in partial fulfilment of Technikon Practical Training Frank shaft is mining both Merensky reef and UG2 reef. The Merensky orebody is almost depleted and this was the reason for starting to mine the UG2 ore reserves. It was decided to mine the UG2 orebody with trackless equipment using a bord and pillar mining method. Frank shaft has been mining the UG2 orebody for nearly 5 years. The T-cut mining method was introduced to see if it could improve the grade of the run of mine (ROM) as well the extraction percentage.

Jan 1, 2005

By J. T. Jordaan

Paper written on project work carried out in partial fulfilment of B. Eng (Mining Engineering) degree This paper addresses the critical parameters that need to be considered when designing a mechanized bord-and-pillar mining layout for a narrow tabular steep dipping orebody. These parameters are : ?Reef dip ?Reef width ?Geological structures within the orebody ?Physical dimensions of the selection of machines ?Gradeability of the selection of machines. The main objective in designing such a layout is to maximize machine efficiencies whilst minimizing dilution. This methodology was then applied in the design of a mechanized bord-and-pillar mining layout for a given piece of ground (Vlakpoort and Moddergat) using a given selection of machines. This piece of ground contains the PGM bearing UG2 Reef with an average thickness of 124 cm and dipping at 18°withadverse strike and dip changes. Two bord-and-pillar layouts were designed for this area. Layout 1 is characterized by the use of strike conveyors to convey ore on strike with an average LHD hauling distance of 35 m. Layout2 uses LHDs for all on strike conveyance of ore with an average hauling distance of 75 m. These two layouts were then technically and financially compared. It was concluded that layout 1 is theoretically superior but layout 2 was chosen due to its greater flexibility and probability of operational success. Layout 2 was also compared to conventional mining and it was concluded to be more economically feasible. However the latter is a proven mining method in these conditions and has a lower risk operational failure. Bord-and-pillar mining has some favourable promises such as improving labour difficulties, lowering operating costs and providing safer working conditions. The success of mechanized bord-and-pillar mining in narrow tabular steep dipping orebodies will depend on the extent of the research and development efforts which need to create and innovate technologies to overcome some of the current limitations stated in the above-mentioned parameters.

Jan 1, 2003

By Nuno Cruz, Saúl Rodríguez

"When executing offshore bored piles there are several specific factors and problems to consider in order to guarantee excavation stability. One of the methods employed to carry out this type of work consists in setting up a floating work platform, typically a barge, and implementing a soil stabilization system that combines a partial steel guiding casing with third generation polymeric drilling fluids. The main aspects to take into consideration when performing offshore pile boring works are soil stabilization, project design, work methodology and operational aspects. An example of a work methodology problem arises before any pile boring work takes place as the steel guiding casing contains water, sometimes salt water. What to do with this water in order to replace it by an adequate polymer fluid will determine the stabilization capacity as soon as the shaft advances below the protection of the casing. Another example of operational problem may derive from barge movements while executing boring activities. This study is the result of extensive field data collection and concrete logging analysis from marine projects using polymers in different continents. The bored pile stability target was set ranging between 2% to 15% of concrete overbreak. Values above 15% or below 2% mean that there is a stability problem. Then the off-target pile’s data is collected, analyzed and classified under categories. Thus, a direct correlation is established between the problem category and the final results. Modifying steps in the pre-established construction methods or operational variables guarantees target results without the need to replace the approved construction methods. As a general conclusion, the worldwide experience in large diameter marine works, allows to provide truthful information and solutions for these problems. In knowing how to follow a logical sequence of work and applying adequate work methodology will be the key for success.GENERALBackgroundTo carry out the drilling process of offshore bored piles there are two main options to take into consideration: drilling the pile by using full guiding casing until final depth; or using a combined system of partial steel guiding casing and support drilling fluids.The knowledge and situations described in this paper come from the experience acquired in different projects where the second method was employed. This construction method consists in installing a steel guiding casing by vibration and thus covering the water table and further stabilizing the soil below it with polymeric fluids until reaching the pile’s final depth. The Fig. 1 schematic shows an example of this method where H corresponds to the length of the steel guiding casing whereas the remainder of the shaft’s length is stabilized by polymer fluid. The entire bored length is full of slurry up to top of casing.In most cases this kind of civil works results from the need to build a bridge or executing port structures in places where the creation of temporary artificial peninsulas with fill material is impracticable or not allowed. Hence the need to use floating work platforms, commonly referred to as barges."

Jan 1, 2017