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By M. R. Carter

The Rochester Mining District is located some twenty-five miles NE of Lovelock, Nevada. The District was discovered and named in the 1860's by prospectors from Rochester, New York. For a number of years, they worked Rochester Canyon, sinking shafts and inclines and making open cuts. After reaching a depth of approximately eighty feet, the miners tapped an underground channel and were driven from these workings by a strong flow of water leaving pumps in the shaft and barely escaping with their lives. With the Rochester workings no longer accessible, the miners went to the southeast and established the Relief Mining District. About 1881, gold was found in the gravel at the mouth of American Canyon, to the east of Rochester. These placers were worked until 1895, first by the Americans who reportedly took out $1 000 000, and later by the Chinese who mined the gravel with great skill. It was estimated that the Chinese took out as much as $10 000 000.

Jan 1, 1987

The Coeur Rochester Mine is one of the largest and lowest cost primary silver mines in the United States. In January, the mine surpassed 3.1 kt (100 million oz) of historic silver production. Rochester is owned and operated by Coeur d’Alene Mines, the world’s largest primary silver producer. Rochester is the world’s seventh largest silver mine. It also produces gold — more than 31.1 t (1 million oz) in historic production. Cash operating costs have averaged 8 cents/g ($2.58/oz) of silver since operations began in 1986.

Jan 1, 2004

By A.A. Grubb, F.L. Wolf

The tests here described were rrlade to obtain information regarding costs, efficiency, etc. of baking cores in an oil-fired oven and two electric ovens, which were installed, early in 1920, in the core room of The Ohio Brass Co. and were used almost continuously during the rest of that year. Operating costs were rather high so a complete test was undertaken early in 1921. The ovens will be referred to as Nos. 1, 2, and 3. Nos. 1 and 2 are electric ovens of different makes while No. 3 is an oil-fired oven made by the firm that made No. 2. The three arc. equipped with similar ventilating devices. They have full-height doors at front and rear. The cores are placed on iron racks, which arc lifted by Cowan trucks and rolled into the ovens through the front doors. When baked, they are removed through the rear doors. Fig. 1 shows the general plan of the elecric ovens while Fig. 2 shows the plan of the oil-fired oven. Oven No. 1 is 91 in. (231 em.) wide, 83 in. (210 em.) high. and 79 in. (200 cm.) deep, inside measurements. The walls are constructed ill panels about 18 in. (46 cm.) wide and 43/16 in. (10.6 em.) thick, packed with blocks of insulating material and covered with sheet iron. Thc concrete floor oil which the owns set is 13 in. (33 cm.) thick. 4 recess about 5 in. (13 cm.) deep was cut in the floor to provide room for the heating units. Channels and plates supported on I beams serve as supports for the trucks and racks. The ventilating system consists of a Sirroco No. 11/2 fan, connected so as to draw air from the top of the oven or from the room, through damper C, and to deliver it either to the bottom of the oven or to the floor; the delivery is controlled by the vane A. The fan 2nd pipes are covered with 1/4-in. (6.3 mm.) asbestos-cement lagging. The heating units have a capacity of 91.4 kw. and arc located along

Jan 1, 1923

By F. L. Wolf, A. A. Grubb

The tests here described were rrlade to obtain information regarding costs, efficiency, etc. of baking cores in an oil-fired oven and two electric ovens, which were installed, early in 1920, in the core room of The Ohio Brass Co. and were used almost continuously during the rest of that year. Operating costs were rather high so a complete test was undertaken early in 1921. The ovens will be referred to as Nos. 1, 2, and 3. Nos. 1 and 2 are electric ovens of different makes while No. 3 is an oil-fired oven made by the firm that made No. 2. The three arc. equipped with similar ventilating devices. They have full-height doors at front and rear. The cores are placed on iron racks, which arc lifted by Cowan trucks and rolled into the ovens through the front doors. When baked, they are removed through the rear doors. Fig. 1 shows the general plan of the elecric ovens while Fig. 2 shows the plan of the oil-fired oven. Oven No. 1 is 91 in. (231 em.) wide, 83 in. (210 em.) high. and 79 in. (200 cm.) deep, inside measurements. The walls are constructed ill panels about 18 in. (46 cm.) wide and 43/16 in. (10.6 em.) thick, packed with blocks of insulating material and covered with sheet iron. Thc concrete floor oil which the owns set is 13 in. (33 cm.) thick. 4 recess about 5 in. (13 cm.) deep was cut in the floor to provide room for the heating units. Channels and plates supported on I beams serve as supports for the trucks and racks. The ventilating system consists of a Sirroco No. 11/2 fan, connected so as to draw air from the top of the oven or from the room, through damper C, and to deliver it either to the bottom of the oven or to the floor; the delivery is controlled by the vane A. The fan 2nd pipes are covered with 1/4-in. (6.3 mm.) asbestos-cement lagging. The heating units have a capacity of 91.4 kw. and arc located along

Jan 1, 1923

By B. Woyski

Many writers, in discussing defects caused by oxidation and gassing of bronzes and red brasses advocate substantially the same cure for both. But from its nature, oxidation cannot take place if there is an excess of fuel in the furnace, while the gases absorbed by some alloys are products of incomplete combustion of the fuel. Hence the metal can be either oxidized or gassed, but it is doubtful whether these actions can take place simultaneously. Oxidation can be easily overcome by the use of deosidizers or it may be avoided by protecting the molten metal with suitable fluxes. Absorption of gascs is more difficult to overcome: the regulation of the air and fuel, so as to produce complete combustion, and the protection of the bath by mineral fluxes arc the most important factors. Gas expulsion, resulting in gas holes, porosity, unsoundness, and swollen or cauliflower-headed risers, is said to have several causes. One writer1 lists the most common causes in the order of their importance, as follows: Superheated metal, dirty or slaggy furnace conditions, using metals low in quality or those previously subjected to bad melting practice, poor grade of fuel, use of newly lined or damp ladles, indiscriminate mixing of scrap or illogical combinations of metal. Superheating the metal usually occurs when the heat is ready to be poured but for some reason must be held in the furnace. In this case, a careful furnace tender tries to avoid overheating the metal by keeping a mild fire; that is, a reducing fire which, unfortunately, results in gassing the metal. A dirty, slaggy furnace may result in gassing the metal by retarding the heating and prolonging the time necessary to bring the metal to the proper temperature, thereby increasing the chances of gassing in uncertain furnace atmosphere. It is doubtful whether rnetals of low quality have anything to do with gassing molten metal, except, possibly in the case of metals containing

Jan 1, 1923

By B. Woyski

Many writers, in discussing defects caused by oxidation and gassing of bronzes and red brasses advocate substantially the same cure for both. But from its nature, oxidation cannot take place if there is an excess of fuel in the furnace, while the gases absorbed by some alloys are products of incomplete combustion of the fuel. Hence the metal can be either oxidized or gassed, but it is doubtful whether these actions can take place simultaneously. Oxidation can be easily overcome by the use of deosidizers or it may be avoided by protecting the molten metal with suitable fluxes. Absorption of gascs is more difficult to overcome: the regulation of the air and fuel, so as to produce complete combustion, and the protection of the bath by mineral fluxes arc the most important factors. Gas expulsion, resulting in gas holes, porosity, unsoundness, and swollen or cauliflower-headed risers, is said to have several causes. One writer1 lists the most common causes in the order of their importance, as follows: Superheated metal, dirty or slaggy furnace conditions, using metals low in quality or those previously subjected to bad melting practice, poor grade of fuel, use of newly lined or damp ladles, indiscriminate mixing of scrap or illogical combinations of metal. Superheating the metal usually occurs when the heat is ready to be poured but for some reason must be held in the furnace. In this case, a careful furnace tender tries to avoid overheating the metal by keeping a mild fire; that is, a reducing fire which, unfortunately, results in gassing the metal. A dirty, slaggy furnace may result in gassing the metal by retarding the heating and prolonging the time necessary to bring the metal to the proper temperature, thereby increasing the chances of gassing in uncertain furnace atmosphere. It is doubtful whether rnetals of low quality have anything to do with gassing molten metal, except, possibly in the case of metals containing

Jan 1, 1923

By N. B. Pilling, R. E. Bedworth

The corrosion of metals is one problem on which time and thought have been expended for many years. In the effort to avert the destructive action of a hostile environment, attention has been directed almost entirely to the conditions under which most metallic structures are called upon to perform, and the extensive and complicated phenomena attending the corrosive action of atmospheric agencies, acting at the ordinary atmospheric temperatures, have been studied, but there is unanimity of opinion regarding many fundamental facts. One neglected phase is the corrosive action of various gases upon metals exposed to temperatures considerably higher than the atmospheric range, and more especially the attack of atmospheric oxygen upon exposed metallic surfaces. That the problem is difficult is connoted by the practical dominance of industrial electric heating by alloys of one type (nickel-chromium). Proprietary interest may account, in part, for the paucity of information available upon even the most general factors determining the behavior of metals and alloys when exposed to such exacting conditions. The present paper gives some conclusions reached as the result of experimental work, extending over several years, on the mechanism and contributory factors of the high-temperature oxidation of a number of simple unalloyed metals; it is free from experimental detail and proof. High-temperature metallic oxidation may be considered as a phase of metallic corrosion. The scheme outlined below, in which corrosive agent and environment are the principal criteria, is one way of analyzing the several groups of corrosion phenomena. Erosion.—Disintegrating or destructive action by physical causes. Corrosion.—Disintegrating or destructive action by chemical causes. Low-temperature Corrosion.—Solid participating phases essentially immobile: (a) Gaseous agent; (b) liquid agent: action electrolytic and action non-electrolytic. High-temperature Corrosion.—Solid participating phases possess diffusive mobility: (a) Liquid agent; (b) gaseous agent: reducing gases, oxidizing gases. (1) Water; (2) miscellaneous elemental and combined oxygen.

Jan 1, 1923

By R. E. Bedworth, N. B. Pilling

The corrosion of metals is one problem on which time and thought have been expended for many years. In the effort to avert the destructive action of a hostile environment, attention has been directed almost entirely to the conditions under which most metallic structures are called upon to perform, and the extensive and complicated phenomena attending the corrosive action of atmospheric agencies, acting at the ordinary atmospheric temperatures, have been studied, but there is unanimity of opinion regarding many fundamental facts. One neglected phase is the corrosive action of various gases upon metals exposed to temperatures considerably higher than the atmospheric range, and more especially the attack of atmospheric oxygen upon exposed metallic surfaces. That the problem is difficult is connoted by the practical dominance of industrial electric heating by alloys of one type (nickel-chromium). Proprietary interest may account, in part, for the paucity of information available upon even the most general factors determining the behavior of metals and alloys when exposed to such exacting conditions. The present paper gives some conclusions reached as the result of experimental work, extending over several years, on the mechanism and contributory factors of the high-temperature oxidation of a number of simple unalloyed metals; it is free from experimental detail and proof. High-temperature metallic oxidation may be considered as a phase of metallic corrosion. The scheme outlined below, in which corrosive agent and environment are the principal criteria, is one way of analyzing the several groups of corrosion phenomena. Erosion.—Disintegrating or destructive action by physical causes. Corrosion.—Disintegrating or destructive action by chemical causes. Low-temperature Corrosion.—Solid participating phases essentially immobile: (a) Gaseous agent; (b) liquid agent: action electrolytic and action non-electrolytic. High-temperature Corrosion.—Solid participating phases possess diffusive mobility: (a) Liquid agent; (b) gaseous agent: reducing gases, oxidizing gases. (1) Water; (2) miscellaneous elemental and combined oxygen.

Jan 1, 1923

By E. H. Dix

During an investigation of high-strength manganese bronze by til Engineering Division of the Air Service, at McCook Field, Dayton, Ohio, particles of a "blue constituent" were noted in the microstructure of most of the bronzes examined. The constitution of the simple copper-zinc base alloy is still a matter of dispute in spite of the fact that the copper-zinc series is one of the oldest industrially important groups of alloys, and has received thc carly co~l+itlcl-ntio11 of scirntific rcsc:trch. Thc diagram, according to the rnost rcrent \vork.' IS shown in Fig. 1. The disputed questions involve the tcrmi~r:~tiorl of the beta field and the lint at 470' C. The parliest expc~imc>ntcr, Rol)erts--~1~11stcri, detectrd an arrest in some of his cooling curves :it approximately this temperature and ascribed them to the formation of a cutectic; it has since been proved that there arc no eutectics in this series. Shepherd? was unable to detect any thermal arrests at this temperature, his. diagram was essentially as shown in Fig. 1, except that the line at 470" ('. was omitted and the beta phase carried down to normal temperature. 1,:ttcr. carpenter and Edwards, by a very painstaking research, definitely established the authenticity of the line but attributed it to the breakdown of the BETA constituent into a cutectoid of alpha and gamma. microscopic evidence of the formation of the cutectoid is doubtful and it seems more likely to he due to an allo-tropic change in the beta constituent as shown by Fig. 1. At least for practical purpose?, it is more convenient to think of the structure of a 60-40 brass as a mixture of alpha and beta prime crystals rather thin alpha plus an unresoluble eutectoid of "apparent beta" as it has often been called. * Chief, Metals branch, Engineering Division, Air Service. 1 0. F. Hudson: Jnl. Inst. of hlvtals (1913) 12, 2 E. S. Shepherd: Jnl. Phys Chrm. (10141 8, 421. H. C. H. Carpenter and O. A. Edwards: Jnl, Inst. of Metals (1911) 5, 127.

Jan 1, 1923

By E. H. Dix

During an investigation of high-strength manganese bronze by til Engineering Division of the Air Service, at McCook Field, Dayton, Ohio, particles of a "blue constituent" were noted in the microstructure of most of the bronzes examined. The constitution of the simple copper-zinc base alloy is still a matter of dispute in spite of the fact that the copper-zinc series is one of the oldest industrially important groups of alloys, and has received thc carly co~l+itlcl-ntio11 of scirntific rcsc:trch. Thc diagram, according to the rnost rcrent \vork.' IS shown in Fig. 1. The disputed questions involve the tcrmi~r:~tiorl of the beta field and the lint at 470' C. The parliest expc~imc>ntcr, Rol)erts--~1~11stcri, detectrd an arrest in some of his cooling curves :it approximately this temperature and ascribed them to the formation of a cutectic; it has since been proved that there arc no eutectics in this series. Shepherd? was unable to detect any thermal arrests at this temperature, his. diagram was essentially as shown in Fig. 1, except that the line at 470" ('. was omitted and the beta phase carried down to normal temperature. 1,:ttcr. carpenter and Edwards, by a very painstaking research, definitely established the authenticity of the line but attributed it to the breakdown of the BETA constituent into a cutectoid of alpha and gamma. microscopic evidence of the formation of the cutectoid is doubtful and it seems more likely to he due to an allo-tropic change in the beta constituent as shown by Fig. 1. At least for practical purpose?, it is more convenient to think of the structure of a 60-40 brass as a mixture of alpha and beta prime crystals rather thin alpha plus an unresoluble eutectoid of "apparent beta" as it has often been called. * Chief, Metals branch, Engineering Division, Air Service. 1 0. F. Hudson: Jnl. Inst. of hlvtals (1913) 12, 2 E. S. Shepherd: Jnl. Phys Chrm. (10141 8, 421. H. C. H. Carpenter and O. A. Edwards: Jnl, Inst. of Metals (1911) 5, 127.

Jan 1, 1923

By W.G. Harbert, C. Upthegrove

DURing the past year considerable work dealing with physical properties of cartridge brass was done at the University of Michigan in cooperation with the Ordnance Department of the U. S. Army. This paper gives some of the data bearing on the effect of the anneal, previous to the final reduction-or rolling, on the physical properties, particularly the hardness. Various phases of the subject of physical properties of cartridge brass have been presented by different investigators. Mathewson and Phillips1 refer to the work of Grard, in 1909, as the first systematic presentation of the relation between temperature and time of anneal, changing of physical properties and microstructure, and the previous reduction by cold rolling. They discuss the relation between time and temperature of annealand the previous reduction by cold rolling; also the relation between physical properties and grain size of annealed brass. The degree of deformation previous to the annealing was found to determine the temperature at which recrystallization and corresponding changes in physical Properties would take place. relation between grain size and Brinell hardness, found the hardness for low-temperature annealing to be dependent on the previous degree of reduction, while for anneals above a certain temperature the hardness after the anneal was independent of the degree of reduction. Actual differences in hardness, due to the degree of reduction, disappear only on annealing at 600" C. or above; though the differences for metal subjected to different degrees of reduction and annealed at temperatures between 350" and 600" C. were found to be relatively small. In their determination of the relationship of grain size to Brinell hardness, Bassett

Jan 1, 1923

By W. G. Harbert, C. Upthegrove

DURing the past year considerable work dealing with physical properties of cartridge brass was done at the University of Michigan in cooperation with the Ordnance Department of the U. S. Army. This paper gives some of the data bearing on the effect of the anneal, previous to the final reduction-or rolling, on the physical properties, particularly the hardness. Various phases of the subject of physical properties of cartridge brass have been presented by different investigators. Mathewson and Phillips1 refer to the work of Grard, in 1909, as the first systematic presentation of the relation between temperature and time of anneal, changing of physical properties and microstructure, and the previous reduction by cold rolling. They discuss the relation between time and temperature of annealand the previous reduction by cold rolling; also the relation between physical properties and grain size of annealed brass. The degree of deformation previous to the annealing was found to determine the temperature at which recrystallization and corresponding changes in physical Properties would take place. relation between grain size and Brinell hardness, found the hardness for low-temperature annealing to be dependent on the previous degree of reduction, while for anneals above a certain temperature the hardness after the anneal was independent of the degree of reduction. Actual differences in hardness, due to the degree of reduction, disappear only on annealing at 600" C. or above; though the differences for metal subjected to different degrees of reduction and annealed at temperatures between 350" and 600" C. were found to be relatively small. In their determination of the relationship of grain size to Brinell hardness, Bassett

Jan 1, 1923

By M.A. Hunter

This paper gives the results of an investigation of the specific resistance and temperature coefficient of the electrical resistance of nickel and its important alloy, monel metal. For most of the pure metals, the temperature coefficient of resistance is approximately 0.004 per degree centigrade at 20" C. Nickel and iron, however, are exceptions. This property is important as it gives us good material for the construction of thermometers and other instruments involving electrical control. A summary of information on this subject has been publishcd by the Bureau of Standards.l The present experiments antedate this publication by several years and as the information obtained is not contained in it, the results of the experiments arc published as additional information. Electrical Properties of Pure Nickel It is generally conceded that the lowest values for electrical resistance are obtained in the purest metal. In the case of nickel, the best material obtainable is electrolytic nickel, which contains approximately 99.80 per cent. nickel, 0.15 per cent. iron, and 0.05 per cent. copper. Any cobalt that may be present is included in the nickel figure. If the elcctrolStic sheet has been deposited without intermission, it is possible to cut a section from the sheet and roll it into wire without melting. By this means a nickel wire may be obtained that is uncontaminated by any of the impurities always taken up by nickel during melting. Two samples of nickel wire obtained from different electrolytic nickels had the follolving electrical resistance and temperature coefficient of electrical resistance: Specific Temp. CofEE. Sample MateRial ReSISTance peR Deg. C. NO. 1 Electrolytic nickel.................... 7.55 0.00550 NO. 2 Electrolytic nickcl ................... 7.60 0.00553 * Rensselacr Polytechnic Institute. Director of Research, Driver-Harris Co. Russell Sage Laboratory, Rensselaer Polyt,ecllnic Institute. 1 U. S. Bureau of Standards, Circular 100 (March, 1921).

Jan 1, 1923

By M. A. Hunter

This paper gives the results of an investigation of the specific resistance and temperature coefficient of the electrical resistance of nickel and its important alloy, monel metal. For most of the pure metals, the temperature coefficient of resistance is approximately 0.004 per degree centigrade at 20" C. Nickel and iron, however, are exceptions. This property is important as it gives us good material for the construction of thermometers and other instruments involving electrical control. A summary of information on this subject has been publishcd by the Bureau of Standards.l The present experiments antedate this publication by several years and as the information obtained is not contained in it, the results of the experiments arc published as additional information. Electrical Properties of Pure Nickel It is generally conceded that the lowest values for electrical resistance are obtained in the purest metal. In the case of nickel, the best material obtainable is electrolytic nickel, which contains approximately 99.80 per cent. nickel, 0.15 per cent. iron, and 0.05 per cent. copper. Any cobalt that may be present is included in the nickel figure. If the elcctrolStic sheet has been deposited without intermission, it is possible to cut a section from the sheet and roll it into wire without melting. By this means a nickel wire may be obtained that is uncontaminated by any of the impurities always taken up by nickel during melting. Two samples of nickel wire obtained from different electrolytic nickels had the follolving electrical resistance and temperature coefficient of electrical resistance: Specific Temp. CofEE. Sample MateRial ReSISTance peR Deg. C. NO. 1 Electrolytic nickel.................... 7.55 0.00550 NO. 2 Electrolytic nickcl ................... 7.60 0.00553 * Rensselacr Polytechnic Institute. Director of Research, Driver-Harris Co. Russell Sage Laboratory, Rensselaer Polyt,ecllnic Institute. 1 U. S. Bureau of Standards, Circular 100 (March, 1921).

Jan 1, 1923

Using a Jarrell-Ash "Compact" direct reading spectrometer, analyses were made of a wide variety of rocks ranging from acidic to ultrabasic types. Statistical evaluation suggests that accuracies comparable with the values obtained by the rapid chemical methods used by the United States Geological Survey will be obtained.The spectrographic method involves fusion of the rock with lithium tetraborate, strontium being incorporated in the flux as the internal standard. The resulting bead is ground with graphite and pressed into a pellet. The counts obtained on two standard pellets are used to correct for instrumental drift.Background readings are made at 4109 Å and corrections for background are made to all lines. Corrections for matrix interferences, both by chemical suppression and optical enhancement, are made. The three corrections of drift, background, and matrix are incorporated into one general expression which has been programmed on magnetic cards, each element requiring a separate card. The cards are placed individually into a desk top computer (an Olivetti Programma 101), which enables true counts to be calculated from the "readout" counts, and the element concentration is then obtained from computer-printed tables by referring to the appropriate value of true counts versus concentration. These tables were prepared by making a polynomial regression analysis of the spectrographic results from 50 standard and analysed samples, a curve of best fit being chosen for each element.The regression coefficients, usually of a fourth or fifth degree equation, together with other relevant data, were fed into a large computer, programmed to print out tables of concentration versus true counts. This technique enables the results obtained to be based on mathematically-derived values rather than on hand-drawn calibration graphs, giving greater inherent accuracy. The technique has been shown to give results of good accuracy and acceptable precision suitable for many geological and geochemical exploration programmes involving the analysis of many rock samples of different types.

Jan 1, 1969

By R. F. Dawson, A. S. Bagnall, K. Barron

"At Smoky River Coal Limited (SRCL), economic occurrences of structurally thickened coal deposits form attractive surface mining targets. These steeply dipping, structurally complex deposits require that special attention be given to pit wall design and operational practices.Where anchor support is feasible, there is potential for reducing footwall waste requirements and/or increasing coal recovery. SRCL has used rock anchors to support footwall slopes since 1985. This paper outlines design considerations and performance of rock anchor support systems at SRCL.Three case histories are included that illustrate the design process for supporting steeply dipping footwall slopes using rock anchors.IntroductionWestern Canada contains vast reserves of high grade coking coal largely located in two belts within the Rocky Mountain Foothills straddling the Alberta/British Columbia border. There are about one billion tonnes of ""clean"" coking coal reserves (Romaniuk and Naidu, 1986) situated near existing mining infrastructure. Within the reserve areas shown in Figure I, a total of six producers operate 10 large mines linked with ports situated on Canada's west coast. Al! of the producers operate conventional shovel/truck surface pits.Surface mineable reserves within some of the mountain coal mines are located on dip slopes or where the geologic structure has thickened the coal near the surface, creating low strip ratio targets. Footwall slopes in these mines are developed parallel to bedding, thus minimizing waste extraction and preventing undercutting of potentially unstable strata. The base of the mineable coal measures in both north and south regions is marked by massive quartz sandstone units (Torrens Member and Moose Mountain Member) which often form the footwall. Footwalls developed within this basal sandstone unit can attain very high unbenched heights often with little risk of instability. In cases where the footwall is developed on weaker strata above this basal unit, stability considerations control slope height when bedding dips exceed about 30°. In these situations it is desirable to assess the benefits of artificial support to increase the unbenched footwall slope height."

Jan 1, 1995

By R. F. Dawson, A. S. Bagnall, K. Barron

"At Smoky River Coal Limited (SRCL), economic occurrences of structurally thickened coal deposits form attractive surface mining targets. These steeply dipping, structurally complex deposits require that special attention be given to pit wall design and operational practices.Where anchor support is feasible, there is potential for reducing footwall waste requirements and/or increasing coal recovery. SRCL has used rock anchors to support footwall slopes since 1985. This paper outlines design considerations and performance of rock anchor support systems at SRCL.Three case histories are included that illustrate the design process for supporting steeply dipping footwall slopes using rock anchors.IntroductionWestern Canada contains vast reserves of high grade coking coal largely located in two belts within the Rocky Mountain Foothills straddling the Alberta/British Columbia border. There are about one billion tonnes of ""clean"" coking coal reserves (Romaniuk and Naidu, 1986) situated near existing mining infrastructure. Within the reserve areas shown in Figure I, a total of six producers operate 10 large mines linked with ports situated on Canada's west coast. Al! of the producers operate conventional shovel truck surface pits.Surface mineable reserves within some of the mountain coal mines are located on dip slopes or where the geologic structure has thickened the coal near the surface, creating low strip ratio targets. Footwall slopes in these mines are developed parallel to bedding, thus minimizing waste extraction and preventing undercutting of potentially unstable strata. The base of the mineable coal measures in both north and south regions is marked by massive quartz sandstone units (Torrens Member and Moose Mountain Member) which often form the footwall. Footwalls developed within this basal sandstone unit can attain very high unbenched heights often with little risk of instability. In cases where the footwall is developed on weaker strata above this basal unit, stability considerations control slope height when bedding dips exceed about 30°. In these situations it is desirable to assess the benefits of artificial support to increase the unbenched footwall slope height."

Jan 1, 1995

By Rolland R. Mates

This paper describes the use of post- tensioned rock anchors to reduce the risk of future damage to a residential structure as a result of coal mine subsidence. The project described in this paper was performed by the Office of Surface Mining Reclamation and Enforcement (OSMRE) of the U. S. Department of the Interior. The OSMRE was created to administer Public Law 95-87, the Surface Mining Control and Reclamation Act of 1977. The responsibilities of OSMRE include "reclamation and restoration of land and water resources, adversely affected by past coal mining including prevention, abatement, control of coal mine subsidence. ?('l) Consequently, OSMRE has been addressing mine subsidence problems since its initial subsidence stabilization project in 1979. Stabilization activities have primarily consisted of supporting the overburden material by injecting materials through drilled bore holes into the underground mine voids. Injection of various materials into mine voids, including fly ash mixtures, coal refuse, cement grout, and gravel has proven to be a successful method of reducing mine subsidence-related surface movements, and has been extensively utilized in mitigating mine subsidence problems. However, the cost of drilling for injection can be extremely high in areas where the depth to the coal seam is great.

Jan 1, 1986

The Main Seam occurs in two 'pods', termed North and South, separated by an east-west oriented 'want' zone (most probably a palaeo-channel). The seam on either side of the 'want' area reaches thicknesses of over 30 metres but the North Main Seam adjacent to the 'want' zone has been split into multiple seams of 10 to 15 m thickness. Rock types in the inter-burden of this area are characterised by inter-bedded sandstones and carbonaceous mudstones varying in thickness from 0.5 to 5 m. In the South Main Seam, an area of un-split coal exists and is characterised by few inorganic partings. Overburden in this area varies geographically from relatively thick mudstones in the south and east part of the coal deposit to inter-bedded sandstones and carbonaceous mudstones adjacent to the 'want' area. The sandstone/mudstone overburden probably represents a splay or splay-channel complex emanating from the larger 'want' area palaeo-channel. Modelling lithological variability is of use because it is one of the factors used in predicting cavability and roof support system design. The coal in both the north and south deposits were found to exhibit highly predictable quality and breakage parameters in relation to the coal geometry. Although ash yield and sulphur are mostly low and not variable, volatile matter and thus fixed carbon, varied in relation to seam thickness. In general, volatile matter (dat) decreased and moisture increased with decreasing seam thickness whereas moisture increased with decreasing seam thickness. In addition to these parameters it was found that the energy needed to crush the coal was lowest at the top and bottom of the seam and, on a whole seam basis, decreased with seam thickness. All of these parameters were found to vary in relation to the vitrain band content of the coal which itself was controlled by seam geometry. These parameters can therefore be modelled and inputted into mining plans and quality control operations.

Jan 1, 1996

The reasons for selecting two stage pebble milling in preference to conventional methods of grinding are discussed. Commissioning of the first section was completed in October, 1969. Improvements in both the operating and engineering aspects were then incorporated in the section commiss ioned in March, 1971.

Jan 1, 1975