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Causes and hazards of dust development during dry spraying
REINFORCEMENT:EARTH
339A
Shotcrete
advantages gained from the application of this emerging technology. (Author)
957262 Durabilite des reparations en beton projete (Durability of shotcrete repairs) A. Lamontague, M. Pigeon & D. Beaupre, Materials & Structures, 28(179), 1995, pp 260-266.
957265 Dimeusionamiento y sostenimiento de minas subterraneas de pizarra (Dimension and support of underground slate mines) J. Taboada Castro, F. Gutierrez Blanco, C. Gonzalez Nicieza & J. Torano Alvarez, Cuadernos Laboratorio Xeoioxico de Laxe, 19, 1994, pp 419-435.
This paper summarizes various test results obtained at Laval University in recent years on this subject. In dry-mix shotcrete, the use of an air entraining admixture diluted in the water used for the shooting increases the deicer salt scaling resistance, because of a significant decrease in the air void spacing factor. The use of such admixtures, irrespective of the type or the dosage (between 10 and 40 ml 1"l water), does not modify the properties of shotcrete significantly except for its compressive strength. A higher dosage leads to a reduction in strength. For wet-mix shotcrete, the use of silica fume seems to bring the same advantages as those obtained in conventional concrete. The advantages are a decrease in drying shrinkage, an increase in the resistance to freeze-thaw cycles, and a small increase in the compressive strength. Also, it seems clear that the spacing factor of the air bubbles in wetmix shotcrete is very important for resistance to freeze-thaw cycles in the presence or absence of deicer salts. The bonding between good quality shotcrete mixtures (with and without steel fibers) and concrete surfaces prepared by hydrodemolition or chipping with jackhammers followed by sandblasting was found to be generally strong and durable. The other types of surface preparation (grinding, chipping with jackhammers
without sandblasting and sandblasting alone) resulted in either lower bonding strengths or a reduction in the bonding strength with time. (English summary) 957263 Ursachen und Gefahren you Staubentwicklung beim Trockeuspritzen (Causes and hazards of dust development during dry spraying) H. Micke, Felsbau, 13(1), 1995, pp 39-41. Tests under practical conditions have shown that dust development during the dry spraying process should not only be regarded as troublesome, but that it also conceals potential hazards. So far no advances have been made in suppressing the dust prodmxd by shotcrete in empirical procedures. The starting point for further development work is determined. It is necessary to aim for stable discharge form the nozzle and solution of the area problem in the spraying process. (English summary)
Direct rock support methods 957264 Pillar recovery using mobile roof supports A. J. Hewitson, Mining Technology, 77(885), 1995, pp 153160. Since 1991 Rox Coal has been using mobile roof supports (MRS) for retreat mining (pillaring) in a bid to improve productivity and safety, reduce costs and increase percentage extraction during this phase of the operation. MRS are basically self contained longwall shields on cat-tracks, operated by radio remote control and used sequentially to replace timber whilst retreat mining. The units have been successfully deployed in a number of mining panels with extracted seam heights ranging from 44 inches to 7 1/2 feet. Safety has been demonstrably improved and productivity rates have approached those of the best longwall installations. This paper demonstrates the philosophy behind this modus operandi, describes the mining operations, gives a technical description of the equipment and details productivity and cost
The dimensions and support of an underground mine of roofing slate in Galice, worked by rooms with continuous pillars was studied. The rock mass was characterized by the empiric and analitic methods, calculating the stable pillar wide along the mine by the theory of attributed area and by a model of finite elements, where the breaking criterion of Hock and Brown was applied. The result was a parabolic relationship between pillar wide and mine length. Stability studies in an isolated stope give an elastic performance on the periphery of the room, without tractions. Although the stability of the mine is good, a systematic support is recommended on the basis of bolts, that will be reinforced with projected concrete at the top, and a singular treatment of the detected wedges. (English summary)
Reinforced earth 957266 Specification profiles for nonwovens used in civil engineering K. Lieberenz, M. Magel & W. Kittelmann, International Textile Bulletin. Nonwovens/Industrial Textiles, 41(1), 1995, pp 16-20. This article outlines, with the use of examples, the multitude of end-use areas for technical textiles in the building industry. In some end-uses the combined action of soil and/or building materials and technical textiles is sufficiently understood to allow clear specification profiles for the manufacture of the textiles. However, often only empirically obtained information is available to help the engineer in the development of technical textiles. End-uses for such textiles include •tration, drainage, protection and stabilization in the form of geotextiles, and cladding, load-bearing and insulating in building construction. (T.King) 957267 Bearing capacity of rectangular footings on geogridreinforced sand T. Yetimoglu, J. T. H. Wu & A. Saglamer, Journal of Geotechnical Engineering - ASCE, 120(12), 1994, pp 20832099. The effects of the depth to the f'u'st layer of reinforcement, vertical spacing of reinforcement layers, number of reinforcement layers, and the size of reinforcement sheet on the beating capacity were investigated. Both the experimental and analytical studies indicated that there was an optimum reinforcement embedment depth at which the bearing capacity was the highest when single-layer reinforcement was used. Also, there appeared to be an optimum reinforcement spacing for multilayer reinforced sand. The bearing capacity of reinforced sand was also found to increase with reinforcement layer number and reinforcement size when the reinforcement was placed within a certain effective zone. (from Authors) 957268 Transient londing-related settlement of a square foundation on geogrid-reinforeed sand
B. M. Das & A. Maji, Geotechnical & Geological Engineer/rig, 12(4), 1994, pp 241-251.
339A
Shotcrete
advantages gained from the application of this emerging technology. (Author)
957262 Durabilite des reparations en beton projete (Durability of shotcrete repairs) A. Lamontague, M. Pigeon & D. Beaupre, Materials & Structures, 28(179), 1995, pp 260-266.
957265 Dimeusionamiento y sostenimiento de minas subterraneas de pizarra (Dimension and support of underground slate mines) J. Taboada Castro, F. Gutierrez Blanco, C. Gonzalez Nicieza & J. Torano Alvarez, Cuadernos Laboratorio Xeoioxico de Laxe, 19, 1994, pp 419-435.
This paper summarizes various test results obtained at Laval University in recent years on this subject. In dry-mix shotcrete, the use of an air entraining admixture diluted in the water used for the shooting increases the deicer salt scaling resistance, because of a significant decrease in the air void spacing factor. The use of such admixtures, irrespective of the type or the dosage (between 10 and 40 ml 1"l water), does not modify the properties of shotcrete significantly except for its compressive strength. A higher dosage leads to a reduction in strength. For wet-mix shotcrete, the use of silica fume seems to bring the same advantages as those obtained in conventional concrete. The advantages are a decrease in drying shrinkage, an increase in the resistance to freeze-thaw cycles, and a small increase in the compressive strength. Also, it seems clear that the spacing factor of the air bubbles in wetmix shotcrete is very important for resistance to freeze-thaw cycles in the presence or absence of deicer salts. The bonding between good quality shotcrete mixtures (with and without steel fibers) and concrete surfaces prepared by hydrodemolition or chipping with jackhammers followed by sandblasting was found to be generally strong and durable. The other types of surface preparation (grinding, chipping with jackhammers
without sandblasting and sandblasting alone) resulted in either lower bonding strengths or a reduction in the bonding strength with time. (English summary) 957263 Ursachen und Gefahren you Staubentwicklung beim Trockeuspritzen (Causes and hazards of dust development during dry spraying) H. Micke, Felsbau, 13(1), 1995, pp 39-41. Tests under practical conditions have shown that dust development during the dry spraying process should not only be regarded as troublesome, but that it also conceals potential hazards. So far no advances have been made in suppressing the dust prodmxd by shotcrete in empirical procedures. The starting point for further development work is determined. It is necessary to aim for stable discharge form the nozzle and solution of the area problem in the spraying process. (English summary)
Direct rock support methods 957264 Pillar recovery using mobile roof supports A. J. Hewitson, Mining Technology, 77(885), 1995, pp 153160. Since 1991 Rox Coal has been using mobile roof supports (MRS) for retreat mining (pillaring) in a bid to improve productivity and safety, reduce costs and increase percentage extraction during this phase of the operation. MRS are basically self contained longwall shields on cat-tracks, operated by radio remote control and used sequentially to replace timber whilst retreat mining. The units have been successfully deployed in a number of mining panels with extracted seam heights ranging from 44 inches to 7 1/2 feet. Safety has been demonstrably improved and productivity rates have approached those of the best longwall installations. This paper demonstrates the philosophy behind this modus operandi, describes the mining operations, gives a technical description of the equipment and details productivity and cost
The dimensions and support of an underground mine of roofing slate in Galice, worked by rooms with continuous pillars was studied. The rock mass was characterized by the empiric and analitic methods, calculating the stable pillar wide along the mine by the theory of attributed area and by a model of finite elements, where the breaking criterion of Hock and Brown was applied. The result was a parabolic relationship between pillar wide and mine length. Stability studies in an isolated stope give an elastic performance on the periphery of the room, without tractions. Although the stability of the mine is good, a systematic support is recommended on the basis of bolts, that will be reinforced with projected concrete at the top, and a singular treatment of the detected wedges. (English summary)
Reinforced earth 957266 Specification profiles for nonwovens used in civil engineering K. Lieberenz, M. Magel & W. Kittelmann, International Textile Bulletin. Nonwovens/Industrial Textiles, 41(1), 1995, pp 16-20. This article outlines, with the use of examples, the multitude of end-use areas for technical textiles in the building industry. In some end-uses the combined action of soil and/or building materials and technical textiles is sufficiently understood to allow clear specification profiles for the manufacture of the textiles. However, often only empirically obtained information is available to help the engineer in the development of technical textiles. End-uses for such textiles include •tration, drainage, protection and stabilization in the form of geotextiles, and cladding, load-bearing and insulating in building construction. (T.King) 957267 Bearing capacity of rectangular footings on geogridreinforced sand T. Yetimoglu, J. T. H. Wu & A. Saglamer, Journal of Geotechnical Engineering - ASCE, 120(12), 1994, pp 20832099. The effects of the depth to the f'u'st layer of reinforcement, vertical spacing of reinforcement layers, number of reinforcement layers, and the size of reinforcement sheet on the beating capacity were investigated. Both the experimental and analytical studies indicated that there was an optimum reinforcement embedment depth at which the bearing capacity was the highest when single-layer reinforcement was used. Also, there appeared to be an optimum reinforcement spacing for multilayer reinforced sand. The bearing capacity of reinforced sand was also found to increase with reinforcement layer number and reinforcement size when the reinforcement was placed within a certain effective zone. (from Authors) 957268 Transient londing-related settlement of a square foundation on geogrid-reinforeed sand
B. M. Das & A. Maji, Geotechnical & Geological Engineer/rig, 12(4), 1994, pp 241-251.