As the excavation of roadway, new fractures will be formed and the pre-existing fractures extend with the redistribution of stress in surrounding rocks. Eventually, fracture zone and bed separation are formed in rocks...As the excavation of roadway, new fractures will be formed and the pre-existing fractures extend with the redistribution of stress in surrounding rocks. Eventually, fracture zone and bed separation are formed in rocks because of the developed fractures. Therefore, mastering the fracture evolution of surrounding rocks is very important to maintain the stability of roadway. The surrounding rocks of main haulage road- way in a certain coal mine is so broken and loose that the supporting is very difficult. Based on compre- hensive anal[ysis of the engineering geological conditions, a sight instrument was used to observe the fractures of internal surrounding rocks, Four indices, i.e., the width of fracture zone W, the number of fractures n, the width of fractures d and rock fracture designation RFD, are put forward to evaluate the fracture dewelopment. According to the evolution rules of the soft rock roadway from this paper, control principles by stages and by regions are presented through the research. At the same time, the best time of grouting reinforcement is determined on the basis of fracture saturation. Field practice shows that the roadway can satisfy normal production during service periods by suitable first support and grouting reinforcement.展开更多
Soft rocks are a still fairly unexplored chapter in rock mechanics. Within this category are the clastic sedimentary rocks and pyroclastic volcanic rocks, of low to moderate lithification （consolidation, cemen- tatio...Soft rocks are a still fairly unexplored chapter in rock mechanics. Within this category are the clastic sedimentary rocks and pyroclastic volcanic rocks, of low to moderate lithification （consolidation, cemen- tation, new formed minerals）, chemical sedimentary rocks and metamorphic rocks formed by minerals witk Mohs hardness less than 3.5, such as limestone, gypsum, halite, sylvite, between the first and phyllites, graphitic schist, chloritic shale, talc, etc., among the litter. They also include any type Of rock that suffered alteration processes （hydrothermal or weathering）. In Argentina the study of low-strength rocks has not received much attention despite having extensive outcrops in the Andes and great impact in the design criteria. Correlation between geomechanical properties （UCS, deformability） to physical index （porosity, density, etc.） has shown promising results to be better studied. There are many studies and engineering projects in Argentina in soft rock geological environments, some cited in the text （Chihuido dam, N. Kirchner dam, J. Cepernic Dam, etc.） and others such as International Tunnel in the Province of Mendoza （Corredor Bioceanico）, which will require the valuable contribution from rock mechanics. The lack of consistency between some of the physical and mechanical parameters explored from studies in the country may be due to an insufficient amount of information and/or non-standardization of criteria for testing materials. It is understood that more and better academic and professional efforts in improv- ing techniques will result in benefits to the better understanding of the geomechanics of weak rocks.展开更多
This paper reports LA-ICP-MS zircon U-Pb ages and REE compositions on detrital zircons （Type 1） and hydrothermal zircons （Type 2） from low-metasedimentary rocks in the Mesoproterozoic Gaoyuzhuang Formation, Pingqu...This paper reports LA-ICP-MS zircon U-Pb ages and REE compositions on detrital zircons （Type 1） and hydrothermal zircons （Type 2） from low-metasedimentary rocks in the Mesoproterozoic Gaoyuzhuang Formation, Pingquan area, Hebei Province that provide important constraints on the tectonic evolution along the northern margin of the North China Block. The detrital zircons are characterized by an oscillatory magmatic core, surrounded by a narrow structureless rim in CL images. They yield 2~7pb/2~tpb ages ranging from 1703 to 2543 Ma with two age peaks at 2473 and 1794 Ma, which is consistent with the Neoarchean and Paleoproterozoic tectono-thermal events recorded in the NCB basement, indicating that the source of the detritus was locally derived. By contrast, the hydrothermal ones are euhedral, sector zoning or internally structureless. They have relatively higher U and Th contents and Th/U ratios （U=139-2918 ppm, Th=35-1327 ppm, Th/U （average） =0.78 vs. U=15-1044 ppm, Th=8-341 ppm, Th/U （average） =0.57 for detrital zircons）. Moreover, they are also enriched in REEs relative to detrital zircons and show a lower positive Ce anomaly （ZREE = 659-2418 ppm vs. 231-611 ppm for detrital zircon; Ce/Ce＊=2-13 vs. 33-174 for detrital zircons）, similar to known hydrothermal zircons derived from many locations. These characteristics, combined with our field petrographic observations, indicate that the hydrothermal zircons possibly formed from a low temperature aqueous fluid. Twelve concordant or near-concordant analyses on hydrothermal zircons yield weighted mean 206pb/238U ages of 325-327 Ma, which provide unambiguous evidence that the northern NCB underwent late Paleozoic low temperature hydrothermal modification. This timing of this hydrothermal event is compatible with that of the late Paleozoic magmatic and metamorphic-deformational events occurred on the northern margin of the NCB, it appears likely that the hydrothermal activity resulted from southward subduction of the Paleo-Asian Oceanic plate underneath the NCB during late Paleozoic.展开更多
基金provided by the National Natural Science Foundation of China (No. 50974118)the Program for New Century Excellent Talents in University (No. NCET-09-0727)+1 种基金the Program for Post graduates Research Innovation in Universities of Jiangsu Province (No. CX10B_149Z)the Priority Academic Program Development of Jiangsu Higher Education Institutions and the State Key Laboratory of Coal Resources and Mine Safety (No.SKLCRSM08X04)
文摘As the excavation of roadway, new fractures will be formed and the pre-existing fractures extend with the redistribution of stress in surrounding rocks. Eventually, fracture zone and bed separation are formed in rocks because of the developed fractures. Therefore, mastering the fracture evolution of surrounding rocks is very important to maintain the stability of roadway. The surrounding rocks of main haulage road- way in a certain coal mine is so broken and loose that the supporting is very difficult. Based on compre- hensive anal[ysis of the engineering geological conditions, a sight instrument was used to observe the fractures of internal surrounding rocks, Four indices, i.e., the width of fracture zone W, the number of fractures n, the width of fractures d and rock fracture designation RFD, are put forward to evaluate the fracture dewelopment. According to the evolution rules of the soft rock roadway from this paper, control principles by stages and by regions are presented through the research. At the same time, the best time of grouting reinforcement is determined on the basis of fracture saturation. Field practice shows that the roadway can satisfy normal production during service periods by suitable first support and grouting reinforcement.
文摘Soft rocks are a still fairly unexplored chapter in rock mechanics. Within this category are the clastic sedimentary rocks and pyroclastic volcanic rocks, of low to moderate lithification （consolidation, cemen- tation, new formed minerals）, chemical sedimentary rocks and metamorphic rocks formed by minerals witk Mohs hardness less than 3.5, such as limestone, gypsum, halite, sylvite, between the first and phyllites, graphitic schist, chloritic shale, talc, etc., among the litter. They also include any type Of rock that suffered alteration processes （hydrothermal or weathering）. In Argentina the study of low-strength rocks has not received much attention despite having extensive outcrops in the Andes and great impact in the design criteria. Correlation between geomechanical properties （UCS, deformability） to physical index （porosity, density, etc.） has shown promising results to be better studied. There are many studies and engineering projects in Argentina in soft rock geological environments, some cited in the text （Chihuido dam, N. Kirchner dam, J. Cepernic Dam, etc.） and others such as International Tunnel in the Province of Mendoza （Corredor Bioceanico）, which will require the valuable contribution from rock mechanics. The lack of consistency between some of the physical and mechanical parameters explored from studies in the country may be due to an insufficient amount of information and/or non-standardization of criteria for testing materials. It is understood that more and better academic and professional efforts in improv- ing techniques will result in benefits to the better understanding of the geomechanics of weak rocks.
基金supported by National Basic Research Program of China (Grant No. 2011CB808800)SINOPEC Project (Grant No. G0800-06-ZS-319)+1 种基金National Natural Science Foundation of China (Grant No. 40621002)"111 Project" (Grant No. B08030)
文摘This paper reports LA-ICP-MS zircon U-Pb ages and REE compositions on detrital zircons （Type 1） and hydrothermal zircons （Type 2） from low-metasedimentary rocks in the Mesoproterozoic Gaoyuzhuang Formation, Pingquan area, Hebei Province that provide important constraints on the tectonic evolution along the northern margin of the North China Block. The detrital zircons are characterized by an oscillatory magmatic core, surrounded by a narrow structureless rim in CL images. They yield 2~7pb/2~tpb ages ranging from 1703 to 2543 Ma with two age peaks at 2473 and 1794 Ma, which is consistent with the Neoarchean and Paleoproterozoic tectono-thermal events recorded in the NCB basement, indicating that the source of the detritus was locally derived. By contrast, the hydrothermal ones are euhedral, sector zoning or internally structureless. They have relatively higher U and Th contents and Th/U ratios （U=139-2918 ppm, Th=35-1327 ppm, Th/U （average） =0.78 vs. U=15-1044 ppm, Th=8-341 ppm, Th/U （average） =0.57 for detrital zircons）. Moreover, they are also enriched in REEs relative to detrital zircons and show a lower positive Ce anomaly （ZREE = 659-2418 ppm vs. 231-611 ppm for detrital zircon; Ce/Ce＊=2-13 vs. 33-174 for detrital zircons）, similar to known hydrothermal zircons derived from many locations. These characteristics, combined with our field petrographic observations, indicate that the hydrothermal zircons possibly formed from a low temperature aqueous fluid. Twelve concordant or near-concordant analyses on hydrothermal zircons yield weighted mean 206pb/238U ages of 325-327 Ma, which provide unambiguous evidence that the northern NCB underwent late Paleozoic low temperature hydrothermal modification. This timing of this hydrothermal event is compatible with that of the late Paleozoic magmatic and metamorphic-deformational events occurred on the northern margin of the NCB, it appears likely that the hydrothermal activity resulted from southward subduction of the Paleo-Asian Oceanic plate underneath the NCB during late Paleozoic.
