Historicamente no Brasil a indústria de extração mineral é responsável por grande porção da economia nacional. Um grande desafio enfrentado pelo setor mineral é a disposição de rejeitos, oriundos das fases de lavra e/ou beneficiamento. Estes materiais são dispostos normalmente em duas modalidades: pilhas de estéril e/ou barragem de rejeitos. Atualmente são discutidos os problemas relacionados com a disposição em barragem de rejeitos, as quais em caso de falha, são potenciais causadoras de grandes prejuízos ambientais, econômicos e sociais. Diversos casos de acidentes em barragens de mineradoras no Brasil endossam os riscos associados à falha das mesmas, os quais motivaram este estudo. Um ponto peculiar no estudo e gerenciamento das barragens de mineração é o caráter multidisciplinar, visto a necessidade de sinergia entre diferentes áreas, como geotécnica, processamento mineral, planejamento de produção, entre outras. Este trabalho se propõem a analisar os riscos associados aos tipos de método construtivos de barramento. Para tanto, são abordados os três métodos construtivos conhecidos: método de alteamento à jusante, de alteamento à montante e da linha de centro, os quais são revisados.
Since the years 1970, several design methods of flexible pavements have considered fatigue bottom-up cracking as the most critical degradation mechanism. However, in recent times, premature distresses originated close to the surface of pavements, especially in those with thick asphalt layers. These distresses are cracks initiating close to the surface and rutting, which are considered as shear failures. Shear failure close to the pavement surface is a complex phenomenon caused by factors like: tirepavement shear stresses, asphalt characteristics and environmental conditions. In this article, besides discussing theoretical aspects related, the behavior of asphalt is characterized by shear strength tests and risk analysis of failure close to the pavement surface. It was found that bitumen modification with SBS remarkably increases cohesion and, consequently, the asphalt shear strength. While the shear strength parameters for asphalt with conventional bitumen, at 25°C, are: c = 480 kPa and angle of internal friction angle(fi) = 46°, the tests on asphalt with SBS modified bitumen, also at 25°C, resulted in c = 1,006 kPa and fi = 40°. Regarding SBS modified asphalt, the increase of test temperature from 25°C to 40°c significantly reduces the cohesive interception from 1,006 kPa to 722 kPa, while the friction angle, which is a function of aggregates internal friction and interlocking, remains the same (40°). The risk of shear failure near surface of a pavement consisting of 8.0 cm of SBS modified asphalt; 45.0 cm of crushed rock layers and 60.0 cm of sand was evaluated. The non-uniformity of contact stresses was taken into account using software EverStress FE. In spite of the structure being safe against shear failure (due to the SBS modified bitumen high cohesion), it was shown that considering the thermal gradient on critical shear stresses computations is of paramount importance in the case of overloading.
The objective of this paper is to understand the behavior of the roof and the cause of roof failure of a coal mining. Eleven roof falls occurred in the mine section in sequence. All the roof falls were surveyed, and the geological features were determined which include rock type, mechanical properties, and thickness. The immediate roof thickness was interpolated to determine the cause of the roof failures which was the inappropriate roof support where the immediate roof is thicker. The average thickness of the immediate roof was determined by the drilling log in 1.2 m (3.9 ft.). The roof support was design based on the average thickness, and the bolt length is 1.5 m (4.9 ft.) in suspension. The challenge was to estimate where the immediate roof gets thicker and to design the support considered to maintain the regular bolt length. This is because the cost and productivity of support operation could increase if the bolt length changes as the roof thickness changes. The idea was to adjust the support for beam building with a fully grouted bolt and rearrange the bolt geometry to keep the roof stable. It means, with the same bolt length the type of roof support would change from suspension to beam building depending on when the roof gets thicker. Two empirical approaches were considered to design the roof support: 1) CMRR and 2) RMR. The entry width is 5 m and the roof support was designed with four bolts per row. Where the roof support must change to beam building, the number of bolts per row changes to five or six. The results of the design and application on underground showed that the approach keeps stable.
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