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High safety pillars stability control using EL beam displacement sensors in Lipica II quarry
Jože Kortnik, Sunny Nwaubani, Andrej Kos, 2014, izvirni znanstveni članek

Opis: In underground Lipica II. quarry for the excavation of natural stone, a modified room-and-pillar mining method is used, that is adjusted to the conditions of the site. In order to support and ensure the stability of underground chambers high safety pillars (HSP) are used. These pillars are made of surrounding stone and therefore intersected by discontinuities. The discontinuities represent high risk to the stability of underground facilities and workmen below/ itself. To ensure their safety the stress and strain parameters in height safety pillars are continuously monitored using two vibrating wire (WV) stressmeters inside the high safety pillars and two EL (Electronic level) beam sensors on the surface of the high safety pillar VS3. In the time period October 2010/June 2012 absolute max. measured deviation with EL beam sensors were D1=0.9 mm and D2=1.1 mm, which does not compromise the stability of the high safety pillar VS3. This paper presents the procedures of wedges deformation monitoring in safety pillars with EL beam sensors in the Lipica II underground natural stone quarry.
Ključne besede: beam sensor, high saftey pillar, monitoring, natural stone, room and pillar mining method
Objavljeno: 14.06.2018; Ogledov: 264; Prenosov: 27
.pdf Celotno besedilo (491,51 KB)
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An analysis of the geomechanical processes in coal mining using the Velenje mining method
Gregor Jeromel, Milan Medved, Jakob Likar, 2010, izvirni znanstveni članek

Opis: With in-depth geomechanical analyses of sub-level mining using the longwall mining method we can identify the relationships between the physical and mechanical parameters of geological materials, depending on the intensity of the coal extraction. The extent and the intensity of the mining operations impose impacts on the stresses and cause deformation changes in the rocks and in the coal seams on a broader area of excavations. The method of sub-level coal extraction requires multi-caving of the hanging-wall layers, which are recompressed, and in sub-level stoping each represents a hanging wall. The repeating processes of caving-in and compression, from the aspect of the theory of plasticity, have been relatively little researched because every such process brings about structural changes in natural, multi-caved and recompressed materials in the hanging wall. The intensity of the coal extraction has direct impacts on the surrounding and distant mining areas. Extensive stress and deformation changes in the surrounding area, and in the mine, represent a safety hazard for the employees, since the supporting system in the mine roadway could collapse. Therefore, a controlled excavation of the coal, and a good understanding of the geomechanical properties of all the materials and processes involved, is extremely important for planning and managing economic production, while also ensuring safe mining operations. A numerical model that allows for in-depth analyses of the geomechanical processes that occur in the hanging wall, the footwall and in the coal seam during sub-level coal excavation, is broadly applicable and highly relevant for analysing the intensity and the level of the caving processes in sub-level coal mining, and for making realistic plans for coal excavation with workers’ safety in mind.
Ključne besede: coal mining, sub-level mining method, longwall coal mining method, carving processes, finite-difference method, FLAC, mathematical model
Objavljeno: 11.06.2018; Ogledov: 340; Prenosov: 61
.pdf Celotno besedilo (589,19 KB)
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The development of a “drive-in” filters dewatering system in the Velenje coal mine using finite-element modelling
Goran Vižintin, Miran Veselič, Andrej Bombač, Evgen Dervarič, Jakob Likar, Đorđe Vukelič, 2009, izvirni znanstveni članek

Opis: During the mining operations at the Velenje coal mine, groundwater has been presenting a constant threat to underground works. The hydrogeological setup is so complex that a lot of structural drilling and well-logging operations were needed in the past to clarify it. Above the lignite seam is a Pliocene and Pleisticene multilayer aquifer system, composed mainly of permeable sand layers and impermeable clay layers. In 1981 the Pliocene aquifers were divided into three packages. Based on the water-table data of each aquifer, pumping tests, chemical analyses of the groundwater and the geophysical properties the Pliocene aquifers directly above the seam, together with impermeable layers, were divided into: a) the first water-bearing sands (Pl1), b) the aquifers 2080 m above the coal seam (Pl2) and c) the upper Pliocene aquifers (Pl3). For the mining operations the most important aquifer of saturated sands is Pl1. The hydraulic pressure of the groundwater in these sands directly affects the safety of the mining. These aquifers are mostly affected by the dewatering activities, too. However, the dewatering wells are constructed in such a way as to capture the whole Pl2 and, somewhere, even a part of the Pl3 complex, too. The water pressure in this multilayer aquifer can reach over 35 bars, so a massive program of drawdown activities has been needed and is still in place to decrease the water table in the area related to the mining operations. Special, multilevel observation wells are used to monitor the water level. A number of 3D finite-difference models (FDMs) were used to estimate the regional groundwater drawdown. It was observed that the FDMs performed well when predicting the regional situation, but the model-predicted drawdown was lower than the observed values at observation points in the area where the dewatering operations using “drive-in” filters have taken place in the past. This is a well-known problem of the FDM: the drawdown being rather a function of the cell size than of the flow net. The risk of water inrushes will increase, especially after 2012 and 2017, when a series of surface-drilled wells, connected into the mine’s pumping-line batteries, will be abandoned due to excavation works and mining-subsidence effects. Consequently, the dewatering schemes had to be completely reviewed. The destroyed, first-order dewatering structures will have to be replaced by a series of “drive-in” filters, drilled from the mine roadways in the area of the planned longwall face operations. For the drive-in filter-system design the FDM does not seem to be appropriate. This is especially so if the error in the drawdown and pumping flow prediction is taken into account. That led, in 2007, to the selection of the finite-element method (FEM) for the prediction of the groundwater drawdown and the water pumping rates in the areas were the underground works will encounter the risk of a water inrush. Based on the FEM prediction the sizing and the layout pattern of the “drive-in” filters were made.
Ključne besede: drive-in filters, groundwater, mining water, mining hydrology, geophysical well login, mathematical modelling
Objavljeno: 06.06.2018; Ogledov: 298; Prenosov: 39
.pdf Celotno besedilo (605,68 KB)
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Optimization of the high safety pillars for the underground excavation of natural stone blocks
Jože Kortnik, 2009, izvirni znanstveni članek

Opis: For the first time in Slovenia, the underground excavation of natural stone blocks was introduced on a trial basis at the Hotavlje I colourful limestone quarry in 1993, and in 2002 also at the Lipica II quarry. This was primarily because of the geological structure of the site, the quarry’s condition, the potentially large amounts of the overburden in the event of an expansion of the surface part of the quarry, and the increasing needs for this raw material, i.e., natural stone. Underground The underground excavation of natural stone blocks is done using a modified room-and-pillar excavation method that is adjusted to each site’s characteristics, with regularly or irregularly distributed high safety pillars. Since the underground excavation of natural stone blocks is performed at a relatively shallow level under the surface, i.e., at a depth of only 10-40 m, the value of the primary vertical stress state is also relatively low (<1.0 MPa). This significantly increases the risk of wedge-shaped pieces or blocks falling out of the ceiling in open, underground spaces. In previous years, special attention was paid to the installation of stress-strain systems for controlling the planned dimensions (width and height) of large, open, underground spaces (rooms) and the dimensions of the high safety pillars, along with continual monitoring and identification of the instability phenomena in the ceiling and sides of the large open spaces (rooms). The paper presents the procedures for the planning, optimization and monitoring of high safety pillars for the underground excavation of natural stone blocks.
Ključne besede: natural stone, high safety pillars, room-and-pillar mining method, underground mining, quarry
Objavljeno: 06.06.2018; Ogledov: 295; Prenosov: 72
.pdf Celotno besedilo (557,08 KB)
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Monitoring and analyses of seismic events at the Velenje coal mine
Jakob Likar, Evgen Dervarič, Milan Medved, Janez Mayer, Goran Vižintin, 2008, izvirni znanstveni članek

Opis: Complaints about ground shaking and tremors were regularly addressed to the management of the Velenje Coal Mine. A micro-seismic monitoring system was set up on the surface in nearby urban areas and also directly in the vicinity of the mining activities. The results of these measurements were carefully analysed and presented to the public together with various safe-vibration-limit standards (in this case national standards). A system for automatically publishing measurements immediately after the event is recorded was also set up. This resulted in a dramatic reduction in the number of complaints. Routine micro-seismic monitoring became part of the regular monitoring of mining activities as some patterns of seismic response to mass mining were revealed.
Ključne besede: mining, rockbursts, seismicity, coal mine Velenje, longwall mining, caving, Slovenia, public response
Objavljeno: 05.06.2018; Ogledov: 316; Prenosov: 43
.pdf Celotno besedilo (368,38 KB)
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Non-linear finite-element modelling of room and pillar mine workings including the strain-softening behaviour of the rock mass
Salim Bensehamdi, Abdelbaki Seriani, 2008, izvirni znanstveni članek

Opis: A two-dimensional model adopting post-failure criteria was used to simulate the behaviour of the rock mass and the development of yield zones around room and pillar mine workings. The model conformed to the strain-softening behaviour of the rock mass and accounted for its post-failure residual strength. The structural-stability-analysis approach accounted for the main features of the mine structures’ yield produced during loading through changes in the rock material’s stiffness and the subsequent evolution of the stresses. A comprehensive parametric analysis was performed and the inevitable effect of the interaction of the roof, pillar and floor on the overall stability limit of the mine was investigated. The numerical results clearly showed that the finite-element linear models could not realistically represent the true behaviour of the mine structure. However, they clearly demonstrated the limitations of the finite-element linear solutions in representing the true behaviour of the mine structure, particularly when the rock-mass structure is relatively weak, and that a non-linear approach was justified.
Ključne besede: non-linear FE analysis, yielding, plastic zones, room and pillar mining, residual strength, stability assessment
Objavljeno: 05.06.2018; Ogledov: 309; Prenosov: 37
.pdf Celotno besedilo (651,93 KB)
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Small scale gold mining effects on the miners and local communities in semi-arid region of Ethiopia
Hailemariam Meaza, Mushir Ali, Solomon Hishe, Zbelo Tesfamariam, 2015, izvirni znanstveni članek

Opis: North Ethiopian highlands are traditionally known for gold mining which has been means of livelihood of the rural community. The present work was conducted to investigate socio- economic conditions of gold miners, ways of obtaining the gold, their earning and negative consequences of the gold mining. On the basis of random sampling, 140 miners were interviewed. Moreover, focus group discussions transect walks and practical observations across the mining sites were made with team leaders on different issues of gold mining and its effects. Descriptive statistics was used to compute socio-economic characteristics, gold harvesting, and income dynamics. ANOVA was run to observe variations of income from gold mining and other sources, 2009 to 2012. The positive effects of gold mining for involved people were regarding income, employment, expenditure on education, health and food consumption. On the other hand, conflicting interest, communicable diseases, aggressive child labour, school dropouts, social disruptions and injuries were challenges of the small scale gold mining. The findings highlight that the income generated from small scale gold mining plays a pivotal role in reducing rural poverty. Therefore, providing integrated training for gold miners can mitigate the challenges of small scale gold mining and thereby to improve livelihoods of the small scale gold miners in Ethiopia.
Ključne besede: gold mining, indigenous methods, highlands, society, transaction, Ethiopia
Objavljeno: 16.04.2018; Ogledov: 406; Prenosov: 59
.pdf Celotno besedilo (468,79 KB)
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Farms and mines: a conflicting or complimentary land use dilemma in western Australia?
Fiona Haslam McKenzie, 2009, pregledni znanstveni članek

Opis: The Western Australian economy has always been underpinned by farming and mining. Over the last five years the economy has experienced phenomenal growth due to unprecedented global demand for resources and increasingly, agricultural land is being given up for mining. Changing land uses challenge industry and community leaders; some communities are overwhelmed by a new population connected with mining, bringing with it a range of social and economic tensions that small communities struggle to cope with. This paper will discuss the conflicting issues regarding land use planning, local and environmental governance and sense of place while also canvassing positive developments that have enhanced community and regional economic development, thus building a resilient future.
Ključne besede: regional economic development, mining and energy sector, agricultural production, Australia
Objavljeno: 26.03.2018; Ogledov: 341; Prenosov: 68
.pdf Celotno besedilo (173,34 KB)
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State aid for the coal sector in the European Union
Piotr Podsiadło, 2015, izvirni znanstveni članek

Opis: This article presents the evolution of the conditions of state aid admissibility to the coal industry, starting with legal regulations within the European Coal and Steel Community, the European Community, and now the European Union. The thesis was formulated that, in connection with the expiry on 31 December 2010 of Council regulation No. 1407/2002, on the basis of which the European Commission allowed aid for the national mining industry in different member states in the period before the onset of the financial and economic crisis, the immediate cause of introduction of the next regulation for mining state aid in the form of Council Decision 2010/787/EU on state aid to facilitate the closure of uncompetitive coal mines was the increasing intensity of the aid for the mining industry in recent years.
Ključne besede: financial and economic crisis, state aid, coal mining sector, legal regulations, the European Union
Objavljeno: 14.11.2017; Ogledov: 535; Prenosov: 87
.pdf Celotno besedilo (297,71 KB)
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Link prediction on Twitter
Sanda Martinčić-Ipšić, Edvin Močibob, Matjaž Perc, 2017, izvirni znanstveni članek

Opis: With over 300 million active users, Twitter is among the largest online news and social networking services in existence today. Open access to information on Twitter makes it a valuable source of data for research on social interactions, sentiment analysis, content diffusion, link prediction, and the dynamics behind human collective behaviour in general. Here we use Twitter data to construct co-occurrence language networks based on hashtags and based on all the words in tweets, and we use these networks to study link prediction by means of different methods and evaluation metrics. In addition to using five known methods, we propose two effective weighted similarity measures, and we compare the obtained outcomes in dependence on the selected semantic context of topics on Twitter. We find that hashtag networks yield to a large degree equal results as all-word networks, thus supporting the claim that hashtags alone robustly capture the semantic context of tweets, and as such are useful and suitable for studying the content and categorization. We also introduce ranking diagrams as an efficient tool for the comparison of the performance of different link prediction algorithms across multiple datasets. Our research indicates that successful link prediction algorithms work well in correctly foretelling highly probable links even if the information about a network structure is incomplete, and they do so even if the semantic context is rationalized to hashtags.
Ključne besede: link prediction, data mining, Twitter, network analysis
Objavljeno: 15.09.2017; Ogledov: 711; Prenosov: 75
.pdf Celotno besedilo (6,98 MB)
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