1. A three-dimensional static numerical model of a complex underground structure in high squeezing groundTina Marolt Čebašek, Jakob Likar, 2015, original scientific article Abstract: The present study assesses high squeezing ground confirmed by empirical and semi-empirical theories. High squeezing ground is often present in underground constructions at great depths, but it is hardly ever researched separately from light and fair squeezing ground. A three-dimensional, static numerical model is developed for a complex underground structure consisting of a shaft, a silo, and a mine roadway at great depth, which is certainly in high squeezing ground. Furthermore, a solution for the entire structure based on shotcrete with incorporated yielding elements is provided. The yielding elements, in general, absorb the strain energy by compressing at a relatively constant stress, but without rebounding. A three-dimensional, static numerical model of a support system with incorporated yielding elements is established in order to demonstrate that the presented forces are under control. Therefore, a failure of the lining is avoided because the stresses in the shotcrete lining are below its load-bearing capacity. It can be concluded that yielding elements incorporated in the shotcrete lining play an important role in the support solution in high squeezing ground.
Keywords: high squeezing ground, numerical model, underground structures, deformations, yielding support element
Published in DKUM: 14.06.2018; Views: 1246; Downloads: 218
 Full text (606,20 KB)
This document has many files! More... |
2. An analysis of the geomechanical processes in coal mining using the Velenje mining methodGregor Jeromel, Milan Medved, Jakob Likar, 2010, original scientific article Abstract: 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.
Keywords: coal mining, sub-level mining method, longwall coal mining method, carving processes, finite-difference method, FLAC, mathematical model
Published in DKUM: 11.06.2018; Views: 1117; Downloads: 96
Full text (589,19 KB)
This document has many files! More... |
3. The development of a “drive-in” filters dewatering system in the Velenje coal mine using finite-element modellingGoran Vižintin, Miran Veselič, Andrej Bombač, Evgen Dervarič, Jakob Likar, Đorđe Vukelič, 2009, original scientific article Abstract: 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 2080 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.
Keywords: drive-in filters, groundwater, mining water, mining hydrology, geophysical well login, mathematical modelling
Published in DKUM: 06.06.2018; Views: 1578; Downloads: 203
Full text (605,68 KB)
This document has many files! More... |
4. Monitoring and analyses of seismic events at the Velenje coal mineJakob Likar, Evgen Dervarič, Milan Medved, Janez Mayer, Goran Vižintin, 2008, original scientific article Abstract: 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.
Keywords: mining, rockbursts, seismicity, coal mine Velenje, longwall mining, caving, Slovenia, public response
Published in DKUM: 05.06.2018; Views: 1163; Downloads: 60
Full text (368,38 KB)
This document has many files! More... |
5. Development of a conceptual material model for structured materials - S_BRICKVladimir Vukadin, Jakob Likar, Vojkan Jovičić, 2005, original scientific article Abstract: Materials known in literature as Soft Rocks & Hard Soils such as claystones, siltstones, flysh, hard soils, marls, etc. received a lot of attention in research community in recent years. It was demonstrated that some of these materials can be described through general theoretical framework (Cotecchia & Chandler [1]), which takes into account the structure as an intrinsic material property that is present in all natural geological materials. The influence of the structure is manifested as an increase in strength and stiffness in a material. Based on a laboratory results and existent theoretical frameworks, a further step was taken with the development of a conceptual constitutive model for structured materials. A model formulated in strain space named BRICK (Simpson [2]) was chosen as a base model and was further developed with the inclusion of structure and destructuring. The new model was named S_BRICK and was tested on a conceptual level where the results of numerical tests on structured and structure less (reconstituted) materials at different stress paths were compared. The results showed that S_BRICK was able to capture stress-strain behavior typical for structured material and could be potentially used for the modeling of Soft Rocks and Hard Soils.
Keywords: geomechanics, soft rocks, hard soils, constitutive material models, structure, destructuring, numerical modeling
Published in DKUM: 15.05.2018; Views: 1438; Downloads: 166
Full text (586,91 KB)
This document has many files! More... |
6. Back analysis of time-dependet displacement at the Trojane tunnel constructionJakob Likar, 2004, original scientific article Abstract: The 2,900-metre double tube tunnel of Trojane forms part of the highway section between Celje and Ljubljana and part of the highway road system connecting Lendava and Koper with adjacent roads. The construction of this section, which is of special importance for the Republic Slovenia, has been going on for almost ten years.
The highway near Trojane where the tunnel is located, lies on a hilly terrain composed of Permian-carboniferous rocks, which are tectonically badly damaged in some places and marked with broad fault zones, containing tectonically remoulded soil of low strength in terms of deformability properties. Even though the amount of waters coming from the hills during the excavation of the tunnel was relatively small, this water, in combination with extremely damaged weak rock caused the increase of deformations at the construction site.
Geological and geotechnical surveying with geometric monitoring and the analyses of stress and deformation changes in the surrounding rocks and support elements were critical in assessing the actual weak-rock conditions during the course of construction. Since the analyses of deformation processes, which had been modelled with PLAXIS 3D TUNNEL PROGRAM, showed great impact on permanent stability of the tunnel, special care was paid to rheological changes in the surrounding rocks and combined in-built support elements.
3D back analyses with SOFT-SOIL-CREEP (SSC) constitutive model, which takes into account rheological phenomena, were carried out. The calculations of primary and secondary stresses and deformations were made for two characteristic areas and determined on the basis of realistic geological mapping during tunnel construction. The first area represented typical rocks of the Trojane tunnel, i.e. shales and siltstone, while the second one was a tectonic zone where geological and geotechnical conditions during excavation were less favourable. The results of back analyses used provided an acceptable possibility for estimating the stress-strain variation during construction as well as an appropriate basis for analysing vertical displacements at the tunnel roof. The calculation results show good correlation with field measurements.
Keywords: tunnels, construction, permain-carboniferous rocks, geological-geotechnical conditions, tunnel support, Trojane tunnel, finite element method, costitutive models, back analyses, field mesurement, time dependent analysis
Published in DKUM: 15.05.2018; Views: 1332; Downloads: 71
Full text (868,88 KB)
This document has many files! More... |
