91. A coupled thermo-hydro-mechanical model of expansive clays subjected to heating and hydratationNadia Laredj, Hanifi Missoum, Karim Bendani, Mustapha Maliki, 2011, izvirni znanstveni članek Opis: The focus of this work is to provide a numerical formulation for coupled thermo-hydro-mechanical processes in unsaturated expansive clays, especially in compacted bentonite, with a multiphase fluid flow. The model is characterized by the presence of a deformable solid matrix filled with two fluid phases (liquid water and air). In the proposed model, both pore-water and air transfers are assumed to be governed by the generalized Darcy’s law. Fully coupled, nonlinear partial differential equations are established and then solved by using a Galerkin weighted residual approach in the space domain and an implicit integrating scheme in the time domain. The model has been validated against an experimental test from the literature, which involves bentonite under laboratory conditions. The calculated relative errors between the experimental and numerical results are 3% for the temperature and 7% for the stresses. Consequently, the developed numerical model predicts satisfactory results, when compared to the experimental test measures. The model is applicable to two-dimensional problems with various initial and boundary conditions; non linear soil parameters can be easily included in this model. Ključne besede: thermo-hydro-mechanical process, unsaturated bentonite, finite element, numerical modelling, expansive clays Objavljeno: 13.06.2018; Ogledov: 18; Prenosov: 3 Celotno besedilo (389,48 KB) |
92. Detecting karstic zones during highway construction using ground-penetrating radarMatevž Uroš Pavlič, Blaž Praznik, 2011, izvirni znanstveni članek Opis: Ground-penetrating radar (GPR) has been applied to determine the subsurface karstic features during the construction of the national highway in the south-eastern part of Slovenia. The highway construction is situated mostly in the dinaric karstic region with a high density of karstic features visible on the surface. Ground-penetrating radar prospecting was done in all areas where a slope was cut into the limestone bedrock. The main purpose of the survey was to map potentially hazardous zones in the highway subsurface and to detect and characterize the karst. The ground-penetrating radar method was used because of the heterogeneous nature of the karst. With its high degree of karsticifaction and geological diversity all conventional methods failed. One of GPR’s main advantages is that, while the penetration depth is limited to several meters, the obtained resolution can be on the scale of centimeters and the measured profile is continuous. Because of the ground-penetrating radar’s limitations with respect to depth, the range surveying was done simultaneously with the road construction using 200-MHz bistatic antenna on the level of the highway plane. All the 2D radargrams were constructed in 3D models where the measurements were made in raster with 2 meters between a single GPR profile. This two-meters spacing was determined as the optimal value in which only a minimal resolution-price tradeoff was made. The gathered results were tested and compared to experimental drillings and excavations so that any anomalies and reflections were calibrated.
The drilling was conducted twice, first to calibrate the radargram reflections and secondly to check and confirm the calibration success. Altogether, over 30 boreholes were drilled at various previously selected locations. The data obtained from the drilling proved to be very helpful with the calibration since anomalies found during the drilling were almost exclusively (over 95%) a result of the propagation of radar waves from the limestone to an air void or from the limestone to a clay pocket.
Drilling test boreholes proved to be a very useful tool for the calibration of the GPR anomalies recorded in 2D radargrams. Such a process showed a near 100 % accuracy with respect to interpreting the subsurface features, with 77% correctly interpreted as caves or clay pockets and 23% wrongly interpreted, where the interpretation was a void but it was indeed partly a clay-filled and partly an air-filled void. The completed survey also showed simultaneous surveying with GPR and road construction is a very efficient and economical way to predict various karstic features and the density of the karstic forms. Ključne besede: karst, ground-penetrating radar, geotechnics, cavities, detection Objavljeno: 13.06.2018; Ogledov: 14; Prenosov: 4 Celotno besedilo (756,55 KB) |
93. The behaviour of a two-componenet back-filling grout used in a tunnel-boring machineDaniele Peila, Luca Borio, Sebastiano Pelizza, 2011, izvirni znanstveni članek Opis: The instantaneous filling of the annulus that is created behind the segment lining at the end of the tail during the TBM advance is an operation of paramount importance. Its main goal is to minimize the surface settlements due to any over-excavation generated by the passage of the TBM. To correctly achieve the goals, a simultaneous back-filling system and the injected material should satisfy the technical, operational and performance characteristics. A two-component system injection for the back-filling is progressively substituting the use of traditional mortars. In this paper different systems of back-filling grout and in particular the two-component system are analyzed and the results of laboratory tests are presented and discussed. Ključne besede: tunneling, mechanized tunneling, segment lining, settlements, back-fill grouting Objavljeno: 13.06.2018; Ogledov: 10; Prenosov: 2 Celotno besedilo (251,43 KB) |
94. Load transfer and stress in a piled gravity retaining wallQun Chen, Li Wan, Changrong He, Zihui Lai, 2010, izvirni znanstveni članek Opis: The piled retaining wall is a new type of railway retaining structure in China. In the current design, the retaining wall, the beam and the piles are assumed to be independent components. Both the mutual action of the retaining wall, the piles and beam, and the influence of the soil or rock foundation on the structure are not fully considered, so that there are some limitations in the current design method. In this paper, using field observations and a three-dimensional finite-element analysis, the lateral earth pressure on the wall back, the stress distributions and the forces of the reinforcements in the beam and the pile were studied. The simulation results were in good agreement with the field observation data. These results revealed that the tensile stresses were very small and that these stresses were positive in most zones in the beam and the pile. It can also be observed that the tensile stresses or forces in the beam and pile obtained in this study were much smaller than those obtained using the current design method. This clarified the fact that the current design method used for the beam and the pile was very conservative and that it should be optimized to consider the effect of the foundation on the whole structure and the interactions among the different components. Ključne besede: piled gravity retaining wall, field observation, finite-element analysis, stress, load transfer mechanism Objavljeno: 11.06.2018; Ogledov: 14; Prenosov: 2 Celotno besedilo (558,92 KB) |
95. How to test the reliability of instruments used in mirotremor horizontal-to-vertical spectral ratio measurementsIzidor Tasič, Franc Runovc, 2010, izvirni znanstveni članek Opis: The reliability of a horizontal-to-vertical spectral ratio (HVSR) curve depends on the results obtained by a verified seismological system. Seismic microzonation provides the basis for a site-specific risk analysis and it can be evaluated using the microtremor HVSR method, where the data are recorded using modern seismological systems. Changes in the transfer function of seismological systems affect the HVSR curve and, consequently, also its interpretation, if these changes are not detected and taken into consideration while performing the microtremor spectral calculations. The reliability of the seismic microzonation performed by such a procedure becomes questionable. An algorithm is developed with a two references system, where the influence of the transfer function on the HVSR curve by the tested system can be evaluated without any a-priori knowledge regarding the transfer functions of any of the systems. This approach is applied to a Lennartz Le-3D/5s seismometer and to a TROMINO seismological system, where two Streckeisen STS2 seismometers are used as the reference systems. Ključne besede: seismic microzonation, horizontal-to-vertical spectral ratio method, ambient vibrations, microtremor, seismic system transfer function, reliability and calibration of seismic systems Objavljeno: 11.06.2018; Ogledov: 16; Prenosov: 3 Celotno besedilo (201,91 KB) |
96. Effect of the initial structure on the behaviour of Chlef sandNoureddine Della, Ahmed Arab, Mostefa Belkhatir, Hanifi Missoum, Claude Bacconnet, Daniel Boissier, 2010, izvirni znanstveni članek Opis: It has been known for many years that initial structure, plays an important part in the results of laboratory testing of natural of silty sands. For this purpose, a series of monotonic undrained triaxial compression tests were carried out on samples composed of Chlef sand with 0.5% non-plastic silt content using two depositional methods (dry funnel pluviation and wet deposition) at different initial relative density (RD= 29%, 50% and 80%). All specimens were subjected to isotropic consolidation of 50 kPa, 100 kPa and 200 kPa. It was found that the initial structure of the soil influences considerably the undrained shear response in terms of maximal deviatoric stress, peak strength and excess pore water pressure. Ključne besede: liquefaction, sand, dry funnel pluviation, wet deposition, density, deviatoric stress, pore pressure Objavljeno: 11.06.2018; Ogledov: 15; Prenosov: 3 Celotno besedilo (2,50 MB) |
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98. Determination of Vs30 for seismic ground classification in the Ljubljana area, SloveniaJanez Rošer, Andrej Gosar, 2010, izvirni znanstveni članek Opis: The shear modulus, known as Gmax, is a key parameter for predicting the static and dynamic behavior of soils. Its value decreases by increasing the shear strain. This is because of reducing the soil’s stiffness as a result of increasing the shear deformation. The increasing of the shear modulus by increasing the shear strain is affected by some of the soil properties, such as the Void ratio (e), the Over consolidated ratio (OCR), the Normal stress (σ), the Plasticity index (PI), the Water content (ω%), the Shear strain rate, the Soil structure, and the Loading history, etc. In this paper, undrained, direct shear tests were conducted to study the effect of the plasticity index (PI) and the normal stress (σ) on the shear behavior and the shear modulus of remolded clays. The results show that the normalized shear modulus at a constant strain will generally increase as the σ and PI increase, and the common empirical equations for undisturbed soils at γ = 0~0.1 might be applicable for the disturbed soils too. Ključne besede: microtremor survey methods, shear-wave velocity, seismic site effect, microzonation, Eurocode 8 Objavljeno: 11.06.2018; Ogledov: 11; Prenosov: 2 Celotno besedilo (1,07 MB) |
99. Effect of plasticity and normal stress on the undrained shear modulus of clayey soilsMehrab Jesmani, Hamed Faghihi Kashani, Mehrad Kamalzare, 2010, izvirni znanstveni članek Opis: The shear modulus, known as Gmax, is a key parameter for predicting the static and dynamic behavior of soils. Its value decreases by increasing the shear strain. This is because of reducing the soil’s stiffness as a result of increasing the shear deformation. The increasing of the shear modulus by increasing the shear strain is affected by some of the soil properties, such as the Void ratio (e), the Over consolidated ratio (OCR), the Normal stress (σ), the Plasticity index (PI), the Water content (ω%), the Shear strain rate, the Soil structure, and the Loading history, etc. In this paper, undrained, direct shear tests were conducted to study the effect of the plasticity index (PI) and the normal stress (σ) on the shear behavior and the shear modulus of remolded clays. The results show that the normalized shear modulus at a constant strain will generally increase as the σ and PI increase, and the common empirical equations for undisturbed soils at γ = 0~0.1 might be applicable for the disturbed soils too. Ključne besede: plasticity index, normal stress, shear modulus, disturbed clayey soils Objavljeno: 11.06.2018; Ogledov: 24; Prenosov: 3 Celotno besedilo (703,46 KB) |
100. An analysis of the geomechanical processes in coal mining using the Velenje mining methodGregor 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: 12; Prenosov: 5 Celotno besedilo (589,19 KB) |