51. Influence of the virtual strain rate of noncohesive granular media on the discrete element methodKiichi Suzuki, 2015, izvirni znanstveni članek Opis: The discrete element method (DEM) is an alternative computational tool for augmenting laboratory experiments because of its advantages in detailing macro- and micro-mechanical information. However, it should be noted that the DEM does not usually consider the convergence for each time step, because of the necessity for a huge calculation time. In that case, it indicates that the uniqueness of the solution is not guaranteed, except in the case of a very small strain rate, even though the behavior looks qualitatively reasonable. At first, the influence of strain rate among numerically imaginary input parameters for a non-cohesive material was investigated for monotonic, biaxial shear tests. Then, new findings were obtained from the DEM simulations. Strain rate has a significant influence on the shear behavior, especially after the peak strength of dense specimens. A quasi-static steady state exists, not a static steady state. The “strong” fabric ratio is closely related to the stress ratio. The maximum slip coordination number occurs around the phase-transformation ratio and the shear band appears around the peak strength. Ključne besede: discrete element method, DEM, induced anisotropy, quasi-static steady state, strain rate, uniqueness Objavljeno: 14.06.2018; Ogledov: 41; Prenosov: 3 Celotno besedilo (690,97 KB) |
52. A three-dimensional static numerical model of a complex underground structure in high squeezing groundTina Marolt Čebašek, Jakob Likar, 2015, izvirni znanstveni članek Opis: 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. Ključne besede: high squeezing ground, numerical model, underground structures, deformations, yielding support element Objavljeno: 14.06.2018; Ogledov: 77; Prenosov: 4 Celotno besedilo (606,20 KB) |
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54. Design optimization for symmetrical gravity retaining wallsErol Sadoğlu, 2014, izvirni znanstveni članek Opis: The optimization for symmetrical gravity retaining walls of different heights is examined in this study. For this purpose, an optimization problem of continuous functions is developed. The continuous functions are the objective function defined as the cross-sectional area of the wall and the constraint functions derived from external stability and internal stability verifications. The verifications are listed as the overturning, the forward sliding, the bearing capacity, the shears in the stem and the bendings in the stem. The heights of the walls are selected as 2.0, 3.0, and 4.0 m in order to investigate the outline of the optimum cross-section and the effect of the wall height on the outline. Additionally, the physical and mechanical properties of the soil are kept constant in order to compare only the effect of the height on the geometry. The upper and lower bounds of the solution space are specified to be as wide as possible and the minimum dimensions suggested for the gravity retaining walls are not taken into account. A common feature of the optimum cross-sections of walls with different heights is to have a very wide lower part like a wall foundation and a slender stem. However, other than the forward sliding constraint, the bending constraints are active at the optimum values of the variables. Ključne besede: gravity retaining wall, nonlinear optimization, continuous variables, interior point method Objavljeno: 14.06.2018; Ogledov: 58; Prenosov: 11 Celotno besedilo (168,77 KB) |
55. Estimating piping potential in earth dams and levees using generalized neural networksXinhua Xue, Xingguo Yang, Xin Chen, 2014, izvirni znanstveni članek Opis: Internal erosion and piping in embankments and their foundations is the main cause of failures and accidents to embankment dams. To estimate the risks of dam failure phenomenon, it is necessary to understand this phenomenon and to develop scientifically derived analytical models that are simpler, easier to implement, and more accurate than traditional methods for evaluation of piping potential. In this study, a generalized regression neural network (GRNN) technique has been applied for the assessment of piping potential, as well, due to its ability to fit complex nonlinear models. The performance of GRNN has been cross validated using the k-fold cross validation method technique. The GRNN model is found to have very good predictive ability and is expected to be very reliable for evaluation of piping potential. Ključne besede: piping, generalized neural network, cross validation, BP neural network Objavljeno: 14.06.2018; Ogledov: 46; Prenosov: 8 Celotno besedilo (463,20 KB) |
56. Experimental research on variation of pore water pressure in constant rate of strain consolidation testHojjat Ahmadi, Hassan Rahimi, Abbas Soroush, Claes Alén, 2014, izvirni znanstveni članek Opis: Constant rate of strain (CRS) consolidation is a rapid test method which is used for determination of compressibility of clayey soils. In a CRS test, the appropriate strain rate is selected based on pore water pressure ratio, i.e. the ratio of pore pressure to total stress. In the present study, to investigate the effect of strain rate on variation of pore water pressure ratio, four different clay samples of different plasticity were tested by CRS apparatus. The results of the experiments showed that the trend of variation of pore water pressure is dependent on the drained water flow regime which may be either Darcy or non-Darcy. The results also indicated that the plasticity of clay does not have considerable effect on variation of pore water pressure. Ključne besede: constant rate of strain, consolidation, pore water pressure ratio, soil plasticity, Darcy and non-Darcy flow Objavljeno: 14.06.2018; Ogledov: 65; Prenosov: 4 Celotno besedilo (576,58 KB) |
57. Correlation between the point load index, $I_{s(50)}$, and the resistance to unconfined compression in limestone from the comunidad Valenciana, SpainManolo Galván, Jorge Preciado, Jose Serón, 2014, izvirni znanstveni članek Opis: The unconfined compression strength is one of the most important engineering parameters in rock mechanics; it is used to characterize and study the behaviour of solid rocks. A good correlation between the unconfined compression strength test (UCS) and the point load strength (PLS) can be very useful, because it allows for faster and cheaper testing than other methods with the same security to calculate the structures and performances of solid rocks. A preliminary step to implement the correlation is to have a good method to determine the resistance to a point load. This determination is correct if we have a sufficient number of tests on specimens of the same nature, but usually this does not occur, and it is necessary to apply a size-correction factor, F = (De/50)α, with α = 0.45. This paper is based on limestone from Comunidad Valenciana, Spain, because it represents a very high percentage of the rocks. The implementation was conducted over 700 field and laboratory tests, of which 255 are PLT tests, 45 are UCS tests, and the rest are other parameters, like porosity and specific weight, Slake Durability, and ultrasonic velocity. Ključne besede: resistance to point load, point load strength, Franklin test, size correction factor, unconfined compression Objavljeno: 14.06.2018; Ogledov: 58; Prenosov: 4 Celotno besedilo (398,58 KB) |
58. Determination of the fabric alteration of marine claysSuchit Gumaste, 2014, izvirni znanstveni članek Opis: This paper presents details of investigations that were conducted to determine the fabric (i.e., the arrangement of soil grains and pores) of undisturbed marine clay samples that were retrieved from 5 m to 65 m below the seabed. Impedance Spectroscopy (IS), which is a non-destructive and non-invasive technique, was employed to determine the electrical conductivities of the marine clay samples in their longitudinal and transverse planes of sedimentation. These results were employed to define the extent of the fabric anisotropy in terms of an anisotropy coefficient, Ae, as a function of depth. In addition, Scanning Electron Microscopy (SEM) and Mercury Intrusion Porosimetry (MIP) were employed to study the fabric and pore-size distribution of these samples, respectively. Based on these investigations it has been observed that Ae increases with sampling depth, which is indicative of the alteration from flocculated fabric, at shallower depths, to the dispersed fabric, at deeper depths. The study highlights the importance and usefulness of the anisotropy coefficient, Ae, for determining the alteration in the fabric of marine clays, due to self-weight consolidation. Ključne besede: marine clays, anisotropy, laboratory tests Objavljeno: 14.06.2018; Ogledov: 55; Prenosov: 8 Celotno besedilo (399,08 KB) |
59. Numerical simulation of the pile integrity test on defected pilesMladen Ćosić, Boris Folić, Radomir Folić, 2014, izvirni znanstveni članek Opis: This paper deals with the development of a discrete numerical 2D and 3D solid pile model with a discontinuity and defects to simulate non-destructive testing using the pile integrity test (PIT). The pile discontinuity and defects were modelled by reducing the specific finite elements and the elastic modulus of concrete. The wave-propagation response of the pile was analyzed based on a step-by-step numerical integration using the Hilber-Hughes-Taylor (HHT) method in the time domain. The concept of a system-response analysis was originally formulated based on the integration of individual reflectograms into a reflectogram surface, which is generated in a 3D cylindrical coordinate system. The use of reflectogram surfaces enables an understanding of wave propagation based on their velocity to a higher level than is usually the case with standard, one-dimensional reflectograms. Changes in the velocity responses on the reflectogram, shifting from a positive to a negative value, point to the locations of discontinuities and defects in the discrete 3D pile model, and there is a clear difference in the reflectograms, depending on the position of the measuring point. The study defines the typological models of the reflectogram: without discontinuities and defects, pile-head defect, defect in the middle of the pile length or a reduced modulus of elasticity in the middle of the pile length, pile-base defect or reduced modulus of elasticity in the pile-base zone and reduced modulus of elasticity in the pile-head zone. Ključne besede: reflectogram surface, numerical pile model, solid finite elements Objavljeno: 14.06.2018; Ogledov: 51; Prenosov: 5 Celotno besedilo (769,91 KB) |
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