31. The dry fraction of unsaturated soilsJulio César Leal Vaca, Gustavo Gallegos Fonseca, Eduardo Rojas González, 2015, izvirni znanstveni članek Opis: An equation to account for the shear strength of unsaturated soils is proposed in this paper. This equation is defined as the equivalent stress, and is an extension of Murray’s equation. This approach applies to the general case of bi-modal structured soils showing a macrostructure and microstructure. The theoretical development considers the existence of a dry fraction in addition to the saturated and unsaturated fractions of the soil. These different fractions are included in a porous model, which allows an evaluation of the parameters of the equivalent stress equation. Finally, the paper includes a comparison between theoretical and experimental results. The comparison shows that the proposed equation can be used to estimate the shear strength of unsaturated soils. Ključne besede: unsaturated soil, shear strength, equivalent stress, water retention curve Objavljeno: 15.06.2018; Ogledov: 117; Prenosov: 3 Celotno besedilo (183,91 KB) |
32. Reinforced piled embankment for a high-speed railway over soft soilYan Zhuang, Xiaoyan Cui, 2015, izvirni znanstveni članek Opis: A geosynthetic, reinforced, piled embankment is an effective and economic method to solve the problems of possible bearing failure, unacceptable settlement and slope instability for an embankment built over soft soil; this has led to its widespread use, especially for high-speed railway embankments. Some design methods have been developed to assess the performance of these reinforced structures, which are mainly based on the results from small-scale models and numerical simulations. However, the reliability of these methods needs to be validated under full-scale field tests. This paper presents a numerical and analytical study for a full-scale field test of the Fengyang high-speed railway embankment. The results were analyzed and discussed in terms of the settlement of subsoil, the stressconcentration ratio (SCR), the axial force and the frictional stress of the pile. They showed that the settlement of the subsoil, from both the finite-element method (FEM) and the analytical method, were in good agreement with the measurement, and thus was a reliable parameter to assess the performance of the piled embankment with reasonable accuracy. The SCR was overestimated by the modified Terzaghi method, with a difference of 25%, while it was underestimated by the FEM, with a difference of approximately 20%. It was also shown that the tensile force in the reinforcement could be effectively assessed using the proposed analytical method, while it was overestimated by the FEM with a difference of 44%. Ključne besede: reinforced piled embankment, high-speed railway, numerical simulation, analytical method Objavljeno: 15.06.2018; Ogledov: 69; Prenosov: 2 Celotno besedilo (578,98 KB) |
33. Numerical modeling of the negative skin friction on single vertical and batter pileMohammad Mahdi Hajitaheri Ha, Mahmoud Hassanlourad, 2015, izvirni znanstveni članek Opis: In this paper the negative skin friction on single vertical and batter piles is investigated. First, a finite-element model (using ABAQUS software) based on the studies Lee et al. and Comodromos and Bareka was developed. After that, the results of the model were compared and validated. Then a single vertical end bearing and a single skin friction pile under different earth-surface loadings were analyzed and the down-drag force as well as the neutral plane location were studied. Subsequently, the performances of the single end bearing and the friction pile, with different inclination angles between 0 and 30º, were analyzed.
Moreover, the sensitivity analysis was implemented using 2-D models. This showed a satisfactory compatibility with the results of the study of Lee et al. and Comodromos and Bareka. Finally, it was concluded that the drag load of the pile and the neutral plane position depend on the condition of the soil surrounding the pile, the 2D or 3D model type , the earth-surface loading intensity, the type of end-bearing pile or friction pile and the pile’s inclination angle. The simulation results agree well with the experimental findings. Ključne besede: negative skin friction, batter pile, down-drag force, neutral plane Objavljeno: 15.06.2018; Ogledov: 70; Prenosov: 4 Celotno besedilo (341,89 KB) |
34. A new method for testing the anti-permeability strength of clay failure under a high water pressureFu-wei Jiang, Ming-tang Lei, Xiao-zhen Jiang, 2015, izvirni znanstveni članek Opis: It is difficult to judge the failure of clay seepage under a high water pressure.This paper presents a new method to assess clay failure based on the anti-permeability strength, which is the critical water pressure to destroy the clay. An experiment is designed to test the value that avoids the problem of the time-consuming, traditional method to test clay seepage deformation. The experimental system and the process of testing are introduced in this paper. With a self-designed experimental system and method, 18 groups of sample were tested. The results show that the clay thickness and the seepage paths influence the anti-permeability strength. It also indicates that water infiltrates into the clay under the condition that its pressure exceeds a minimum value (P0). Ključne besede: clay failure, seepage deformation, anti-permeability strength, high water pressure Objavljeno: 15.06.2018; Ogledov: 80; Prenosov: 2 Celotno besedilo (249,24 KB) |
35. A stability assessment of coastal cliffs using digital imageryIgor Ružić, Čedomir Benac, Ivan Marović, Suzana Ilić, 2015, izvirni znanstveni članek Opis: The investigated area around the Stara Baška settlement (the island of Krk, NE channel part of the Adriatic Sea) is in a delicate geodynamic balance. Marine erosion is quite prominent and the recorded cliff retreat between 1966 and 2004 was from 4 to 5 metres. The cliff slopes are formed in talus breccias. Strong waves and formations of wave-cut notches are the main causes of the cliff’s instability. The secondary causes are the weathering and erosion of the soil and rocks on the cliff. The slump of the cliff slope can occur in a rock mass with higher strength parameters, where the notches are cut a few metres inward into the toe of the cliff slope. A combined method for the stability analysis of the coastal cliffs was tested; this incorporates the cantilever-beam model and the structure-from-motion (SfM) photogrammetry. This method can provide highly detailed 3D geometrical data of the cliff, which can then be used in the calculations of the stability model. This is particularly important in a stability analysis of lithologically heterogeneous rocks such as breccias with varied geometry, which cannot be easily replaced by a rectangular surface. The simple and useful SfM method overcomes the limitations of traditional surveys in estimating the cliff overhang surface and the notch length. Ključne besede: marine erosion, cliff stability, SfM photogrammetry, Krk island, Adriatic sea Objavljeno: 15.06.2018; Ogledov: 69; Prenosov: 4 Celotno besedilo (865,75 KB) |
36. Numerical simulation of intact rock behaviour via the continuum and Voronoi tesselletion modelsTeja Fabjan, Diego Mas Ivars, Vladimir Vukadin, 2015, izvirni znanstveni članek Opis: The numerical simulation of intact rock microstructure and its influence on macro-scale behaviour has received a lot of attention in the research community in recent years. Generating a grain-like structure with polygonal area contacts is one of the avenues explored for describing the rock’s microstructure. A Voronoi tessellation implemented in the Universal Distinct-Element Code (UDEC) is used to generate models with a polygonal microstructure that represent intact rock. The mechanical behaviour of the Voronoi polygons is defined by micro-properties, which cannot be measured directly in the laboratory. A numerical calibration procedure is needed to produce the macroscopic response of a model that corresponds to the material behaviour measured during a laboratory experiment. In this research, Brazilian, direct tensile, uniaxial compressive and biaxial test models are constructed to simulate the intact rock behaviour under a standard laboratory stress. An extensive series of parametric sensitivity analyses are executed in order to understand the influence of the input micro-properties on every model test behaviour and predict the relation between the micro-properties and the model’s macro response. The results can be treated as general guidelines for a complete and efficient intact rock calibration procedure. In parallel, a continuum-based model using the Mohr-Coulomb constitutive relationship is running as a benchmark. It has been shown that the Voronoi-based models through their microstructure approach better reproduce the Brazilian to direct tensile strength ratio, and show a better representation of the dilation, crack pattern and post-peak behaviour in comparison to continuum models. Ključne besede: distinct-element method, parametric sensitivity analysis, intact rock, Voronoi tessellation, micromechanical properties, standard laboratory test Objavljeno: 15.06.2018; Ogledov: 27; Prenosov: 2 Celotno besedilo (1,57 MB) |
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38. New computational models for better predictions of the soil-compression indexAhmet Demir, 2015, izvirni znanstveni članek Opis: The compression index is one of the important soil parameters that are essential for geotechnical designs. Because laboratory and in-situ tests for determining the compression index (Cc) value are laborious, time consuming and costly, empirical formulas based on soil parameters are commonly used. Over the years a number of empirical formulas have been proposed to relate the compressibility to other soil parameters, such as the natural water content, the liquid limit, the plasticity index, the speciﬁc gravity. These empirical formulas provide good results for a specific test set, but cannot accurately or reliably predict the compression index from various test sets. The other disadvantage is that they tend to use a single parameter to estimate the compression index (Cc), even though Cc exhibits spatial characteristics depending on several soil parameters. This study presents the potential for Genetic Expression Programming (GEP) and the Adaptive Neuro-Fuzzy (ANFIS) computing paradigm to predict the compression index from soil parameters such as the natural water content, the liquid limit, the plastic index, the specific gravity and the void ratio. A total of 299 data sets collected from the literature were used to develop the models. The performance of the models was comprehensively evaluated using several statistical verification tools. The predicted results showed that the GEP and ANFIS models provided fairly promising approaches to the prediction of the compression index of soils and could provide a better performance than the empirical formulas. Ključne besede: compression index, statistical analysis, genetic expression programming, adaptive neuro-fuzzy, empirical equations Objavljeno: 14.06.2018; Ogledov: 59; Prenosov: 3 Celotno besedilo (274,65 KB) |
39. Relationship between the compressive and tensile strengths of lime-treated clay containing coconut fibresVivi Anggraini, Bujang Huat, Afshin Asadi, Haslinda Nahazanan, 2015, izvirni znanstveni članek Opis: The effects of coconut fibre on the mechanical characteristics of lime-treated clay are investigated in this study. The lime-treated clay specimens were prepared with a variety of coconut-fibre contents, i.e., 0.5%, 1%, 1.5% and 2%, in terms of the weight of dry soil. The stabilized specimens were tested at 7, 28 and 90 days after the treatment in order to observe the evolution of the mechanical resistance with time. The results of the unconfined compressive strength tests were used to determine the relationships between the compressive strengths and the indirect tensile strengths of the stabilized soil. Furthermore, the optimum percentage of coconut fibre mixed in the soil/lime mixtures was 1% of the dry mass and reinforcement at 90 days increases the peak compressive strength and the indirect tensile strength. Coconut-fibre inclusion changes the brittle behaviour of the lime-treated clay soil to give it a more ductile character. Ključne besede: coconut fibre, lime, compressive strength, indirect tensile strength, clay soil, failure characteristics Objavljeno: 14.06.2018; Ogledov: 40; Prenosov: 2 Celotno besedilo (755,61 KB) |
40. Analysis of a dilatometer test in over-consolidated sediments, basin of the Duero river, SpainFélix Escolano Sánchez, Manuel Bueno Aguado, 2015, izvirni znanstveni članek Opis: A dilatometer test is a useful method for in-situ geotechnical surveys. It can be compared with the results obtained using a mathematical model. The mathematical model of concentric rings shown in this article is governed by the constitutive equation of the “Hardening Soil Model”. A large number of tests made on the Dueñas Geological Facies, with a consistency ranging from firm clays to soft rocks, are compared to the model results. In this way, the “Hardening Soil Model” parameters are adjusted to the Dueñas Facies materials. Ključne besede: Dueñas, geotechnical parameters, hardening soil model, soft rocks and clays deformation Objavljeno: 14.06.2018; Ogledov: 53; Prenosov: 2 Celotno besedilo (409,71 KB) |