1. A general analytical solution to the one-dimensional consolidation problem for unsaturated soil under various loading conditionsJiwei Li, Changfu Wei, Yanlin Zhao, 2018, izvirni znanstveni članek Opis: A general analytical solution is developed for the onedimensional consolidation problem of unsaturated soil under various time-dependent loading conditions based on a differential transformation method (DTM). In particular, analytical solutions are obtained for different relationships between the coefficients in the governing equations for unsaturated soil consolidation. The Fourier series expansion technique is adopted to account for both the continuous differentiable loading and the periodic piecewise loading. A comparison between the results of the current solution and the existing theoretical solution indicates that the proposed solution yields excellent results, while it is straightforward to obtain the analytical solution of the unsaturated consolidation problems. It was also found that the variations in the coefficients in the governing equations can significantly influence the dissipation of both the excess pore-air pressure and the excess pore-water pressure, though the magnitudes of their variations are different. Ključne besede: one-dimensional consolidation problem, unsaturated soil, analytical solution, time-dependent loading Objavljeno v DKUM: 11.10.2018; Ogledov: 1312; Prenosov: 517 Celotno besedilo (814,44 KB) Gradivo ima več datotek! Več... |
2. Modified coefficient of subgrade reaction to laterally loaded pilesAyhan Gurbuz, 2018, izvirni znanstveni članek Opis: An accurate prediction of the load capacity of a laterally loaded pile at a permissible displacement is an important concern at the design stage. In contrast to many sophisticated methods, Broms’ method based on moment equilibrium has been preferred by engineers to predict the load capacities of laterally loaded piles due to both its simplicity and because it is established on a way of hand calculation. However, Broms’ method typically overestimates a pile’s lateral load capacity as it requires a constant coefficient of horizontal subgrade reaction (nh) into analyses, regardless of the magnitude of the pile’s top displacement. In this study, modified coefficients of subgrade reactions(nh*) that are sensitive to the pile’s top displacement in cohesionless soils are first proposed to improve the performance level of Broms’ method for the prediction of the load capacity of a laterally loaded pile as the pile’s top displacement increases. The modified values of nh* are calibrated using 45 independently free-head, single-driven, full-scale pile tests from 23 sites in cohesionless soils. It is demonstrated that Broms’ method with nh* would correctly estimate a pile’s lateral load-deflection behavior with accuracy levels similar to more complicated methods. Ključne besede: Broms' method, coefficient of horizontal subgrade reaction, p-y curves, strain wedge model Objavljeno v DKUM: 11.10.2018; Ogledov: 1264; Prenosov: 584 Celotno besedilo (735,27 KB) Gradivo ima več datotek! Več... |
3. A simplified method to analyze pile-supported and geosynthetic-reinforced embankments and the influence significance analysis of the design parametersLiu Feicheng, Zhang Jianjing, Yan Shijie, Cao Licong, 2018, izvirni znanstveni članek Opis: A simplified method for evaluating a pile-supported embankment reinforced with geosynthetic (PGRS embankment) is proposed in this paper. The method takes into account not only the arching effect, the membrane effect of the deflected geosynthetic, and the subsoil reaction, but also the pile head settlement, which makes the method applicable for floating piles, as well as piles seated on a firm soil layer. The settlement of the subsoil surface is considered to consist of two parts: (a) the settlement of the subsoil surface equals that of the pile cap with no deformation in geosynthetic yet; (b) the subsoil surface subsides along with the geosynthetic deforming, and the deflected geosynthetic being considered as catenary shaped. The formula for the maximum differential settlement between the subsoil surface and the piles is worked out by analyzing the force equilibrium of the geosynthetic and the stress-strain relationship of the geosynthetic at the edge of the pile cap. The comparison of the calculated results with the observed data and the six current analytical methods has been implemented to verify the proposed method. The influence of the tensile stiffness of the geosynthetic, compression modulus of soft soil, soft soil thickness, embankment height, internal friction angle of the embankment fill and the pile spacing on the subsoil reaction, the stress concentration ratio (SCR) and the tension of the geosynthetic are investigated using the proposed method. The influence significance of these factors has been investigated using the evaluation theory of binary variance analysis for the non-repeatability tests, which helps optimize the design of the PGRS embankment. Ključne besede: pile-supported embankment, geosynthetic, simplified method, influence significance, binary variance analysis Objavljeno v DKUM: 11.10.2018; Ogledov: 1292; Prenosov: 478 Celotno besedilo (1,23 MB) Gradivo ima več datotek! Več... |
4. Effect of particle roundness and morphology on the shear failure mechanism of granular soil under strip footingBabak Karimi Ghalehjough, Suat Akbulut, Semet Çelik, 2018, izvirni znanstveni članek Opis: This study investigates the effect of particles roundness and morphology on the shear failure mechanism of soil. A strip footing was modeled under laboratory conditions. Calcareous soil was tested with three roundness classes: angular, rounded and well-rounded shapes with sizes of 0.30 mm to 4.75 mm. These were divided into six different groups at three relative densities of 30%, 50% and 70%. A series of photographs was taken during the tests and analyzed using the particle image velocimetry (PIV) method to understand the soil-deformation mechanism. The results showed that increasing the sample sizes increased the affected area of the soil. At the same time, increasing the relative density caused a punching failure mechanism that went towards the general failure. The shear failure mechanism of the soil changed from general toward punching shear failure with increasing particle roundness. This effect was larger with the smaller materials. Underneath the affected layers of soil, the angular samples were deeper than the rounded and well-rounded samples. The affected depth in the angular soil was approximately 1.5B in the smallest size group. This was more than 3B and near 4B in the largest size group. Both the sides and the underlying soil layers should be considered on angular soils. The area under the footing becomes more important than the side parts after increasing the roundness of the particles. Ključne besede: particle roundness, morphology of particles, shear failure mechanism, strip footing, PIV method, ultimate bearing capacity Objavljeno v DKUM: 11.10.2018; Ogledov: 1507; Prenosov: 489 Celotno besedilo (701,47 KB) Gradivo ima več datotek! Več... |
5. Evaluation of the constriction size reduction of granular filters due to upstream cohesive base-soil erosionSamira Azirou, Ahmed Benamar, Abdelkader Tahakourt, 2018, izvirni znanstveni članek Opis: This study is devoted to filter-constrictions analysis and its application with respect to void and constrictions reduction during soil filtration. The experimental investigation involves combined Hole Erosion-Filtration tests using several soils and filters. The base soils are lean clays and the granular filters are selected according to the usual filtration criteria. The combination of the experimental data for porosity variation and the analytical results from the Constriction Size Distribution (CSD) analysis was used to evaluate the constrictions size reduction subsequent to the filtration process. The filtration depth was also estimated according to the retained soil mass and the porosity reduction deduced from the measured hydraulic conductivity. An analytical model of the CSD was applied to the experimental results in order to assess the constrictions reduction. As regards the obtained results, a nonuniform constriction reduction was suggested according to the effective filtration depth, advocating a dynamic filter action. Ključne besede: granular filter, internal erosion, constriction, porosity, filtration index Objavljeno v DKUM: 11.10.2018; Ogledov: 1371; Prenosov: 558 Celotno besedilo (653,76 KB) Gradivo ima več datotek! Več... |
6. A geostress measurement method based on an integrated drilling and optical microscopic imaging systemJinchao Wang, Chunying Wang, Zengqiang Han, Yiteng Wang, Xinjian Tang, 2018, izvirni znanstveni članek Opis: Conventional geostress measurement methods are limited by deficiencies including the measurable depth, the complexity, and the long duration of operation. To address these problems and achieve the measurement of geostress in deep wells under conditions of complex high pressures and high temperatures, we propose a new measurement method for geostress based on an integrated drilling and optical microscopy system. Its innovative integrated structure eliminates the problems associated with complex procedures and depth limits, and avoids rock creep caused by long delays, significantly improving the accuracy and range of the measurements. It works by using microscopic imaging and direct contact probes to capture the changes of a borehole’s cross-sectional outlines before and after stress relief. The resulting images are analyzed with search circles to obtain the positions of probe apices, which can be fitted into ellipses that describe the outlines, and calculate the state of the stress. The validity and accuracy of the method was verified by in-door tests and field applications in the ZK1 borehole. The results show that: (1) the integrated system can be used to measure micrometer-grade deformations; (2) the searchcircle approach can accurately obtain the positions of probe apices; and (3) the stress measurement method based on the system is accurate and feasible. Ključne besede: geostress, probe, optical microscopy, measurement while drilling, search circle Objavljeno v DKUM: 11.10.2018; Ogledov: 1437; Prenosov: 562 Celotno besedilo (1,26 MB) Gradivo ima več datotek! Več... |
7. Shear modulus of clay-sand mixtures using bender element testAli Firat Cabalar, M. M. Khalaf, Zuheir Karabash, 2018, izvirni znanstveni članek Opis: Bender-element (BE) tests were conducted on clay-sand mixtures to investigate the variation of small strain-shear modulus (Gmax) with the sand content and the physical characteristics (size, shape) of the sand grains in the mixtures. Three different gradations (0.6–0.3 mm, 1.0–0.6 mm and 2.0–1.0 mm) of sands having distinct shapes (rounded, angular) were added to a low-plasticity clay with mixture ratios of 0% (clean clay), 10%, 20%, 30%, 40%, and 50%. For the purposes of performing a correlation analysis, unconfined compression (UC) tests were also carried out on the same specimens. The tests indicated that both the Gmax and unconfined compressive strength (q u) values of the specimens with angular sand grains were measured to be lower than those with rounded sand grains, for all sizes and percentages. As the percentage of sand in the mixture increases, the Gmax values increase, while the qu values decrease. The results further suggested that the Gmaxvalues decrease as the q u values decreases as the size of the sand grains reduces. Ključne besede: sand, clay, bender element, unconfined compressive strength Objavljeno v DKUM: 11.10.2018; Ogledov: 1382; Prenosov: 362 Celotno besedilo (844,22 KB) Gradivo ima več datotek! Več... |
8. Effects of particle characteristics on the shear strength of calcareous sandPham Huu Ha Giang, P. O. Van Impe, W. F. Van Impe, Patrick Menge, Veerle Cnudde, Wim Haegeman, 2017, izvirni znanstveni članek Opis: The paper presents a 3D analysis (3DA) to evaluate the particle shape and size of silica and calcareous sands. The particles of calcareous sand are found to be less spherical than those of silica and crushed calcareous sands. Furthermore, the results indicate that the average sphericity (SPH) holds an inverse relationship to the particle size. However, in each sample the larger particles have higher SPHs than the smaller particles. In addition, the 3DA yields smaller particles than the sieve analysis (SA). Owing to a variety of particle shapes, causing particle interlocking, especially for calcareous sand, the particles cannot pass through the sieves by their shortest dimension. This paper discusses the effects of particle characteristics on the shear strength properties. Although the calcareous sand shows higher peak and residual shear strength properties, it tends to reach a lower shear strength at a small shear strain and a lower dilation than the silica sand. Moreover, the findings prove that the residual shear strength increases with the mean particle size. The sample with smaller particles shows less dilation under low vertical stress, while high vertical stress yields less compression. The relationship between the particle shape and shear strength properties is discussed based on the 3DA results. Ključne besede: shear strength, sphericity, particle shape, calcareous sand Objavljeno v DKUM: 18.06.2018; Ogledov: 1069; Prenosov: 62 Celotno besedilo (875,50 KB) Gradivo ima več datotek! Več... |
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10. An unsaturated-soils approach to the bearing capacity of foundation structuresTaha Taskiran, 2017, izvirni znanstveni članek Opis: Unsaturated soils are maintaining their importance for researchers and there is still much need to investigate the many engineering aspects of these soils. A new technique is proposed here to predict the variation of the bearing capacity of unsaturated soils with matric suction. The proposed method is an extension of conventional bearing-capacity theories and conceptually based on the logarithmic model of the shear strength of unsaturated soils, which only include one unknown, unsaturated parameter (the airentry value, AEV). The possibility of predicting the unsaturated bearing capacity of soils is shown by the saturated effective shear-strength parameters c' and Ø' and the AEV from the soil-water retention curve (SWRC). Considering the necessity of validating new methods with other researchers’ data, the proposed equation is tested using the published unsaturated experimental study by the author, in addition to some reported experimental studies on the shear strength for unsaturated soils and also a model footing loading on unsaturated sand under controlled suction conditions. The results of the study indicate that there is a good comparison between the “unsaturated bearing capacities” obtained via predicted and measured unsaturated strength parameters (ctotal , Ø) and also between the measured/ calculated bearing values of a model footing loading. Consequently, it is shown that, without needing complex unsaturated testing facilities, the proposed equation is capable of predicting the unsaturated bearing capacity for both fine-grained and sandy soils, requiring only one unsaturated parameter, which can be obtained from the SWRC or predicted using the basic soil-index properties. Ključne besede: unsaturated soils, unsaturated bearing capacity, suction strength, foundation design Objavljeno v DKUM: 18.06.2018; Ogledov: 1143; Prenosov: 69 Celotno besedilo (347,24 KB) Gradivo ima več datotek! Več... |