1. A fundamental study of the performance of X-section cast-in-place concrete single pilesYu Wang, Yaru Lv, Dongdong Zhang, Jieying Zhou, 2016, original scientific article Abstract: X-section cast-in-place concrete (XCC) piles are used because they have a higher bearing capacity than circularsection cast-in-place concrete (CCC) piles of the same cross-sectional area. Although the bearing capacity of XCC piles has been studied, the performance of XCC single piles, especially for the stress-transfer mechanism dependent on the geometrical effects, is still not fully understood. This paper reports two comparative field static load tests on an XCC and a CCC single pile of the same cross-sectional area. In addition, corresponding threedimensional numerical back-analyses are performed to provide a fundamental understanding. The measured and computed results reveal that the XCC single pile has an approximately 25% higher ultimate bearing capacity than the CCC single pile. This is because the XCC single pile has an approximately 20% larger total side resistance, which is caused by a 60% larger pile perimeter and a slightly smaller unit side resistance. Lateral soil arching effects are developed, causing a non-uniform effective normal stress and a shear stress across the circumference of the XCC single pile. It is suggested that XCC single piles have a higher efficiency in terms of material saving compared with CCC single piles.
Keywords: X-section cast-in-place concrete pile, field static load test, three-dimensional numerical back-analysis, stresstransfer mechanism, side resistance, soil arching
Published in DKUM: 15.06.2018; Views: 1452; Downloads: 183
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2. Evolutionary-based prediction of ε50 for the lateral load-displacement behavior of piles in clayBabak Ebrahimian, Aida Nazari, 2013, original scientific article Abstract: Analyzing piles that are subjected to lateral loads reveals that their behavior depends on the soil’s resistance at any point along the pile as a function of the pile’s deflection, known as the p-y curve. On the other hand, the deformation characteristics of soil defined as “the soil strain at 50% of maximum deviatoric stress (ε50)” have a considerable effect on the generated p-y curve. In this research, several models are proposed to predict ε50 specifically for designing the very long pile foundations of offshore oil and gas platforms in the South Pars field, Persian Gulf, Iran. Herein, ε50 is evaluated using extensive soil data, including in-situ and laboratory test results using evolutionary polynomial regression (EPR). The effects of the undrained shear strength, the normalized tip resistance of the cone penetration test, the over-burden pressure, the plasticity index and the over-consolidation ratio on ε50 are investigated in marine clays. It is demonstrated that the normalized cone tip resistance, which is an indication of the soil’s undrained shear strength, leads to more realistic ε50 values compared with the laboratory-derived undrained shear strength parameter. In addition, the application of the soil-index properties and the over-burden pressure in the models, improves their estimation quality. Furthermore, the results of full-scale lateral pile load tests at different sites are used in order to validate the performance of the proposed models when it comes to predicting the behavior of the lateral piles.
Keywords: p-y curve, laterally loaded pile, piezocone penetration test, PCPT, marine clay, evolutionary polynomial regression, EPR, South Pars field
Published in DKUM: 14.06.2018; Views: 1081; Downloads: 86
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3. Numerical analysis of circular footings on natural clay stabilized with a granular fillMurat Ornek, Mustafa Laman, Ahmet Demir, Abdulazim Yildiz, 2012, original scientific article Abstract: In this study, numerical predictions of the scale effect for circular footings supported by partially replaced, compacted, layers on natural clay deposits are presented. The scale- effect phenomenon was analyzed according to the footing sizes. Numerical analyses were carried out using an axisymmetric, two-dimensional, finite-element program. Before conducting the analysis, the validity of the constitutive model was validated using field tests performed by authors with seven different footing diameters up to 0.90 m and with three different partial replacement thicknesses. It is shown that the behavior of the circular footings on natural clay soil and the partial replacement system can be reasonably well represented by the Mohr Coulomb model. The Mohr-Coulomb model parameters were derived from the results of conventional laboratory and field tests. After achieving a good consistency between the results of the test and the numerical analysis, the numerical analyses were continued by increasing the footing diameter up to 25 m, considering the partial replacement thickness up to two times the footing diameter. The results of this parametric study showed that the stabilization had a considerable effect on the bearing capacity of the circular footings and for a given value of H/D the magnitude of the ultimate bearing capacity increases in a nonlinear manner with the footing diameter. The Bearing Capacity Ratio (BCR) was defined to evaluate the improved performance of the reinforced system. It was found, based on numerical and field-test results that the BCR of the partially replaced, natural clay deposits increased with an increase in the footing diameter and there was no significant scale effect of the circular footing resting on natural clay deposits.
Keywords: scale effect, circular footing, field test, finite-element analysis, natural clay, granular fill
Published in DKUM: 13.06.2018; Views: 1223; Downloads: 154
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