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دانلود مقالات انگلیسی گرایش مهندسی ژئوتکنیک رفتن به صفحه : قبلی  1, 2, 3 ... 77, 78, 79, 80  بعدی
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عضو شده در: 7 مهر 1385
پست: 37412

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پست تاریخ: چهار‌شنبه 27 خرداد 1394 - 18:38    عنوان:   پاسخگویی به این موضوع بهمراه نقل قول

Reliability of Soil Water Content Measurements by Calcium Carbide Gas Pressure Method for Small Specimens
2014
Sami Arsoy|Erdinc Keskin|Mehmetr Ozgu
Abstract :
Calcium carbide gas pressure (CCGP) method is a rapid measurement procedure for obtaining soil water content (SWC), which relies on the chemical reaction of the calcium carbide reagent with the water in soil pores. Currently, the method is limited to soil samples of 20 g or larger. However, test equipment for much smaller sample size does exist, and there is a need in quantifying the reliability of SWC measurements of small samples. The research involved a total of 232 tests that were carried out on 22 different soil types containing particles no larger than No.4 sieve size. Water contents of the soil specimens with varying wetness were measured with both the conventional oven-drying and the CCGP methods. The error distribution analysis indicated that the CCGP method, as used in this study, estimates the SWC for all soil types with a mean absolute discrepancy around 0.3% and 0.2% with general and soil specific calibrations, respectively. It was found that CCGP method is reliable for SWC determination of small specimens up to 20% of SWC if the manufacturer’s instructions are followed.
Keywords :
Soil water content, calcium carbide, oven-drying, speedy, moisture
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عضو شده در: 7 مهر 1385
پست: 37412

تشکر: 3351
تشکر شده 18469 بار در 8611 پست

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امتیاز: 210699
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پست تاریخ: چهار‌شنبه 27 خرداد 1394 - 18:48    عنوان:   پاسخگویی به این موضوع بهمراه نقل قول

The Influence of Seepage and Gravitational Loads on Elastoplastic Solution of Circular Tunnels
2014
Ahmad Fahimifar|Hamed Ghadami|Masoud Ahmadvand
Abstract :
In this paper, an elastoplastic model is proposed to analyze the circular tunnels below the groundwater table under axial-symmetric condition, considering the effects of seepage and gravitational loads. In the proposed method, the strain-softening behavior model and Hoek-Brown failure criterion are used. To evaluate the effect of gravitational loads and variations of pore pressure, the equations concerning different directions around the tunnel (crown, wall, and floor) are derived. Since, the derived differential equations do not have closed-form solution in the plastic zone, the numerical finite difference method is applied. Considering the strain-softening behavior of the rock mass, the problem in the plastic zone is solved through a stepwise method, where the strength parameters of the rock mass varies step-by-step from their maximum values to the constant values. Besides, the stresses, strains, and deformations of the rock mass also vary step-by-step from elastoplastic boundary to tunnel boundary values. Furthermore, the closed-form analytical solutions are obtained for the elastic zone. The accuracy and application of the proposed method is demonstrated by a number of examples. The results well exhibited the effects of dilatancy angle and increment of elastic strain in the plastic zone. Based on the results obtained, ignoring the effects of gravitational loads and seepage will definitely produce computational errors.
Keywords :
Underwater Tunnels, Seepage, Gravitational Loads, Elastoplastic Solution, Strain-Softening
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عضو شده در: 7 مهر 1385
پست: 37412

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تشکر شده 18469 بار در 8611 پست

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امتیاز: 210699
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پست تاریخ: چهار‌شنبه 27 خرداد 1394 - 19:06    عنوان:   پاسخگویی به این موضوع بهمراه نقل قول

Safety evaluation of shallow tunnel based on elastoplastic-viscoplastic analysis
2014
Mohammad Maleki ‎|Mohsen Mousivand ‎
Abstract :
Application of an elastoplastic-viscoplastic constitutive model for tunnel safety evaluation is presented in this paper. For achieving this purpose, in the first step, through FLAC code, the model parameters were identified for a section of Tehran Towheed tunnel (as a case study) by a back analysis process. In the second step, with definition of two safety parameters related to short term (time-independent) and long term (time-dependent) behaviors, the safety of tunnel was assessed. For short term behavior which is related to excavation phase of tunnel, the elastoplastic part plays the essential role, so the safety parameter was defined based on hardening variable of constitutive model. But for long term behavior, time-dependent deformation will be generated during time, thus evaluation of safety was done by comparison of current shear strain and a defined limit shear strain based on experimental data. The results of back analysis showed a good capacity of model in reproduction of tunnel behavior. Application of defined safety parameters on Towheed tunnel indicates that stability of tunnel is guaranteed during construction stages and long term situation.
Keywords :
soft ground; NATM; elastoplastic; viscoplastic; constitutive model; FLAC 2D
Reference and download

_________________
مرجع کاربردی طراحی سازه های فولادی با نرم افزار ETABS 2013 و SAFE ورژن 12 : http://goo.gl/zkqFfH

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عضو شده در: 7 مهر 1385
پست: 37412

تشکر: 3351
تشکر شده 18469 بار در 8611 پست

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امتیاز: 210699
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پست تاریخ: چهار‌شنبه 27 خرداد 1394 - 19:17    عنوان:   پاسخگویی به این موضوع بهمراه نقل قول

Analytical reliability assessment of liquefaction potential based on cone penetration test results
2014
A. Johari|A.R. Khodaparast
Abstract :
Determination of site liquefaction potential and taking deterrent action can prevent a significant damage to structures. In this way, a probabilistic liquefaction assessment can develop potential flexibility and risk management decisions. Based on the advantage of probabilistic assessment, considerable research has been carried out in the past few years on liquefaction potential. In this research,the jointly distributed random variables method is used as an analytical method for probabilistic analysis and reliability assessment of liquefactionpotential based on cone penetration test results.The selected stochastic parameters are corrected CPT tip resistance and stress reduction factor, which are modeled using a truncated normal probability density function and the peak horizontal earthquake acceleration ratio and earthquake magnitude, which are considered to have a truncated exponential probability density function. The depth of water table and fines content are regarded as constant parameters. The results are compared with those of the Monte Carlo simulation. Comparison of the results and parametric analysis indicates very good performance of the proposed approach in assessment of reliability. A sensitivity analysis shows that themoment magnitudeis the most effective parameter in soil liquefaction potential.
Keywords :
Reliability, Jointly distributed random variables method, Monte Carlo simulation, Liquefaction, Standard penetration test
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_________________
مرجع کاربردی طراحی سازه های فولادی با نرم افزار ETABS 2013 و SAFE ورژن 12 : http://goo.gl/zkqFfH

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عضو شده در: 7 مهر 1385
پست: 37412

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امتیاز: 210699
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پست تاریخ: چهار‌شنبه 27 خرداد 1394 - 19:19    عنوان:   پاسخگویی به این موضوع بهمراه نقل قول

Effect of Intermediate Principal Stress Parameter on Cyclic Behavior of Sand
2014
Fardin Jafarzadeh|Mostafa Zamanian
Abstract :
Soils have an anisotropic response and changing the inclination (α) and magnitude of the major principal stress will affect the collapse potential and brittleness as well as the shear strength and shear stiffness. In this paper the effect of stress path with changing in intermediate principal stress on the dynamic behavior of Babolsar sand is studied. A series of undrained monotonic and cyclic tests on loose sand with induced anisotropy were conducted using automatic hollow cylinder apparatus. Special attention was paid to the significant role of the intermediate principal stress parameter (b) in the deformation behavior of sand during cyclic loading. Results show that at constant α, confining stress and fabric; variation ofb has significant effect on the strain amplitudes but it would not change contractive or dilative behavior of specimens. The variation of b has high effect on liquefaction resistance but has no effect on the mobilized friction angle at steady state. It is shown that confining stress has significant effect on soil response (the strain development, excess pore water pressure generation and shear modulus and damping ratio). Moreover by increasing the confining stress, the effect of b value on cyclic behavior will be more pronounced.
Keywords :
sand, intermediate principal stress, anisotropy, cyclic hollow cylinder apparatus, stress path
Reference and download

_________________
مرجع کاربردی طراحی سازه های فولادی با نرم افزار ETABS 2013 و SAFE ورژن 12 : http://goo.gl/zkqFfH

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عضو شده در: 7 مهر 1385
پست: 37412

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امتیاز: 210699
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پست تاریخ: چهار‌شنبه 27 خرداد 1394 - 19:31    عنوان:   پاسخگویی به این موضوع بهمراه نقل قول

Study on the failure behavior of three different stabilized problematic soils
2014
E. Aflaki|P. Sedighi|A. Eslami
Abstract :
In this study laboratory testing of e ectiveness of cement treatment has been made on geotechnical parameters of problematic soils encountered in southern coast line of Caspian Sea, Iran. Gorgan loess, Rasht clay, and Anzali sand were selected in this research. Addition of cement was found to improve workability and increased uncon ned compressive strength, and elastic modulus of soils signi cantly. Triaxial test results indicated that cement treatment not only improved shear strength remarkably, but also it changed the type of failure greatly from ductile to brittle behavior. The large scale direct shear test results showed signi cant improvement in shear strength and shear modulus. Besides, the brittle behavior of cement treated samples was observed. Eventually, it was found that the trend of failure envelope of cement treated samples was non-linear, and some failure criteria such as modi ed Grith theory, Hoek-Brown theory, and the Johnston criterion can describe the soil cement behavior satisfactorily.
Keywords :
Failure criteria; Cement treatment; Shear strength; Soaked condition; Problematic soils.
Reference and downlaod

_________________
مرجع کاربردی طراحی سازه های فولادی با نرم افزار ETABS 2013 و SAFE ورژن 12 : http://goo.gl/zkqFfH

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عضو شده در: 7 مهر 1385
پست: 37412

تشکر: 3351
تشکر شده 18469 بار در 8611 پست

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امتیاز: 210699
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پست تاریخ: چهار‌شنبه 27 خرداد 1394 - 19:34    عنوان:   پاسخگویی به این موضوع بهمراه نقل قول

Influence of Fines Content and Type on the Small-2 strain Shear Modulus of Sand
2014
Nima Akbari Paydar|Mohammad Mehdi Ahmadi
Abstract :
Small-strain shear modulus, G0, is an important fundamental soil property. Although many studies have been conducted on this property for clean sands and pure clays,small-strain behavior for mixtures of sand and fines has been less addressed. Thispaper presents the results of a comprehensive laboratory study on G0 value of sandcontaining various amounts of different fines. To this aim, bender elements wereintegrated into a conventional triaxial apparatus, and shear wave velocity wasmeasured on samples of sand with different amounts of highly-plastic, medium- plastic, low-plastic, or non-plastic fines at different void ratios. Measuring the shearwave velocity and thus obtaining G0 at different void ratios and effective stresses, theintrinsic parameters that characterize G0 were determined for the tested materials.This allowed the effects of fines type and content on the G0 value of sand to beevaluated in a systematic manner. The G0 values of different sand-fines mixtureswere compared based on different density parameters. Results show that G0 of siltyand clayey sands is affected by both fines content and fines type. Therefore, in orderto estimate G0 of sand-fines mixture, not only the fines content but also theirplasticity needs to be properly accounted.
Keywords :
Small-strain shear modulus; Sand; Fines content; Plastic fines; Non-plastic fines
Reference and download

_________________
مرجع کاربردی طراحی سازه های فولادی با نرم افزار ETABS 2013 و SAFE ورژن 12 : http://goo.gl/zkqFfH

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عضو شده در: 7 مهر 1385
پست: 37412

تشکر: 3351
تشکر شده 18469 بار در 8611 پست

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امتیاز: 210699
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پست تاریخ: چهار‌شنبه 27 خرداد 1394 - 19:35    عنوان:   پاسخگویی به این موضوع بهمراه نقل قول

Improved Support Vector Machine Regression in Multi-Step-Ahead Prediction for Tunnel ‎Surrounding Rock Displacement ‎
2014
Baozhen YAO ‎|Jinbao YAO ‎|Mingheng ZHANG ‎|Lan YU ‎
Abstract :
A dependable long-term prediction of tunnel surrounding rock displacement is an effective way to predict the rock displacement values into the future. A multi-step-ahead prediction model, which is based on support vector machine (SVM), is proposed for tunnel surrounding rock displacement prediction. To improve the performance of SVM, parameter identification is used for SVM. In addition, to treat with the time-varying features of tunnel surrounding rock displacement, a forgetting factor is introduced to adjust the weights between new and old data.At last, the data from the Chijiangchong tunnel are selected to examine the performance of the prediction model. Comparative results were presented between SVMFF (SVM with a forgetting factor) and artificial neural network with a forgetting factor (ANNFF) show that SVMFF is generally better than ANNFF. This indicates that a forgetting factor can effectively improve the performance of SVM, especially for the time-varying problems.
Keywords :
Multi-Step-Ahead Prediction; Tunnel; Surrounding Rock Displacement; SVM; Forgetting Factor
Reference and download

_________________
مرجع کاربردی طراحی سازه های فولادی با نرم افزار ETABS 2013 و SAFE ورژن 12 : http://goo.gl/zkqFfH

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عضو شده در: 7 مهر 1385
پست: 37412

تشکر: 3351
تشکر شده 18469 بار در 8611 پست

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امتیاز: 210699
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پست تاریخ: چهار‌شنبه 27 خرداد 1394 - 19:39    عنوان:   پاسخگویی به این موضوع بهمراه نقل قول

Centrifuge modeling of pile-soil-pile interaction considering relative density and toe condition
2014
A. Saeedi Azizkandi|M.H. Baziar|M. Modarresi|H. Salehzadeh|H. Rasouli
Abstract :
In a group of installed piles, the stresses applied from one pile to soil may have overlaps with another pile which leads to the changes in bearing capacity and settlement of each individual pile. In order to predict the performance of those piles, interaction coecients, based on elasticity theory proposed by Mindlin, are widely applied. In this paper, the e ect of soil relative density and also toe condition on the interaction between two similar piles in sandy soil is presented using centrifuge modeling. To achieve this objective, 22 tests have been conducted to investigate the e ect of soil relative density and another 11 tests were performed to study the contribution of pile toe and shaft in the interactions. The results showed that the value of soil relative density has an important role in the coecient of interaction which has not been considered in previously reported correlations. For this reason a modi cation has been proposed for the Randolph and Wroth equation to consider soil relative density. Accuracy prediction of the new modelwas compared with the Randolph and Wroth equation with the aid of di erent statistical parameters. This comparison indicated the superiority of the proposed model over previous methods.
Keywords :
Pile-soil-pile interaction; Relative density ratio; Toe and shaft interactions; Centrifuge modeling.
Reference and downlaod

_________________
مرجع کاربردی طراحی سازه های فولادی با نرم افزار ETABS 2013 و SAFE ورژن 12 : http://goo.gl/zkqFfH

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عضو شده در: 7 مهر 1385
پست: 37412

تشکر: 3351
تشکر شده 18469 بار در 8611 پست

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امتیاز: 210699
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پست تاریخ: چهار‌شنبه 27 خرداد 1394 - 19:52    عنوان:   پاسخگویی به این موضوع بهمراه نقل قول

Estimation on bearing capacity of shallow foundations in heterogeneous deposits using analytical and numerical methods
2014
R. Jamshidi Chenari|N. Zhalehjoo|A. Karimian
Abstract :
In situ soil properties are spatially variable parameters causing soil deposits to be heterogeneous. Heterogeneity consists of two components: (i) A deterministic trend and (ii) The residual component. This paper presents the e ect of di erent components of soil heterogeneity on the ultimate bearing capacity of a vertically loaded shallow foundation resting on clay deposits. The numerical model used in this study is based on nite di erence simulations, employing FLAC 5.0. Results of numerical analysis are compared with other simple and analytical solutions. For heterogeneous soil deposits, considering both linear and bi-linear deterministic trends, nite di erence tools were found to be able to reffect salient features of heterogeneity in bearing capacity estimation. An equivalent homogeneous analysis solution is introduced, in order to allow for heterogeneity, by adopting a representative depth for shear strength measurements. Stochastic variationof shear strength is shown to induce under conservatism by solely relying upon deterministic estimations.
Keywords :
Shear strength;Shallow foundations;Bearing capacity;Finite di erencemethod;Heterogeneity;Equivalent homogeneity.
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_________________
مرجع کاربردی طراحی سازه های فولادی با نرم افزار ETABS 2013 و SAFE ورژن 12 : http://goo.gl/zkqFfH

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