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Papers by Babak Ebrahimian
Springer series in geomechanics and geoengineering, Dec 30, 2014
This research is focused on the numerical investigations of the evolution of shear bands and pola... more This research is focused on the numerical investigations of the evolution of shear bands and polar effects within a planar layer of cohessionless and dry sand material under shearing. In this regard, micro-polar (Cosserat) continuum is used to account for micro-rotations, couple stresses and size effect in sand. In particular, extending the non-polar version of the employed elasto-plastic soil model is presented within the framework of Cosserat continuum. Non-linearity is considered in constitutive relations and geometry for the finite element implementation. It is demonstrated that strain localization with a finite thickness occurs under large quasi-static shearing. Location, thickness and evolution of strain localization are strongly affected by the rotating resistance of boundary grains of sand layer and the boundary conditions of entire system. The localization patterns are different within finite and infinite shear layers, depending on the prescribed lateral boundary conditions.
Springer Series in Geomechanics and Geoengineering, 2014
This paper investigates the influence of the length scale of a cohesionless granular soil specime... more This paper investigates the influence of the length scale of a cohesionless granular soil specimen on the evolution of shear resistance in the direct shear interface test. Numerical simulations are carried out for two different specimen sizes using a micro-polar hypoplastic material model and the finite element method in the updated Lagrange frame. Due to the presence of the lateral rigid boundaries of shear box, the deformation and stress fields become significantly inhomogeneous. Correspondingly, the mobilized shear resistance and the shear band thickness are not constant along the interface. It is shown that, for the case of medium rough wall, some shear localization occurs along part of the interface between the sand specimen and the rough bottom surface and some shear localization takes place within the sand specimen. The evolution of the average mobilized friction angle obtained from the interface shear test is also influenced by the scaling effect of the testing device particularly at the beginning of shearing.
International journal of maritime technology, Sep 15, 2014
Amirkabir Journal of Civil Engineering, Nov 22, 2021
Ocean Engineering, 2012
Abstract In this paper, several new models are developed based on a soft computing technique for ... more Abstract In this paper, several new models are developed based on a soft computing technique for predicting undrained shear strength ( s u ) of marine clays at South Pars field, Persian Gulf, Iran. For this purpose, numerous piezocone penetration tests (PCPTs) data are used along with laboratory and in-situ measurements of s u . In this regard, evolutionary polynomial regression (EPR) is used instead of conventional simple linear regression analysis in order to correlate s u and cone tip resistance more precisely. According to five developed models (models I to V), it is found that the tip resistance corrected for pore water pressure effect ( q t ) yields slightly better estimation of s u , compared to the raw cone tip resistance ( q c ) obtained directly from PCPT. Additionally, the cone tip resistance is correlated much more precisely with s u data obtained from torvane test than that of unconsolidated undrained (UU) triaxial test. The EPR-based models offer a considerable improvement in estimating s u based on cone penetration test data and can predict s u with minimum error in comparison with other theoretical and empirical models. The models are also verified successfully by the data obtained from another survey area, outside the main survey area which has been used to develop the models.
Frontiers of Architecture and Civil Engineering in China, 2010
A numerical study is conducted to investigate the dynamic behavior of earth dams. The numerical i... more A numerical study is conducted to investigate the dynamic behavior of earth dams. The numerical investigation employs a fully nonlinear dynamic finite difference analysis incorporating a simple elastic perfectly plastic constitutive model to describe the stress-strain response of the soil and the Rayleigh damping to increase the level of hysteretic damping. The extended Masing rules are implemented into the constitutive
Article History: Received: 22 Jun. 2021 Accepted: 02 Jan. 2022 Offshore oil and gas extraction st... more Article History: Received: 22 Jun. 2021 Accepted: 02 Jan. 2022 Offshore oil and gas extraction structures at shallow waters are conventionally supported by long driven steel pipe piles. In recent years, the direct CPTor CPTu-based pile design methods have broadly been used to predict the bearing capacity of offshore piles in a more reliable manner. On the other hand, previous investigations have shown that the pile capacity is time-dependent (set-up and relaxation phenomena). However, time effects are missing in most CPTor CPTu-based prediction methods. The main objective of this paper is to estimate the axial compressive bearing capacity of the offshore steel pipe piles driven in the marine clay deposits of the Persian Gulf based on some popular CPT/CPTu as well as static -based prediction methods. The estimated results are compared with the measured capacities obtained from the Pile Dynamic Analyzer (PDA) and the Case Pile Wave Analysis Program (CAPWAP). The measured values have b...
International Journal for Numerical and Analytical Methods in Geomechanics, 2011
Archives of Mechanics, 2021
This article shows the outcomes of a systematic series of finite element (FE) calculations releva... more This article shows the outcomes of a systematic series of finite element (FE) calculations relevant to the shear behavior of a particulate-continuum interface system under different normal boundary conditions. In this respect, shearing of a thin and long granular Cosserat layer in the vicinity of a rigid moving wall with varied surface roughness values is analyzed under constant normal pressure and constant volume conditions. The material behavior is defined with a special elasto-plastic Cosserat model, taking into account micro-rotation, micro-curvature, couple stress, and mean particle size. The interaction between the layer of boundary particles and the surface roughness of the adjoining bottom wall is modeled by the rotation resistance of particles along the wall surface. Herein, the coupled effects of normal confining constraints imposed on the layer and the surface roughness of the bottom wall, are considered on the response of granular material under shearing. The influences ...
Steel pipe piles are used as the foundation of marine structures such as bridges, hydrocarbon ext... more Steel pipe piles are used as the foundation of marine structures such as bridges, hydrocarbon extraction platforms, wind turbines and anchoring elements. Due to the importance and high construction cost of these structures, any weakness and failure in their pile foundations can lead to catastrophic economic, environmental and social damages. Therefore, accurate analysis, safe design and reliable determination of their bearing capacities are of particular importance. In this study, the compressive axial bearing capacity of 24 long offshore driven steel pipe piles in the cohesive sediments of the Persian Gulf is estimated using 10 methods based on direct results of cone penetration test (CPT and CPTu) and 5 methods based on static analysis. The bearing capacity values obtained from these methods are compared and validated with the corresponding measured data attianed from the pile dynamic analysis tests. Then, the performance of these methods are analyzed in terms of accuracy and qual...
This study presents numerical modeling of the dynamic behavior of an earth dam rested on a liquef... more This study presents numerical modeling of the dynamic behavior of an earth dam rested on a liquefiable foundation. Numerical simulations are carried out using effective stress-based, fully coupled nonlinear dynamic analysis approach. The Finn-Byrne model with extended Masing rules is employed to model pore pressure generation in the liquefied soils. In this regard, Masing rules are implemented into the constitutive relations to precisely explain the nonlinear response of soil under general cyclic loading. As a result, the soil shear stiffness and hysteretic damping can change with loading history. Pore pressure is accumulated as a function of the cyclic shear strain amplitude. The procedure of calibrating the constructed numerical model with well-documented centrifuge test data is addressed. Acceptable agreements are shown between the results obtained from the current investigation and those of experimental observations available in the literature. Afterwards, the dynamic response o...
Analyzing piles subjected to lateral loads significantly depends on soil resistance at any point ... more Analyzing piles subjected to lateral loads significantly depends on soil resistance at any point along the pile as a function of pile deflection, known as p-y curve. On the other hand, the deformation characteristics of soil defined as “the soil strain at 50% of maximum deviatoric stress (ε50)” has considerable effect on the generated p-y curve. In this research, several models are proposed to predict ε50 specifically for designing very long pile foundations of offshore oil and gas platforms in South Pars field, Persian Gulf, Iran. Herein, ε50 is evaluated from extensive soil data of marine clays including in-situ and laboratory test results using evolutionary polynomial regression (EPR). It is demonstrated that the normalized cone tip resistance, which is an indication of soil undrained shear strength, leads to more realistic ε50 values compared with the laboratory-derived undrained shear strength parameter. Furthermore, the results of a numerical study on lateral pile-soil system ...
Mechanics Based Design of Structures and Machines
Springer series in geomechanics and geoengineering, Dec 30, 2014
This research is focused on the numerical investigations of the evolution of shear bands and pola... more This research is focused on the numerical investigations of the evolution of shear bands and polar effects within a planar layer of cohessionless and dry sand material under shearing. In this regard, micro-polar (Cosserat) continuum is used to account for micro-rotations, couple stresses and size effect in sand. In particular, extending the non-polar version of the employed elasto-plastic soil model is presented within the framework of Cosserat continuum. Non-linearity is considered in constitutive relations and geometry for the finite element implementation. It is demonstrated that strain localization with a finite thickness occurs under large quasi-static shearing. Location, thickness and evolution of strain localization are strongly affected by the rotating resistance of boundary grains of sand layer and the boundary conditions of entire system. The localization patterns are different within finite and infinite shear layers, depending on the prescribed lateral boundary conditions.
Springer Series in Geomechanics and Geoengineering, 2014
This paper investigates the influence of the length scale of a cohesionless granular soil specime... more This paper investigates the influence of the length scale of a cohesionless granular soil specimen on the evolution of shear resistance in the direct shear interface test. Numerical simulations are carried out for two different specimen sizes using a micro-polar hypoplastic material model and the finite element method in the updated Lagrange frame. Due to the presence of the lateral rigid boundaries of shear box, the deformation and stress fields become significantly inhomogeneous. Correspondingly, the mobilized shear resistance and the shear band thickness are not constant along the interface. It is shown that, for the case of medium rough wall, some shear localization occurs along part of the interface between the sand specimen and the rough bottom surface and some shear localization takes place within the sand specimen. The evolution of the average mobilized friction angle obtained from the interface shear test is also influenced by the scaling effect of the testing device particularly at the beginning of shearing.
International journal of maritime technology, Sep 15, 2014
Amirkabir Journal of Civil Engineering, Nov 22, 2021
Ocean Engineering, 2012
Abstract In this paper, several new models are developed based on a soft computing technique for ... more Abstract In this paper, several new models are developed based on a soft computing technique for predicting undrained shear strength ( s u ) of marine clays at South Pars field, Persian Gulf, Iran. For this purpose, numerous piezocone penetration tests (PCPTs) data are used along with laboratory and in-situ measurements of s u . In this regard, evolutionary polynomial regression (EPR) is used instead of conventional simple linear regression analysis in order to correlate s u and cone tip resistance more precisely. According to five developed models (models I to V), it is found that the tip resistance corrected for pore water pressure effect ( q t ) yields slightly better estimation of s u , compared to the raw cone tip resistance ( q c ) obtained directly from PCPT. Additionally, the cone tip resistance is correlated much more precisely with s u data obtained from torvane test than that of unconsolidated undrained (UU) triaxial test. The EPR-based models offer a considerable improvement in estimating s u based on cone penetration test data and can predict s u with minimum error in comparison with other theoretical and empirical models. The models are also verified successfully by the data obtained from another survey area, outside the main survey area which has been used to develop the models.
Frontiers of Architecture and Civil Engineering in China, 2010
A numerical study is conducted to investigate the dynamic behavior of earth dams. The numerical i... more A numerical study is conducted to investigate the dynamic behavior of earth dams. The numerical investigation employs a fully nonlinear dynamic finite difference analysis incorporating a simple elastic perfectly plastic constitutive model to describe the stress-strain response of the soil and the Rayleigh damping to increase the level of hysteretic damping. The extended Masing rules are implemented into the constitutive
Article History: Received: 22 Jun. 2021 Accepted: 02 Jan. 2022 Offshore oil and gas extraction st... more Article History: Received: 22 Jun. 2021 Accepted: 02 Jan. 2022 Offshore oil and gas extraction structures at shallow waters are conventionally supported by long driven steel pipe piles. In recent years, the direct CPTor CPTu-based pile design methods have broadly been used to predict the bearing capacity of offshore piles in a more reliable manner. On the other hand, previous investigations have shown that the pile capacity is time-dependent (set-up and relaxation phenomena). However, time effects are missing in most CPTor CPTu-based prediction methods. The main objective of this paper is to estimate the axial compressive bearing capacity of the offshore steel pipe piles driven in the marine clay deposits of the Persian Gulf based on some popular CPT/CPTu as well as static -based prediction methods. The estimated results are compared with the measured capacities obtained from the Pile Dynamic Analyzer (PDA) and the Case Pile Wave Analysis Program (CAPWAP). The measured values have b...
International Journal for Numerical and Analytical Methods in Geomechanics, 2011
Archives of Mechanics, 2021
This article shows the outcomes of a systematic series of finite element (FE) calculations releva... more This article shows the outcomes of a systematic series of finite element (FE) calculations relevant to the shear behavior of a particulate-continuum interface system under different normal boundary conditions. In this respect, shearing of a thin and long granular Cosserat layer in the vicinity of a rigid moving wall with varied surface roughness values is analyzed under constant normal pressure and constant volume conditions. The material behavior is defined with a special elasto-plastic Cosserat model, taking into account micro-rotation, micro-curvature, couple stress, and mean particle size. The interaction between the layer of boundary particles and the surface roughness of the adjoining bottom wall is modeled by the rotation resistance of particles along the wall surface. Herein, the coupled effects of normal confining constraints imposed on the layer and the surface roughness of the bottom wall, are considered on the response of granular material under shearing. The influences ...
Steel pipe piles are used as the foundation of marine structures such as bridges, hydrocarbon ext... more Steel pipe piles are used as the foundation of marine structures such as bridges, hydrocarbon extraction platforms, wind turbines and anchoring elements. Due to the importance and high construction cost of these structures, any weakness and failure in their pile foundations can lead to catastrophic economic, environmental and social damages. Therefore, accurate analysis, safe design and reliable determination of their bearing capacities are of particular importance. In this study, the compressive axial bearing capacity of 24 long offshore driven steel pipe piles in the cohesive sediments of the Persian Gulf is estimated using 10 methods based on direct results of cone penetration test (CPT and CPTu) and 5 methods based on static analysis. The bearing capacity values obtained from these methods are compared and validated with the corresponding measured data attianed from the pile dynamic analysis tests. Then, the performance of these methods are analyzed in terms of accuracy and qual...
This study presents numerical modeling of the dynamic behavior of an earth dam rested on a liquef... more This study presents numerical modeling of the dynamic behavior of an earth dam rested on a liquefiable foundation. Numerical simulations are carried out using effective stress-based, fully coupled nonlinear dynamic analysis approach. The Finn-Byrne model with extended Masing rules is employed to model pore pressure generation in the liquefied soils. In this regard, Masing rules are implemented into the constitutive relations to precisely explain the nonlinear response of soil under general cyclic loading. As a result, the soil shear stiffness and hysteretic damping can change with loading history. Pore pressure is accumulated as a function of the cyclic shear strain amplitude. The procedure of calibrating the constructed numerical model with well-documented centrifuge test data is addressed. Acceptable agreements are shown between the results obtained from the current investigation and those of experimental observations available in the literature. Afterwards, the dynamic response o...
Analyzing piles subjected to lateral loads significantly depends on soil resistance at any point ... more Analyzing piles subjected to lateral loads significantly depends on soil resistance at any point along the pile as a function of pile deflection, known as p-y curve. On the other hand, the deformation characteristics of soil defined as “the soil strain at 50% of maximum deviatoric stress (ε50)” has considerable effect on the generated p-y curve. In this research, several models are proposed to predict ε50 specifically for designing very long pile foundations of offshore oil and gas platforms in South Pars field, Persian Gulf, Iran. Herein, ε50 is evaluated from extensive soil data of marine clays including in-situ and laboratory test results using evolutionary polynomial regression (EPR). It is demonstrated that the normalized cone tip resistance, which is an indication of soil undrained shear strength, leads to more realistic ε50 values compared with the laboratory-derived undrained shear strength parameter. Furthermore, the results of a numerical study on lateral pile-soil system ...
Mechanics Based Design of Structures and Machines