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    Numerical investigation into the effects of geometrical and loading parameters on lateral spreading behavior of liquefied layer

    , Article Acta Geotechnica ; 2013 , Pages 1-13 ; 18611125 (ISSN) Pak, A ; Seyfi, S ; Ghassemi, A ; Sharif University of Technology
    2013
    Abstract
    Numerical simulation of liquefaction-induced lateral spreading in gently sloped sandy layers requires fully coupled dynamic hydro-mechanical analysis of saturated sandy soil subjected to seismic loading. In this study, a fully coupled finite element model utilizing a critical-state two-surface-plasticity constitutive model has been applied to numerically investigate the effects of surface/subsurface geometry on lateral spreading. Using a variable permeability function with respect to excess pore pressure ratio is another distinctive feature of the current study. The developed code has been verified against the results of the well-known VELACS project. Lateral spreading phenomenon has been... 

    Evaluation of variable permeability model in simulation of seismic behavior of uniform level and gently sloping sand layers

    , Article Earth Sciences Research Journal ; Volume 24, Issue 3 , 2020 , Pages 328-336 Ghassemi, A ; Seyfi, S ; Shahir, H ; Sharif University of Technology
    Universidad Nacional de Colombia  2020
    Abstract
    In this study, a fully coupled dynamic finite element model was employed for numerical simulation of the response of level to gently sloping saturated sand layers subjected to cyclic loading. This model utilized a critical state two-surface-plasticity constitutive model to simulate the cyclic behavior of sandy soil. Moreover, a recently proposed variable permeability function was implemented in the numerical model to reflect the effects of soil permeability variations during the liquefaction phenomenon. The numerical model was validated by simulating a number of well-documented geotechnical centrifuge tests with different relative density of sand, base acceleration time history, and surface... 

    Assessment of Effectivness of Compaction Improvement for Liquefaction Mitigation of Saturated Sand Deposits Based on Performance Levels of Shallow Foundations

    , Ph.D. Dissertation Sharif University of Technology Shahir, Hadi (Author) ; Pak, Ali (Supervisor) ; Ghannad, Mohammad Ali (Supervisor)
    Abstract
    Settlement and tilt of structures due to liquefaction of subsoil layers is a major cause of damage during earthquake. One of the main approaches to reduce terrible effects of liquefaction on shallow foundations is ground improvement. Among the variety of ground improvement methods, the densification-based methods have been more paid attention for liquefaction mitigation. For liquefaction hazard mitigation using densification methods, three basic values should be determined i.e. depth, lateral extent, and degree of improvement (percent increase in Dr). In the current design practice, the need for ground improvement is usually decided based on the semi-empirical methods for assessment of... 

    Prediction of lateral spreading displacement on gently sloping liquefiable ground

    , Article Geotechnical Frontiers 2017, 12 March 2017 through 15 March 2017 ; Issue GSP 281 , 2017 , Pages 267-276 ; 08950563 (ISSN) Ghasemi Fare, O ; Pak, A ; Geo-Institute (G-I) of the American Society of Civil Engineers; Industrial Fabrics Association International (IFAI) ; Sharif University of Technology
    American Society of Civil Engineers (ASCE)  2017
    Abstract
    A fully coupled numerical analysis using Biot's theory with u-p formulation considering variable permeability during liquefaction is used in this study to simulate liquefaction induced lateral spreading phenomenon. A centrifuge test performed on liquefiable soil at Rensselaer Polytechnic Institute is simulated using the developed model. The numerical results are in good agreement with experimental observations. A number of numerical simulations under different geometric, site-specific, and ground acceleration parameters have been carried out in the course of this study. Based on the statistical analysis conducted on the results of 31 different models, a new relation is proposed for... 

    Investigation of the influence of permeability coefficient on the numerical modeling of the liquefaction phenomenon

    , Article Scientia Iranica ; Volume 19, Issue 2 , 2012 , Pages 179-187 ; 10263098 (ISSN) Rahmani, A ; Ghasemi Fare, O ; Pak, A ; Sharif University of Technology
    2012
    Abstract
    The soil permeability coefficient plays a key role in the process of numerical simulation of the liquefaction phenomenon. Liquefaction causes a considerable increase in soil permeability, due to the creation of easier paths for water flow. The work presented in this paper tries to investigate the effects of permeability coefficient on the results of numerical modeling of the liquefaction phenomenon. To do this, a fully coupled (u-P) formulation is employed to analyze soil displacements and pore water pressures. Two different versions of a well-calibrated critical state bounding surface plasticity model, which possesses the capability to utilize a single set of material parameters for a wide... 

    Evaluation of variation of permeability in liquefiable soil under earthquake loading

    , Article Computers and Geotechnics ; Volume 40 , 2012 , Pages 74-88 ; 0266352X (ISSN) Shahir, H ; Pak, A ; Taiebat, M ; Jeremić, B ; Sharif University of Technology
    2012
    Abstract
    Liquefaction phenomenon is usually accompanied by large amounts of settlement owing to disruption of soil structure. In addition to that, large settlement also occurs by a significant increase in soil permeability during seismic excitation. To properly simulate the post-liquefaction settlement, it is important to take the compressibility properties of the liquefied sand as well as the permeability increase into account. Using initial permeability coefficient in the course of simulation of liquefaction leads to underestimation of settlement. In addition to that, using unrealistic values for permeability may cause erroneous predictions of other aspects of soil behavior. Therefore, an accurate...