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Showing 12 results for Numerical Modeling

M.h. Bagheripour, S.m. Marandi,
Volume 3, Issue 2 (6-2005)

Arational approach is introduced for numerical modeling of unbounded soil foundations based on coupled dynamic periodic infinite and conventional finite elements (IFE-FE). The model can be applied for analysis of various dynamic problems in geomechanics, especially in Soil Structure Interaction (SSI), where determination of stiffness properties and response of unbounded soil domains are of prime importance. In numerical SSI analysis, there exists important problems a) the discretization of natural soil foundation, especially defining the boundaries to prevent reflecting body waves and avoiding spurious results, b) the definition of the matrices related to the soils impedance functions which are essentially dependant on the excitation frequency, c) the evaluation of free field motion of the natural foundation, especially those of irregular geometry and material diversity. An efficient way and integrated solution to these important problems is found to be the use of periodic infinite elements. The wave equation of motion is derived numerically for discretization of the soil domain. Shape functions and mapping coordinates for dynamic periodic infinite elements are presented in this paper. The accuracy of the IFE is examined for the evaluation of free field motion of a visco-elastic soil foundation. Derivation of impedance function is shown and leads to the determination of dynamic stiffness characteristics of the unbounded soil medium including spring and dashpot coefficients. Application of the approach introduced here is shown by analysis of SSI for a semi-tall building subjected to earthquake loading. Other advantages of the approach are the substantial reduction in degrees of freedom involved in numerical SSI analysis, the computational time and costs without sacrificing the accuracy of the results.
M.h. Baziar, A. Ghorbani, R. Katzenbach,
Volume 7, Issue 3 (9-2009)

The pile-raft foundation is a combination of a raft foundation with piles. Pile-raft foundation has been widely designed, assuming all structure loads to be transferred to piles without considering contribution of the load taken by contact surface between raft and soil. Methods of analysis currently used in practice are based upon relatively conservative assumptions of soil behavior or on the less realistic soil-structure interaction. In this study the bearing -settlement behavior of combined pile-raft foundations on medium dense sand was investigated. 1g physical model test was performed on a circular rigid raft underpinned with four model piles. Numerical simulation was also carried out on the model test, using FLAC-3D, to show compatibility of the numerical analysis with the test. The obtained results showed very good accuracy of the numerical method used in this study as long as the applied load does not exceed the working load, while the performance of numerical model was relatively good for the loads beyond working load.
A. R. Majidi, A.a. Mirghasemi, M. Arabshahi,
Volume 9, Issue 4 (12-2011)

In the current study, an effort is made to determine three dimensional bearing capacity of rectangular foundations using Discrete

Element Method. The soil mass is modeled as discrete blocks connected with Winkler springs. Different factors affect the geometry

of failure surface. Six independent angles are used to define the failure surface. By trial and error, the optimum shape of failure

surface beneath the foundation can be found. The paper includes the derivation of the governing equations for this DEM based

formulation in three dimensional state as well as parametric sensitivity analyses and comparison with other methods. Moreover,

using the current method, bearing capacity coefficients are presented for various friction angles and foundation aspect ratios.

R. Mahin Roosta, A. Alizadeh,
Volume 10, Issue 2 (6-2012)

In the first impounding of rockfill dams, additional settlements occur in upstream side in saturated rockfills due to collapse
phenomenon even high rainy seasons can cause additional deformation in the dumped rockfills. Unfortunately these
displacements are not taken into account in the conventional numerical models which are currently used to predict embankment
dam behavior during impounding. In this paper to estimate these displacements, strain hardening-strain softening model in Flac
is modified based on the laboratory tests, in which same impounding process in such dams is considered. Main feature of the
model is reproduction of nonlinear behavior of rockfill material via mobilized shear strength parameters and using collapse
coefficient to display induced settlement due to inundation. This mobilization of shear strength parameters associated with some
functions for dilatancy behavior of rockfill are used in a finite difference code for both dry and wet condition of material. Collapse
coefficient is defined as a stress dependent function to show stress release in the material owing to saturation. To demonstrate
how the model works, simulation of some large scale triaxial tests of rockfill material in Gotvand embankment dam is presented
and results are compared with those from laboratory tests, which are in good agreement. The technique could be used with any
suitable constitutive law in other coarse-grained material to identify collapse settlements due to saturation

M. Mortazavi Zanjani, A. Soroush,
Volume 11, Issue 2 (11-2013)

This paper presents results of a thorough study on the phenomenon of rupture propagation of reverse faults from the bedrock

foundation through homogeneous clayey embankments, mainly at the end of construction, with complementary analyses for the

steady state seepage through the embankment. The study is performed by means of numerical analyses with a nonlinear Finite

Element Method, verified beforehand through simulating fault propagations in an existing horizontal soil layer experiment.

Multiple cases considering three slopes & three clayey soils for the embankment and five fault dip angles, activated in several

locations of base of the embankment, are analyzed. The results show that ruptures in the embankment follow optimal paths to

reach the surface and their near-surface directions are predictable with respect to corresponding theories of classical soil

mechanics. Various types of rupture in the embankment are produced on the basis of the rupture types, the embankment base is

divided into three distinguishable zones, which can be used for interpretation of fault ruptures behavior. The effects of materials

and slope of the embankment, fault dip angle, and fault’s point of application in the bedrock-soil interface on the rupture paths

are studied in depth.

Y.y. Chang, C.j. Lee, W.c. Huang, W.j. Huang, M.l. Lin, W.y. Hung, Y. H. Lin,
Volume 11, Issue 2 (11-2013)

This study presents a series of physical model tests and numerical simulations using PFC2D (both with a dip slip angle=60° and

a soil bed thickness of 0.2 m in model scale)at the acceleration conditions of 1g, 40g, and 80 g to model reverse faulting. The soil

deposits in prototype scale have thicknesses of 0.2 m, 8 m, and 16 m, respectively. This study also investigates the evolution of a

surface deformation profile and the propagation of subsurface rupture traces through overlying sand. This study proposes a

methodology for calibrating the micromechanical material parameters used in the numerical simulation based on the measured

surface settlements of the tested sand bed in the self-weight consolidation stage. The test results show that steeper surface slope

on the surface deformation profile, a wider shear band on the major faulting-induced distortion zone, and more faulting appeared

in the shallower depths in the 1-g reverse faulting model test than in the tests involving higher-g levels. The surface deformation

profile measured from the higher-g physical modeling and that calculated from numerical modeling show good agreement. The

width of the shear band obtained from the numerical simulation was slightly wider than that from the physical modeling at the

same g-levels and the position of the shear band moved an offset of 15 mm in model scale to the footwall compared with the results

of physical modeling.

J. Nazari Afshar, M. Ghazavi,
Volume 12, Issue 1 (1-2014)

The Stone-column is a useful method for increasing the bearing capacity and reducing settlement of foundation soil. The prediction of accurate ultimate bearing capacity of stone columns is very important in soil improvement techniques. Bulging failure mechanism usually controls the failure mechanism. In this paper, an imaginary retaining wall is used such that it stretches vertically from the stone column edge. A simple analytical method is introduced for estimation of the ultimate bearing capacity of the stone column using Coulomb lateral earth pressure theory. Presented method needs conventional Mohr-coloumb shear strength parameters of the stone column material and the native soil for estimation the ultimate bearing capacity of stone column. The validity of the developed method has been verified using finite element method and test data. Parametric studies have been carried out and effects of contributing parameters such as stone column diameter, column spacing, and the internal friction angle of the stone column material on the ultimate bearing capacity have been investigated.
M. B. Esfandiari Sowmehsaraei, R. Jamshidi Chenari,
Volume 12, Issue 1 (1-2014)

Soil reinforced with fiber shows characteristics of a composite material, in which fiber inclusion has a significant effect on soil permeability. Concerning to the higher void ratio of carpet fibers, at first stages it may be expected that an increase in fiber content of the reinforced soil would result in an increase in permeability of the mixture. However, the present article demonstrates that fiber inclusion will decrease the permeability of sand-fiber composite.A series of constant head permeability tests have been carried out to show the effects and consequently, a new system of phase relationships was introduced to calculate the dry mass for the sand portion of the composite. Monte Carlo simulation technique adopted with finite element theory was employed to back calculate the hydraulic conductivity of individual porous fibers from the laboratory test results. It was observed that the permeability coefficient of the porous fibers are orders of magnitude less than the skeletal sand portion due to the fine sand particle entrapment and also the fiber volume change characteristics.
E. Lotfi, S. Delfan, A. Hamidi, H. Shahir, Gh. Fardi,
Volume 12, Issue 1 (1-2014)

In saturated soils, heating induces thermal expansion of both grains and the pore fluid. Lower thermal expansion coefficient of aggregates results in the increase of pore pressure and reduction of the effective stress besides subsequent volume changes due to the dissipation of pore pressure and heat transfer. Dissipation of thermally induced pore pressure with time is a coupled thermo-hydro-mechanical (THM) phenomenon, involving gradients of pore pressure and temperature, hydraulic and thermal flows within the mass of soil and changes in the mechanical properties with temperature. The objective of this paper is presentation of a numerical method to determine the effect of temperature on consolidation of clays. In this regard, the finite element code, PISA is used for one dimensional THM analysis of porous media. The analysis performed using both linear elastic and elastoplastic Cam clay models. Modified Cam clay model was applied in elastoplastic analysis. Variation of temperature, displacements and pore pressure determined with time and compared with numerical solutions of other researchers. Also it was indicated that implementation of coupled THM analysis yields better results for displacements compared to the hydro mechanical (HM) one. Application of elastoplastic constitutive model instead of linear elastic one indicated that preconsolidation pressure has an important effect on results of analysis.
M. Heidarzadeh, A. A. Mirghasemi, H. Niroomand,
Volume 13, Issue 1 (3-2015)

We report engineering experiences from the critical task of relief well installation under high artesian flow conditions at the downstream toe of the Karkheh earth dam, Iran. Due to the establishment of excessive uplift pressure at the downstream toe of the Karkheh dam, installation of a series of new relief wells was considered to permanently relieve part of these pressures. The mentioned uplift pressure, as high as around 30 m above the ground level, was produced in a confined conglomerate aquifer bounded above and below by relatively impervious mudstone layers which reduced the safety factor of the dam toe to below 1.0. Investigations on the shortcomings of the old relief wells installed at the dam site showed that the main problems were: insufficient well numbers, insufficient well diameters, irregular well screens causing their blockage by time passing, and insufficient total opening area. Despite engineering difficulties and associated risk of downstream toe instability, installation of new relief wells was successfully completed under high artesian flow conditions” was successfully completed. The employed technique for the construction of the new relief wells under flowing artesian conditions was based on: 1) cement grouting and casing of the well, 2) telescopic drilling, 3) application of appropriate drilling fluid, and 4) controlling the artesian flow by adding a long vertical pipe to the top of the relief wells. Numerical modeling of seepage for the Karkheh dam foundation showed that, as a result of the installation of the new relief wells, the safety factor of the downstream toe increased to the safe value of 1.3 for the normal reservoir water level.
Hanane Dob , Salah Messast, Abdelhamid Mendjel, Marc Boulon, Etienne Flavigny,
Volume 14, Issue 7 (10-2016)

Considerable strains appear in the structures during accumulation of the irreversible strains of the subgrade under the effect of the cyclic loads. If the number of cycles is very large, even a small strain after accumulation becomes significant and sometimes harmful. In this study, a simple numerical modeling of the behavior of sand under cyclic loading is proposed. The suggested approach consists, in drained condition, in determining the parameters characterizing the average cyclic path of the soil under the effect of the number of cycles duly characterized and translating the cyclic effect by a volumetric strain cumulated by a variation of the module of the soil. In this study, we are interested in cyclic triaxial compression tests simulated by a finite element calculation. While proposing an analogy between the cyclic pseudo creep and the soft soil creep model (SSCM), on the first hand we propose an equivalence between the cyclic parameters and the parameters of SSCM, and on the other an equivalence time number of cycles will be established. The application of the formulation suggested on a shallow foundation under cyclic loading confirms the good adaptation of the model suggested to this type of problem.

Sohrab Karimi, Hossein Bonakdari, Azadeh Gholami, Amir Hossein Zaji,
Volume 15, Issue 2 (3-2017)

Dividing open channels are varied types of open channel structures used to provide water for irrigation channels, agriculture and wastewater networks. In the present study the mean velocity is calculated in different dividing angles within the branches channel through the use of artificial Neural Network (ANN) and coputational fluid dynamices (CFD) models. First the ANSYS-CFX model is used to simulate the flow pattern within the branch with a 90° angle. The results of the CFX model correspond fairly well to the results of the experimental model with Mean Absolute Percentage Error (MAPE) of 5%. After verifying, two CFX model are generated in 30° and 60° angle in different width ratios of 0.6, 0.8, 1, 1.2, and 1.4, and the mean velocities are obtained by flowmeter. Following that ANN model trained and tested through the use of a set of experimental and CFX datas. The comparison showed that the ANN model has an acceptable level of accuracy in predicting the dividing open channel mean flow velocity with mean value R2 of 0.93. Comparing the results indicated that ANN model with the MAPE of 1.8% performs better in 0.8 m width ratio. Also, in this width ratio the MAPE are equal to 1.58, 1.87, and 2.04 % in 30°, 60°, and 90° deviation angles respectively and therefore the model performs better in 30° angle.

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