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Showing 36 results for Subject: Seismic Geotechnique

Arash Nayeri, Kazem Fakharian,
Volume 7, Issue 4 (12-2009)
Abstract

Abstract: This paper presents the results of pullout tests on uniaxial geogrid embedded in silica sand under monotonic and cyclic pullout forces. The new testing device as a recently developed automated pullout test device for soil-geogrid strength and deformation behavior investigation is capable of applying load/displacement controlled monotonic/cyclic forces at different rates/frequencies and wave shapes, through a computer closed-loop system. Two grades of extruded HDPE uniaxial geogrids and uniform silica sand are used throughout the experiments. The effects of vertical surcharge, sand relative density, extensibility of reinforcement and cyclic pullout loads are investigated on the pullout resistance, nodal displacement distributions, post-cyclic pullout resistance and cyclic accumulated displacement of the geogrid. Tell-tale type transducers are implemented along the geogrid at several points to measure the relative displacements along the geogrid embedded length. In monotonic tests, decrease in relative displacement between soil and geogrid by increase of vertical stress and sand relative density are the main conclusions structural stiffness of geogrid has a direct effect on pullout resistance in different surcharges. In cyclic tests it is observed that the variation of post-cyclic strength ranges from minus 10% to plus 20% of monotonic strength values and cyclic accumulated displacements are increased as normal pressure increase, but no practical specific comment can be made at this stage on the post-cyclic strength of geogrids embedded in silica sand. It is also observed that in loose sand condition, the cyclic accumulated displacements are considerably smaller as compared to dense sand condition.
A. Ghanbari, M. Ahmadabadi,
Volume 8, Issue 2 (6-2010)
Abstract

Inclined retaining walls with slopes less than perpendicular are appropriate candidates in several

engineering problems. Yet, to the knowledge of authors, only a few analytical solution for calculation of active earth

pressure on such walls, which will be usually smaller than the same pressure on vertical ones, has been presented

neither in research papers nor in design codes. Considering limit equilibrium concept in current research, a new

formulation is proposed for determination of active earth pressure, angle of failure wedge and application point of

resultant force for inclined walls. Necessary parameters are extracted assuming the pseudo-static seismic coefficient

to be valid in earthquake conditions. Moreover, based on Horizontal Slices Method (HSM) a new formulation is

obtained for determining the characteristics of inclined walls in granular and or frictional cohesive soils. Findings of

present analysis are then compared with results from other available methods in similar conditions and this way, the

validity of proposed methods has been proved. Finally according to the results of this research, a simplified relation

for considering the effect of slope in reduction of active earth pressure and change in failure wedge in inclined

retaining walls has been proposed.


S.m. Moosavi, M.k. Jafari , M. Kamalian, A. Shafiee ,
Volume 8, Issue 2 (6-2010)
Abstract

Ground differential movements due to faulting have been observed to cause damage to engineered structures

and facilities. Although surface fault rupture is not a new problem, there are only a few building codes in the world

containing some type of provisions for reducing the risks. Fault setbacks or avoidance of construction in the proximity

to seismically active faults, are usually supposed as the first priority. In this paper, based on some 1-g physical

modelling tests, clear perspectives of surface fault rupture propagation and its interaction with shallow rigid

foundations are presented. It is observed that the surface fault rupture could be diverted by massive structures seated

on thick soil deposits. Where possible the fault has been deviated by the presence of the rigid foundation, which

remained undisturbed on the footwall. It is shown that the setback provision does not give generally enough assurance

that future faulting would not threaten the existing structures.


H. Soltani-Jigheh, A. Soroush,
Volume 8, Issue 2 (6-2010)
Abstract

Mixed clayey soils occur as mixtures of sand (or gravel) and clay in widely varying proportions. Their

engineering behavior has not been comprehensively studied yet. An experimental program, comprising monotonic,

cyclic, and post-cyclic triaxial tests was undertaken on compacted clay-granular material mixtures, having different

proportions of clay and sand or gravel. This paper presents the results of cyclic triaxial tests and explains the behavior

of the mixtures based on number of loading cycles, cyclic strain amplitude, granular material content, grain size, and

effective confining pressure. The results indicate an increase in degree of degradation and cyclic loading-induced pore

water pressure as the number of loading cycles, cyclic strain and granular material content increase. Also the results

show that the grain size has no significant effect on the degree of degradation and cyclic loading-induced pore water

pressure in the specimens. The effect of granular material content on pore water pressure during cyclic loading in

equal-stress-level was also examined. The pore water pressure increases with the increase of granular material

content.


F. Jafarzadeh, H. Farahi Jahromi, E. Abazari Torghabeh,
Volume 8, Issue 2 (6-2010)
Abstract

Investigating the parameters influencing the behavior of buried pipelines under dynamic loading is of great

importance. In this study the soil structure interaction of the pipelines with the surrounding soil was addressed using

shaking table tests. Wave propagation along the soil layers was also included in the study. The semi infinite nature of

the field was simulated using a laminar shear box. The soil used in the experiments was Babolsar coastal sand (Iran).

PVC pipes were used due to their analogy with the field. Eight models were constructed with the first four models

having uniform base. In the next models, the non-uniformities of real ground were simulated using a concrete pedestal

installed at the very bottom of the shear box. Pipe deformations under dynamic loading, acceleration distribution in

height, soil settlement and horizontal displacements were measured by strain gauges, acceleratometers and

displacement meters. Analyzing the obtained data, influence of different parameters of dynamic loading such as

acceleration, frequency, soil density, base conditions and shaking direction to pipe axis on the acceleration

amplification ratio and pipe deformation were investigated. Also in order to study the effect of dynamic loading on two

different materials, soil and pipe, the horizontal strains were compared


H. Shahnazari, M. Esmaeili, H. Hosseini Ranjbar,
Volume 8, Issue 2 (6-2010)
Abstract

Considerations on the explosion resistant design of special infrastructures have increased in the recent

years. Amongst the various types of infrastructures, road and railway tunnels have a unique importance due to their

vital role in connection routes in emergency conditions. In this study, the explosion effects of a projectile impacting on

a railway tunnel located in a jointed rock medium has been simulated using 2D DEM code. Primarily, a GP2000

projectile has been considered as a usual projectile and its penetration depth plus its crater diameter were calculated

in rock mass. The blast pressure was, then, calculated via empirical formula and applied on the boundary of crater as

input load. Finally, the wave pressure propagation through the jointed rock medium was investigated. In part of the

study a sensitivity analysis has been carried out on jointed rock parameters such as joint orientation, dynamic modulus

and damping ratio. Their effects on tunnel lining axial force as well as bending moment have also been investigated.


S.m. Mir Mohammad Hosseini, A.a. Hajimohammadi, A. R. Hajimohammadi,
Volume 8, Issue 2 (6-2010)
Abstract

Seismic piezocone device (SCPTu) together with Resonant Column and Cyclic Triaxial test apparatus are

employed to measure small strain shear modulus (G0) of carbonate sandy and clayey soils of southern coasts of Iran.

A large area of southern regions of Iran is formed from clay, silt and sand. In this study, maximum shear modulus that

is derived from both field (by seismic piezocone) and laboratory (by Resonant Column and Cyclic Triaxial) tests on

soil samples from the southern region, indicated a meaningful effect of sample disturbance. Results show that in

laboratory tests, loose samples tend to become denser and therefore exhibit greater stiffness whereas dense samples

tend to become looser, showing a reduction in stiffness. According to the results of the present study, there are narrow

limits of soils shear moduli for which the laboratory tests and the field measurements yield approximately the same

amounts. This limit of shear moduli is about 30-50(MPa) for clay deposits and 70-100 (MPa) for sandy deposits. Since

the shear moduli of soils in small strains can also be computed from the shear wave velocity, also correlations based

on parameters derived from SCPTu test for shear wave velocity determination of sandy and clayey soils of the studied

area are presented. This study shows that shear wave velocity can be related to both corrected tip resistance and total

normal stress. The measurements of the damping ratio and shear module, because of a great disturbance of stiff

deposits during the sampling process and also due to considerable differences between the laboratory and field

results, by the laboratory approaches are not reliable and advised.


S. A. Sadrnejad, S. A. Ghoreishian Amir,
Volume 8, Issue 2 (6-2010)
Abstract

A semi-micromechanical multilaminate model is introduced here to predict the mechanical behavior of soils.

This model is like a bridge between micro and macro scale upon the satisfaction of minimum potential energy level

during any applied stress/strain increments. The concept of this model is based on a certain number of sampling planes

which constitute the elastic-plastic behavior of the soil. The soil behavior presents as the summation of behavior on

these planes. A simple unconventional constitutive equations are used in each of the planes to describe the behavior

of these planes separately. An unconventional plasticity can predict the soil behavior as a smooth curve with

considering plastic deformation due to change of stress state inside the yield surface. The model is capable of

predicting softening behavior of the soil in a reasonable manner due to using unconventional plasticity. The influences

of induced anisotropy are included in a rational way without any additional hypotheses owing to in-nature properties

of the multilaminate framework. Results of this model are compared with test data and reasonable agreement is found.


P. Alimohammadi, N. Shariatmadari, M.a. Abdoli, H. Ghiasinejad, A. Mansouri,
Volume 8, Issue 2 (6-2010)
Abstract

Hydrologic Evaluation of Landfill Performance (HELP) model is one of the most accepted tools to simulate

the hydrological attributes of landfills. Although some major deviations from real values has been reported about the

calculated results for leachate generation by HELP model but other researchers and/or engineers in practice have

used it in some places to estimate amount of leachate produced in the landfills. On the Other hand this model is

elaborated and mainly used in developed countries with the waste having low moisture content and also in climatic

conditions with high precipitation. This research investigated the applicability of the model in arid areas, by

construction of two 30m× 50m (effective horizontal length) test cells in Kahrizak landfill (longitude=51°, 20',

latitude= 35° 27' degrees), and monitoring the real leachate generation from each one. A set of field capacity and

saturated water conductivity tests were also performed to determine basic hydrologic properties of municipal waste

landfilled. A comparison was made between values calculated by HELP model and recorded values, shows that a

prediction of leachate on annual basis can be done by HELP model with acceptable accuracy but when the infiltration

of water to waste body increases due to leachate production, the model intents to underestimate water storage capacity

of the landfill, which lead to deviation of calculated values from real ones.


Rouzbeh Dabiri, Faradjollah Askari, Ali Shafiee, Mohammad Kazem Jafari,
Volume 9, Issue 2 (6-2011)
Abstract

Laboratory data, which relate the liquefaction resistance of Firoozkooh sand and non-plastic silt mixtures to shear wave velocity are

presented and compared to liquefaction criteria derived from seismic field measurements by Andrus and Stokoe [1]. In the work

described herein, cyclic triaxial and resonant column tests were conducted on specimens of clean sand and sand-silt mixtures with silt

content up to 60%, prepared at different densities. Cyclic undrained strength and small strain shear wave velocity were determined

for identical specimens formed by undercompaction method. It was found that silt content affects cyclic resistance and shear wave

velocity. In addition, the laboratory results indicated that using the existing field-based correlations will overestimate the cyclic

resistance of the Firoozkooh sand-silt mixtures when silt content is 60%. For clean sand and the specimens containing up to 30% fines,

results of this study on cyclic resistance are fairly consistent with Andrus and Stokoe correlations. These findings suggest the need for

further evaluation of the effects of non-plastic fines content upon liquefaction criteria derived from seismic field measurements.


Mohammad Hassan Baziar, Habib Shahnazari, Hassan Sharafi,
Volume 9, Issue 2 (6-2011)
Abstract

This paper discusses the applicability of a simple model to predict pore water pressure generation in non-plastic silty soil during

cyclic loading. Several Stress-controlled cyclic hollow torsional tests were conducted to directly measure excess pore water pressure

generation at different levels of cyclic stress ratios (CSR) for the specimens prepared with different silt contents (SC=0% to 100%).

The soil specimens were tested under three different confining pressures (&sigma'3= 60, 120, 240 kPa) at a constant relative density

(Dr=60%), with different silt contents. Results of these tests were used to investigate the behavior of silty sands under undrained

cyclic hollow torsional loading conditions. In general, beneficial effects of the silt were observed in the form of a decrease in excess

pore water pressure and an increase in the volumetric strain. Modified model for pore water pressure generation model based on

the test results are also presented in this paper. Comparison of the proposed pore pressure build up model with seed’s model

indicates the advantage of proposed model for soil with large amount of silt.


M. Miraboutalebi, F. Askari, O. Farzaneh,
Volume 9, Issue 4 (12-2011)
Abstract

In this paper, the effect of bedrock inclination on seismic performance of slopes is investigated. The study was conducted based

on dynamic analysis of different slopes, evaluation of the earthquake acceleration in sliding mass, and calculating the

permanent displacement of the slope, using Newmark sliding block. The investigation indicates that variation of the bedrock

inclination may cause the acceleration magnitude and the displacement in the sliding mass to reach to their maximum level.

This may happen in conditions that the mean period of the acceleration time history on failure surface (Tmt) and the

predominant period of the slope (Ts ) are close to each other. Typical results are presented and discussed. A two dimensional

model of a typical slope was considered and conducting dynamic analyses, the slope performance was studied for different

geometries, strength parameters and shear wave velocities. Such a performance has been studied by assessing the record of

acceleration in sliding mass (the mass above the critical sliding surface) and calculating the slope displacement using Newmark

method. It is shown that neglecting the effect of bedrock inclination, would lead to non-real results in assessing the seismic slope

performance.


A. Hassanipour, A. Shafiee, M.k. Jafari,
Volume 9, Issue 4 (12-2011)
Abstract

Shear modulus and damping ratio are important input parameters in dynamic analysis. A series of resonant column tests was

carried out on pure clays and sand-clay mixtures prepared at different densities to investigate the effects of aggregate content,

confining stress, void ratio and clay plasticity on the maximum shear modulus and minimum damping ratio. Test results revealed

an increase in the maximum shear modulus of the mixture with the increase in sand content up to 60%, followed by a decrease

beyond this value. It was also found that the maximum shear modulus increases with confining stress, and decreases with void

ratio. In addition, minimum damping ratio increases with sand content and clay plasticity and decreases with confining stress.

Finally, on the basis of the test results, a mathematical model was developed for the maximum shear modulus.


J. Jalili, M. K. Jafari, A. Shafiee, J. Koseki, T. Sato,
Volume 10, Issue 2 (6-2012)
Abstract

A series of tests and also numerical analyses were conducted to explore the mechanical behavior of a mixture of coarse gravelsize
particles floating in a matrix of silt, sand or clay. The research is a step forward in an ongoing investigation on behavior of
composite clay, which is used as the core material of some large embankment dams all over the world. After providing the reader
with an overall image about behavior of such materials through the literature, the paper focuses on a predominant feature of the
composite soil behavior: increase of non-deformable solid inclusions in a mixture leads to formation of heterogeneity of stress
field, excess pore water pressure and strain distribution along the specimens. This paper mainly probes formation of such
heterogeneity by the aid of special experiments and also numerical analyses. In addition to loading details, it is clarified through
the paper that position of inclusions relative to loading direction also affects heterogeneity of stress/strain and excess pore water
pressure distribution through the mixture. Despite the former, the latter redistributes with a rate proportional to material
hydraulic conductivity.


A. Ghanbari, E. Hoomaan, M. Mojallal,
Volume 11, Issue 1 (5-2013)
Abstract

For calculating the natural frequency of structures such as buildings, chimneys, bridges and silos appropriate analytical

formulas exist. However, in the case of retaining walls undergoing the soil pressure at one side, calculating the natural frequency

is not a straightforward task and requires the effects of soil-structure interactions to be considered. By modeling the soil as series

of linear springs, a new formulation is presented in this article, to calculate the natural frequency of retaining walls. This formula

considers the vertical cross sectional width change, and hence, enables us to calculating the natural frequency of retaining walls

with different types of backfill. The geometrical properties of the retaining walls and its bending rigidity together with the soil’s

modulus of elasticity and its Poisson’s ratio are the most important parameters to calculate. A comparison of the results for

retaining walls with constant cross section obtained from the suggested method with those of the software analyses was carried

out and good agreement was detected. A second comparison of the results with those of other researchers revealed that the natural

frequency of flexible retaining wall is an upper bound for natural frequency of rigid walls. The Selected shape function is also

very close to the real shape mode.


H. Alielahi, M. Kamalian, J. Asgari Marnani, M. K. Jafari, M. Panji,
Volume 11, Issue 1 (5-2013)
Abstract

In this paper, an advanced formulation of a time-domain two-dimensional boundary element method (BEM) is presented and

applied to calculate the response of a buried, unlined, and infinitely long cylindrical cavity with a circular cross-section subjected

to SV and P waves. The applicability and efficiency of the algorithm are verified with frequency-domain BEM examples of the

effect of cylindrical cavities on the site response analysis. The analysis results show that acceptable agreements exist between

results of this research and presented examples. For a shallow cavity, the numerical results demonstrate that vertically incident

SV wave reduces the horizontal components of the motion on the ground surface above the cavity, while it significantly increases

the vertical component for a dimensionless frequency (&eta) of 0.5 and h/a=1.5. The maximum values of normalized displacements

in vertical component of P waves are larger than horizontal component of SV waves for &eta=1.0. For a deeply embedded cavity,

the effect of the cavity on the surface ground motion is negligible for incident SV wave, but it increases the vertical component of

the displacement for incident P wave. Additionally, far and near distances from the center of the cavity show different amplitude

patterns of response due to the cavity effect. Increasing the distance from the center of the cavity, the amplitude of displacement

and the effect of the cavity attenuates significantly.


F. Askari, M. R. Arvin, O. Farzaneh,
Volume 11, Issue 2 (11-2013)
Abstract

Seismic stability of slopes is typically evaluated by conventional methods under the assumption that the slope is subjected to an

earthquake just for one time. In general, time histories of loadings on slopes are unknown and loads are of variable repeated

nature. Shakedown phenomenon can be considered as a safe state for slopes subjected to variable repeated loadings. In this study,

lower bound dynamic shakedown theorem is employed for the seismic stability of slopes as a comprehensive verification. A

numerical method applied previously to evaluate roads under the traffic loads was modified to make it appropriate for dynamic

shakedown analysis in the present study. The numerical method is based on the combination of finite element and linear

programming methods. Critical PGA is employed as a comparative parameter to compare shakedown and pseudostatic methods.

Results show that, unlike pseudostaic method, shakedown approach is able to consider dynamic properties of load and slope.

Also, it is indicated that contrary to pseudostaic approach, shakedown solutions are different for slopes and embankments.

Shakedown and pseudostaic critical PGA versus dynamic properties of load and slope creates four distinct zones. It is shown that

the forgoing zones can be used as appropriate tools for seismic zonation of slopes based on their short term and long term safety


M. Biglari, I. Ashayeri,
Volume 11, Issue 2 (11-2013)
Abstract

Seismic ground motion is profoundly affected by geometrical and mechanical properties of soil deposits overlaying bedrock.

Local seismic ground response of saturated soil deposits was studied in literature by applying the effects of soil stress state

and index properties on the strain-dependent normalized shear modulus reduction, G/G0, and damping ratio, D, curves in an

equivalent linear analysis. However, experimental investigations revealed that, G0, G/G0, and D of unsaturated soils are

influenced by stress state as well as suction. This study presents the results of linear and equivalent linear seismic ground response

analysis of unsaturated soil deposits incorporating suction effects on G/G0 and D curves. Seismic ground response analyses were

done with the computer program EERA for three sets of soil profiles, which are included in saturated, constant and linearly

variable suction unsaturated soil deposits. The results of current study present the magnitude of variation in natural frequency,

amplification ratio and spectral acceleration of unsaturated soil deposits.


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

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.


M. Fadaee, M.k. Jafari, M. Kamalian, M. Moosavi, A. Shafiee,
Volume 11, Issue 2 (11-2013)
Abstract

During past earthquakes, many instances of building damage as a result of earthquake surface fault rupture have been observed.

The results of investigating a potential mitigation scheme are presented in this paper. Such plan provides a wall in the soil with

the aim of surface displacement localization in the narrow pre-determined location. This may reduce the risk of the future rupture

downstream the wall. To evaluate the efficiency of the method, this paper (i) provides validation through successful class “A”

predictions of 1g model tests for fault deviation by weak wall and (ii) conducts sensitivity analyses on fault position, fault offset

and wall shear strength. It is shown that wall can be designed to deviate rupture path even downstream of the wall can be

protected.



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