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Showing 33 results for Triaxial

Baziar M.h., Asna Ashari M.,
Volume 2, Issue 3 (9-2004)
Abstract

An experimental study was carried out to evaluate the liquefaction resistance of silty sand utilizing laboratory techniques. In this study, liquefaction potential of silty sand by using cyclic triaxial tests on frozen samples retrieved from calibration chamber and constructed samples by dry pouring method were investigated. Correlation between cone penetration resistance and cyclic strength of undisturbed silty sand samples are also examined using CPT calibration chamber and cyclic triaxial tests. The cone penetration tests were performed on silty sand samples with fine contents ranging from 0% to 50% and overburden stresses in the range of 100-300 kPa. Then the soil sample in calibration chamber, in the same way that soil samples were prepared during CPT sounding, was frozen and undisturbed soil specimen retrieved from frozen soil sample were tested using cyclic triaxial tests. Analysis of results indicates that the quality of frozen samples is affected by fine content and overburden pressures. Also, using data obtained in this research, the relationship between cone tip resistance and cyclic resistance ratio (CRR) for silty sand soils will be presented. These correlations are in relatively good agreement with field case history data. Also increasing confining pressure in silty sand material increases the cone tip resistance and generally, cyclic resistance ratio increases by increasing silt content.
Saleh Zadeh H., Ghazanfari E.,
Volume 2, Issue 4 (12-2004)
Abstract

To study the behavior of carbonate sands parametrically, some monotonic triaxial testswere carried out on Kish carbonate sand. The sample was provided from Kish Island beach. Inorder to examine the effect of density and confining pressure, samples in loose and dense stateswere tested under different confining pressures. For studying the effect of drainage andconsolidation, different stress paths were followed. Also to study the effect of particle crushing indrained tests all samples were graded before and after testing. Comparison between loose anddense samples in both drained and undrained tests showed that with increasing confiningpressure, the reduction in shear resistance in loose samples is less than dense samples and theincrement rate of particle crushing in loose samples is more than dense samples. In the range oflow confining pressures both loose and dense samples showed dilation response. With increasingconfining pressure, the loose samples tended to exhibit contraction and the rate of dilation indense samples reduced. Because recovering undisturbed sample of carbonate sediments is veryhard or even impossible so the effect of soil disturbance is not studied in this research.
M. Naderi,
Volume 3, Issue 1 (3-2005)
Abstract

Having observed the costly failures of different cutoff walls, that had been constructed according to the mix design specified by reputable consultants in Iran, a research programme was conducted to study the effects of constituent materials on the properties of plastic concrete. The main properties, such as compressive strength, biaxial and triaxial strains, permeability, and modulus of elasticity have been investigated using different mixes, obtained from prototype production line plant, situated on site, because it was realized that the site production line and the systems employed have major effects on the properties of plastic concrete. Statistical analysis of the results, revealed the coefficients of influence of main constituent materials of plastic concrete namely cement, bentonite, aggregate and water on its compressive strength and modulus of elasticity. Having realized the cancelling effects of bentonite and aggregates on the measured properties, some equations relating the quantities of cement and water to the compressive strength and modulus of elasticity are introduced. Effects of clay and hydrated lime powder, as fillers were also investigated leading to the proposal of limits for their safe and economic use. Since most of the cutoff walls are buried structures, failure strains under both uniaxial and triaxial tests, with values of cohesion and internal friction, are also presented in this paper.
Saleh Zadeh H., Procter D.c., Merrifield C.m.,
Volume 3, Issue 3 (9-2005)
Abstract

The unique behaviour of carbonate materials under shear loading has stimulated in investigating of their geological and engineering properties.Carbonate soils composed of calcium or other carbonates and most abundant in tropical marine environments are of interest from geotechnical view, especially for offshore engineers engaged with Fossil-based fuel exploitation. This was initiated in the early 1960's, when the first offshore borings in the Persian Gulf identified layers of calcarenite and thick layers of sand containing visible shell fragments.For the purpose of exploiting gas and oil resources in hot and temperate climates (e.g. Persian Gulf) off-shore structures have been placed on carbonate soils. The carbonate sediments are high crushable compared with low crushable sediments such as quartzic soils.To examine the crushability of these problematic sediments a series of monotonic compression, extension and post-cyclic triaxial tests under different densities and confining pressures was carried out to study the crushing behaviour of "Rock" carbonate sand obtained from Cornwall, England.It was shown that crushing coefficient decreases with increasing in maximum principal effective stress ratio for both loose and dense states. It seems that for skeletal carbonate sand maximum and minimum dry densities will be changed during shearing loading. In other words, even though the sample has experienced an increase in density, it may also have experienced a reduction in relative density.
H. Soltani-Jigheh, A. Soroush,
Volume 4, Issue 3 (9-2006)
Abstract

This paper presents the results of a series of monotonic and post-cyclic triaxial tests carried out on a clay specimen and three types of clay-sand mixed specimens. The focus of the paper is on the post-cyclic mechanical behavior of the mixed specimens, as compared to their monotonic behavior. Analyses of the tests results show that cyclic loading degrade undrained shear strength and deformation modulus of the specimens during the post-cyclic monotonic loading. The degradation depends on the sand content, the cyclic strain level and to some degrees to the consolidation pressure.
A.a. Khosroshahi, S.a. Sadrnejad,
Volume 5, Issue 1 (3-2007)
Abstract

A framework for development of constitutive models including damage progress, based on semi-micromechanical aspects of plasticity is proposed for concrete. The model uses sub-loading surface with multilaminate framework to provide kinematics and isotropic hardening/softening in the ascending/descending branches of loading and can be able to keep stress/stain paths histories for each plane separately. State of stresses on planes is divided to four basic stress patterns i.e. pure compression, increasing compression-and shear, decreasing compression-shear and tension-shear and used in derivation of plasticity equations. Under this kind of categorized form the model is capable of predicting behavior of concrete under any stress/strain path such as uniaxial, biaxial and triaxial in the monotonic and cyclic loading, Also this model is capable of predicting the effects of principal stress/strain axes rotations and consequent plastic flow and has the potential to simulate the behavior of material with anisotropy, fabric pattern, slip/weak planes and crack opening/closing. The material parameters of model are calibrated by optimum fitting of the basic test data available in the literature. The model results under both monotonic and cyclic loading have been compared with experimental results to show capability of model.
S.a. Naeini, R. Ziaie-Moayed,
Volume 5, Issue 2 (6-2007)
Abstract

Series of undrained monotonic triaxial tests and cone penetration tests were conducted on loose silty sand samples to study correlation between undrained shear strength of silty sands (Sus) and piezocone test results. CPT tests were conducted at 27 silty sand samples in calibration chamber. The results indicate that, in low percent of silt (0-30%), as the silt content increases, the undrained shear strength (Sus) and cone tip resistance (qc) decreases. It is shown that, fines content affects undrained shear strength (Sus) and cone tip resistance (qc) similarly. On the basis of obtained results, equations were proposed to determine the normalized cone tip resistance (qc1n) and undrained shear strength (Sus) of silty sand in term of fines content. Finally based on those equations, a correlation between normalized cone tip resistance and undrained shear strength of silty sand is presented. It is shown that the normalized undrained shear strength and normalized cone tip resistance of loose silty sands (F.C. <30%) decreases with increase of silt contents.
S.n. Moghaddas Tafreshi, A. Asakereh,
Volume 5, Issue 4 (12-2007)
Abstract

Conventional investigations on the behavior of reinforced and unreinforced soils are often investigated at the failure point. In this paper, a new concept of comparison of the behavior of reinforced and unreinforced soil by estimating the strength and strength ratio (deviatoric stress of reinforced sample to unreinforced sample) at various strain levels is proposed. A comprehensive set of laboratory triaxial compression tests was carried out on wet (natural water content) non-plastic beach silty sand with and without geotextile. The layer configurations used are one, two, three and four horizontal reinforcing layers in a triaxial test sample. The influences of the number of geotextile layers and confining pressure at 3%, 6%, 9%, 12% and 15% of the imposed strain levels on sample were studied and described. The results show that the trend and magnitude of strength ratio is different for various strain level. It implies that using failure strength from peak point or strength corresponding to the axial-strain approximately 15% to evaluate the enhancement of strength or strength ratio due to reinforcement may cause hazard and uncertainty in practical design. Hence, it is necessary to consider the strength of reinforced sample compared with unreinforced sample at the imposed strain level. Only one type of soil and one type of geotextile were used in all tests.
M.a. Khan, A. Usmani, S.s. Shah, H. Abbas,
Volume 6, Issue 2 (6-2008)
Abstract

In the present investigation, the cyclic load deformation behaviour of soil-fly ash layered system is

studied using different intensities of failure load (I = 25%, 50% and 75%) with varying number of cycles (N =

10, 50 and 100). An attempt has been made to establish the use of fly ash as a fill material for embankments of

Highways and Railways and to examine the effect of cyclic loading on the layered samples of soil and fly ash.

The number of cycles, confining pressures and the intensity of loads at which loading unloading has been

performed were varied. The resilient modulus, permanent strain and cyclic strength factor are evaluated from

the test results and compared to show their variation with varying stress levels. The nature of stress-strain

relationship is initially linear for low stress levels and then turns non-linear for high stress levels. The test

results reveal two types of failure mechanisms that demonstrate the dependency of consolidated undrained

shear strength tests of soil-fly ash matrix on the interface characteristics of the layered soils under cyclic

loading conditions. Data trends indicate greater stability of layered samples of soil-fly ash matrix in terms of

failure load (i) at higher number of loading-unloading cycles, performed at lower intensity of deviatoric stress,

and (ii) at lower number of cycles but at higher intensity of deviatoric stress.


Mahmoud Hassanlourad, Hosein Salehzadeh, Habib Shahnazari,
Volume 6, Issue 2 (6-2008)
Abstract

In this paper shear behavior of two calcareous sands having different physical properties are

investigated using drained and undrained triaxial tests. The investigated sands are obtained from two different

zones located in Persian Gulf, Kish Island and Tonbak region. Analysis based on energy aspects show that

friction angle in these soils, having crushable particles, is formed of three components: substantial internal

friction angle, dilation and particle breakage angle. Dilation component is available in the two investigated

sand. Particle breakage component is a function of grains hardness, structure and geometry shape. Particles

breakage decreases the volume of sample during drained tests and creates positive pore water pressure during

undrained tests. Two investigated sands show different amount of dilation and particle breakage under similar

conditions. Simultaneous dilation and particles crushing and different amount of them result in different shear

behavior of the two studied sands. Energy aspects are used to determine the effect of particle crushing on the

shear strength. There is a suitable compatibility between relative breakage of grains and consumed energy

ratio for particle breakage.


Amir Hamidi, S. Mohsen Haeri,
Volume 6, Issue 3 (9-2008)
Abstract

The deformation and stiffness characteristics of a cemented gravely sand was investigated using triaxial equipment. The triaxial tests were conducted in both dry and saturated undrained conditions. Artificially cemented samples are prepared using gypsum plaster as the cementing agent. The plaster was mixed with the base soil at the weight percentages of 1.5, 3, 4.5 and 6. The applied confining pressure varied between 25 to 500 kPa in triaxial tests. The process of yielding of the soil was investigated for the considered soil and the bond and final yield points were identified for the cemented soil with different cement contents. The variations of deformation and stiffness parameters with cement content and confining stress were studied as well. Some of the parameters were determined for both drained and undrained conditions to investigate the effect of drainage condition on the stiffness and yield characteristics of the tested cemented gravely sand. According to the results, the difference between drained and undrained tangent stiffness decreases with increase in confining stress. Finally the effect of cement type was investigated as an important parameter affecting the stiffness at bond yield. The rate of increase in tangent stiffness at bond yield changes with cement content for different cementing agents.
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.


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.


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.


M. Hassanlourad, H. Salehzadeh, H. Shahnazari,
Volume 9, Issue 4 (12-2011)
Abstract

The effects of cementation and the physical properties of grains on the shear behavior of grouted sands are investigated in this

paper. The consolidated-undrained triaxial shear behavior of three grouted carbonate sands with different physical properties,

including particle size distribution, particle shape and void ratio, was studied. Two sands were obtained from the north shores

of the Persian Gulf, south of Iran, called Hormoz and Kish islands sands, and one sand was obtained from the south beaches

of England and called Rock beach sand. The selected sands were grouted using a chemical grout of sodium silicate and tested

after one month of curing. Test results showed that the effect of bonding on the shear behavior and strength depends on the bond

strength and confining pressure. In addition, the shear behavior, yield strength and shear strength of grouted sands under

constant conditions, including the initial relative density, bonds strength, confining pressure and loading, were affected by the

physical properties of the sands. Furthermore, the parameters of the Mohr-Coulomb shear strength failure envelope, including

the cohesion and internal friction angle of grouted sands under constant conditions, were affected by the physical properties

and structure of the soils.


A. Soroush, R. Jannatiaghdam,
Volume 10, Issue 2 (6-2012)
Abstract

This paper studies thoroughly and deeply the results of about one hundred triaxial compression tests on thirty types of rockfill
materials. The materials are categorized in accordance with their particles shape (angular / rounded) and gradation
characteristics. The main tool of the study is the Hyperbolic Model developed by Duncan and Chang. The focus of the study is
on the variations of deformation modulus of the materials (Ei and Et) with confining stress (&sigma3). Features of the mechanical
behavior of the rockfill materials, as compared with the general behavior of soils, are highlighted through the exponent
parameter (n) of the Hyperbolic Model. It is shown that high confining stresses may have adverse effects on the deformation
modulus of the rockfill materials and make them softer. The particle breakage phenomenon which happens during compression
and shearing is found as the main factor responsible for the above effects and, in general, responsible for controlling the
behavior of the materials. For the rockfill materials of this study, two correlations for estimating the initial elasticity modulus (Ei)
and the internal friction angle (&phi) in terms of particles shape, confining pressure (&sigma3), and coefficient of uniformity (Cu) are
suggested.


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

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


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. H. Eghbali, K. Fakharian,
Volume 12, Issue 1 (1-2014)
Abstract

Portland cement can be mixed with sand to improve its mechanical characteristics. Many studies are reported in literature on this topic, but the effect of principal stress rotation has not been investigated yet. Considering the inherent anisotropy of most sands, it is not clear whether the added cement shall contribute to equal increase in strength and stiffness at vertical and horizontal directions or not. Furthermore, it is not well understood how the cement as an additive in non-compacted (loose) sand compared to compacted (dense) sand without cement, contribute to improving the material behavior in undrained condition such as limiting the deformations and the liquefaction potential. In this research, undrained triaxial and simple shear tests under different stress paths are carried out on different mixtures of Portland cement (by adding 1.5, 3 and 5 percent) with clean sand to investigate the effect of principal stress rotations. The triaxial test results revealed that the cement mixture reduces the anisotropy, while it improves the mixture mechanical properties compared to compacted sand without cement. The results of the simple shear tests validated the triaxial test results and further clarified the effect of the  parameter or rotation of principal stresses on the behavior of cemented sand mixtures.
J. Nazari Afshar, M. Ghazavi,
Volume 12, Issue 1 (1-2014)
Abstract

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.

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