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Showing 33 results for Shear Strength

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.
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.
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.


M. Reza Esfahani,
Volume 6, Issue 3 (9-2008)
Abstract

In this paper, the effect of cyclic loading on punching strength of flat slabs strengthened with Carbon Fiber Reinforced Polymer (CFRP) sheets is studied. Experimental results of ten slab specimens under monotonic and cyclic loading are analyzed. Eight specimens were strengthened with CFRP sheets on the tensile face of the slabs and the two other specimens were kept un-strengthened as control specimens. The width of CFRP sheets varied in different specimens. After the tests, the punching shear strength of specimens under cyclic loading was compared with those with monotonic loading. The comparison of results shows that cyclic loading decreases the effect of CFRP sheets on punching shear strengthening. This decrease was more for the specimens with a larger value of reinforcing steel ratio. Therefore, it can be concluded that for specimens with large reinforcing steel ratios, cyclic loading may completely eliminate the effect of CFRP sheets on shear strengthening of slabs.
H. Salehzadeh, M. Hassanlourad, D.c. Procter, C.m. Merrifield,
Volume 6, Issue 4 (12-2008)
Abstract

The unique behaviour of carbonate sediments under shear loading has stimulated in investigating of their geological and engineering properties. Their shapes are very different varying from needle shaped to platy shaped. Hence, it is important to examine their fabric effect on soil response under shearing condition. To this aim a series of small scale laboratory element testing were carried out on North Cornwall Rock" beach sand. Non-cemented and cemented Carbonate sand response under compression and extension loading and different initial density and confining pressure with samples allowed to be drained were investigated and compared. The results show that the sand shear strength under Extension loading is lower than compression regarding to anisotropic fabric due to platy and needle shape of grains. The anisotropy is reduced with increasing the confining pressure and initial relative density with non-cemented sand. Furthermore, present of cement bounds reduces the anisotropy especially in low confining pressures.
A. Hamidi, M. Alizadeh, S.m. Soleimani,
Volume 7, Issue 1 (3-2009)
Abstract

There are limitations in experimental studies on sand-gravel mixtures due to the small size of testing

specimens. Due to this problem, many researchers have worked on prediction of the shear strength of mixture by testing

the sandy fraction of soil alone and developed empirical relationships. Most of the previous relationships have been

determined for low surcharge pressures in which particle breakage does not affect the shear strength parameters.

However, the particle breakage affects the relationships in higher confinements. At the present study, the results of

large scale direct shear tests on sand and sand-gravel mixtures was used to investigate the shear behavior and

dilatancy characteristics in a wider range of surcharge pressures. The gravel content, relative density, surcharge

pressure and gravel grain size were considered as variables in testing program. The relationships between shear

strength characteristics of sand and sand-gravel mixtures were determined considering dilation characteristics of the

soil. In this regard, the minimum void ratio was found as a useful indirect index that relates uniquely to the critical

state friction angle independent of soil gradation. The relations between critical state or peak friction angles of the

mixture with minimum void ratio were determined as a function of surcharge pressure. The correlations could be useful

for determination of the strength parameters of sand-gravel composites by testing sandy fraction of mixture.


A. Arabzadeh, A.r. Rahaie, A. Aghayari,
Volume 7, Issue 3 (9-2009)
Abstract

In this paper a new method based on Strut-and-Tie Model (STM) is proposed to determine the shear capacity of simply supported RC deep beams and an efficiency factor for concrete with considering the effect of web reinforcements. It is assumed that, the total carried shear force by RC deep beam provided by two independent resistance, namely diagonal concrete strut due to strut-and-tie mechanism and the equivalent resisting force resulted by web reinforcements, web reinforcing reduces the concrete compression softening effect with preventing from the diagonal cracks opening or concrete splitting. The unknown function and parameters are determined from 324 experimental results obtained by other researchers. To validate the proposed method, the obtained results are compared with some of the existing methods and codes such as ACI 318-05 and CSA. The results indicate that the proposed method is capable to predict the shear strength of variety of deep beams with acceptable accuracy.
Khelifa Harichane, Mohamed Ghrici, Said Kenai,
Volume 9, Issue 2 (6-2011)
Abstract

When geotechnical engineers are faced with cohesive clayey soils, the engineering properties of those soils may need to be

improved to make them suitable for construction. The aim of this paper is to study the effect of using lime, natural pozzolana or

a combination of both on the geotechnical characteristics of two cohesive soils. Lime or natural pozzolana were added to these

soils at ranges of 0-8% and 0-20%, respectively. In addition, combinations of lime-natural pozzolana were added at the same

ranges. Test specimens were subjected to compaction tests and shear tests. Specimens were cured for 1, 7, 28 and 90 days after

which they were tested for shear strength tests. Based on the experimental results, it was concluded that the combination limenatural

pozzolana showed an appreciable improvement of the cohesion and internal friction angle with curing period and

particularly at later ages for both soils.


Abolfazl Arabzadeh, Reza Aghayari, Ali Reza Rahai,
Volume 9, Issue 3 (9-2011)
Abstract

An experimental-analytical investigation was conducted to study the behavior of high-strength RC deep beams a total of sixteen

reinforced concrete deep beams with compressive strength in range of 59 MPaOf'c O65 MPa were tested under two-point top

loading. The shear span-to-effective depth ratio a/d was 1.10 all the specimens were simply supported and reinforced by

vertical, horizontal and orthogonal steel bars in various arrangements. The test specimens were composed of five series based

on their arrangement of shear reinforcing. The general behavior of tested beams was investigated. Observations were made on

mid-span and loading point deflections, cracks form, failure modes and shear strengths. The test results indicated that both

vertical and horizontal web reinforcement are efficient in shear capacity of deep beams, also the orthogonal shear reinforcement

was the most efficient when placed perpendicular to major axis of diagonal crack. Concentrating of shear reinforcement within

middle region of shear span can improve the ultimate shear strength of deep beam. The test results were then compared with the

predicted ultimate strengths using the ACI 318-08 provisions ACI code tended to either unsafe or scattered results. The

performed investigations deduced that the ACI code provisions need to be revised.


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.


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


M. Gharouni Nik, M. Fathali,
Volume 11, Issue 1 (5-2013)
Abstract

Geometrical profile (roughness) of joint surfaces influences the behaviour of rock joints under shear loading. With regard to the

dilation, there are two models of direct shear test that may simulate the original loading condition existing in the location from

where the specimens have been sampled. The first model in which the normal load is constant (CNL) and the discontinuity is free

to dilate in shearing, represents typical situations such as movement of a block on a surface slope as a result of its own weight.

The second model in which the dilatancy is prohibited (VNL), simulates the condition of a block confined in a rock mass in an

underground opening. A shear test conducted under restricted normal displacement (dilation) will generally yield considerably

higher shear strength than one conducted under constant normal stress. In this research, both types of tests were conducted on

smooth and rough surfaces of specimens made from rock like material. The results of the VNL and the CNL direct shear tests on

regular teeth-shaped profile discontinuities indicates that at all levels of normal load, the linear Mohr-Coulomb criterion was not

valid for rough surfaces that subscribed to the power law equations. Increasing normal load emphasized the difference between

the results obtained from two methods, although for lower normal loads the results were nearly similar.


H. Ziari, H. Divandari,
Volume 11, Issue 2 (6-2013)
Abstract

Pavement permanent deformations due to lack of shear strength in mixture are a major reason of rutting. Any simple test to determine mixtures resistance to permanent deformation isn’t distinguished in the 1st level of SUPERPAVE mix design method and prevalent methods for evaluating mixture rut resistance are expensive and time-consuming. Two aggregate types, gradations, asphalt cements and filler types were used in this research to present a prediction model for rutting based on flow number. A mathematical model to estimate flow number of dynamic creep test was developed using model parameters and gyratory compaction slope. The model is validated using Neural Network and Genetic Algorithm and makes it possible to evaluate mixtures shear strength while optimum asphalt content is being determined in laboratory. So not only there is no need to expensive test instruments of rutting or dynamic creep but a remarkable time saving in mix design procedure is achievable.
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.


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.
M. B. Esfandiari Sowmehsaraei, R. Jamshidi Chenari,
Volume 12, Issue 1 (1-2014)
Abstract

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.
A. Eslami, I. Tajvidi, M. Karimpour-Fard,
Volume 12, Issue 1 (1-2014)
Abstract

Three common approaches to determine the axial pile capacity based on static analysis and in-situ tests are presented, compared and evaluated. The Unified Pile Design (UPD), American Petroleum Institute (API) and a SPT based methods were chosen to be validated. The API is a common method to estimate the axial bearing capacity of piles in marine environments, where as the others are currently used by geotechnical engineers. Seventy pile load test records performed in the northern bank of Persian Gulf with SPT profile have been compiled for methods evaluation. In all cases, pile capacities were measured using full scale static compression and/or pull out loading tests. As the loading tests in some cases were in the format of proof test without reaching the plunging or ultimate bearing capacity, for interpretation the results, offset limit load criteria was employed. Three statistical and probability based approaches in the form of a systematic ranking, called Rank Index, RI, were utilized to evaluate the performance of predictive methods. Wasted Capacity Index (WCI) concept was also applied to validate the efficiency of current methods. The evaluations revealed that among these three predictive methods, the UPD is more accurate and cost effective than the others.
C. Vieira,
Volume 12, Issue 1 (1-2014)
Abstract

This paper presents a simplified approach to estimate the resultant force, which should be provided by a retention system, for the equilibrium of unstable slopes. The results were obtained with a developed algorithm, based on limit equilibrium analyses, that assumes a two-part wedge failure mechanism. Design charts to obtain equivalent earth pressure coefficients are presented. Based on the results achieved with the developed computer code, an approximate equation to estimate the equivalent earth pressure coefficients is proposed. Given the slope angle, the backslope, the design friction angle, the height of the slope and the unit weight of the backfill, one can determine the resultant force for slope equilibrium. This simplified approach intends to provide an extension of the Coulomb earth pressure theory to the stability analyses of steep slopes and to broaden the available design charts for steep reinforced slopes with non-horizontal backslopes

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