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Showing 10 results for Dilation

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.
Mahin Roosta R., Sadaghyani M.h., Pak A.,
Volume 3, Issue 3 (9-2005)
Abstract

Existence of discontinuities causes higher deformability and lower strength in rock masses. Thus joints can change the rock mass behaviour due to the applied loads. For this reason properties and orientation of the joint sets have a great effect on the stability of rock slopes. In this paper, after introducing some numerical methods for evaluating the factor of safety for the stability of slopes, stability of jointed rock slopes in the plane strain condition is investigated with the strength reduction technique this method is modified and applied in the multilaminate framework. First of all, stability of one homogeneous rock slope is investigated and compared with the limit equilibrium method. Then stability of a layered rock slope is analyzed with some modifications in the strength reduction technique. Effects of orientation, tensile strength and dilation of layered joint sets on the factor of safety and location of the sliding block are explained.
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.


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.


G. Ghodrati Amiri, A. Asadi,
Volume 7, Issue 4 (12-2009)
Abstract

Future design procedures for civil structures, especially those to be protected from extreme and blast related

loads, will need to account for temporal evolution of their frequency content. There are, however, several instances

where acceleration time histories are required as seismic input. For example, to determine the ultimate resistance and

to identify modes of structures’ failure, a nonlinear time history analysis is needed. In other cases, acceleration time

histories are required for linear analyses. Many seismic codes require this type of analysis for buildings which have

irregularities. The process of time-frequency analysis made possible by the wavelet transform provides insight into the

character of transient signals through time-frequency maps of the time variant spectral decomposition that traditional

approaches miss. In this paper an approach is examined and a new method for processing the ground motion which is

modeled as a non-stationary process (both in amplitude and frequency), is proposed. This method uses the best basis

search algorithm with wavelet packets. In this approach, the signal is expressed as a linear combination of timefrequency

atoms which are obtained by dilations of the analyzing functions, and are organized into dictionaries as

wavelet packets. Several numerical examples are given to verify the developed models.


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.


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.
Mr. Mehdi Goorani, Dr. Amir Hamidi,
Volume 13, Issue 2 (6-2015)
Abstract

This paper presents a model for prediction of the mechanical behavior of sand-gravel mixtures using generalized plasticity and critical state concepts. Proposed model is based on the difference between critical state lines of sand and sand-gravel mixture in e-Lnp' plane. A generalized plasticity model is considered as the base model for sandy soil. Its state parameter, dilation rate and hardening function are modified to involve the effects of gravel particles on the behavior of mixture. Gravel content is considered as a physical parameter for determination of four new added parameters of the model. Verification of the proposed model performed considering four sets of experiments conducted by different researchers on poorly graded sand-gravel mixtures. According to the results, proposed model provides satisfactory qualitative and quantitative predictions of the behavior of sand-gravel mixture. Stress- strain behavior besides volumetric strains in drained condition and induced pore pressure during undrained loading are satisfactory predicted which indicates the possibility of its application in boundary value problems of geotechnical engineering.
Kazem Fakharian, Ali Borhani,
Volume 14, Issue 4 (6-2016)
Abstract

The behavior of Chamkhaleh sand and three other recognized sands namely, Babolsar, Firouzkuh and Standard (Ottawa) sands are compared using triaxial apparatus under undrained monotonic loading conditions. Chamkhaleh and Babolsar sands are supplied naturally from southern Caspian Sea shorelines, whereas artificial Firouzkuh and Standard sands were supplied commercially. Samples were prepared using wet tamping with regard to the reduced compaction effect at relative density of 15% under isotropic consolidation pressures of 100, 300 and 500 kPa. The results of triaxial tests have indicated that Chamkhaleh sand has much more dilation tendency than the other sands. In order to evaluate the reasons behind this behavior, the spherecity and roundness of all the four sand particles were measured using an image processing method. It was revealed that the spherecity of the four sands is not much different, but Chamkhaleh sand is more angular than the other sands. For comparison of the dilative response of the sands in undrained triaxial tests, a “dilation tendency index” is introduced. This index may be used as a criterion for measuring the dilation of sands in undrained tests. Results have shown that the internal friction angle under the steady state condition is more dependent on the shape of particles than the maximum strength condition. For spherecities greater than 0.5, the dependency rate of sand behavior on the roundness is decreased.



Volume 15, Issue 6 (9-2017)
Abstract

In this study, the shear strength parameters of the Kaolinite clay, as the control material, and the Kaolinite clay reinforced by different percentages of two different types of crumb rubber content have been evaluated. The consolidated drained and unconsolidated undrained triaxial and California bearing ratio tests have been conducted on the control and crumb rubber reinforced soils. Addition of crumb rubber would improve shear strength parameters such as cohesion, friction and dilation angles, stiffness and the ductility of the reinforced soil. 5, 10 and 15 % (by the weight of dry soil) of crumb rubber content were used in this study which were undergone confining stress levels of 100, 200 and 300 kPa and an optimum crumb rubber content is found, which results in the maximum bearing capacity of the soil. Also, due to the non-linearity of the failure mode of reinforced soil and inadequacy of Mohr–Columb envelope for describing the behaviour, a failure mode is proposed for the clay soils reinforced by crumb rubber. This failure criterion is useful for failure envelope of clay-rubber matrix.



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