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Showing 10 results for Unsaturated

Shooshpasha I.,
Volume 1, Issue 2 (12-2003)

This study was designed to investigate the local volume changes induced by swelling pressure in unsaturated stand-bentonite bused buffer material. A laboratory mixture of sodium bentonite (lilt/ well graded silica stool in equal proportion by do weight was used for moisture floss experiments in both ambient and elevated temperatures. Experimental results have shown that tit high water content locations within the tested specimens, the density was reduced by .3.57% from its initial values clue to swelling. The swelling pressure was calculated by 4 different models as a function of distance. The calculated results have indicated that the density distribution within the .specimen is affected by swelling potential distribution. The calculated swelling pressure values van as u function of water content, reaching I MPa at the source of water intake, i.e., at high water content, and 2 MPa cot the heater .side, i.e., cot low water content .one.
Habib Shahnazari, Hosein Salehzadeh, Amin Askarinejad,
Volume 6, Issue 1 (3-2008)

Classical soil mechanics involves the study of fully saturated soils. However, many problems encountered in geotechnical engineering practice involve unsaturated soil, in which behavior is significantly different from classical saturated soil. Negative pore pressure and capillary forces develop a virtual cohesion between the grains of semi saturated soils. This kind of cohesion is dependent on different factors such as grain size, saturation degree, soil-water characteristic curve and relative density of the soil. In this research the virtual cohesion of fine silty sand with 5% water content and a saturation degree of 17% is estimated. A vertical slope is constructed and is accelerated in the geotechnical centrifuge until failure. During the test, the model was monitored by a wireless video camera, attached to the strong box. The cohesionless tested sand was unsaturated. Based on the scaling laws and considering parameters such as sample unit weight, failure acceleration and the sample dimensions, a slope stability analysis was performed, and the virtual cohesion generated in the sample was calculated. The factor of safety of the prototype modeled in the centrifuge is calculated either by Finite Element Method and Finite Difference Method by using the resulted virtual cohesion from physical modeling. Results of this research show the validity of physical modeling for calculating the virtual cohesion in unsaturated silty sand.
Hasan Ghasemzadeh,
Volume 6, Issue 2 (6-2008)

Solute transport in unsaturated porous media can be viewed as a coupled phenomenon with water

and heat transport, together with mechanical behaviour of media. In this paper, solute transport is formulated

mathematically considering heat and water flow in deformable porous media. Advection, dispersion and

diffusion of chemical species in the liquid phase are considered. Convection and conduction for heat flow is

taken into account. Water flow is considered in both vapour and liquid phases. Equilibrium equation, energy

conservation, mass conservation and linear momentum for water, gas and solute are written and solved

simultaneously using finite element method. The developed model is validated by solving some examples and

comparing results with the results of experimental observation.

Hamed Farshbaf Aghajani, Abbas Soroush, Piltan Tabatabaie Shourijeh,
Volume 9, Issue 4 (12-2011)

Evaluating the rate and maximum height of capillary rise is of prime interest in unsaturated soil mechanics. Antecedent solutions

to this problem have dwelled mostly on determining the maximum capillary rise height, overlooking moisture and suction changes

in the capillary region. A comprehensive improved solution for the capillary rise of water in soils is presented. Salient features of

the formulation including consideration of initial soil suction (if any) prior to capillary rise, and determination of water content

variation in the capillary region are elaborately discussed. Results reveal that suction head variation within the capillary region

is non-linear, where the curvature decreases as water rises to higher elevations. The solution is verified and compared with

existing solutions, by means of two sets of experimental data available in the literature. The comparison suggests that the

improved formulation is more accurate and versatile than previous solutions for capillary rise.

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

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.

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

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.
I. Ashayeri, M. Kamalian, M. K Jafari, M. Biglari, Ma. Mirmohammad Sadeghi,
Volume 12, Issue 2 (4-2014)

This paper presents time domain fundamental solutions for the extended Biot's dynamic formulations of two-dimensional (2D) unsaturated poroelasticity. Unsaturated porous media is considered as a porous media in which the voids are saturated with two immiscible fluids, i.e. liquid and gas. At first, the corresponding explicit Laplace transform domain fundamental solution is obtained in terms of skeleton displacements, as well as liquid and gas pressures. Subsequently, the closed-form time domain fundamental solutions are derived by analytical inversion of the Laplace transform domain solutions. Finally, a set of numerical results are presented which verifies the accuracy of the analytically inversed transient fundamental solution and demonstrates some salient features of the elastic waves in unsaturated media..
M. Mojezi, M.k. Jafari, M. Biglari,
Volume 13, Issue 3 (12-2015)

Experimental study of the cyclic behavior of unsaturated materials is more complex than that of the saturated materials due to the required equipment, experience and time. Furthering investigations in the field of unsaturated materials is necessary to better understand its complexity and sensitivity of unsaturated cyclic parameters to different determinants such as suction path, stress path, loading speed, deviatoric stress amplitude, physical specifications, and etc. To this end, the main focus of this study has been to analyze the effects of factors such as mean net stress and deviatoric stress levels in fast cyclic loading on the cyclic behavior of a normally consolidated unsaturated fine-grained trade soil, namely the Zenoz kaolin. Various unsaturated tests were performed in three mean net stress levels and three amplitudes of cyclic deviatoric stress levels. Results showed that increase of suction in the same strain level leads to increase in stiffness in normally consolidated samples (i.e. increase in elastic modulus and shear modulus and decrease in damping ratio). Also, in the same suction value and strain level, increase of the mean net stress during the isotropic consolidation causes to the denser normally consolidated samples and results to increase of elastic modulus and shear modulus, and decrease of damping ratio.

Junxin Liu, Chunhe Yang, Jianjun Gan, Yutian Liu, Wei Liu, Qiang Xie,
Volume 15, Issue 6 (9-2017)

Abstract: Rainfall is an important triggering factor influencing the stability of soil slope. Study on some influences of the rainfall on the instability characteristics of unsaturated soil embankment slope has been conducted in this paper. Firstly, based on the effective stress theory of unsaturated soil for single variable, fluid-solid coupling constitutive equations were established. Then, a segment of red clay embankment slope, along a railway from Dazhou to Chengdu, damaged by rainfall, was theoretical and numerical-simulating researched by considering both the runoff-underground seepage and the fluid-solid coupling. The failure characteristics of the embankment slope and the numerical simulation results were in excellent agreement. In the end, a sensitivity analysis of the key factors influencing the slope stability subjected to rainfall was performed with emphasis on damage depth as well as infiltration rainfall depth. From the analysis in this paper, it was concluded that the intensity of rainfall, rainfall duration and long-term strength of soil have most effect on slope stability when subjected to rainfall. These results suggest that the numerical simulation can be used for practical applications.

Volume 15, Issue 6 (9-2017)

Pile load tests and numerical analysis of a small-scale model pile in unsaturated clayey soil are presented in this paper. A small-scale model pile was simulated to bear a static axial loading in unsaturated soil using finite element method. All parameters used in the finite element method were obtained in laboratory tests, including the direct shear test, interface direct shear test, and filter paper method. The numerical analysis results were compared with the pile load test results. The results show that the general trend of pile load and pile head settlement relationship obtained by the numerical analysis shows a good consistence with the pile load test results. With increasing water content of the soil, the matric suction, dilatancy angle and shear strength decrease, and consequently the ultimate bearing capacity of pile decreases.

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