• Geomechanics and Engineering
• /
• v.28 no.4
• /
• pp.405-419
• /
• 2022

Cavity expansion and contraction solutions for cylindrical and spherical cavities in unsaturated residual soils are presented in this paper. Varying soil state in the plastic zone is accounted by a numerical approach, wherein an element-by-element discretization of the plastic zone of both expanding and contracting cavities is carried out. Unlike existing methods utilizing self-similarity technique, the solution procedure enables the prediction of entire soil-state at any stage of expansion and subsequent contraction. It is also applicable for both cavity creation and expansion problems. The approach adopts constant contribution of suction to effective stress (constant X^s drainage condition) for analysis. The analysis procedure is validated by interpreting the previously reported pressuremeter test results in lateritic residual soil. The typical cavity expansion and contraction characteristics of unsaturated Indian lateritic soil were then examined using this solution procedure. The effect of initial soil-state on cavity limit pressure, plastic radius, reverse yield pressure, and reverse plastic radius are also presented.

• Journal of the Korean Geotechnical Society
• /
• v.23 no.10
• /
• pp.57-64
• /
• 2007

Since matric suction of unsaturated soil was related to soil and ground water contaminations, it is very important to analyze its mechanism that was represented by shear characteristics. In three phases of soil, a little air makes the condition of unsaturated soil on contract or shrinkage surface between water and air. Capillarity and suction in pore of unsaturated soil cause surface tension and surface force so it makes negative pore water pressure and increases effective stress as a result. Therefore, negative pore water pressure in partially saturated soil affects the soil structure and degree of saturation and it is important to evaluate accurately unsaturate flow and behavior. In this study, the shear strength characteristics of the seven sandy soils were investigated using consolidated drained triaxial tests with special emphasis on the effects of the negative pore pressure and the matric suction. These tests involved shearing under either a constant net confining pressure and varying matric suction or under a constant matric suction and varying net normal stress.

• Geomechanics and Engineering
• /
• v.20 no.3
• /
• pp.221-232
• /
• 2020

In many tropical regions, soil structures often fail under constant loads as a result of decreasing matric suction due to water infiltration. Most of the previous studies have been performed by infiltrating water in the soil specimen by keeping shear stress constant at 85-90% of peak shear strength in order to ensure specimen failure during water infiltration. However, not many studies are available to simulate the soil behavior when water is infiltrated at lower shear stress and how the deformations affect the soil behavior if the failure did not occur during water infiltration. This research aimed at understanding both the strength and deformation behavior of unsaturated soil during the course of water infiltration at 25%, 50% and 75% of maximum deviatoric stress and axial strain by keeping them constant. A unique stress-strain curve expresses the transient situation from unsaturated condition to failure state due to water infiltration is also drawn. The shearing-infiltration test results indicate that the water infiltration reduces matric suction and increase soil deformation. This research also indicates that unsaturated soil failure problems should not always be treated as shear strength problems but deformation should also be considered while addressing the problems related to unsaturated soils.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.16 no.8
• /
• pp.5654-5663
• /
• 2015

In the unsaturated soil, suction, the negative pore water pressure leads to increases of the yield stress and the plastic shear stiffness of the soil skeleton due to the growth in interparticle stress. Therefore, in this study, the stress-strain relationship based on cyclic elasto-plastic constitutive model extended for unsaturated soil considering the 1st and the 2nd yield functions was induced in order to account for these effects of suction under the dynamic loading condition such as the earthquake. Through the program code considering this relationship and the routine of the cyclic loading with the reversion of loading direction, the numerical simulation of the cyclic triaxial test under the unsaturated condition would be possible. It is expected that the results of this study possibly contribute to the accuracy improvement on the prediction of unsaturated soil behavior under the dynamic loading condition.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
• /
• 2001.09a
• /
• pp.47-50
• /
• 2001

The laboratory tests were peformed to investigate the relationship between electrical resistivity and the unsaturated subsurface condition and to evaluate the contamination due to leachate based on measuring electrical resistivity. For weathered granite soil, the electrical resistivity of soil decreases as moisture density increases. The electrical resistivity of soil decreases as the concentration of leachate in pore fluid increases since leachate contains various ionic constituents. And the modified Archie's equation for applying to unsaturated sand is derived by regression analysis.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
• /
• 2003.09a
• /
• pp.302-305
• /
• 2003

The electrokinetic remediation tests for natural soil contaminated by lead are performed on unsaturated conditions, in which the degree of saturation is controlled through the changes in water content and the constant unit weight. At the degree of saturation of 70% the small acid range and electrical potential is developed. The changes in the water content are little above the saturation of 90%. But it is increased by 1.7 times at the degree of saturation of 70%. Finally, the efficiency of extraction is improved at 70% than 100%.

• Journal of the Korean GEO-environmental Society
• /
• v.16 no.10
• /
• pp.5-14
• /
• 2015

Suction affects the unsaturated soil as the negative pore pressure, and leads to increases of the yield stress and the plastic shear stiffness of the soil skeleton due to the growth in interparticle stress. Hence, in this study, in order to account for these effects of suction under the dynamic loading condition such as the earthquake, the element simulation of the cyclic triaxial test using induced stress-strain relation based on cyclic elasto-plastic constitutive model extended for unsaturated soil considering the $1^{st}$ and the $2^{nd}$ yield functions was conducted. Through the stress path, stress-strain relation and relation between volumetric strain and axial strain, it was seen in all the cases that the simulation results demonstrated a good agreement with the experimental results. It is expected that the results of this study possibly contribute to the accuracy improvement on the prediction of unsaturated soil behavior under the dynamic loading condition.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.31 no.1D
• /
• pp.83-90
• /
• 2011

A need still exists that the unsaturated condition is to be considered when evaluating the infiltration and drainage capacity for compacted geomaterials in road foundation or embankments. For this reason, numerical analysis were used to analyze the time-dependent unsaturated infiltration and drainage condition depending on various geomaterial types. Therefore, laboratory data from the soil-water characteristic curve tests on geomaterials were adopted from previous studies. In addition, the unsaturated permeability was estimated using SWCC. Then the infiltration and drainage performance of unsaturated compacted soils were evaluated under various conditions based on the proposed method. The results demonstrated that the effect of initial suction and SWCC path on each material could be substantial and the proper application on analysis is very important to enhance the prediction on each capacity.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.31 no.1D
• /
• pp.73-82
• /
• 2011

Generally, an unsaturated condition was not considered to predict the long-term strength and drainage behaviors on compacted road foundations. However, it is logical way to consider the unsaturated condition and hysteresis behavior on road foundations like subbase and subgrade. For more quantitative analysis, rational experimental approach requires proper laboratory tool and material model, and hydraulic properties of pavement geomaterials under unsaturated conditions. In this study, therefore, laboratory data from the soil-water characteristic curve tests were used to predict suction and unsaturated permeability on pavement foundations and the results were analyzed based on the nonlinear fitting model considered. In addition to that, the unsaturated moisture capacity of each material is discussed.

• Journal of the Korean GEO-environmental Society
• /
• v.8 no.4
• /
• pp.67-74
• /
• 2007

Many studies for slope stability studies have indicated that the infiltration of rainwater into a slope decrease the slope stability. In order to minimize damage caused by slope failure, most design codes suggest that the slope stability be analyzed by saturated condition during rainy season. However it would be excessively conservative condition that every soil slope is saturated in rainy season irrespective of rainfall intensity, soil type and slope geometry. In addition, because most soil slopes are in an unsaturated state, it is necessary to consider the unsaturated characteristics of slope. This paper suggests a prediction method of saturation time for the weathered granite soil slopes due to rainfalls. The finite element analysis of transient water flow through unsaturated slope was used to investigate effects of soil-water characteristics, permeability at saturation, slope geometry, and rainfall intensity. From the result of these analyses, the prediction charts considering soil-water characteristics, permeability at saturation, and slope height were proposed in this study. It is possible to the time required to be saturated slope after rainfall.