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

• Journal of Ocean Engineering and Technology
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• v.27 no.1
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• pp.59-66
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• 2013

A suction anchor is one of the most popular anchors for deepsea floating systems. An anchor used for catenary mooring is predominantly under a horizontal load. In this study, the behavior of a suction anchor installed in cohesionless soil was investigated when the anchor was mainly subjected to a horizontal load induced by a catenary line. In order to study the behavior of the suction anchor, 3D FEM analysis models were developed and analyzed. Depending on the location of the load (padeye), the ultimate horizontal load was monitored. The distributions of the reaction forces around the anchor induced by the seabed were analyzed using the circumferential stress to understand the behavior of the suction anchor under a horizontal load.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.1224-1227
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• 2006

It has been recognized unsaturated soil behaviour playing an important role in geomechanics. Up to now, only a few experimental data are available for the technical difficulties related to both volume changes and suction measurements. In this study, the volume changes of unsaturated compacted silty soil were monitored with proximeter (i.e. non-contactable transducer) during various triaxial compression tests, which gave a realistic estimation in the volume changes of unsaturated soil sample. The measurement of volume changes were performed with 0.5% of the maximum error under the axial strain ratio of less than 10%. The experimental results have revealed that the mechanical behaviour of unsaturated soil can be significantly affected by the matric suction. During the shearing processes, the level of maximum deviator stress under the initial suction pressure of 50kPa was higher than that under the initial suction pressure of 10kPa. On the other hand, the volume changes became smaller under the increase in the initial suction pressure.

• Geomechanics and Engineering
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• v.30 no.4
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• pp.373-382
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• 2022

Unsaturated soil at high suctions is widespread. Many civil engineering projects are related to the hydro-mechanical behavior of unsaturated soils at high suctions, particularly in arid and semiarid areas. To investigate water retention behaviors of nine clayey soils (one is classified as fat clay and the others are classified as lean clay according to the unified soil classification system), the high suction (3.29-286.7 MPa) was imposed on the specimens at zero net stress by the vapor equilibrium technique. In this paper, the effect of void ratio on the water retention behavior at high suction was discussed in detail. Validation data showed that soil types, i.e., different mineralogical compositions, are critical in the soil water retention behavior at a high suction range. Second, the hysteresis behavior at a high suction range is mainly related to the clay content and the specific surface area. And the mechanism of water retention and hysteresis behavior at high suctions was discussed. Moreover, the maximum suction is not a unique value, and it is crucial to determine the maximum suction value accurately, especially for the shear strength prediction at high suctions. If the soil consists of hydrophilic minerals such as montmorillonite and illite, the maximum suction will be lower than 10⁶ kPa. Finally, using the area of hysteresis to quantify the degree of hysteresis at a high suction range is proposed. There was a good correlation between the area of hydraulic hysteresis and the specific surface area.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1199-1203
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• 2008

It has been recognized that unsaturated soil behavior plays an importantrole in geomechanics. In the last decade several constitutive models have been proposed and used in the analysis. Many of them, however, are constructed in the frame work of rate independent model such as elasto-plastic one. Although rate dependency is an important characteristics of soil for both saturated and unsaturated soils, very few models have been developed taking account of rate dependency. In the present paper, we have developed an elasto-viscoplastic model considering an effect of suction based on the overstress-type viscoplasticity with soil structure degradation. In the model, we have adopted an averaged pore pressure composed of pore water pressure and air pressure to determine the effective stress.

• 한국도로학회:학술대회논문집
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• 2011.03a
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• pp.141-146
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• 2011

• Geomechanics and Engineering
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• v.30 no.3
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• pp.219-231
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• 2022

Geotechnical materials such as silt, fine sand, or coarse granular soils may be unstable under undrained shearing or during rainfall infiltration starting an unsaturated state. Some researches are available describing the instability of coarse granular soils in drained or undrained conditions. However, there is a need to investigate the instability mechanism of unsaturated silty soil considering the effect of degree of compaction and net confining stress under partially and fully drained conditions. The specimens in the current study are compacted at 65%, 75%, & 85% degree of compaction, confined at pressures of 60, 80 & 120 kPa, and tested in partially and fully drained conditions. The tests have been performed in two steps. In Step-I, the specimens were sheared in constant water content conditions (a type of partially drained test) to the maximum shear stress. In Step-II, shearing was carried in constant suction conditions (a type of fully undrained test) by keeping shear stress constant. At the start of Step-II, PWP was increased in steps to decrease matric suction (which was then kept constant) and start water infiltration. The test results showed that soil instability is affected much by variation in the degree of compaction and confining stresses. It is also observed that loose and medium dense soils are vulnerable to pre-failure instability i.e., instability occurs before reaching the failure state, whereas, instability in dense soils instigates together with the failure i.e., failure line (FL) and instability line (IL) are found to be unique.

• Journal of the Korean GEO-environmental Society
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• v.13 no.4
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• pp.45-51
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• 2012

The shear strength of weathered granite soils under unsaturated condition was evaluated by $K_0$ consolidated triaxial tests. Various matric suctions in the unsaturated triaxial tests were applied using suction-controlled triaxial test apparatus for weathered granite soils obtained in Daegu. Soil water characteristic curve (SWCC) laboratory tests for drying and wetting procedure were performed and van Genuchten curves were fitted by experimental results. The contribution of matric suction in unsaturated soils is directly correlated to effective stress and evaluated from SWCCs. The effective stresses were estimated from these SWCCs and the relationship between effective stress and unsaturated shear strength was determined. In the effective stress description, the unsaturated shear strength with respect to various suctions indicates unique relationship and almost the same as that of the saturated envelope.

• Journal of the Korean Geotechnical Society
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• v.27 no.1
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• pp.41-52
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• 2011

The hypothesis on effective stress of unsaturated soil is validated by $K_0$ consolidation results of triaxial tests for the compacted residual soil. The stress characteristic curve (SSCC) can describe unsaturated soil behavior on water contents, which was defined from shear strength or from soil water characteristic curves. In this study, it was found that the stress path of $K_0$ consolidation can also define the SSCC. The effective stress was defined by SSCC. $K_0$ paths for various matric suctions could be described as a unique line by effective stress. The measured values of $K_0$ were interpreted by effective stress as a constant with respect to matric suction. Since the SSCC from $K_0$ consolidation agrees with that from the shear strength, the SSCC from soil water retention curve could describe effective stress behavior consistently on both $K_0$ consolidation path and stress at failure. The effective stress based on SSCC can describe the entire unsaturated behavior from consolidation to failure.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.6C
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• pp.287-294
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• 2009

Suction Drain Method is a relatively new technique to improve soft ground using vacuum pressure which can be directly applied to the soft ground through drains that the pore water pressure around them are decreased without changing total stress. This can accelerate volume changes and increase strength of the ground. This paper shows the results of field test of the suction drain method applied at dredged and reclaimed clay. To evaluate the improvement effects of soft ground by the suction drain method, this paper analyzed real-time field measurements to the results of the laboratory tests and numerical analysis. The comparisons of the settlement and shear strength between suction drain method and surcharge preloading method show possibilities for replacement of the preloading methods. The settlements by suction drain method were 2.3 times larger and undrained shear strength were 300%~400% higher than surcharge method. Moreover, the water content is decreased about 30% and the preconsolidation pressure is increased about $0.52kgf/cm^2$.