• Journal of the Korean Geotechnical Society
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• v.28 no.5
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• pp.95-107
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• 2012

Even though the importance of predicting build-up of pore pressure under cyclic loading is recognized, effective stress analysis is rarely performed due to difficulties in selecting the parameters for the pore pressure model. In this paper, a new stress based numerical model for predicting pore pressure under cyclic loading is developed. The main strength of the model is that it is easy-to-use, requiring only the CSR-N curve in selecting the parameters. Another advantage of the model is that it can be used for any loading pattern and therefore can be implemented in an effective stress time-domain dynamic analysis code. The accuracy of the model is validated through its comparisons with measurements in literature and laboratory test data collected in Korea. Further comparisons with another stress based pore pressure model highlighted the superiority of the proposed model.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.5
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• pp.47-56
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• 2003

In this paper, the cyclic soil behavior model. which can accommodate the cyclic hardening, was developed by modifying the original parallel IWAN model. In order to consider the irrecoverable plastic strain of soil. the cyclic threshold strain, above which the backbone curve deviates from the original curve, was defined and the accumulated strain was determined by summation of the strains above the cyclic threshold in the stress-strain curve with applying Masing rule on unloading and reloading curves. The isotropic hardening elements are attached to the original parallel IWAN model and the slip stresses in the isotropic hardening elements are shown to increase according to the hardening functions. The hardening functions have a single parameter to account for the cyclic hardening and are defined by the symmetric limit cyclic loading test in forms of accumulated shear strain. The model development procedures are included in this paper and the verifications of developed model are discussed in the companion paper.

• Membrane Journal
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• v.25 no.3
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• pp.268-275
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• 2015

Effects of aeration intensity on local fouling were investigated in submerged membrane modules. Higher liquid velocities were observed at the section with the lower fiber packing density. The liquid velocity is increased with increasing the gas-liquid injection factor. The high shear stress coincided with the high liquid velocity. The shear stress increases with the increasing of gas-liquid injection factor and the liquid velocity improves with the increasing of gas-liquid injection factor. Irreversible fouling resistance ($R_{ir}$) of the fiber position is significant in a local region of high suction pressure near the suction point of the fiber (position 1). The ratio of $R_{ir}/R_m$ and $R_{ir}/R_r$ of position 1 was highest compared to the position 2 and 3. Irreversible fouling resistances results confirmed the preferential deposition of foulants near the suction part of the fiber where the local suction pressure is the highest and correspondingly, more particles are accumulated to the membrane surface. The effects of local fouling along the fiber length are significant factors to optimize the design of submerged modules.

• Journal of the Korean GEO-environmental Society
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• v.11 no.12
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• pp.5-11
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• 2010

If the groundwater in rock joint is changed into ice, it induces the stress increment by volume increase. Also, if the ice is changed into groundwater again, the stress in joint decreases by volume decrease. The accumulated displacement and fatigues of joints are increased by the stress-hysterisis, induced from the continuous frost-thawing. Also the shear strength is decreased by them continuously. The stress-hysterisis is affected by the atmospheric temperature changes, whose behavior is visco-elasticity, usually. Therefore, Kelvin model could be used to analyze the frost-thawing behavior in winter. The measured data of total 5 points are examined, which are composed of 3 points of shallow joints and 2 points of deep joints. Because shallow weathered rocks have many joints, a lot of Kelvin model are connected and the behaviors are complicated. In case of deep joints, simple Kelvin model is applied and the behaviors are also simple.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.30 no.6
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• pp.306-318
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• 2018

In order to evaluate the seismic capacity of massive vertical type breakwaters which have intensively been deployed along the coast of South Korea over the last two decades, we carry out the preliminary numerical simulation against the PoHang, GyeongJu, Hachinohe 1, Hachinohe 2, Ofunato, and artificial seismic waves based on the measured time series of ground acceleration. Numerical result shows that significant sliding can be resulted in once non-negligible portion of seismic energy is shifted toward the longer period during its propagation process toward the ground surface in a form of shear wave. It is well known that during these propagation process, shear waves due to the seismic activity would be amplified, and non-negligible portion of seismic energy be shifted toward the longer period. Among these, the shift of seismic energy toward the longer period is induced by the viscosity and internal friction intrinsic in the soil. On the other hand, the amplification of shear waves can be attributed to the fact that the shear modulus is getting smaller toward the ground surface following the descending effective stress toward the ground surface. And the weakened intensity of soil as the number of attacking shear waves are accumulated can also contribute these phenomenon (Das, 1993). In this rationale, we constitute the numerical model using the model by Hardin and Drnevich (1972) for the weakened shear modulus as shear waves go on, and shear wave equation, in the numerical integration of which $Newmark-{\beta}$ method and Modified Newton-Raphson method are evoked to take nonlinear stress-strain relationship into account. It is shown that the numerical model proposed in this study could duplicate the well known features of seismic shear waves such as that a great deal of probability mass is shifted toward the larger amplitude and longer period when shear waves propagate toward the ground surface.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.2
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• pp.195-204
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• 2004

A series of constant creep and repeated creep tests are performed to investigate the behavior of visco-elasto-plastic materials of chemical grouted sands. In the result of constant creep test, the material exhibits three types of shear strain : elastic, plastic, viscoelastic. The elastic, plastic and viscoelastic strains are linear, i.e., the strains are proportional to the stresses for loading. Good agreement is found between the predicted viscoelastic and test results by the power law and the generalized model. In the repeated creep test, the instantaneous recoverable strain is time-independent and the magnitude of accumulated plastic strain increases with number of cycles. Also it is seen that the accumulated plastic strains are approximately proportional to stress. There are no significant differences between test results predicted values for first cycle, and the differences increase relatively insignificantly with number of cycles.

• Earthquakes and Structures
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• v.7 no.5
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• pp.843-859
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• 2014

In the present study, the seismic performance of structural walls with boundary elements confined by conventional tie hoops and steel fiber concrete (SFC) was investigated. Cyclic lateral loading tests on four wall specimens under constant axial load were performed. The primary test parameters considered were the spacing of boundary element transverse reinforcement and the use of steel fiber concrete. Test results showed that the wall specimen with boundary elements complying with ACI 318-11 21.9.6 failed at a high drift ratio of 4.5% due to concrete crushing and re-bar buckling. For the specimens where SFC was selectively used in the plastic hinge region, the spalling and crushing of concrete were substantially alleviated. However, sliding shear failure occurred at the interface of SFC and plain concrete at a moderate drift ratio of 3.0% as tensile plastic strains of longitudinal bars were accumulated during cyclic loading. The behaviors of wall specimens were examined through nonlinear section analysis adopting the stress-strain relationships of confined concrete and SFC.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.3B
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• pp.281-287
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• 2009

In this study, the behavior of breasting dolphin caused by the maximum wave height in the coastal area of Incheon has been investigated. The dynamic deflection, shear stress and moment of pile are analyzed using the coefficient of horizontal subgrade reaction resulted from loading tests for different DWT (Dead Weight Tonnage). The dynamic characteristics of pile in accumulated and dredged soils show almost the same pattern. It is shown that the resistance of dolphin to external load increases as the diameter of pile increases. The bettered pile dolphin is more than 10 times stable than the vertical pile type based on the study of dynamic characteristics of dolphin.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.5
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• pp.399-405
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• 2010

The accumulated displacements and fatigues of rock are increased by the stress-hysteresis, induced from repeated frost-thawing. Also the shear strength is decreased by them continuously. The stress-hysteresis is affected by the atmospheric temperature changes, whose behavior is visco-elasticity, usually. Therefore, to do ideal body analysis, Kelvin model could be used to analyze the frost-thawing behavior in winter. In general, rock slope failure occurs by the deterioration of rocks, which is caused by the repetition of freezing-thawing process. In order to keep the safety of such rock mass structures the deterioration process of rock needs to be described quantitatively using some meaningful parameters. In this work, the deterioration process in freezing-thawing cycle of tuff, which is a famous soft porous rock, is investigated through laboratory tests and successfully described as a differential equation for the change of porosity. And then, the deterioration of the mechanical properties of rock, such as Young's modulus and uniaxial compressive strength, are quantitatively described as a function of the porosity.

• Journal of the Korean GEO-environmental Society
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• v.20 no.3
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• pp.39-46
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• 2019

The liquefaction is a phenomenon that the effective stress becomes zero due to the rapidly accumulated excess pore water pressure when a strong load acts on the ground for a short period of time, such as an earthquake or pile driving, resulting in the loss of the shear strength of the ground. Since the Geongju and Pohang earthquake, liquefaction brought increasing domestic attention. This liquefaction can be assessed mainly through the semi-empirical procedures proposed by Seed and Idriss (1982) and the liquefaction risk based on the penetration resistance obtained from borehole DB and SPT. However, the geotechnical information data obtained by the in-situ tests or boring information fundamentally have an issue of the representative of the target area. Therefore, this study sought to construct a ground information database by classifying and reviewing the ground information required for liquefaction assessment, and tried to solve the representative problem of the soil layer that is subject to liquefaction evaluation by performing spatial interpolation using GIS.