• Journal of the Korean Geotechnical Society
• /
• v.33 no.4
• /
• pp.47-56
• /
• 2017

Aseismic designs of pile-supported wharves are commonly performed utilizing simplified dynamic analyses, such as multi-mode spectral analyses. Simplified analyses can be useful for evaluating the limit state of structures. However, several pile-supported wharves, that have been damaged during past earthquakes, have shown that soil deformation and soil-pile dynamic interaction significantly affect the entire behavior of structures. Such behavior can be captured by performing nonlinear effective stress analyses, which can properly consider the dynamic interactions among the soil-pile-structure. The present study attempts to investigate the earthquake performance of a pile-supported wharf utilizing a three-dimensional numerical method. The damaged pile-supported wharf at the Kobe Port during the Hyogo-ken Nambu earthquake (1995) is selected to verify the applicability of the numerical modeling. Analysis results showed a suitable agreement with the observations on the damaged wharf, and the significant effect of excess pore pressure development and pile-soil dynamic interaction on the seismic performance of the wharf.

• The Korean Journal of Physiology and Pharmacology
• /
• v.22 no.3
• /
• pp.291-300
• /
• 2018

The purpose of the present work is to establish an ultra-minimal invasive percutaneous puncture inoculation method for a VX2 orthotopic lung cancer rabbit model with fewer technical difficulties, lower mortality of rabbits, a higher success rate and a shorter operation time, to evaluate the growth, metastasis and apoptosis of tumor by CT scans, necropsy, histological examination, flow cytometry and immunohistochemistry. The average inoculation time was 10-15 min per rabbit. The tumorbearing rate was 100%. More than 90% of the tumor-bearing rabbits showed local solitary tumor with 2-10 mm diameters after two weeks post-inoculation, and the rate of chest seeding was only 8.3% (2/24). The tumors diameters increased to 4-16 mm, and irregularly short thorns were observed 3 weeks after inoculation. Five weeks post-inoculation, the liquefaction necrosis and a cavity developed, and the size of tumor grew further. Before natural death, the CT images showed that the tumors spread to the chest. The flow cytometry and immunohistochemistry indicated that there was less apoptosis in VX2 orthotopic lung cancer rabbit model compared to chemotherapy drug treatment group. Minimal invasive percutaneous puncture inoculation is an easy, fast and accurate method to establish the VX2 orthotopic lung cancer rabbit model, an ideal in situ tumor model similar to human malignant tumor growth.

• Journal of Welding and Joining
• /
• v.27 no.6
• /
• pp.74-79
• /
• 2009

Titanium and titanium alloy can be reproduced immediately even if oxide films($TiO_2$) break apart in sea water. Therefore, since titanium demonstrates large specific strength and outstanding resistance to stress corrosion cracking, crevice corrosion, pitting and microbiologically influenced corrosion in sea water environment, it has been widely applied to heat exchanger for ships. In particular, with excellent elongation, pure titanium may be deemed as optimal material for production of heat exchanger plate which is used with wrinkles formed for efficient heat exchange. Conventional plate type heat exchanger prevented leakage of liquid through insertion of gasket between plates and mechanical tightening by bolts and nuts, but in high temperature and high pressure environment, gasket deterioration and leakage occur, so heat exchanger for LPG re-liquefaction device etc do not use gasket but weld heat exchanger plate for use. On the other hand, since welded plate cannot be separated, it is important to obtain high quality reliable welds. In addition, for better workability and production performance, lasers that can obtain weldment with large aspect ratio and demonstrate fast welding speed even in atmospheric condition not in vacuum condition are used in producing products. So far, 1st report and 2nd report compared and analyzed embrittlement degrees by bead colors of weldment through quantitative analysis of oxygen and nitrogen and measurement of hardness as fundamental experiment for the evaluation of titanium laser welding, and evaluated the welding performance and mechanical properties of butt welding. This study welded specimens in various conditions by using laser and GTA welding machine to apply edge welding to heat exchanger, and evaluated the mechanical strength through tensile stress test. As a result of tensile test, laser weldment demonstrated tensile strength 4 times higher than GTA welds, and porosity could be controlled by increasing and decreasing slope of laser power at overlap area.

• Geomechanics and Engineering
• /
• v.28 no.5
• /
• pp.505-520
• /
• 2022

In recent years, geotextile-encased gravel columns (usually called stone columns) have become a popular method to increasing soil shear strength, decreasing the settlement, acceleration of the rate of consolidation, reducing the liquefaction potential and increasing the bearing capacity of foundations. The behavior of improved loose base-soil with gravel columns under shear loading and the shear stress-horizontal displacement curves got from large scale direct shear test are of great importance in understanding the performance of this method. In the present study, by performing 36 large-scale direct shear tests on sandy base-soil with different fine-content of zero to 30% in both not improved and improved with gravel columns, the effect of the presence of gravel columns in the loose soils were investigated. The results were used to predict the shear stress-horizontal displacement curve of these samples using support vector machines (SVM). Variables such as the non-plastic fine content of base-soil (FC), the area replacement ratio of the gravel column (Arr), the geotextile encasement and the normal stress on the sample were effective factors in the shear stress-horizontal displacement curve of the samples. The training and testing data of the model showed higher power of SVM compared to multilayer perceptron (MLP) neural network in predicting shear stress-horizontal displacement curve. After ensuring the accuracy of the model evaluation, by introducing different samples to the model, the effect of different variables on the maximum shear stress of the samples was investigated. The results showed that by adding a gravel column and increasing the Arr, the friction angle (ϕ) and cohesion (c) of the samples increase. This increase is less in base-soil with more FC, and in a proportion of the same Arr, with increasing FC, internal friction angle and cohesion decreases.

• Journal of the Korean Geotechnical Society
• /
• v.22 no.5
• /
• pp.13-26
• /
• 2006

The purpose of this study is to examine the method of liquifaction potential occuring at the reclaimed land in Incheon district and to compare the result obtained by the method based on the earthquake of 6.5 magnitude. In addition, the effects of ground improvement and liquifaction potential were evaluated on the basis of SPT and CPT, which have been performed before and after the compaction pilot test. As a result, we realized that the bigger the energy of dynamic compaction test was, the better effect we got. After the dynamic compaction test, as the strength of ground increased, the safe factor also increased. It was evaluated that the method of dynamic compaction improved the seismic performance. Accordingly, the method of the quality control of reclaimed land based on dynamic compaction method was presented.

• Geomechanics and Engineering
• /
• v.35 no.4
• /
• pp.449-464
• /
• 2023

Advanced nonlinear effective stress constitutive models are started to be frequently used in one-dimensional (1D) and two-dimensional (2D) site response analysis for assessment of porewater generation and liquefaction potential in soft soil deposits. The emphasis of this research is on the assessment of the implementation of this category of models at the element stage. Initially, the performance of a coupled porewater pressure (PWP) and constitutive models were evaluated employing a catalogue of 40 unidirectional cyclic simple shear tests with a variety of relative densities between 35% and 80% and effective vertical stresses between 40 and 80 kPa. The authors evaluated three coupled constitutive models (PDMY02, PM4SAND and PDMY03) using cyclic direct simple shear tests and for decide input parameters used in the model, procedures are recommended. The ability of the coupled model to capture dilation as strength is valuable because the studied models reasonably capture the cyclic performance noted in the experiments and should be utilized to conduct effective stress-based 1D and 2D site response analysis. Sandy soils may become softer and liquefy during earthquakes as a result of pore-water pressure (PWP) development, which may have an impact on seismic design and site response. The tested constitutive models are mathematically coupled with a cyclic strain-based PWP generation model and can capture small-strain stiffness and large-strain shear strength. Results show that there are minor discrepancies between measured and computed excess PWP ratios, indicating that the tested constitutive models provide reasonable estimations of PWP increase during cyclic shear (r_u) and the banana shape is reproduced in a proper way indicating that dilation and shear- strain behavior is well captured by the models.

• The Korean Journal of Food And Nutrition
• /
• v.25 no.3
• /
• pp.637-643
• /
• 2012

This study was performed to increase the utilization of rice and improve the productivity of jochung, traditional food in Korea. Two kinds of jochung products were prepared from steamed rice(SR) and wet-milled rice flour(WRF) by rice cultivated from 2006 to 2010. It is common to add a liquefying enzyme for rice liquefaction(4 $m{\ell}$/1,000 g rice, at $90{\sim}95^{\circ}C$, 3 h) and saccharogenic enzyme with malt(45 g/1,000 g rice, at $55{\sim}57^{\circ}C$, 6 h). In order to evaluate the quality characteristics of jochung, producing rate, pH, solidity, reducing sugar, dextrose equivalence(D.E.), viscosity, total phenolic compound, color value and sensory evaluation were carried out. In terms of the producing rate of jochung, WRF jochung was produced about 7.4% much more than SR jochung. There was no difference in producing rate between the jochung cultivated from 2006 to 2010 rice. The pH varied from 4.86~5.66, solidity was 79.48~82.28%. Color L value was 25.82~27.92, a value of 1.28~2.81, b value were 2.98~4.33. The results of sensory evaluation for jochung, as a whole, received higher score than for the commercial product(Daesang Co., Ltd, Seoul, Korea), overall acceptability score was the highest in the 2008SR. Reducing sugar, dextrose equivalence(D.E.) and total phenolic compounds were determined to be higher WRF jochung than SR jochung, while viscosity was lower WRF jochung than SR jochung. These results are thought to be due to increased surface area of rice by milling. SR jochung manufacturd by wet-milled rice flour will increase the producing rate for jochung, thereby saving manufacturing time and costs.

• Journal of the Korean Geotechnical Society
• /
• v.28 no.7
• /
• pp.31-40
• /
• 2012

In most design codes, soils are classified as either sandy or clayey soils, and appropriate design equations for each soil type are used to estimate their soil behaviour. However, sand-fine mixtures, which are typically referred to as intermediate soils, are somewhere at the middle of sandy or clayey soils, and therefore a unified interpretation of soil behaviour is necessary. In this paper, a series of cyclic shear tests were carried out for three different combinations of sand-fine mixtures with various fines content. Silica-sand mixture and fines (Iwakuni natural clay, Tottori silt, kaolinite) were mixed together with various mass ratios, while paying attention to the changes of void ratios expressed in terms of sand structure. The cyclic shear strengths of the mixtures below the threshold fines content were examined with the increasing fines contents. As a result, as the fines contents increased, their cyclic deviator stress ratios decreased for dense samples while it increased for loose samples. Additionally, cyclic deviator stress ratio of the mixtures was estimated using the concept of equivalent granular void ratio.

• Journal of the Korean Geotechnical Society
• /
• v.20 no.2
• /
• pp.115-124
• /
• 2004

Granular compaction pile has the load bearing capacity of the soft ground increase and has the settlement of foundation built on the reinforced soil reduce. The granular compaction group piles also have the consolidation of the soft ground accelerate and prevent the liquefaction caused by earthquake using the granular materials such as sand, gravel, stone etc. However, this method is not widely used in Korea. The granular compaction piles are constructed by grouping them with a raft system. The confining pressure at the center of bulging failure depth is a major variable in estimating the ultimate bearing capacity of the granular compaction piles. Therefore, a share of loading is determined considering the effect of load concentration ratio between the granular compaction piles and surrounding soils, and the variation of the magnitude of the confining pressure. In this study, a method for the determination of the ultimate bearing capacity is proposed to apply a change of the horizontal pressure considering bulging failure depth, surcharge, and loaded area. Also, the ultimate bearing capacity of the granular compaction pile is evaluated on the basis of previous study(Kim et al., 1998) on the estimation of the ultimate bearing capacity and compared with the results obtained from laboratory scale model tests and DEM numerical analysis using the PFC-2D program.

• Journal of the Korean GEO-environmental Society
• /
• v.8 no.4
• /
• pp.57-65
• /
• 2007

Earthquake is one of the factors to affect the stability of geotechnical structures. Numerous past earthquakes have shown that earthquakes have taught that damage of soil structures could occur on fine soils as well as coarse soils. For that reason, earthquake-induced decreasing tendency for strength on both coarse and fine soils has been investigated using direct simple shear (DSS) tests in laboratory. Based on the testing results the decreasing tendency for strength on coarse and fine soils is clearly identified in terms of the concept of volume decrease potential and plasticity index, respectively. Most of the soils except the weathered soil have shown similar reduction tendency of strength with the increasing number of cycles. Liquefaction strength of coarse and fine soils appears to decrease with the increment of volume decrease potential and the decrement of plasticity index, respectively. Reduction of strength on the weathered soil is particularly remarkable rather than others, which might be owing to the collapse phenomenon. From the DSS test results for soils, proposed is a simple method to evaluate strength decrement with the increasing number of cycles, and it can help estimate decrement of strength with the number of cycles easily.