• Journal of the Korean GEO-environmental Society
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• v.11 no.3
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• pp.23-32
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• 2010

In this study, Generally sandbag was used to reinforce slope or restore levee by using the in-situ material. To increase shear strength of sandbag, the Velcro system was effective for geosynthetic interface and make up for the weakness of shear strength between sandbag to sandbag. In this study, shear properties of geosynthetic-geosynthetic and geosynthetic-soil were evaluated from large scale direct shear tests. The cohesion and the angle of internal friction of each interface was evaluated. And laboratory model tests were performed to compare strength of reinforcement with strength of none reinforcement. As a result of this study, the cohesion and the angle of internal friction of each interface was increased, especially the cohesion was increased more than the angle of internal friction. Also according to the result of model test, the bearing capacity was increased by 20%.

• Journal of the Korean Geotechnical Society
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• v.20 no.9
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• pp.17-23
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• 2004

Strength and deformation characteristics of oyster shell-sand mixtures were investigated to utilize waste oyster shell being treated as a waste material. Standard penetration test (SPT) is a common method to obtain in-situ strength in sand. However, in case of oyster shell-sand mixtures, there was no information between SPT N-value and internal friction angle of mixture soils. In this paper SPT experiments from several large scaled model chamber tests and large scaled direct shear tests were carried out with varying unit weight of oyster shell-sand mixtures. Appropriate correlations were in tile study observed among N-value, unit weight and internal friction angle, which make it possible to estimate in-situ strength from SPT and the coefficient of volume compressibility from the confined compression tests to compute the settlement of oyster shell-sand mixtures.

• Corrosion Science and Technology
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• v.13 no.3
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• pp.112-119
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• 2014

In this work, it is aimed to develop the fabrication method of axial stress corrosion cracking (SCC) defects having various sizes, on the outer diameter surface of the steam generator (SG) tubings. To control the length of the artificial SCC defect, the specific area of the SG tubing samples was exposed to an acidic solution after a sensitization heat treatment. During the exposure to an acidic solution, a direct current potential drop (DCPD) method was adopted to monitor the crack depth. The size of the SCC defect was first evaluated by an eddy current test (ECT), and then confirmed by a destructive examination. From the comparison, it was found that the actual crack length was well controlled to be similar to the length of the surface exposed to an acidic solution (5, 10, 20 or 30 mm in this work) with small standard deviation. From in-situ monitoring of the crack depth using the DCPD method, it was possible to distinguish a non-through wall crack from a through wall crack, even though the depth of the non-through wall crack was not able to be precisely controlled. The fabrication method established in this work was useful to simulate the SCC defect having similar size and ECT signals as compared to the field cracks in the SG tubings of the operating Korean PWRs.

• Journal of the Korean Geotechnical Society
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• v.18 no.5
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• pp.27-35
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• 2002

To construct pipe lines, culverts, or other utility lines, temporary slopes formed by excavating the compacted embankment are frequently met with in the field. Ignoring stability analyses for such slopes and applying inappropriate slope inclinations often result in safety problems. In this study, stability of such slopes were investigated considering the influence of anisotropic shear strength of the layered compacted ground. A series of stability analyses were conducted for slopes varying the slope angle and the height, and assuming isotropic and anisotropic shear strength conditions, respectively. The anisotropic shear strength of the compacted soil was determined from the direct shear test for layered soil blocks varying the inclination angle between the horizontal shear surface and the direction of the soil layer. As a result of the analyses, it has been concluded that the appropriate slope inclination f3r a temporary slope could vary in accordance with the consideration of anisotropy. However, the factor of safety as well as the location of the failure surface did not show significant variation.

• The Korean Journal of Physiology and Pharmacology
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• v.8 no.1
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• pp.21-25
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• 2004

People in tropics have the ability to tolerate heat by residential permanence in the tropics. Previously, we have shown that African and Thai subjects who lived for whole their lives in only their respective countries sweat less under hot conditions than South Koreans who also lived whole their lives in Korea. The difference in sweating responses was attributed to the dissimilar central and peripheral sweating mechanisms operating in people from both groups. In the present study, acetylcholine (ACh), the primary transmitter for the sudomotor functions, was iontophoretically administered to South Koreans and Africans to determine the characteristic sudorific responses of their acclimatized biologic make-up to their respective environments. Using quantitative sudomotor axon reflex test (QSART), direct (DIR) and axon reflex (AXR) responses were evaluated. The findings revealed that the sweat onset-time among South Koreans was 0.91 min earlier than among Africans (P<0.01). The axon reflex sweat volume of nicotine receptor activity AXR(1) and sweat volume of muscarinic receptor activity DIR(2) among South Koreans were 79% and 53% greater (P<0.01), respectively. These results indicate that the reduced thermal sweating among Africans is at least in part attributed to the diminished sensitivity of sweat glands to ACh.

• Korean Journal of Veterinary Service
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• v.16 no.1
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• pp.1-10
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• 1993

Samples of bulk herd milk, foremilk, last milk (stripping) and individual cow sample were collected and their somatic cell number were counted with Fossomatic counter (FCC), Coulter counter(CC), direct microscopic somatic cell count(DMSCC) and Califormia mastitis test (CMT), The results were compared and summarized as follows : 1. Mean somatic cell counts of 120 bulk herd milk samples obtained by DMSCC, FCC and CC were 433,203, 481,213 and 676,245 respectively. 2. Mean somatic cell counts of 116 foremilk samples obtained by DMSCC, FCC and CC were 515,035, 611,845 and 725,051 respectively 3. Mean somatic cell counts of 87 last milk samples obtained by DMSCC, FCC and CC were 718,506, 839,874 and 1,041,160 respectively. 4. Mean somatic cell counts of 57 individual cow samples obtained by DMSCC, FCC and CC were 449,258, 491,018 and 521,315 respectively. 5. Mean somatic cell counts of all samples increased with the increasing CMT score, and the cell counts were higher by CC than by FCC. 6. The correlation coefficients between the somatic cell counts by CMT and CC were 0.926 in bulk herd milk, 0.707 in foremilk 0.688 in last milk and 0.675 in individual cow sample, respectively 7. The correlation coefficients between the somatic cell counts by CMT and FCC were 0. 945 in bulk herd milk, 0.705 in foremilk 0.694 in last milk and 0.727 in individual cow sample, respectively. 8. The correlation coefficients between the somatic cell counts by CC and FCC were 0.978 in bulk herd milk, 0.997 in foremilk 0.983 in last milk and 0.985 in individual cow sample, respectively.

• Journal of the Korean Geotechnical Society
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• v.36 no.6
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• pp.35-46
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• 2020

The input parameters for numerical simulation of the liquefaction phenomenon need to be properly evaluated from laboratory and field tests, which are difficult to be performed in practical situations. In this study, the numerical simulation of the cyclic direct simple shear test was performed to analyze the applicability of Finn and PM4Sand models among the constitutive models for liquefaction simulation. The analysis results showed that the Finn model properly predicted the time when the excess pore water pressure reached the maximum, but failed to simulate the pore pressure response and the stress-strain behavior of post-liquefaction. On the other hand, the PM4Sand model properly simulated those behaviors of the post liquefaction. Finally, the evaluation procedure and the equations of the input parameters in the PM4Sand model were developed to mach the liquefaction cyclic resistance ratio corresponding to design conditions.

• Geomechanics and Engineering
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• v.18 no.4
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• pp.407-415
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• 2019

A controlled low strength material (CLSM) is a highly flowable cementitious material used for trench backfilling. However, when applying vertical loads to backfilled trenches, shear failure or differential settlement may occur at the interface between the CLSM and natural soil. Hence, this study aims to evaluate the characteristics of the interface friction between the CLSM and soils based on curing time, gradation, and normal stress. The CLSM is composed of fly ash, calcium sulfoaluminate cement, sand, silt, water, and an accelerator. To investigate the engineering properties of the CLSM, flow and unconfined compressive strength tests are carried out. Poorly graded and well-graded sands are selected as the in-situ soil adjacent to the CLSM. The direct shear tests of the CLSM and soils are carried out under three normal stresses for four different curing times. The test results show that the shear strengths obtained within 1 day are higher than those obtained after 1 day. As the curing time increases, the maximum dilation of the poorly graded sand-CLSM specimens under lower normal stresses also generally increases. The maximum contraction increases with increasing normal stress, but it decreases with increasing curing time. The shear strengths of the well-graded sand-CLSM interface are greater than those of the poorly graded sand-CLSM interface. Moreover, the friction angle for the CLSM-soil interface decreases with increasing curing time, and the friction angles of the well-graded sand-CLSM interface are greater than those of the poorly graded sand-CLSM interface. The results suggest that the CLSM may be effectively used for trench backfilling owing to a better understanding of the interface shear strength and behavior between the CLSM and soils.

• Steel and Composite Structures
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• v.31 no.6
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• pp.601-615
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• 2019

In cold-formed steel (CFS) structures, such as trusses, wall frames and columns, the use of back-to-back built-up CFS angle sections are becoming increasingly popular. In such an arrangement, intermediate fasteners are required at discrete points along the length, preventing the angle-sections from buckling independently. Limited research is available in the literature on the axial strength of back-to-back built-up CFS angle sections. The issue is addressed herein. This paper presents the results of 16 experimental tests, conducted on back-to-back built-up CFS screw fastened angle sections under axial compression. A nonlinear finite element model is then described, which includes material non-linearity, geometric imperfections and explicit modelling of the intermediate fasteners. The finite element model was validated against the experimental test results. The validated finite element model was then used for the purpose of a parametric study comprising 66 models. The effect of fastener spacing on axial strength was investigated. Four different cross-sections and two different thicknesses were analyzed in the parametric study, varying the slenderness ratio of the built-up columns from 20 to 120. Axial strengths obtained from the experimental tests and finite element analysis were used to assess the performance of the current design guidelines as per the Direct Strength Method (DSM); obtained comparison showed that the DSM is over-conservative by 13% on average. This paper has therefore proposed improved design rules for the DSM and verified their accuracy against the finite element and test results of back-to-back built-up CFS angle sections under axial compression.

• Journal of the Korean Geosynthetics Society
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• v.17 no.4
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• pp.189-197
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• 2018

A sprayable waterproofing membrane which has relatively high adhesive property onto concrete enables faster construction with better waterproof performance compared with a conventional sheet membrane. However, the sprayable waterproofing membrane is a recently developed material and its performance and behavior with structures are not sufficiently reported. Therefore, in this study, the shear behavior of sprayable waterproofing membrane was numerically analyzed using the results of previous studies of composite shotcrete with sprayable waterproofing membrane. From the previous study, shear behavior of shotcrete with sprayable waterproofing membrane was different from shotcrete case and there was a limitation to express the behavior of the interface in general shear strength method. Therefore, in this study, the direct shear test was numerically simulated using two contact models, and then the best suitable method to express the shear behavior of the sprayable waterproofing membrane was suggested.