• Journal of the Korean GEO-environmental Society
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• v.21 no.6
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• pp.19-25
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• 2020

In the recent downtown works, there are frequent cases where the work on existing piles is impossible due to the influence from lack of space and surrounding environment. In such cases, there has been growing cases of using the micropile method that is available to work with the small equipment and asserts the bearing capacity of the existing piles. The micropile method is a type of drilled shaft with the diameter of a pile to be around 75 mm~300 mm that, even for a case where it has certain surrounding structure, foundation and spatial obstacle, there is almost no work difficulty and the work is feasible under all types of soil conditions. In addition, the work can be done in places where the ceiling of the building is low with less vibration and noise in the work process that such method is significantly used for foundation reinforcement of existing buildings. With respect to the motion characteristics that are changed depending on the foundational characteristics or when the micropile is applied with compression or tensile force, there is very few studies conducted. Therefore, under this study, through the data analysis of the field loading test regarding the micropile worked in the fields, it clarifies the settlement and characteristics of bearing capacity following the embedded condition of the ingredients and piles that consist the foundation if the compression and tensile force are applied to the micropile, and by facilitating the statistical analysis program, SAS, to carry out the analysis on the main elements influencing on settlement of the micropile and bearing capacity.

• Journal of the Korean Geotechnical Society
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• v.32 no.8
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• pp.5-14
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• 2016

The leakage of water under sewer pipelines is one of main sources of sinkholes in urban areas. We performed laboratory model tests to investigate the presence of cavities using impact-echo method, which is a nondestructive test method. To simulate a concrete sewer pipe, a thin concrete plate was built and placed over container filled with sand. The cavity was modeled as an extruded polystyrene foam box. Two sets of tests were performed, one over sand and the other on cavity. A new impact device was developed to apply a consistent high frequency impact load on the concrete plate, thereby increasing the reliability of the test procedure. The frequency and transient characteristics of the measured reflected waveforms were analyzed via fast Fourier transform and short time Fourier spectrum. It was shown that the shapes of Fourier spectra are very similar to one another, and therefore cannot be used to predict the presence of cavity. A new index, termed resonance duration, is defined to record the time of vibration exceeding a prescribed intensity. The results showed that the resonance duration is a more effective parameter for predicting the presence of a cavity. A value of the resonance period was proposed to estimate the presence of cavity. Further studies using various soil types and field tests are warranted to validate the proposed approach.

• Journal of the Korean Geotechnical Society
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• v.27 no.6
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• pp.17-26
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• 2011

Ground anchor method is one of the most popular reinforcing technology in Korea. For the sound monitoring of slope reinforced by permanent anchor for a long period, monitoring the tension force of ground anchor is very important. However, special technology except conventional load cell has not been developed for this purpose. In this paper, a new method is described to replace the conventional strain gauge and V.W. type load cell which has been commonly used as a prestress force monitoring tool for a short-term and long-term. Four 11.5 m long strain detectable tension type anchors were made using FBG sensor embedded tendon since FBG sensor is smaller than strain gauge type load cell and does not have noise from electromagnetic wave. Each two set strain detectable tension type anchors were installed into the different ground conditions, i.e., soft rock and weathered granite soil. Prestress force of ground anchor was monitored during the loading-unloading step from in-situ pullout test using proposed FBG sensor embedded in the tendon and the conventional load cell Test results show that the prestress force monitored from FBG sensor may well be used practically, for it almost matches with that measured from expensive load cell.

• Journal of Plant Biotechnology
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• v.34 no.1
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• pp.11-17
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• 2007

Previously developed transgenic watermelon rootstocks (gongdae) inserted by CGMMV-CP were examined to test the virus tolerance levels. In the restricted plastic house, the $T_{3}$ watermelon rootstock showed tolerance to CGMMV until 70 days after inoculation on the leaves while the non-transformed watermelon rootstock became susceptible at 20 days after inoculation. In the field, tolerance efficiency of transgenic rootstocks maintained up to 40% at 71 days after contamination with CGMMV in the soil while all of the non-transformed rootstocks became susceptible at 37 days with the same condition. In the same field, transgenic rootstocks showed more tolerance to CGMMV than the non-transformed rootstocks as those were inoculated on the leaves, but it showed only 10 days delay before being susceptible. Therefore, transgenic rootstocks have a characteristic of delay effect against CGMMV susceptibility, rather than resistance character. From $T_{3}$ rootstocks homozygous for the CGMMV-CP horticulturally favorable individuals were selected for further breeding and a transgenic line was finally obtained at the $BC_{1}T_{5}$. A material transfer experiment was conducted to find out if the DNA, RNA or expressed protein in the transgenic rootstocks could move to the grafted scion (non-transformed watermelon, Super-Kumcheon). PCR, northern, and western blot analysis were performed and no evidence of transferring of those materials from rootstock to scion was ever found.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.40 no.4
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• pp.437-443
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• 1995

Concerns on use of excess amount of chemical fertilizier and pesticide in current farming system turns both of the producer and consumer of agricultural products to an organic farming which use a less chemicals and more natural manure. Rice-duck farming system is one of the strategy to meet the purpose and this experiment was carried out to find the effect of the rice-duck farming system on the quality and yields of rice. 20day-old rice seedling were mechanically transplanted in sandy-loam paddy field and 21 day-old ducks were raised from 3 weeks after transplanting with population of 30 heads per 10a. The plots were consists of reduce fertilizer(70%) with and without duck-raising. The conventional fertilizer treatment without duck-raising was used as check. The results obtained are summarized as follows. The weeds population of test plots which were raised with duck for 3 consecutive years was less than that of test plots without duck-raising, though a speciffic population of Echinochola crusgallis were increased. The weed control effect was higer in duck-raising than in check at the maximum tillering stage but, not at later stages of rice plant. It was found that the small animals and insects inhibiting in the rice field were reduced by duck-treatment, however, there were also damages of grass leaf roller at booting stage in the plots of duck-raising. In rice-duck plot, dark green leaf color were found: 41.8 of SPAD value than 38.6 of SPAD in check plot. Higher root activity and surface soil oxidation were also observed in rice-duck plot than check plot. 3% of the increase in yield was observed by duck-treatment. However, the expected increase of the palatability wsa not observed. This may be due to the unfavorable weather conditions during the rice growing in this expriment.

• Journal of the Korean Geotechnical Society
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• v.30 no.9
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• pp.19-28
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• 2014

It is necessary to understand the behavior of the soils for the dredging constructions. The objective of this study is to estimate void ratio and density changes of the dredged soils by using the geophysical testing methods. A series of laboratory tests is performed to obtain geotechnical index properties of the specimen, retrieved from the west coastal of Korea. The sedimentation and self-weight consolidation tests are carried out with observing changes of the interfacial height and the elastic wave velocities. The same amounts of the soils are poured into the testing column at intervals of 12 hours until the interheight reaches to a certain level. After the completion of the sedimentatation and self-weight consolidation tests, downward permeability test is performed to assess a tidal influence in the nearshore. The mini resistance cone is penetrated into the specimen to measure the electrical resistivity with depth. All tests are completely finished, the weight of specimens are measured to calculate the void ratio with the depth. Experimental results show that the aspects of the self-weight consolidation are invisible during dredging process because of rapid sedimentation characteristics of ML. However, the elastic wave velocities increase with increasing in the effective stresses. During permeability test, measured permeability and the elastic wave velocities maintain almost identical values. Void ratio based on the elastic wave velocities changes linearly with time during the step dumpings. Void ratio estimated by the electrical resistivity represents the repeatedly layered depositions according to the step-by-step dumpings. Void ratio determined by soil sampling is similar to those of elastic waves and electrical resistivity profiles. This experimental study demonstrates that the geophysical testing methods may be an effective method for evaluating the behavior of dredged soils.

• Journal of the Korean Geotechnical Society
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• v.29 no.3
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• pp.51-60
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• 2013

The slime, deposited in the bored pile due to falling soil particle, reduces the bearing capacity of bored pile and thus the stability of construction also decreases. The weight pendulum and iron have been used for estimating the slime thickness based on the subjective judgment and thus the previous method has a limitation of reliability. The objective of this paper is to suggest the method for estimating the slime thickness by using characteristics of electrical resistivity as scientific method. The temperature-compensation resistivity probe (TRP), which has a conical shape and the diameter of 35.7mm, is applied to the measurement of the electrical resistivity in the borehole during penetration. The field tests are carried out for estimating the slime thickness in the application site of bored pile. The slime thickness is calculated through the difference between excavation depth of borehole and measured data. Furthermore, the laboratory tests are also conducted for investigating effects of casing, time elapsing and relative density by using the specimen of slime. The laboratory test supporting the suggested method is reasonable for determining the slime depth. The paper suggests that the electrical resistivity method may be a useful method for detecting slime thickness and the method is expected to be applicable to various sites of bored piles.

• Journal of the Korean GEO-environmental Society
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• v.18 no.8
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• pp.23-32
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• 2017

For exposed slopes, the weathering degree over time has a major effect on the engineering properties of rocks and the slope stability. Rocks are gradually changed by weathering into soil over time, and the resulting physical, chemical and mechanical changes of rocks affect the engineering stability of the slope. However, there are not many ways to objectively evaluate the weathering degree of a slope. In this study, therefore, to investigate the weathering characteristics of rocks, granite, gneiss and shale distributed in the Chungbuk region were sampled by weathering stage and changes in their component minerals and tissues were investigated. Furthermore, artificial weathering was induced using the freezing and thawing test and quantitatively investigated through porosity and absorption rate. In addition, the changes of microcracks due to artificial weathering were evaluated through box fractal dimension ($D_B$). Through mineralogical study the phase change of constituting minerals, the growth of secondary minerals, the development of micro-cracks and the fabric changes due to weathering were observed. The mineralogical, chemical and engineering evaluations of the weathering degree through the experimental results in this study are expected to be useful for analyzing the weathering characteristics and causes by rock type and for proposing a methodology to evaluate the degradation of physical properties comparatively and quantitatively.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.2
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• pp.169-175
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• 1992

The Maximum Dry Density (${\gamma}_{dmax}$) and the Optimum Moisture Content (${\omega}_{opt}$) of the soil samples are determined from the compaction curve plotted with the laboratory compaction test results. But in this study three reported tests, and tests on the silty clay and the sandy silt samples are reviewed through the interpolation methods using an equation of the Moisture-Density relations induced from Lagrange's Interpolation Formula without drawing the compaction curves. As the results of the study ${\gamma}_{dmax}$ and ${\omega}_{opt}$, were calculated rapidly and simply using the equation and approached to the results from the compaction curves, and also due to the differences of the ${\gamma}_{dmax}$ and ${\omega}_{opt}$, calculated from the equation between the compaction curves were within $0.01g/cm^3$(0.5%) and 0.4% respectively the method in this study be recommended as a simple method determining ${\gamma}_{dmax}$ and ${\omega}_{opt}$, during the laboratory compaction tests.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.12
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• pp.737-746
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• 2019

Most landslides in the country are shallow failures triggered by intense rainfall. Many researchers have revealed the possibility of predicting shallow failure through the volumetric water content (VWC). This study examined how to determine shallow failure using the gradient characteristics of the volumetric water content. For this, flume experiments were conducted using weathered granite soil. To confirm the saturation state of the surface layer under a rainfall intensity of 30 and 50mm/hr, VWC sensors were installed at depths of 10 and 20 cm on the upper, middle and lower slope. The test results showed that a shallow failure determination using VWC could be applied limitedly according to the slope degree. In addition, the effective cumulative rainfall due to the rainfall infiltration velocity is considered the main factor for the failure time. The failure prediction using the gradient of the VWC depends on the installation location and depth of the sensor. According to the experimental data, the measured value at 20 cm below the slope was most effective. Therefore, an analysis method of VWC and the method of selecting the installation location confirmed through this study can provide important data for presenting the measurement criteria using VWC in the future.