• Korean Journal of Environment and Ecology
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• v.36 no.5
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• pp.535-549
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• 2022

Damage to forests, such as broken or falling trees, has increased due to the increased intensity and frequency of abnormal climate events, such as strong winds and heavy rains. However, it is difficult to respond to them in advance based on prediction since structural defects such as cavities and bumps inside trees are difficult to identify with a visual inspection. Non-invasive sonic tomography (SoT) is a method of estimating internal defects while minimizing physical damage to trees. Although SoT is effective in diagnosing internal defects, its accuracy varies depending on the species. Therefore, it is necessary to analyze the reliability of its measurement results before applying it in the field. In this study, we measured internal defects in wood by cross-applying destructive resistance micro drilling on old Pinus densifloraSiebold & Zucc. and Ginkgo bilobaL., which are representative tree species in Korea, to verify the reliability of SoT and compared the evaluation results. The t-test for the mean values of the defect measurement between the two groups showed no statistically significant difference in pine trees and some difference in ginkgo trees. Linear regression analysis results showed a positive correlation with an increase in defects in SoT images when the defects in the drill resistance graph increased in both species.

• Journal of Conservation Science
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• v.38 no.2
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• pp.87-95
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• 2022

This aimed to species identification and tree-ring dating of wooden elements used in the Myeongjeong-gate of the Changgyeong-palace, Seoul, Korea. Of the 79 wooden elements evaluated, 78 were confirmed to be hard pines and one belonged to Abies spp.. Cores of the wooden elements were collected using a drill for tree-ring dating, and ring-width plots of individual samples were constructed using the TSAP software. The tree-ring dating results for the outermost ring of 58 hard pine wooden elements revealed the following felling dates: early spring of 1604-late fall of 1615, late fall of 1706-early spring of 1707, and late fall of 1828-late fall of 1834. The obtained felling dates of the 1600s and 1800s were found to be consistent with those in the construction and repair records of the Annals of Joseon Dynasty, Gwanghaegun's Diary and Changgyeonggung Yeonggeondogam Uigwe. However, the obtained felling dates of the 1700s were not consistent with those in the construction and repair records. Therefore, additional confirmation of repairs that were not included in the records was possible using tree-ring dating.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.41 no.2
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• pp.215-222
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• 1996

This study was conducted to compare the growth and yield, and to determine the optimum planting date and density in two improved black soybean varieties. The two varieties were planted by driller attached a tractor on May 21 and June 19, 1993, and treated five planting densities, respectively. Yield of Gumjeongkong 1 was similer for both planting dates, but that of Suwon 157 was remarkably reduced on June 19 planting compared to May 21. There was significant differences between planting dates in stem length, number of branches, seeds per plant, seed weight and yield. Planting density, also, significantly affected on stem length, number of branches and seeds per plant. Statistically significant interactions between planting date$\times$variety and planting date$\times$planting density were found at almost all characteristics, except between variety$\times$planting density. Optimum planting date and density of Gumjeongkong 1 for high yield were June 19 and 33, 000 plants per l0a, and those of Suwon 157 were May 21 and 22, 000 plants per l0a, respectively. The coefficient of variation at different planting densities was high at stem length, number of branches, seeds per plant and yield, but low at number of main stem node, seeds per pod and 100 seed weight.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.40 no.1
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• pp.33-38
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• 1995

This experiment was conducted to elucidate the effect of the midsummer drainage times on lodging characters, field lodging and yield in direct seeding rice culture in puddled soil. Dongjinbyeo was seeded at May 11 by seeding machine with 4cm of furrow depth and drained, one（50days after seeding DAS）） two （30DAS and 50DAS）, and three times （30DAS, and 50DAS and 60DAS）. The results are as follows. Culm length was shorten and the wall of N3, N4 were thicken as the drain-age times were increased. As the drainage times were increased breaking weights were increased but the lodging index were decreased. Lodging was occurred seriousely at none drainage, but wasn't occurred two or three times drainage. Yield was higher at 1~2 times drainage compared with none and three times drainage. Therefore, two times midsummer drainage is recommend-able water management method for direct seeding rice culture in puddled soil.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.40 no.6
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• pp.731-737
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• 1995

This experiment was carried out at National Crop Experiment Station in 1994 to obtain basic information of growth characters and yield of rice under various nitrogen split application methods on different soil textures in direct seeding on dry paddy. Hwaseongbyeo sown on April 27 by flat drill seeding, and irrigation was done at 3 leaf stage after seedling establishment. Number of seedling stand was 159~177 seedlings per $m^2$ regardless of soil texture and nitrogen application method. Number of panicle per unit area in loam was higher than in sandy loam, and it also was higher in top dressing plots, which were 3 times application at rate of 40-30-30% (3rd leaf stage -7th leaf stage -panicle initiation stage) and 4 times application 10-30-30-30%(basal-3rd leaf stage -7th leaf stage -panicle initiation stage), than in conventional method. Leaf colour, leaf area index and dry matter production at heading stage were highest at top dressing plots among the nitrogen application methods in both sandy loam and loam. Lodging index in top dressing plots increased by low breaking weight with long culm. There were field lodging of degree 3 in top dressing plots. Rice yield in sandy loam, loam increased by 7~9%, 6~9% in top dressing of nitrogen, respectively.

• Journal of the Korean Geotechnical Society
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• v.23 no.11
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• pp.87-98
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• 2007

For the quick rehabilitation of a fire-damaged tunnel structure, it is the most important procedure to investigate the fire-induced damaged zone rapidly. This study aims to propose a new drilling resistance testing method by which mechanical properties of tunnel concrete lining altered by high temperature can be estimated easily and continuously. Especially, it alms to derive the relationships to estimate mechanical properties of mortar and concrete materials from drilling parameters. To obtain the optimum testing condition, a series of drilling resistance tests were carried out for mortar specimens. When the rotation per minute of drill bit, tile penetration rate and the bit diameter were 1,300 rpm, 1.40 mm/sec, and 10 mm respectively, the deviation of measured drilling resistance forces was minimal. Under the optimum testing condition, the relationships between drilling resistance and mechanical properties of mortar specimens were shown to be very favorable. The concept of replacing a mean value of resistance farces measured during drilling with the resistance energy was proposed to consider the effects of randomly distributed aggregates inside a concrete material on drilling resistance. When the concept was applied to concrete materials, a favorable relationship between actual compressive strength and drilling resistance energy was also successfully derived.

• Journal of the Korean Geotechnical Society
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• v.26 no.1
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• pp.5-19
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• 2010

Geo-layer information is important to determine pile length and estimate residual settlement in the construction site. An overall spatial distribution of geo-layers in the entire construction site can be predicted using drill-log information. In this study, the geo-layer distribution at Song-do area was estimated by kriging and inverse distance weighting methods, and a cross validation was adopted to verify the reliability of estimation results. The analysis results indicate that the best fitted theoretical variogram model to the experimental variogram does not always provide the most reliable estimation in the kriging method. The proper $\alpha$ value of inverse distance weighting method must be determined by types of geo-layer, because the $\alpha$ value is affected by types of geo-layer. Results of the kriging method show more reliable results than those of inverse distance weighting method, and the structure of geo-layer distribution could be evaluated by variogram in the kriging method.

• Journal of the Korean Geotechnical Society
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• v.23 no.7
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• pp.57-64
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• 2007

This study proposes a method to estimate drilling torque during ground boring with an aid of electrical energy required for rotating a boring-auger. Ground boring is commonly used in geotechnical engineering such as preboring precast pile installation, soil-cement grouting, ground exploration and so forth. In order to understand the correlation between required electrical energy to rotate the boring auger and the drilling torque, a small laboratory apparatus was designed and a pilot study was performed. The apparatus rotates common drill bits of $D=5{\sim}25mm$ in CBR specimens. The velocity of a bit is 19 RPM and predefined using a reduction gear which connects a main rotation axis to a 25 Watts AC electrical motor shaft. In the middle of drilling the motor current increments and the drilling torque were measured and the correlation between the current and the torque was obtained through linear square fits. Based on the correlation the acquired motor current during drilling was applied to predict the drilling torque in consequent testing and the prediction results were compared to the measured torque. The comparison leads a conclusion that the motor current during drilling using electrical power may be a good indicator to estimate/determine strength characteristics of the ground.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.42 no.2
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• pp.197-208
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• 2022

The existence of shallow bedrock and the desire to use underground space necessitate the use of blasting methods. The standard blasting method under water after drilling is associated with certain technical difficulties, including reduced detonation power, the use of a fixed charge per delay, and decoupling. However, there is no blasting method to replace the existing blasting method. In this paper, a dry hole charged with ANFO blasting is assessed while employing a dry hole pumping system to remove water from the drill borehole. Additional standard blasting is also utilized to compare the blasting performances of the two methods. The least-squares linear regression method is adopted to analyze the blasting vibration velocity quantitatively using the measured vibration velocity for each blasting method and the vibration velocity model as a function of the scaled distance. The results show that the dry hole charged with ANFO blasting will lead to greater damping of the blasting vibration, more energy dissipation to crush the surrounding rock, and closer distances for the allowable velocity of the blasting vibration. Also, standard blasting shows much longer influencing distances and a wider range of the blasting pattern. The pilot test confirms the blasting efficiency of dry hole charged with ANFO blasting.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.43 no.4
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• pp.493-499
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• 2023

Recently, with the development of construction machinery, low-vibration construction machine such as Tricone-Bits, which can drill both soil and rock layers and minimize vibration, is being used frequently. However, although many studies have been conducted on the prediction of vibration values for earth augers and pile drivers, the reality is that studies on the effects of vibration on low-vibration drilling equipment are lacking. In this paper, ground vibration values for Tricone-Bits were measured, and a vibration distance damping formula was proposed using this. In addition, after predicting the vibration of the earth auger and pile driver using the previously proposed vibration distance damping formula, the degree of vibration damping for the Tricone-Bits was evaluated by comparing and analyzing it. As a result, the Tricone-Bits showed a vibration reduction effect of 97% and 93% compared to these machine and It will help with management and prediction of the ground vibration effects evaluation on the low-vibration equipment such as Tricone-Bits.