• Journal of the Korean Geotechnical Society
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• v.18 no.3
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• pp.13-21
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• 2002

An extensive tension experiment was carried out to examine the variation of tensile strength in moist sand having moisture contents in the range of 0.5% < w < 4.0% with newly developed direct tension apparatus. It was observed that tensile strength of sand varied as functions of moisture content, relative density, presence of fines, and level of precompression. Tensile strength increases with increasing moisture content and fines, and this trend is more noticeable at increasing relative densities. However, the influences of relative density and fines on the tensile strength are substantially dependent on the water content. These effects are reduced at low moisture levels (w < 0.5%). The precompression effects also depend on the water content but less on the duration and level of the precompression.

• Smart Structures and Systems
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• v.20 no.6
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• pp.739-757
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• 2017

The main goal of this study is to investigate the hysteretic behavior of polyurethane rubber springs in compression with and without precompression. The precompression is introduced to provide rigid force in the behavior, and thereby a precompressed rubber spring can be used for a restoring element. For the goal, this study prepares nine rubber springs for three suites which are all cylindrical in shape with a hole at the center. The rubber springs in each suite have different dimensions of diameter and length but have similar shape factors; thus, they are designed to have a similar compressive stiffness. Three rubber springs from the nine are tested with increasing compressive strain up to 30% strain to investigate the behavior of the rubber springs without precompression as well as the effect of the loading strain. The nine springs are compressed up to 30% strain with increasing precompressive strain from 0 to 20% at increments of 5%. The study analyzes the effective stiffness and damping ratio of the rubber springs with and without precompression, and the rigid force of the precompressed rubber springs is discussed. Finally, this study suggests a regression method to determine the minimum required precompression to eliminate residual strain after unloading.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.43 no.4
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• pp.413-420
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• 2023

Among the seismic structures for reducing earthquake damage, the seismic control structure is a technology that can efficiently improve seismic performance and secure economic feasibility by simply applying a damper. However, existing dampers have limitations in terms of durability due to required seismic performance and material plasticity. In this study, we proposed a polyurethane damper with enhanced recovery characteristics by applying precompression to polyurethane, which basically shows elastic characteristics, and applying superelastic shape memory alloy (SSMA). To verify the characteristics of the polyurethane damper, the concept was first established, and the design details were completed by selecting SSMA and steel, and selecting the precompression size as design variables. In addition, structural tests were conducted to derive response behavior and analyze force resistance performance, residual displacement, recovery rate, and energy dissipation capacity. As a result of the analysis, the polyurethane damper showed that various performances improved when the SSMA wire was applied and the precompression increased.

• Explosives and Blasting
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• v.26 no.2
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• pp.29-37
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• 2008

In general, the size of tunnel cross section in construction site is $50{\sim}200m^2$. But, electric cable tunnel, telecommunication cable tunnel, mine tunnel. Waterproof tunnel have small cross section less than $20m^2$. There are so many problem at small sectional tunnel: restriction of equipment, dead pressure by precompression, loss of efficiency, increase of work time. Especially, explosives remainder by precompression of previous detonation is serious problem. To find its measures of dead pressure (explosives remainder), the following series of progress have been conducted: (1) survey of previous study (2) investigate causes of dead pressure (3) set up of its measures (4) application and appraisal at tunnel site. The measures, change of cut pattern, hole space over 40cm, adjustment of delay time, are proved by experimental results.

• Journal of Korean Society of Steel Construction
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• v.28 no.4
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• pp.223-229
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• 2016

This study proposes a new technology for a smart damper with flag-shaped behavior using the combination of magnetic friction and rubber springs. The magnet provides friction and, thus, energy dissipation, and the rubber springs with precompression contribute to present self-centering capacity of the damper. To verify their performance, this study conducts dynamic tests of magnet frictional dampers and precompressed rubber springs. For the purpose, hexahedron Neodymium (NdFeB) magnets and polyurethane rubber cylinders are used. In the dynamic tests, loading frequency varies from 0.1 to 2.0 Hz. The magnets provide almost perfect rectangular behavior in force-deformation curve. The rubber springs are tested without or with precompression. The rubber springs show larger rigid force with increasing precompression. Lastly, this study discusses combination of rigid-elastic behavior and friction to generate 'flag-shaped' behavior for a smart damper and suggests how to combine the magnets and the rubber springs to obtain the flag-shaped behavior.

• Proceedings of the KSEE Conference
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• 2008.10a
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• pp.17-28
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• 2008

국책사업이나 SOC의 확충을 위한 도로 및 철도의 건설에서 적용되는 터널의 단면크기를 보면, $50m^2$에서부터 $100m^2$이상의 중 대단면 터널이 주를 이루고 있으나, 전력구, 통신구, 소규모로 운영되는 광산의 채광용 터널, 용수를 위한 도수로터널 등 특수한 용도로 설계, 시공되고 있는 터널에서는 $20m^2$이하의 단면크기를 갖는 경우가 있다. 이러한 소단면 터널의 경우에는 협소한 작업공간으로 인하여 적용공법 뿐만 아니라 장비의 사용 또한 제약을 받게 되어 작업효율이 저하되고 공사기간이 늘어나게 되는 등 여러 가지 문제점을 안고 있다. 특히, 에멀젼 폭약을 사용하는 발파에서 먼저 기폭된 발파공의 충격압력에 의해 인접공의 폭약이 예비압축(Precompression)되어 사압현상을 일으키고 잔류약을 발생시키는 사례가 종종 발생하고 있다. 사압현상은 당해 발파의 실패와 함께 2차적인 사고의 위험요인이 될 수 있으므로 이를 방지하기 위한 대책을 수립하여야 한다. 이를 위해 기존 문헌을 통하여 사압현상의 원인과 발생 가능성을 검토하였고, 국내에서 주로 사용되는 에멀전폭약의 수중 내충격성시험과 충격압력 전달시험을 실시하여 사압현상의 발생정도를 측정하였으며, 사압현상이 발생한 소단면 터널현장을 대상으로 대책을 수립하여 적용하였다. 심발방법을 변경하여 전단의 충격압력을 견딜 수 있는 공간격을 확보하고 뇌관의 초시간격을 적절하게 배치한 발파패턴을 적용한결과, 사압현상을 억제하고 잔류약의 발생을 감소시켜 계획 굴진장을 확보하고 파쇄석의 크기를 감소시키는 등 양호한 결과를 얻을 수 있었다.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.10a
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• pp.95-102
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• 1999

It is important to estimate the magnitude of settlement and the time of primary consolidation in geotechnical engineering projects. For these purposes, site explorations and laboratory tests are usually performed. However, the mechanical properties determined from laboratory tests on the samples obtained by different sampling techniques show different trends. In this study, three types of consolidation test were carried out on the soil samples obtained by three different sampling techniques (76mm tube, 76mm piston, and block samples), to verify the effect of sample disturbance on consolidation properties. It was found that sampling methods have influence on the $\varepsilon$ - log $\sigma$'$_{v}$ relationship. While insignificant difference of compression indices from the samples obtained by different sampling techniques was observed in compression region, these values showed a different trend in precompression region. The values of $c_{v}$ and k of block samples had a tendency to be larger than those of piston and tube samples. At consolidation pressure larger than $\sigma$'$_{p}$, however, these properties became similar regardless of sampling methods. The block and piston samples gave slightly higher values of $C_{a/}$ $C_{c}$ than tube samples. In the results of I $L_{EOP}$ and CRS test, it was observed that the values of $\sigma$'$_{p measured}$/$\sigma$'$_{p best estimated}$ of Yang-San clay decreases when strain becomes larger than 1.0% and that precompression strain of block samples is in the range of 1.5~2.0% while those of piston and tube samples are 1.75~3.75%. It was also shown that the values of $\sigma$'$_{p}$ of block samples exceed those of piston and tube samples by about 6~10%.6~10%.%.%.%.%.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.03b
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• pp.309-316
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• 2000

When highly compressible, clayey soil layers lies at a limited depth and large consolidtion settlements are expected as the result of construction, precompression of soil may be used to minimize postconstruction settlement. In this study, we tried to find the possibility about the effect of ground improvement using flat dilatometer at the Inchon International Airport where preloading was installed. Field and laboratory tests were performed for soft ground before and after preloading in order to check the effectiveness of the soft ground improvement and compared with the test results of dilatometer which obtained before and after preloading at the same location Field tests such as flat dilatometer, vane, CPTu tests were performed before and after preloading and undisturbed samples are obtained to carry out laboratory tests. As comparing results, after preloading, unit weight, effective stress, undrained shear strength were increased and we can also check the decrease of consolidation late caused of decrease of void ratio. Furthermore, it is assumed that the possibility on the effect of ground improvement by using the flat dilatometer

• Journal of Ginseng Research
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• v.41 no.3
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• pp.339-346
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• 2017

Background: In this study, we investigated how to convert the Panax ginseng DNA sequence code and chemical fingerprints into a two-dimensional code. In order to improve the compression efficiency, GATC2Bytes and digital merger compression algorithms are proposed. Methods: HPLC chemical fingerprint data of 10 groups of P. ginseng from Northeast China and the internal transcribed spacer 2 (ITS2) sequence code as the DNA sequence code were ready for conversion. In order to convert such data into a two-dimensional code, the following six steps were performed: First, the chemical fingerprint characteristic data sets were obtained through the inflection filtering algorithm. Second, precompression processing of such data sets is undertaken. Third, precompression processing was undertaken with the P. ginseng DNA (ITS2) sequence codes. Fourth, the precompressed chemical fingerprint data and the DNA (ITS2) sequence code were combined in accordance with the set data format. Such combined data can be compressed by Zlib, an open source data compression algorithm. Finally, the compressed data generated a two-dimensional code called a quick response code (QR code). Results: Through the abovementioned converting process, it can be found that the number of bytes needed for storing P. ginseng chemical fingerprints and its DNA (ITS2) sequence code can be greatly reduced. After GTCA2Bytes algorithm processing, the ITS2 compression rate reaches 75% and the chemical fingerprint compression rate exceeds 99.65% via filtration and digital merger compression algorithm processing. Therefore, the overall compression ratio even exceeds 99.36%. The capacity of the formed QR code is around 0.5k, which can easily and successfully be read and identified by any smartphone. Conclusion: P. ginseng chemical fingerprints and its DNA (ITS2) sequence code can form a QR code after data processing, and therefore the QR code can be a perfect carrier of the authenticity and quality of P. ginseng information. This study provides a theoretical basis for the development of a quality traceability system of traditional Chinese medicine based on a two-dimensional code.

• Geotechnical Engineering
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• v.10 no.4
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• pp.167-180
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• 1994

A series of long term consolidation tests were conducted under loading -unloading and loading(pc) -unloading(p.) -reloading(p,) conditions using reconstituted clay in order to investigate the effect of stress history on secondary consolidation characteristics and the applicability of the secondary consolidation model suggested by Bjerrum to overconsolidated clays. According to the test results, the secondary compression settlement affected by the stress history in the first half of experimental period and the coefficient of secondary compression, C‥‥ is dependent on overconsolidation ratio, OCR(p,1 p.), maBium OCR (p./p.), and unloading duration time. Moreover the coefficient of secondary consolidation in the latter half of experimental period Cn is mainly affected by OCR and it gradually reduces with OCR increment. Finally the comparison of the experimental results with the Bjerrum model indicates that the Bjerrum model can be applied beyond certain range of stress history in the overconsolidated clay.