• Journal of the Korean Geotechnical Society
• /
• v.37 no.11
• /
• pp.51-60
• /
• 2021

River scour erodes the soil around the pier, reducing the lateral bearing capacity of the pier and lowering the stability of the structure. In this study, in order to examine the effect of scouring on the stability of the structure, an experiment was performed to measure the natural frequency of the pier according to the excavation of the surrounding ground. Impact vibration test was conducted on the pier with the caisson foundation of the Mangyeonggang Bridge, which is scheduled to be demolished. Accelerometers were attached to the top, center, and bottom of the pier and the acceleration responses were measured by hitting those three points. The experimental results showed that the top hit showed consistent and reasonable results of the acceleration responses according to the hitting position. The measured accelerations were converted to the frequency domain through Fast Fourier Transform (FFT), and then the natural frequency was determined. In addition, to analyze the scour effect on the natural frequency of the pier, the ground around the pier was excavated and the natural frequency change was analyzed. As a result, the natural frequency showed the decreasing tendency according to the excavation depth, but the decrease was small due to the large stiffness of the caisson foundation.

• Proceedings of the Safety Management and Science Conference
• /
• 2009.04a
• /
• pp.167-175
• /
• 2009

전 세계적으로 이상 고온, 폭우, 가뭄, 지진, 해일 등이 빈번하게 발생하고 있다. 그 피해 규모도 앞으로 계속 커질 전망이다. 경제활동의 주체인 기업이 이러한 자연 재해로 인하여 지속적이고 안정적으로 운영되지 못하게 된다면 이는 기업자체는 물론 치 열한 글로벌 경쟁체제 속에서 국가경쟁력향상에 상당한 타격을 줄 수 있다. 하지만 우리나라의 기업은 선진국에 비해 상대적으로 자연재해 발생 시 체계적인 방재시스템을 구축하지 못하고 있다. 본 논문에서는 자연재해저감기술 개발의 필요성과 선진국가의 사례들을 통한 우리나라의 자연재해저감기술이 나아갈 방향성을 모색하고자 한다.

• The Optical Journal
• /
• s.105
• /
• pp.42-42
• /
• 2006

전략물자라 함은 군사적 목적으로만 이용되는 군전용의 물자만이 아닌 민수품까지도 포괄하는 개념이다. 전략물자에 포함되는 민수품은 군사적 목적으로도 사용될 수 있는 품목으로서 국제적으로는 이중용도(Dual Use)품목으로 불리어진다. 이러한 군전용 물품과 이중용도품목이 분쟁국가나 국제평화를 저해할 우려가 있는 국가로 수출이 되어 군사력의 과도한 확장에 이용되지 않도록 하기위한 제도가 전략물자 수출통제제도이다. 국제사회에서 안보와 평화를 위한 규범으로 시행되고 있는 전략물자 수출통제 강화 추세에 적절히 대응하지 못할 경우, 우리 업체의 피해는 물론 국가 이미지에 심대한 타격을 받을 수 있으므로 우리나라도 정부·기업이 역할을 분담하는 방향으로 전략물자 수출통제 강화방안이 마련되었다. 본 고에서는 기업리스크 관리를 위한 전략물자 무역관리를 위해 한국무역협회에서 발간한‘알기 쉽게 풀어 쓴 전략물자 무역관리’내용을 발췌하여 연재한다.

• The Optical Journal
• /
• s.102
• /
• pp.42-43
• /
• 2006

전략물자라 함은 군사적 목적으로만 이용되는 군전용의 물자만이 아닌 민수품까지도 포괄하는 개념이다. 전략물자에 포함되는 민수품은 군사적 목적으로도 사용될 수 있는 품목으로서 국제적으로는 이중용도(Dual Use)품목으로 불리어진다. 이러한 군전용 물품과 이중용도품목이 분쟁국가나 국제평화를 저해할 우려가 있는 국가로 수출이 되어 군사력의 과도한 확장에 이용되지 않도록 하기위한 제도가 전략물자 수출통제제도이다. 국제사회에서 안보와 평화를 위한 규범으로 시행되고 있는 전략물자 수출통제 강화 추세에 적절히 대응하지 못할 경우, 우리 업체의 피해는 물론 국가 이미지에 심대한 타격을 받을 수 있으므로 우리나라도 정부·기업이 역할을 분담하는 방향으로 전략물자 수출통제 강화방안이 마련되었다. 본 고에서는 기업리스크 관리를 위한 전략물자 무역관리를 위해 한국무역협회에서 발간한‘알기 쉽게 풀어 쓴 전략물자 무역관리’내용을 발췌하여 연재한다.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2010.05a
• /
• pp.1242-1246
• /
• 2010

호우기간 동안 내리는 빗방울의 타격에 의해 흙 입자는 침출수와 함께 이동하여 지표 아래 공극을 막는다. 다져진 지표면은 유출과 토양 유실의 원인이 된다. 발생원으로부터 유실되는 토양을 Polyacrylamide(PAM)과 지표피복재를 이용하여 저감하는 연구를 하였다. PAM은 토양 입자의 결합력을 강화시키고 이탈을 방지하여 토양 유실을 감소시키는데 효과적이다. 이 연구의 목적은 PAM을 덧붙인 볏짚거적, 볏짚거적+톱밥, 볏짚거적+왕겨 등을 이용하여 인공강우 동안 토양 유실을 저감하는 효과를 조사하는 것이다. 실험은 1시간 동안 강우를 모의했으며, 실험 도중에 6~7회 수질 샘플을 채취하였다. 초기유출시간은 총 4차 실험중에 2차를 제외한 나머지에서 볏짚거적+왕겨+PAM이 가장 느리게 유출되었다. SS와 탁도 항목에서 1차 실험을 제외한 나머지 실험에서 볏짚거적+톱밥+PAM이 효과적이었다. 단순히 PAM을 사용하는 것보다 잔여물(residue)을 같이 혼합한 피복재료가 토양 유실과 유출을 저감하는데 더욱 효과적인 것으로 나타났다. 본 연구 결과는 향후 농촌지역에 토양 유실저감에 필요한 자료로 활용할 수 있을 것이라 판단된다.

• Journal of the Korean Geotechnical Society
• /
• v.29 no.12
• /
• pp.105-111
• /
• 2013

The standard penetration test (SPT) has been widely used because of its usability, economy, and many correlations with soil properties among other factors. In SPT, hammer energy is an important factor to evaluate and calibrate N values. To measure hammer energy, an instrumented SPT rod was developed considering that stress waves transferring on rods during SPT driving are the same as stress waves transferring on piles due to pile driving. Using this idea, an instrumented SPT rod with a pile driving analyzer was applied as a pile capacity prediction tool in this study. In order to evaluate this method, SPT and dynamic cone tests with the instrumented SPT rod were conducted and also 2 pile load tests were performed on pre-bored steel pipe piles at the same test site. End bearings were predicted by CAPWAP analysis on force and velocity waves from dynamic cone penetration tests and SPT. Comparing these predicted end bearings with static pile load tests, a new prediction method of the end bearing capacity using the instrumented SPT rod was proposed.

• Journal of the Korea Society for Simulation
• /
• v.24 no.4
• /
• pp.35-41
• /
• 2015

Recoil system for 40mm automatic gun is a device developed to absorb the shock of explosion. It is impossible to conduct pinpoint strike due to recoil if very high explosive shock, which is generated when an automatic gun fires shells, can't be absorbed. This study covers development and verification of analysis model for recoil system by utilizing a multi-domain software. The research process is as in the following. First, an analysis model is developed to verify damping characteristics through understanding of design intention. Second, environment which is identical to a field test is set up on analysis tool after putting explosive force that is measured through the test into the analysis model. Finally, the analysis model for recoil system using the multi-domain software is verified if it has effectiveness with a comparison between internal pressure of the recoil system along with displacement of gun barrel and the field test result.

• Geotechnical Engineering
• /
• v.12 no.6
• /
• pp.51-64
• /
• 1996

After the model open-ended pile attached with strain gages was driven into a pressure chamber, in which the saturated microfine sand was contained, the static compression loading test was performed for that pile. Based on the test results, ultimate pile capacity was determined. Then, either simulated earthquake shaking or sinusoidal shaking was applied to the pile with the sustained certain level OP ultimate pile load. Then, pile capacity degradations characteristics during shaking were studied. Pile capacity degradation during two different shakings were greatly different. During the simulated earthquake shaking, capacity degradation depended upon the magnitude of applied load. When the load applied to the pile top was less than 70% of ultimate pile capacidy, pile capacity degradation rate was less than 8%, and pile with the sustained ultimate pile load had the degradation rate of 90%. Also, most of pile capacity degradation was reduced in outer skin friction and degradation rate was about 80% of ultimate pile capacity reduction. During sinusoidal shaking, pile capacity degradation did not depend on the magnitude of applied load. It depended on the amplitude and the frequency , the larger the amplitude and the fewer the frequency was, the higher the degradation rate was. Reduction pattern of unit soil plugging (once depended on the mode of shaking. Unit soil plugging force by the simulated earthquake shaking was reduced in the bottom 3.0 D, of the toe irrespective of the applied load, while reduction of unit soil plugging force by sinusoidal shaking was occurred in the bottom 1.0-3.0D, of the toe. Also, the soil plugging force was reduced more than that during simulated earthquake shaking and degradation rate of the pile capacity depended on the magnitude of the applied load.

• Journal of the Korean Geosynthetics Society
• /
• v.18 no.3
• /
• pp.45-53
• /
• 2019

In this study, it was analyzed the cases of bored PHC piles designed for the building foundations. The overall length of the piles varies within a maximum of 35 m. However, the average length was 17.0 to 18.9 m depending on the kind of the bedrock, with no significant difference. The socket length entered into the bedrock was designed with approximately 58% of the whole piles being 1m, the minimum length of the specification, and up to 5m. Although the range in design efficiency was very large, on average it was about 70%, consistent with the usual known extent. Applications with low design efficiency were mainly shown on the foundation of low-rise buildings or rides with low design load. On the weathered rock, the design load, which governs the design result was widely distributed at 65 to 97% of allowable bearing capacity of ground. The ratio of allowable axial load of piles to allowable bearing capacity of ground is also widely distributed between 36 and 115%, so optimization efforts are required along with design efficiency. On the other hand, the allowable bearing capacity on the soft or hard rock was highly equal, mostly within 90% of the allowable axial load of piles. In the design, the end bearing resistance averaged over 75% of the allowable bearing capacity. However, the results of the dynamic pile load test show that the end bearing resistance was predominant under the E.O.I.D conditions, and in some cases, the end bearing resistance was at least 25% under the restrike conditions.

• Journal of the Korean Geosynthetics Society
• /
• v.18 no.4
• /
• pp.1-13
• /
• 2019

The purpose of this study is to examine the effect of soft ground improvement by dynamic replacement with utilizing crushed rock. In order to understand the ground improvement effect when applying dynamic replacement method with crushed rock, the laboratory test and field test were performed. The internal friction angle and apparent cohesion were derived through direct shear test. The dynamic replacement characteristics were identified by analyzing the weight, drop, and number of blows needed for dynamic replacement. Through the field plate bearing test and density test, the bearing capacity and settlement of the improved ground were measured, and the numerical analysis were conducted to analyze the behavior of the improved ground. In this study, it proposes modified soil experimental coefficient(C_DR) to 0.3~0.5 in the dynamic replacement method with crushed rock. Also when applying the dynamic replacement method using crushed rock, the particle size range is less than 100 mm, D₉₀ is less than 80 mm and D₁₅ is more than 30 mm.