• Journal of the Korean Geosynthetics Society
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• v.14 no.3
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• pp.1-12
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• 2015

During installing sheet piles for an impermeable wall or a retaining wall, vibratory hammers are widely used. Among vibratory hammers, a hydraulic hammer is used most commonly. However, a hydraulic hammer causes excessive vibration and noise due to resonance by change of natural frequency according to movements of eccentric shaft when the hammer starts and stops. In this study, new variable amplitude type hammer is developed in order to reduce the vibration and noise due to resonance produced in starting and stopping the hammer. By controlling horizontal angle in two pairs of eccentric body inside of the hammer, the amplitude and vibration of the new hammer can be controlled. The performance tests with the new hammer and existing hammers such as the hydraulic hammer and electric hammer are carried out, and the new hammer shows reduced vibration and noise results in comparison with existing hammers from performance tests. Also, this study shows that penetration rates of sheet pile using the new hammer increase due to impellent force of a backhoe in comparison with the electric hammer and penetration rate increase in comparison with a general hydraulic hammer, since the new hammer can control the amplitude during penetration of sheet pile according to soil condition.

• Journal of the Korean Geosynthetics Society
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• v.17 no.1
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• pp.111-118
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• 2018

In case of excavation of the tunnel under weak ground conditions, such as fault zone, leg pile reinforcement with the purpose of suppressing tunnel crown settlement and side wall displacement is commonly applied. There are convergence, crown settlement, leg settlement, and the axial force of leg as a main factor for confirming the safety of support considering the installation angle and length of leg pile reinforcement according to the increase in rate of change of tunnel cross-section. In particular, the influence of right corner settlement, among variables for safety confirmation during excavation, has been analyzed as the dominant factor in the most important priority management showing larger displacement tendency than the increase in rate of the cross-section. And, it was analyzed that the occurrence tendency of axial force on leg pile reinforcement showed the influence of behavior according to the friction support concept mechanism of the pile reinforcement rather than the increase in rate of tunnel cross-section, as it showed a small increase compared to the increase rate of the tunnel cross-section which did not show a great correlation from the viewpoint of the change of the axial force by the length of each leg pile reinforcement with regards to the change in rate of increase in tunnel cross-section. If a certain length of the leg pile reinforcement is selected based on the above grounds, even if the cross-section of the tunnel in poor ground condition is somewhat larger, it has been proved to be a more reasonable method considering the workability and economical efficiency by not extending the length of the leg pile reinforcement by force.

• Geotechnical Engineering
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• v.14 no.3
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• pp.73-94
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• 1998

In the present study, a method of the three-dimensional limit equilibrium stability analysis of shape of the potential failure wedge for the concave-shaped excavation corner is assumed on the basis of the results of the FLACSU program analysis. Estimation of the three-dimensional seepage forces expected to act on the failure wedge is made by solving the three-dimensional continuity equation of flow with appropriate boundary conditions. By using the proposed method of three-dimensional stability analysis of the concave-shaped excavation corner, a parametric study is performed to examine the reinforcement effect of skew soil nailing system, range of the efficient skew angles and seepage effect on the overall stability. Also examined is the effect of an existence of the right-angled excavation corner on three-dimensional deflection behaviors of the convex-shaped skew soil nailing walls. The results of analyses of the convexshaped excavation corner with skew soil nailing system is further included to illustrate the effects of various design parameters for typical patterns of skew nails reinforcement system.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.6D
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• pp.793-801
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• 2011

Existing specifications of road pavement require contractors to meet only materials and construction conditions regardless of pavement life. There are limitation of developing road pavement technology and possibility causing dispute between ordering organization and contractor with this type of specification. Research efforts to introduce performance warranty contracting are in progress in the field of road pavement to improve the problems. The performance warranty contracting gives the contractors opportunity to select materials and construction methods as they like. But they should satisfy a certain level of performance during a given period. The performance indicator and threshold value of pavement which are main elements of the warranty specification should be defined first to introduce the performance warranty contracting successfully. In this study, the performance indicator, threshold value, and warranty duration of asphalt pavement were investigated by reviewing literatures on performance warranty contracting of some states of the US. Major distresses influencing the performance of the asphalt pavement were investigated at 24 national expressway lines and national highway lines in 16 regions, and the data were analyzed to be compared to the cases of the US. Development of rational performance warranty specification for domestic asphalt pavement is expected based on the research results.

• International Journal of Highway Engineering
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• v.12 no.3
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• pp.59-70
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• 2010

More than 10 different cases of airline overrun accidents happened annually home and abroad in recent years. So the government put the guidelines to protect that kinds of accidents, which is named 'Runway End Safety Area'. However, the great part of airports are far from the standards, because most of the airports have been built before the guidelines. Moreover, in many cases natural obstacles, ambiance, and local area developments obstruct the extension of the runway to meet the criteria. For these reasons, the Federal Aviation Administration (FAA) recommends that the aviation fields construct 'Aircraft Rapid Arresting System(ARAS)' at the end of the runway. Many airdromes have been constructing the system and some airports have already completed the construction. In this research, our team performed a basic study about low strength perlite concrete to provide the proper material with 'ARAS'. As a result, the unit weight of the low strength perlite concrete was $4.5{\sim}6.4kN/m^3$ and uniaxial compressive strength was measured in the range of $400{\sim}1,470kN/m^2$. In addition, we tested penetration compressive strength by using CBR tester, and we observed that the strength was increased after around 60% of penetration rate. Also, 40% of penetration rate was measured through the penetration test with dump trucks.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.1036-1039
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• 2005

하상유지시설의 하류에 설치되는 바닥보호공은 국내의 경우 일반적으로 사석(riprap)이나 돌망태(gabion mattress) 등을 이용하여 시공되고 있으며, 바닥보호공에 사용되는 재료는 유속에 따라 적절한 입경의 재료를 결정하여 사용하게 된다. 1970년대 중반부터 적절한 하상보호공 재료를 결정하기 위한 연구는 사석, 돌망태, 콘크리트 보호 블록 등에 대하여 순차적으로 이루어져 왔다, 초기 연구는 주로 사석에 대해서 이루어졌으며, 중량과 유속 관계를 이용하여 사석 입경 결정 공식을 제안하였으며, 점차 수심 및 하상 경사, 난류 강도 등을 고려하여 재료 입경 결정 공식을 정밀화시켜왔다. 공식에 난류 강도를 고려하기 시작하면서, 단순한 하상보호공 재료를 결정하기 위해서 제안되었던 공식들은 하천 구조물 하류에 설치되는 바닥보호공으로 관심의 대상이 옮겨가기 시작하였다. 기존의 공식들이 일반적인 평탄한 하상보호공으로부터 구조물 하류의 바닥보호공 까지 그 적용이 확장되었던 반면에, Escarameia와 May는 연구의 대상을 수리구조물 하류의 강한 난류 흐름이 발생하는 구간으로 범위를 한정하여 연구를 진행하였으며, Izbash 형태의 식을 기초로 하여, 난류 강도가 주요 변수가 되는 입경 결정 공식을 제안하였다. 본 연구에서는 Escarameia와 May의 연구 결과를 기초로 하여, 국내 하상유지시설 하류에 설치되는 사석 바닥보호공 재료의 입경을 결정하기 위한 실험을 수행하였다. 하천설계기준을 만족하는 실험용 보를 설치한 후 유량 및 실험에 사용된 사석의 입경을 변화시키면서, 유속을 측정하여, 입경별 한계 유속(threshold velocity)의 상관관계를 분석하였다. 실험 결과, Escarameia와 May가 제안한 공식을 더 확장하여 적용할 수 있는 실험 공식으로 개선하였으며 다양한 조건에 대한 실험을 수행하여 보다 정밀한 공식으로 개선할 수 있었다.$10,924m^3/s$ 및 $10,075m^3/s$로서 실험 I의 $2,757m^3/s$에 비해 통수능이 많이 개선되었음을 알 수 있다.함을 알 수 있다. 상수관로 설계 기준에서는 관로내 수압을 $1.5\~4.0kg/cm^2$으로 나타내고 있는데 $6kg/cm^2$보다 과수압을 나타내는 경우가 $100\%$로 밸브를 개방하였을 때보다 $60\%,\;80\%$ 개방하였을 때가 더 빈번히 발생하고 있으므로 대상지역의 밸브 개폐는 $100\%$ 개방하는 것이 선계기준에 적합한 것으로 나타났다. 밸브 개폐에 따른 수압 변화를 모의한 결과 밸브 개폐도를 적절히 유지하여 필요수량의 확보 및 누수방지대책에 활용할 수 있을 것으로 판단된다.8R(mm)(r^2=0.84)$로 지수적으로 증가하는 경향을 나타내었다. 유거수량은 토성별로 양토를 1.0으로 기준할 때 사양토가 0.86으로 가장 작았고, 식양토 1.09, 식토 1.15로 평가되어 침투수에 비해 토성별 차이가 크게 나타났다. 이는 토성이 세립질일 수록 유거수의 저항이 작기 때문으로 생각된다. 경사에 따라서는 경사도가 증가할수록 증가하였으며 $10\% 경사일 때를 기준으로 $Ro(mm)=Ro_{10}{\times}0.797{\times}e^{-0.021s(\%)}$로 나타났다.천성 승모판 폐쇄 부전등을 초래하는 심각한 선천성 심질환이다. 그러나 진단 즉시 직접 좌관상동맥-대동맥 이식술로 수술적 교정을 해줌으로써 좋은 성적을 기대할 수 있음을 보여주었다.특히 교사들이 중요하게 인식하는 해방적 행동에 대한 목표를 강조하여 적용할 필요가 있음을 시사하고 있다.교하여 유의한 차이가 관찰되지 않았다. 또한 HSP 환자군에서도

• Journal of the Korea Concrete Institute
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• v.19 no.5
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• pp.569-575
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• 2007

The repair of concrete surfaces does not normally take into account structural tolerance for longer service lift and better capabilities of concrete structures. In particular, the repair of surface spelling completes as mortar is applied, which does not display additional structural performances. The use of crimped wire mesh for better construction and fracture resistance, however, expects to have some reinforcement effects. Particularly, it is also expected that the repair of bottom part in structures built between bridges like irrigation structures results in the increase of flexural resistance. Therefore, this study is intended to perform the repair using crimp wire mesh and examine strength depending on the repair section and depth. For this, a slab with 150 mm in depth, 3,000 mm in length and 600 mm in width and total 8 objects to experiment such as upper part, upper whole, bottom part, bottom whole and crimp wire mesh reinforced are manufactured to perform flexural performance. The results of the analysis show that yield strength and failure load increase as the depth of repair materials in the experiment reinforced with crimp wire mesh get bigger. In the same condition, repair of bottom part is able to increase internal force of bending force. Besides, the results show that partial repair of structures under bending force cannot produce flexural performance. Consequently, the repair method with crimp wire mesh results in the increase of flexural resistance.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.8
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• pp.3729-3744
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• 2011

As the size of structures become larger by civil and architectural structures becoming large, deeply underground, and high-rise, the conditions of underground foundation vary according to the location that the lack of bearing capacity locally because of ununiform of foundation in some parts is frequent. Generally, when the foundation is not homogeneous, the acquisition of safety through applying the most conservative foundation method possible becomes the focus to secure the stability of the superstructures. It is considered as because of inability to verify the application and stability and application of construction of different foundations through an outlined review because of lack of study in case of different foundation of mixed use of direct foundation and pile foundation. Therefore, through measurement interpretation of the different foundation in which the direct foundation and pile foundation are mixed in use, the grounds in which the hypothetical bearing capacity changes dramatically was modeled to evaluate the applicability of different foundations. Also, based on the results of measurement interpretation, various foundations are created by using plaster, Joomunjin standard soil, and rubble to conduct an indoor model test to compare and analyze the movement of pile foundation and different foundations. Based on such research results, the stability and applicability of the different foundations which is more efficient and economical than the existing foundations in case of grounds in which the bearing capacity changes dramatically by comparing and analyzing the different foundations (direct foundation + pile foundation) with the conservative pile foundation and mat foundation. As a result, when the different foundation is applied, the overall settlement amount increased than the conservative pile foundation. However, the difference was very minute and it has been confirmed to be no issue as a result of assessment of stability of the differential settlement of structures through critical angle displacement.

• Journal of Bio-Environment Control
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• v.20 no.1
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• pp.50-57
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• 2011

This study investigates the structural safety of typical greenhouse to be utilized for developing plant factory. New long-span greenhouse systems were presented according to the results of structural analyses performed by finite-element program, ABAQUS. Reasonable values of design loads such as wind and snow loads in the Greenhouse Design Specifications (1995) were applied to check the new greenhouse systems. It was concluded that the new greenhouse systems were consistently safe enough to resist to both wind load and snow load. The new greenhouse system can be used to make simple and economic plant factory.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.4
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• pp.705-713
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• 2016

For the soft ground construction, the factors not considered in the design stage occurs in the construction stage so that they cause the increase of the construction cost due to the structural stability and the design change. The subject of the study is the construction section of the industrial complex access road made in the Ochang region of Chungcheongbuk-do. The study is concerned with selecting the soft ground handling method such as the replacement method using rock debris and the surcharge reflecting the service load as the soft ground handling measure and analyzing the effect of reducing the construction cost with the stability of structures and the reduction of the construction period. The soft ground in the study section consists of sandy and cohesive soil and is 2.4m to 5.5m deep. It is distributed unevenly between the 1.5m to 5.9m stratums under the ground surface. Settlement is not serious, but the future uneven settlement and difference are expected so that the future settlement behavior is estimated by analyzing the site measurement results after the soft ground treatment. Moreover, in consideration of the regional characteristics and economic efficiency, soil with good quality is replaced with rock debris as the replacement material so that 29% of the construction cost is reduced due to the increase of stability and the reduction of duration. If the estimation of the dispersion of the pore water pressure within the dam body and the change of the underground water level and the relation of the actually measured soft ground with consolidation is studied further on the basis of the study, it is expected that the behavior of the soft ground will be correctly estimated in various site conditions.