• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.442-451
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• 2008

The evaluation of field degree of consolidation on soft clays has been an important problem in geotechnical areas. Monitoring either settlements or pore water pressures has been widely applied in the filed, but occasionally they have some problems. This study addresses the suggestion and application of another method for evaluating the degree of consolidation using shear wave velocities. A research site where soft clay layers were consolidated by surcharging loads was chosen. Laboratory tests were performed to determine the relation between shear wave velocity and effective stress. Field seismic tests were conducted several times during the consolidation of the clay layers. The tests results show that the shear wave velocity increased significantly as clays consolidated. The shear wave velocities at each field stress states were derived from the laboratory results and the degree of consolidation was evaluated by comparing the shear wave velocities obtained by laboratory and field seismic methods. In most stress states, the degree of consolidation evaluated using the shear wave velocity matched well with that obtained from field settlement record, showing the potential of applying the method using shear waves in the evaluation of field degree of consolidation on soft clay deposits.

• Membrane and Water Treatment
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• 제9권3호
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• pp.173-179
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• 2018

Microcystin-LR, one of algal toxins induced by the eutrophication of a reservoir, is known to be harmful to human by adversely affecting our liver and brain. Hypochlorous acid is very efficient to remove Microcystin-LR in a clear well. The previous researches showed that CT, pH and temperature affected removal rate in batch tests. It was noted that hydrodynamic properties of clear well could also influence its removal rate. A mathematical model was built using an axial dispersion reactor model and software was used to simulate the removal rate. The model consisted of the second order differential equations including dispersion, convection, Microcystin-LR reaction with chlorine. Kinetic constants were obtained through batch tests with chlorine. They were $0.430{\times}10^{-3}L/mg/sec$ and $0.143{\times}10^{-3}L/mg/sec$ for pH 7.0 and 8.1, respectively. The axial dispersion reactor model was shown to be useful for the numerical model through conservative tracer tests. The numerical model successfully estimated the removal rate of Microcyctin-LR in a clear well. Numerical simulations showed that a small dispersion number, low pH and long hydraulic retention time were critical for higher removal rate with same chlorine dosage. This model could be used to optimize the operation of a clear well during an eutrophication season.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 춘계 학술발표회
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• pp.376-387
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• 2009

Piled raft foundation is a geotechnical composite construction to support the superstructure by pile-soil-raft interaction. General conventional design for piled raft doesn't consider the contribution of a raft. This is very conservative and requires more piles to satisfy the factor of safety. It is important to evaluate the load sharing features of piled raft. In this research, this characteristics of piled raft evaluated using both centrifuge and numerical modelings. The ultimate bearing capacity of piled raft foundation was also evaluated and predicted through comparisons of ultimate bearing capacity of single pile (SP), unpiled raft (UR), freestanding pile group (FPG) and piled raft (PR). $\xi_{pr}$ and $\eta$ were determined by centrifuge model tests to simply evaluate the ultimate bearing capacity of piled raft and bearing capacity of piled raft was predicted using the calibrated numerical model based on the centrifuge tests and laboratory tests data.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 세계 도시지반공학 심포지엄
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• pp.877-883
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• 2009

Shaking table tests are performed to evaluate the dynamic group pile effect in fine sand. Single pile tests and $2{\times}4$ group pile tests are performed on 3D pile spacing. Dynamic p-y backbone curves are obtained to evaluate dynamic group pile effect by using dynamic p-y curve of single pile. And dynamic group pile p-multiplier is estimated by dynamic p-y backbone curve. Dynamic p-multiplier can be calculated by using subground reaction ratio of dynamic p-y backbone curve which is the same displacement of p-y curve peak point As the result, dynamic group pile effects are evaluated in terms of a shaking frequency, a shaking acceleration, and a relative density. Dynamic group pile p-multiplier is the largest at lead pile, and the value decrease at middle pile and trail pile. p multiplier increases as increasing input acceleration and decreasing relative density. This results coincide with NCHRP's research which suggest p multiplier increases as increasing pile cap displacement.

• 한국도로학회:학술대회논문집
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• 한국도로학회 2008년도 추계학술대회 논문집
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• pp.93-102
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• 2008

An energy based crack growth model is developed in this study to simulate the propagation of top-down cracking in asphalt pavements. A viscoelastic fracture mechanics approach, generalized J integral, is employed to model the crack growth of asphalt concrete. Laboratory fatigue crack propagation tests for three different asphalt mixtures are performed at various load levels, frequencies and temperatures. Disk-shaped specimens with a proper loading fixture and crack growth monitoring system are selected for the tests. It is observed from the tests that the crack propagation model based on the generalized J integral is independent of load levels and frequencies, while the traditional Paris' law model based on stress intensity factor is dependent of loading frequencies. However, both models are unable to take care of the temperature dependence of the mixtures. The fatigue crack propagation model proposed in this study has a good agreement between experimental and predicted crack growth lives, which implies that the energy based J integral could be a better parameter to describe fatigue crack propagation of viscoelastic materials such as asphalt mixtures.

• Geomechanics and Engineering
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• 제32권1호
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• pp.97-110
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• 2023

The coefficient of lateral earth pressure at rest in loose sand during virgin loading, K₀ , and during unloading, K'₀ , have been determined from laterally confined load-unload tests. The tests included measurement of lateral pressure with null pressure gauges, side wall friction with newly designed friction meters and applied pressure and base pressure with load cells. The importance of accounting for side-wall friction when evaluating the distribution of vertical pressure over the height of the soil specimen was demonstrated. Relatively uniform friction was observed during loading, but this was not the case during unloading unless friction reduction measures were employed. While the measured value of K₀ was found to be close to, if slightly higher than the value commonly estimated on the basis of friction angle, φ', the ratio of K'₀ to K₀ was found to reasonably fit an expression of the form K'₀/K₀ = 1 + C·log(OCR), with C equal to 1 in the present tests.

• Geomechanics and Engineering
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• 제29권4호
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• pp.407-420
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• 2022

Embedded piles, which are typically used in Korea, are precast piles inserted into prebored ground with cement paste. Dynamic pile tests tend to underestimate the bearing capacity of embedded piles because of the undeveloped shaft resistance prior to the curing of the cement paste and the insufficient energy transferred after the curing. In this study, a resistance combination method using the base resistance before the cement paste is cured and the shaft resistance after the cement paste is cured is proposed to obtain a combined load-settlement curve from dynamic pile tests. Two pairs of embedded piles with diameters of 600 and 500 mm are installed. Each pair comprises one pile for the dynamic pile test and another pile for the static load test. The shape of the load-settlement curve obtained using the proposed method is similar to that obtained from the static load test. Thus, the resistances evaluated using the proposed method at selected settlements are similar to those obtained from the static load test. This study shows that the resistance combination method may be used effectively in dynamic pile tests to accurately evaluate the bearing capacity of embedded piles.

• 한국환경보건학회지
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• 제50권4호
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• pp.291-301
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• 2024

Background: Based on rapid industrial development, environmental pollution has emerged as a social problem and exposure to environmental diseases is increasing. The number of patients suffering environmental diseases in Daejeon Metropolitan City is also steadily increasing, and the prevalence of atopic dermatitis there is the highest in the country. Objectives: In order to minimize exposure to harmful factors for the prevention and management of environmental diseases, an environmental disease management system suitable for the environmental characteristics of each region is needed. Basic preliminary research should be conducted to identify environmental hazards in Daejeon Metropolitan City and establish a management system. Methods: Among the households (about 50 people) participating in the 2022 Indoor Environment Remote Measurement (IoT) program, households (children aged 5 or older and adults) with insufficient results for indoor air quality measurement and symptoms related to environmental diseases were selected. The subjects were tested for living conditions, blood tests, biomarker analysis (immunoglobulin E, Eosinophil count, histamine) and multiple allergy antigen tests (MAST, 93 types). Results: Participants were 53.7% female and 46.3% male, and the average age showed an even age distribution. IgE and eosinophil count were positively correlated, and significant results were found for atopic dermatitis and IgE (p<0.05). Typical risk factors observed in the survey was the amount of indoor ventilation, chemical exposure, heredity, house dust mites, fungi, and food. Conclusions: The purpose of this study was to help establish a regional management system for environmental diseases, research and diagnosis of environmental diseases. This study is meaningful in that it is a study with customized consulting suitable for the environment of Daejeon Metropolitan City. If the limitations are addressed and continuous research is conducted, it will be helpful for the management, diagnosis, and research of environmental diseases.

• 한국지반환경공학회 논문집
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• 제7권2호
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• pp.15-24
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• 2006

본 연구에서는 수평재하시험과 공내수평재하시험 결과를 이용하여 지반반력계수를 각각 분석하였다. 또한 이들 값과 수평재하시험 실시 위치에서의 N치를 이용하여 도로교표준시방서, 일본토목학회, Hukuoka식, 일본도로협회 제안식으로 산정한 수평방향 지반반력계수를 비교 및 분석하여 제안식별 적용성을 평가하고자 하였다. 수평방향 지반반력계수 산정시 지반의 변형계수가 큰 영향을 미치는 것으로 볼 때 합리적인 지반의 변형계수 산정이 매우 중요하며, 제안식별 변형계수 적용에 대해 재하시험 결과를 이용하여 검토하였다. 특히 공내수평재하시험 결과를 이용하여 지반반력계수를 산정하는 방법은 수평변위를 고려할 수 없는 등의 문제점이 있는 것으로 나타나 사질토 지반의 수평방향 지반반력계수 산정시 말뚝의 직경과 수평변위를 고려할 수 있는 식을 제안하였으며, 아울러 N치를 이용한 지반의 변형계수를 고려하는 제안식에 대해서는 수평재하시험과 비교하여 지반의 변형계수 추정식을 제안하였다.

• 산업경영시스템학회지
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• 제20권44호
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• pp.393-399
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• 1997

This study is concerned with reliability technology. In order to achieve the quality level of items for consumer's satisfaction, tests for the item's reliability are essential. This article deals with a method and real field application to plan reliability testing. Especially the environmental conditions and methods such as screening test for electronic components will be shown. As well, we will explore methods and field applications with respect to mechanic destructive tests and non destructive tests.