• Geomechanics and Engineering
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• 제3권2호
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• pp.153-167
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• 2011

Traditional design methods of bearing capacity of shallow foundations are deterministic in the sense that they do not explicitly consider the inherent uncertainty associated with the factors affecting bearing capacity. To account for such uncertainty, available deterministic methods rather employ a fixed global factor of safety that may lead to inappropriate bearing capacity predictions. An alternative stochastic approach is essential to provide a more rational estimation of bearing capacity. In this paper, the likely distribution of predicted bearing capacity of strip footings subjected to vertical loads is obtained using a stochastic approach based on the Monte Carlo simulation. The approach accounts for the uncertainty associated with the soil shear strength parameters: cohesion, c, and friction angle, ${\phi}$, and the cross correlation between c and ${\phi}$. A set of stochastic design charts that assure target reliability levels of 90% and 95%, are developed for routine use by practitioners. The charts negate the need for a factor of safety and provide a more reliable indication of what the actual bearing capacity might be.

• Journal of Advanced Marine Engineering and Technology
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• 제37권8호
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• pp.905-910
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• 2013

열교환기의 나선형 튜브에 난류모형을 적용하여 유동해석을 수행하였다. 난류모형은 Spalart-Allmaras과 k-${\varepsilon}$이고 시뮬레이션에는 정렬격자를 적용하였다. 레이놀즈 수 영향을 규명하기 위하여 Navier-Stokes 방정식을 풀어 속도벡터, 압력, 잔차, 마찰계수를 재연하였다. 나선형튜브는 원심력을 증가하여 튜브의 바깥부분에 벽전단 응력을 크게 하였다. 열전도율과 마찰저항의 증가는 곡률에 기인하며 튜브의 내부방향으로는 벽 전단응력이 감소했다. 원심력은 유체의 에너지를 증가시켜서 바깥쪽으로 열전도율을 증가시켰고 이는 내부유동의 압력강하 및 관마찰계수가 상호 밀접한 관계가 있음을 규명하여 주었다. 본 수치결과는 검증을 위하여 타 계산에서 얻어진 마찰계수 결과와 비교하였다.

• 한국철도학회논문집
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• 제8권4호
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• pp.367-371
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• 2005

Pile foundations are utilized when soil is so weak that shallow foundations are not suitable or point load is concentrated in small area. Such soil can be formed by the land reclamation works which have extensively been executed along the coastal line of southern and western parts of the Korean Peninsula. The working load at pile is sometimes subjected to not only compression load but also lateral load sad uplift forces. But in most of the practice design, uplift capacity of pile foundation is not considered and estimation of uplift capacity is presumed on the compression skin friction. This study was carried out to determine that the effect of embedment ratio and loading rate on uplift adhesion factor of concrete pile driven in clay. Based on the test results, the critical embedment ratio is about 9. Adhesion factor is constant under the critical embedment ratio, and decreasing over the critical embedment ratio. Also, adhesion factor is increased with the loading rate is increased.

• 한국지반신소재학회논문집
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• 제16권2호
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• pp.55-66
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• 2017

본 연구에서는 지반 특성에 관계없이 일률적으로 적용되는 피에조콘 관입속도 2cm/s 조건 하에서, 저소성 실트 지반의 경우 부분배수 내지는 완전 배수 현상이 발생된다는 관점에서 저소성 실트 지반의 비배수전단강도선과 완전배수 전단강도선 사이에서의 피에조콘계수($N_{kt}$)에 의한 전단강도 분포 경향을 기준으로 부분배수 전단강도를 평가하였다. 그 결과, 인천, 화성 및 군산 저소성 실트 지반의 부분배수 내부마찰각(${\varphi}^{\prime}$)은 $3{\sim}15^{\circ}$에서 분포하는 것으로 분석되었다. 한편, 강제치환 역해석 결과 및 비압밀비배수 삼축시험으로부터 얻어진 내부마찰각(${\varphi}^{\prime}$)은 소성지수 감소에 따라 $2{\sim}14^{\circ}$의 범위에서 분포되어, CPTU 데이터에 의한 부분배수 내부마찰각(${\varphi}^{\prime}$)과 유사한 경향을 나타내어 이에 대한 적용성을 확인할 수 있었다.

• 한국지반신소재학회논문집
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• 제8권4호
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• pp.27-34
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• 2009

본 연구에서는 토목섬유가 층상으로 보강된 슬래그 재료의 전단강도와 변형특성을 다루었다. PET mat와 같은 토목섬유에 의한 보강이 슬래그의 전단강도와 변형특성에 미치는 영향을 조사 및 분석하기 위해 압밀배수 조건 하에서의 대형삼축압축시험을 수행하였다. 연구에 사용된 슬래그 재료는 현장에서 사용되는 재료와 동일한 재료로서 scale effect로 인한 문제점은 없었다. 토목섬유로 보강된 슬래그의 응력-변형율 거동은 무보강시 보다 다일러턴시의 양이 작고, 축변형율 증가시 항복 이후에도 축차응력이 증가하는 변형율경화(strain hardening) 거동을 나타내었다. 토목섬유로 보강된 슬래그 재료의 겉보기 점착력과 내부마찰각 등의 강도정수는 보강되지 않은 경우의 값보다 1.2-1.4배 정도 크고, 구속압 수준이 클수록 커지는 것으로 나타났다. 따라서 슬래그를 사용한 제방의 설계나 시공시 슬래그 재료에 토목섬유를 층상으로 보강하여 사용할 경우에는 강도증가 효과에 의해 안전율을 향상시킬 수 있을 것으로 기대된다.

• Geomechanics and Engineering
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• 제19권1호
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• pp.49-60
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• 2019

Crack instability propagation during coal and rock mass failure is the main reason for electromagnetic radiation (EMR) generation. However, original cracks on coal and rock mass are hard to study, making it complex to reveal EMR laws and mechanisms. In this paper, we prefabricated cracks of different inclinations in coal and rock samples as the analogues of the native cracks, carried out uniaxial compression experiments using these coal and rock samples, explored, the effects of the prefabricated cracks on EMR laws, and verified these laws by measuring the surface potential signals. The results show that prefabricated cracks are the main factor leading to the failure of coal and rock samples. When the inclination between the prefabricated crack and axial stress is smaller, the wing cracks occur first from the two tips of the prefabricated crack and expand to shear cracks or coplanar secondary cracks whose advance directions are coplanar or nearly coplanar with the prefabricated crack's direction. The sample failure is mainly due to the composited tensile and shear destructions of the wing cracks. When the inclination becomes bigger, the wing cracks appear at the early stage, extend to the direction of the maximum principal stress, and eventually run through both ends of the sample, resulting in the sample's tensile failure. The effect of prefabricated cracks of different inclinations on electromagnetic (EM) signals is different. For samples with prefabricated cracks of smaller inclination, EMR is mainly generated due to the variable motion of free charges generated due to crushing, friction, and slippage between the crack walls. For samples with larger inclination, EMR is generated due to friction and slippage in between the crack walls as well as the charge separation caused by tensile extension at the cracks' tips before sample failure. These conclusions are further verified by the surface potential distribution during the loading process.

• 산업기술연구
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• 제28권B호
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• pp.81-89
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• 2008

This paper is results of investigating the dominant factors influencing to coefficient of consolidation in horizontal direction of Korean marine clays and their correlations through literature review. From the results of analyzing data obtained from field tests such as piezocone penetration and dilatometer tests as well as laboratory tests, coefficient of consolidation in the horizontal direction was found to increase with increase of stiffness index of soil while it decreases with the increase of dissipation time of pore pressure developed during field tests. In general, the coefficient of consolidation in the horizontal direction tends to increase with increase of undrained shear strength and preconsolidation pressure although correlation between them are relatively low. Friction ratio has a high correlation with coefficient of consolidation in the horizontal direction in case of friction ratio being greater than 1.0. For methods of estimating coefficient of consolidation in the horizontal direction with different testing device, values obtained from methods of P2-logt and DMT-A with dilatometer were quite similar to values from piezocone penetration test. Consistency of soil is quite proportional to coefficient of consolidation in the horizontal direction. Clear correlation between coefficients of consolidation in the horizontal and the vertical directions could not be found. coefficient of consolidation in the horizontal direction estimated from the results of field test tends to be 1.13~3.11 times greater than that obtained from laboratory tests.

• Geomechanics and Engineering
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• 제31권5호
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• pp.453-460
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• 2022

It is essential for geotechnical engineers to conduct studies and make predictions about the stability of slopes, since collapse of a slope may result in catastrophic events. The Gaussian process regression (GPR) approach was carried out for the purpose of predicting the factor of safety (FOS) of the slopes in the study that was presented here. The model makes use of a total of 327 slope cases from Iran, each of which has a unique combination of geometric and shear strength parameters that were analyzed by PLAXIS software in order to determine their FOS. The K-fold (K = 5) technique of cross-validation (CV) was used in order to conduct an analysis of the accuracy of the models' predictions. In conclusion, the GPR model showed excellent ability in the prediction of FOS of slope stability, with an R² value of 0.8355, RMSE value of 0.1372, and MAPE value of 6.6389%, respectively. According to the results of the sensitivity analysis, the characteristics (friction angle) and (unit weight) are, in descending order, the most effective, the next most effective, and the least effective parameters for determining slope stability.

• Journal of Advanced Research in Ocean Engineering
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• 제2권3호
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• pp.99-111
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• 2016

Seabed affected by scouring, sedimentation, and siltation occurrences often cause exposure, which induces risks to existing structures or crude oil or gas pipeline buried subsea. In order to prevent possible risks, more economical structure installation methodology is proposed in this study by predicting and managing the risk. Also, the seabed does not only consist of sandy material, but clayey soil is also widespread, and the effect of undrained shear strength should be considered, and by cyclic environmental load, pore water pressure will occur in the seabed, which reduces shear strength and allows particles to move easily. Based on previous research regarding sedimentation or erosion, the average value of external environmental loads should be applied; for scouring, a 100-year period of environmental conditions should be applied. Also, sedimentation and erosion are mainly categorized by the bed load and suspended load; also, they are calculated as the sum of bed load and suspended load, which can be obtained from the movement of particles caused by sedimentation or erosion.

• Journal of Advanced Marine Engineering and Technology
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• 제21권2호
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• pp.126-135
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• 1997

Drag reduction in polymer solutions is the phenomenon where by extremely dilute solutions of high molecular weight polymers exhibit frictional resistance to flow much lower than the pure solvent. This effect, largely unexplained as yet, has attracted the attention of polymer scientists and fluid flow specialists. Although applications are beginning to appear, the principle interest to data has been in attempting to relate the effect to the fluid mechanics of turbulent flow. Drag reduction in two phase flow can be applied to the transport of crude oil, phase change system such as chemical reactor, and pool and boiling flow. But the research on drag reduction in two phase flow is not intensively investigated. Therefore, experimental investigations have been carried out to analyze the drag reduction produced by polymer addition in the single phase and two phase flow system. The objectives of the proposed investigation are primarily in identifying and developing high performance polymer additives for fluid transportations with the benefits of turbulent drag. Also we want to is to evaluate the drag reduction in horizontal flow by measuring pressure drop and mean velocity. Experimental results show higher drag reduction using co - polymer(A611P) then using polyacrylamide (PAAM) and faster degradation using PAAM than using A611P under the same superficial velocity.