• 청정기술
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• 제12권1호
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• pp.11-18
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• 2006

poly[hexamethylene carbonate]glycol(PHMCG)과 isophorone diisocyanate (IPDI), dimethylol propionic acid(DMPA)를 이용하여 수분산성 폴리우레탄을 합성하였다. 또한 여기에 나노 clay(PM) 및 이를 각기 다른 유기화제로 개질시킨 C15A와 C30B를 첨가하여 폴리우레탄/clay 나노복합재료를 제조하였다. 제조된 나노복합재료에서의 clay의 분산정도를 XRD를 이용하여 조사하였으며 clay가 첨가된 경우의 기계적 물성 및 열적성질을 UTM 과 TGA를 통하여 분석한 결과, C15A가 첨가된 경우 나노clay가 폴리우레탄에 가장 잘 분산된 것으로 관찰되었으며, 기계적 물성과 열적 물성이 C30B 또는 PM을 첨가한 경우보다 높게 측정되었다. 이로부터 clay에서 개질유기화제의 종류 및 함량이 나노복합재료의 최종물성에 영향을 주는 것을 알 수 있었다.

• 한국지반공학회논문집
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• 제15권6호
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• pp.131-142
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• 1999

본 연구는 전응력 개념에 근거한 비등방경화 구성관계를 적용하여 유한요소해석을 수행하는 데 목적이 있다. 이에 동반논문에서 제안한 비등방경화 구성모델에 대하여 내재적인 응력적분과 일관된 접선계수를 정식화하였다. 그리고 이러한 알고리즘을 비선형 유한요소해석 코드에 구현하여 정확도와 수렴성을 확보한 해석을 수행하였다 시험성토사례에 대한 해석을 통하여 제안된 구성모델은 von Mises규준에 의한 해석에 비하여 성토고에 따른 지반의 변위를 더욱 합리적으로 표현할 수 있음을 알 수 있었다. 또한 지반의 강도를 적합하게 산정하여 제안된 구성모델이 매우 정확하게 실제 거동을 모사할 수 있었다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.924-931
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• 2005

In this study, we intended to compare and examine several settlement management methods by analyzing measurement results of a site of the industrial complex at ${\bigcirc}{\bigcirc}$ province. We predicted and analyzed the amount of final settlement by using generally used final settlement methods as like Hyperbola method, Hoshino methods and Asaoka method. And then, We compared the predicted results with that of measurement. On the basis of comparison of the three methods, Hyperbola method was the most convenient and accurate method of the three methods and if a sufficient time was given enough after embankment construction, the use of Hoshino method was possible. In the case of the Asaoka methods, it was possible to know that it had an approaching tendency to the measured one with increasing time interval spent on analysis. Therefore, in order to predict settlement behavior more accurately it is needed to understand their advantages and shortcomings sufficiently and pay attention to application to the real site.

• 한국안전학회지
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• 제33권1호
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• pp.81-87
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• 2018

The seismic response, the natural frequencies and the mode shapes of an offshore wind turbine with twisted tripod substructure subject to various pile-ground interactions are discussed in this paper. The acceleration responses of the tower head by four historical earthquakes are presented as the seismic response, while the other loads are assumed as ambient loads. For the pile-ground interactions, the fixed, linear and nonlinear models are employed to simulate the interactions and the p-y, t-z and Q-z curves are utilized for the linear and nonlinear models. The curves are designed for stiff, medium and soft clays, and thus, the seven types of the pile-ground interactions are used to compare the seismic response, the acceleration of the tower head. The mode shapes are similar to each other for all types of pile-ground interactions. The natural frequencies, however, are almost same for the three clay types of the linear model, while the natural frequency of the fixed support model is quite different from that of the linear interaction model. The wind turbine with the fixed support model has the biggest magnitude of acceleration. In addition, the nonlinear model is more sensitive to the stiffness of clay than the linear pile-ground interaction model.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1998년도 지반조사위원회 봄 학술세미나
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• pp.37-46
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• 1998

Several researchers have developed a number of theoretical time factors to determine the coefficient of consolidation by biezocone excess pore water dissipation test in soft clay deposits. However, depending on the assumptions and analytical techniques, the estimated coefficient of consolidation could be in a considerably wide range even for a specific degree of consolidation. These solutions are obtained from an initial excess porewater pressure distribution which can be determined from. either the cavity expansion theory or the strain path method. The 야ssipation of the initial excess porelvater pressure has been usally simulated by means of linear-uncoupled consolidation analysis and then the dissipation curve is normalized by the initial excess porewater pressure for easy use. However. since there is no guidelines or rules on which method gives the best solution for obtaining the coefficient of consolidation from the dissipation curve, the final selection was only based on engineer's extrience and Judgements. Thus, such an arbitrary selection might be inappropriate for a specific site to characterize the consolidation behavior. In this paper, we reviewed various theoretical time factors and, based on this consideration, we mentioned needs for researches in selecting a specific solution that is compatible for Korean clays. Also we listed some source of errors that can be encountered in the procedure of dissipation analysis.

• Geomechanics and Engineering
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• 제16권6호
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• pp.635-642
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• 2018

Braced excavation systems are commonly required to ensure stability in construction of basements for shopping malls, underground transportation and other habitation facilities. For excavations in deposits of soft clays or residual soils, stiff retaining wall systems such as diaphragm walls are commonly adopted to restrain the ground movements and wall deflections in order to prevent damage to surrounding buildings and utilities. The ground surface settlement behind the excavation is closely associated with the magnitude of basal heave and the wall deflections and is also greatly influenced by the possible groundwater drawdown caused by potential wall leakage, flow from beneath the wall, flow from perched water and along the wall interface or poor panel connections due to the less satisfactory quality. This paper numerically investigates the influences of excavation geometries, the system stiffness, the soil properties and the groundwater drawdown on ground surface settlement and develops a simplified maximum surface settlement Logarithm Regression model for the maximum ground surface settlement estimation. The settlements estimated by this model compare favorably with a number of published and instrumented records.

• Geomechanics and Engineering
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• 제16권6호
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• pp.577-588
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• 2018

A major concern in deep excavation project in soft clay deposits is the potential for adjacent buildings to be damaged as a result of the associated excessive ground movements. In order to accurately determine the wall deflections using a numerical procedure such as the finite element method, it is critical to use the correct soil parameters such as the stiffness/strength properties. This can be carried out by performing an inverse analysis using the measured wall deflections. This paper firstly presents the results of extensive plane strain finite element analyses of braced diaphragm walls to examine the influence of various parameters such as the excavation geometry, soil properties and wall stiffness on the wall deflections. Based on these results, a multivariate adaptive regression splines (MARS) model was developed for inverse parameter identification of the soil relative stiffness ratio. A second MARS model was also developed for inverse parameter estimation of the wall system stiffness, to enable designers to determine the appropriate wall size during the preliminary design phase. Soil relative stiffness ratios and system stiffness values derived via these two different MARS models were found to compare favourably with a number of field and published records.

• 자연, 터널 그리고 지하공간
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• 제21권1호
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• pp.101-112
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• 2019

This case study presented a simplified failure mechanism approach used as a preliminary deformation prediction for the Mexico City's metro system expansion. Because of the Mexico City's difficult subsoils, Line 12 project was considered one of the most challenging projects in Mexico. Mexico City's subsurface conditions can be described as a multilayered stratigraphy changing from soft high plastic clays to dense to very dense cemented sands. The Line 12 trajectory crossed all three main geotechnical Zones in Mexico City. Starting from to west of the City, Line 12 was projected to pass through very dense cemented sands corresponding to the Foothills zone changing to the Transition zone and finalizing in the Lake zone. Due to the change in the subsurface conditions, different constructions methods were implemented including the use of TBM (Tunnel Boring Machine), the NATM (New Austrian Tunneling Method), and cut-and-cover using braced Diaphragm walls for the underground section of the project. Preliminary crown and excavation front deformations were determined using a simplified failure mechanism prior to performing finite element modeling and analysis. Results showed corresponding deformations for the crown and the excavation front to be 3.5cm (1.4in) and 6cm (2.4in), respectively. Considering the complexity of Mexico City's difficult subsoil formation, construction method selection becomes a challenge to overcome. The use of a preliminary results in order to have a notion of possible deformations prior to advanced modeling and analysis could be beneficial and helpful to select possible construction procedures.

• Geomechanics and Engineering
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• 제25권3호
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• pp.221-231
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• 2021

A two dimensional model of linearly elastic soil spring used for the settlement analysis of the flexible mat foundation is suggested in this study. The spring constants of the soils underneath the foundation were modeled assuming uniformly vertical load applied onto the foundation. The soil spring constants were back calculated using the three-dimensional finite element analysis with Midas GTS NX program. Variation of the soil spring constants was modeled as a two-dimensional polynomial function in terms of the normalized spatial distances between the center of foundation and the analytical points. The Lysmer's analog spring for soils underneath the rigid foundation was adopted and calibrated for the flexible foundation. For validations, the newly proposed soil spring model was incorporated into a two dimensional finite difference analysis for a square mat foundation at the surface of an elastic half-space consisting of soft clays. Comparative study was made for elastic soils where the shear wave velocity is 120~180 m/s and the Poisson's ratio varies at 0.3~0.5. The resulting foundation settlements from the two dimensional finite difference analysis with the proposed soil springs were found in good agreement with those obtained directly from three dimensional finite element analyses. Details of the applications and limitations of the modified Lysmer's analog springs were discussed in this study.

• 지질공학
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• 제14권4호
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• pp.371-379
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• 2004

본 연구는 호남해안 7개 지역에 대한 연약점토의 토질조사 자료를 분석하여 지반의 물리적${\cdot}$역학적 토질특성과 제 토질정수들 간의 경험방정식을 도출하였다. 기본 물성 값을 분석한 결과 대부분이 통일분류상 CL, CH에 해당되며 자연함수비가 액성한계를 초과하는 지역이 많아 불안정한 상태를 보였다. 압축지수는 자연함수비, 액성한계, 초기간극비와 상관성을 보였으며 호남지역의 연약점토는 일반적으로 사용되는 Terzaghi & Peck의 식 Cc = 0.009(LL -10)과 비교 시 전반적으로 위쪽에 분포하는 것으로 나타났다. 또한, 기존의 국내의 연구결과와는 유사한 분포를 보였으며 압축지수 상관관계식에서 호남해안지역이 경기해안과 경남해안의 관계식의 기울기보다 상대적으로 약간 높게 나타나 액성한계, 초기간극비, 자연함수비의 변화에 따른 압축지수의 변화가 크게 됨을 알 수 있었다. 액성한계와 소성지수는 상관계수(R)가 0.93으로 매우 높은 상관성을 보였으며 자연함수비와 액성한계, 자연함수비와 초기간극비와의 관계에도 상관성을 보여 경험방정식을 제시하였다.