• Geomechanics and Engineering
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• 제20권3호
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• pp.191-205
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• 2020

Soil shear strength parameters play a remarkable role in designing geotechnical structures such as retaining wall and dam. This study puts an effort to propose two accurate and practical predictive models of soil shear strength parameters via hybrid artificial neural network (ANN)-based models namely genetic algorithm (GA)-ANN and particle swarm optimization (PSO)-ANN. To reach the aim of this study, a series of consolidated undrained Triaxial tests were conducted to survey inherent strength increase due to addition of polypropylene fibers to sandy soil. Fiber material with different lengths and percentages were considered to be mixed with sandy soil to evaluate cohesion (as one of shear strength parameter) values. The obtained results from laboratory tests showed that fiber percentage, fiber length, deviator stress and pore water pressure have a significant impact on cohesion values and due to that, these parameters were selected as model inputs. Many GA-ANN and PSO-ANN models were constructed based on the most effective parameters of these models. Based on the simulation results and the computed indices' values, it is observed that the developed GA-ANN model with training and testing coefficient of determination values of 0.957 and 0.950, respectively, performs better than the proposed PSO-ANN model giving coefficient of determination values of 0.938 and 0.943 for training and testing sets, respectively. Therefore, GA-ANN can provide a new applicable model to effectively predict cohesion of fiber-reinforced sandy soil.

• 지구물리
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• 제4권3호
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• pp.197-203
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• 2001

변동수압에 의한 해저 포화 사질틍의 연적 간극수압 분로를 이론 및 실험적으로 연구하였다. 실험에 의해 모래표면에 작용하는 수압은 모래층으로 전달되며 진폭이 감쇠하고 상이 지연되며, 유효응력이 0이 되는 액상화 현상이 특별 조건에서 발생한다. 이러한 실험결과는 탄성 대수층에 대한 지하수문제와 같은 이론으로 잘 설명된다. 해석에 의한 액상화의 주요 특징은 다음과 같다: 1)액상회 심도는 진폭 및 변동수압의 주파수 증가에 따라 증가한다. 2) 수량(水量)을 증가시키고 모래층 내의 공기가 많아짐에 따라 액상화 심도가 증가한다. 특히, 공기의 적은 양도 액상화에 크게 영향을 미친다. 3)압축율이 증가함에 따라 액상화 심도는 감소한다. 4)투수 계수값이 어느 특정값 이상이 되면 투수계수 값이 증가함에 따라 액상화 심도가 감소한다.

• 공학논문집
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• 제4권1호
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• pp.125-135
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• 2002

변동수압에 의한 해저 포화 사질층의 연직 간극수압 분포를 이론 및 실험적으로 연구하였다. 실험에 의해 모래표면에 작용하는 수압은 모래층으로 전달되며 진폭이 감쇠하고 상이 지연되며, 유효응력이 0이 되는 액상화 현상이 특별 조건에서 발생한다. 이러한 실험결과는 탄성 대수층에 대한 지하수문제와 같은 이론으로 잘 설명된다. 해석에 의한 액상화의 주요 특징은 다음과 같다: 1) 액상화 심도는 진폭 및 변동수압의 주파수 증가에 따라 증가한다. 2) 수량을 증가시키고 모래층 내의 공기가 많아짐에 따라 액상화 심도가 증가한다. 특히, 공기의 적은 양도 액상화에 크게 영향을 미친다. 3) 압축율이 증가함에 따라 액상화 심도는 감소한다. 4) 투수 계수값이 어느 특정값 이상이 되면 투수계수값이 증가함에 따라 액상화 심도가 감소한다.

• Tribology and Lubricants
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• 제31권2호
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• pp.56-61
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• 2015

In this study, we investigated the effectiveness of an ultrasonic nanocrystal surface modification (UNSM) technique on the mechanical and wear properties of tungsten carbide (WC). The UNSM technique is a newly developed surface modification technique that increases the mechanical properties of materials by severe plastic deformation. The objective of this study was to improve the wear resistance of press die made of WC by applying the UNSM technique. We observed the microstructures of the untreated and UNSM-treated specimens using a scanning electron microscope (SEM), and energy-dispersive X-ray spectroscopy (EDX) was used to investigate the chemical composition. The SEM observations showed the pore size and the number of pores decreased after the UNSM treatment. We assessed the wear behavior of both the untreated and UNSM-treated specimens using a scratch test. The test results showed that the wear resistance of the UNSM-treated specimens increased by about 46% compared with the untreated specimens. This may be attributed to increased hardness, reduced surface roughness, induced compressive residual stress, and refined grain size following the application of the UNSM technique. In addition, we found that the UNSM treatment increased the carbon concentration to 63% from 33%. We expect that implementing the findings of this study will lead to an increase in the life of press dies.

• Geomechanics and Engineering
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• 제22권5호
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• pp.397-414
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• 2020

In this paper, practical predictive models for soil shear strength parameters are proposed. As cohesion and internal friction angle are of essential shear strength parameters in any geotechnical studies, we try to predict them via artificial neural network (ANN) and neuro-imperialism approaches. The proposed models was based on the result of a series of consolidated undrained triaxial tests were conducted on reinforced sandy soil. The experimental program surveys the increase in internal friction angle of sandy soil due to addition of polypropylene fibers with different lengths and percentages. According to the result of the experimental study, the most important parameters impact on internal friction angle i.e., fiber percentage, fiber length, deviator stress, and pore water pressure were selected as predictive model inputs. The inputs were used to construct several ANN and neuro-imperialism models and a series of statistical indices were calculated to evaluate the prediction accuracy of the developed models. Both simulation results and the values of computed indices confirm that the newly-proposed neuro-imperialism model performs noticeably better comparing to the proposed ANN model. While neuro-imperialism model has training and test error values of 0.068 and 0.094, respectively, ANN model give error values of 0.083 for training sets and 0.26 for testing sets. Therefore, the neuro-imperialism can provide a new applicable model to effectively predict the internal friction angle of fiber-reinforced sandy soil.

• Tribology and Lubricants
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• 제34권6호
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• pp.270-278
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• 2018

STS 316L prepared by additive manufacturing (AM) exhibits deterioration of mechanical properties and wear resistance due to the presence of defects such as black-of-fusion defects, internal porosity, residual stress, and anisotropy. In addition, high surface roughness (integrity) of AM products remains an issue. This study aimed to apply ultrasonic nanocrystal surface modification (UNSM) technology to STS 316L prepared by AM to increase the surface hardness, to reduce the surface roughness, and to improve the friction and wear behavior to the level achieved by bulk material manufactured using traditional processes. Herein, the as-received and polished specimens were treated by UNSM technology and their resulting properties were compared and discussed. The results showed that UNSM technology increased the surface hardness and reduced the surface roughness of the as-received and polished specimens. These results can be attributed to grain size refinement and pore elimination from the surface. Moreover, the friction of the as-received and polished specimens after UNSM technology was lower compared to those of the as-received and polished specimens, but no significant differences in wear resistance were found.

• 한국지반환경공학회 논문집
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• 제20권3호
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• pp.39-46
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• 2019

액상화란 느슨한 사질토 지반에서 지진과 같은 큰 진동하중이 발생하여 과잉간극수압이 급격히 증가해 전단강도를 상실하는 현상으로 국내 포항에서 발생한 액상화 현상과 더불어 그 관심이 증가하고 있는 추세이다. 이러한 액상화 평가는 주로 Seed and Idriss(1982)가 제시한 반경험적 방법을 통해 수행할 수 있으며 시추공 DB와 SPT에서 얻어진 관입저항력을 기초로 액상화 위험을 평가할 수 있지만 획득된 시추공 DB는 일정 구역을 대표하지 못하는 문제를 내재하고 있다. 따라서 본 연구는 액상화 평가의 필요한 지반정보를 분류 및 검토하여 지반정보의 DB구축방안을 모색하고 지리정보시스템(GIS)을 활용하여 공간보간을 수행해 액상화 평가 대상이 되는 지층의 대표성 문제를 해소하고자 하였다. 액상화 발생이 예상되는 지층의 두께를 정의하는 방안에 따라 세 가지 지층심도DB구축 방안을 제시하였고 교차검증을 통해 제시한 구축방안의 정밀도를 비교, 분석하여 액상화 평가에 적합한 지층심도DB구축 방안을 제시하였다.

• 터널과지하공간
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• 제32권2호
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• pp.144-159
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• 2022

본 연구에서는 지반의 열-수리-역학적 복합거동을 모델링하기 위한 순차적 접근법 기반의 시뮬레이터를 개발하고 적용된 연계해석 알고리즘의 계산성능을 분석하였다. 본 연구의 순차적 연계해석에서는 다공성 매질의 열 및 유체거동 분석을 위한 오픈소스 기반의 OpenGeoSys 수치코드와 역학해석을 위한 상용 소프트웨어 FLAC3D가 연동되었다. 해석해가 주어진 열-수리-역학적 복합거동 문제를 토대로 개발된 시뮬레이터에 대한 벤치마크 테스트가 수행되었다. 적용된 벤치마크 문제는 완전포화된 지반 내 점열원 작용 시 지반거동(시간에 따른 온도, 간극수압, 응력, 변형 변화)과 관계된다. 해석해와 수치해석 시뮬레이션 결과를 비교 분석하고 연계해석 시뮬레이터의 적정성을 조사하였다.

• Nuclear Engineering and Technology
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• 제54권10호
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• pp.3631-3640
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• 2022

Uranium mill tailing ponds (UMTPs) are risk source of debris flow and a critical source of environmental U and Rn pollution. The technology of microbial induced calcium carbonate precipitation (MICP) has been extensively studied on reinforcement of UMTs, while little attention has been paid to the effects of MICP on U & Rn release, especially when incorporation of metakaolin and bacillus subtilis (MBS). In this study, the reinforcement and U & Rn immobilization role of MBS -MICP solidification in different grouting cycle for uranium mill tailings (UMTs) was comprehensively investigated. The results showed that under the action of about 166.7 g/L metakaolin and ~50% bacillus subtilis, the solidification cycle of MICP was shortened by 50%, the solidified bodies became brittle, and the axial stress increased by up to 7.9%, and U immobilization rates and Rn exhalation rates decrease by 12.6% and 0.8%, respectively. Therefore, the incorporation of MBS can enhance the triaxial compressive strength and improve the immobilization capacity of U and Rn of the UMTs bodies solidified during MICP, due to the reduction of pore volume and surface area, the formation of more crystals general gypsum and gismondine, as well as the enhancing of coprecipitation and encapsulation capacity.

• Geomechanics and Engineering
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• 제27권5호
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• pp.465-479
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• 2021

One of the important causes of building and infrastructure failure, such as bridges on pile foundations, is the placement of the piles in liquefiable soil that can become unstable under seismic loads. Therefore, the overarching aim of this study is to investigate the seismic behavior of a soil-pile system in liquefiable soil using three-dimensional numerical FEM analysis, including soil-pile interaction. Effective parameters on concrete pile response, involving the pile diameter, pile length, soil type, and base acceleration, were considered in the framework of finite element non-linear dynamic analysis. The constitutive model of soil was considered as elasto-plastic kinematic-isotropic hardening. First, the finite element model was verified by comparing the variations on the pile response with the measured data from the centrifuge tests, and there was a strong agreement between the numerical and experimental results. Totally 64 non-linear time-history analyses were conducted, and the responses were investigated in terms of the lateral displacement of the pile, the effect of the base acceleration in the pile behavior, the bending moment distribution in the pile body, and the pore pressure. The numerical analysis results demonstrated that the relationship between the pile lateral displacement and the maximum base acceleration is non-linear. Furthermore, increasing the pile diameter results in an increase in the passive pressure of the soil. Also, piles with small and big diameters are subjected to yielding under bending and shear states, respectively. It is concluded that an effective stress-based ground response analysis should be conducted when there is a liquefaction condition in order to determine the maximum bending moment and shear force generated within the pile.