• 지구물리
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• 제6권4호
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• pp.277-294
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• 2003

구조물의 시간경과에 따른 변형 및 성능저하 현상은 인위적 요인 및 시간경과에 따른 지반상태의 변화 혹은 지반 변위요인의 누적에 의해 발생한다 본 연구에서는 경상남도 경주시에 위치한 첨성대를 연구대상으로 설정하였다. 첨성대는 약 1,300여 년 전 건립된 석축구조물로서 지반침하로 약간 기울어져 있으며 일부 석재 사이의 틈이 벌어져 있는 상태이다 본질적인 대책수립을 위하여 본 연구에서는 이러한 목적을 위하여 차원 레이저스캐닝시스템에 의한 형상 역공학적 연구 물리탐사에 의한 지반공학적 특성 연구 및 고유진동수 측정에 의한 첨성대의 동적특성 등의 다음과 같은 연구들을 수행하였다 첫째 정밀측량에 의한 첨성대의 정밀한 변형량 측정 및 지속적인 변위측정을 위하여 차원 레이저 스캐닝에 의한 첨성대의 차원 공간위치정보를 취득하여 형상역공학에 의한 차원 벡터 이미지 형상구현 및 첨성대의 크기 변위량 변위방향 등 여러 가지 제원을 구하고자 하였다 둘째 다양한 비파괴적 물리탐사 방법들을 적용하여 첨성대 및 주변 지반의 물성분포 및 지반특성을 파악하고자 하였다 한편 다양한 물리탐사를 통하여 향후 유사한 조사에 있어서 적절한 물리탐사 방법을 제시하고자 하였다 셋째 경주 첨성대의 1/10모형에 대한 동적특성실험 및 실물에 대한 고유진동수 측정을 통해 첨성대의 구조적 특성을 연구하여 첨성대의 구조특성 및 상태판단 및 동적특성 파악에 의한 내진성능을 판단하고자 하였다.

• Geosciences Journal
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• 제22권6호
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• pp.871-880
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• 2018

During and shortly after the 2017 Pohang Earthquake ($M_w$ 5.4), sand blows were observed around the epicenter for the first time since the beginning of instrumental seismic recording in South Korea. We carried out field surveys plus satellite and drone imagery analyses, resulting in observation of approximately 600 sand blows on Quaternary sediment cover in this area. Most were observed within 3 km of the epicenter, with the farthest being 15 km away. In order to investigate the ground's susceptibility to liquefaction, we conducted a trench study of a 30 m-long sand blow in a rice field 1 km from the earthquake epicenter. The physical characteristics of the liquified sediments (grain size, impermeable barriers, saturation, and low overburden pressure) closely matched the optimum ground conditions for liquefaction. Additionally, we found a series of soft sediment deformation structures (SSDSs) within the trench walls, such as load structures and water-escaped structures. The latter were vertically connected to sand blows on the surface, reflecting seismogenic liquefaction involving subsurface deformation during sand blow formation. This genetic linkage suggests that SSDS research would be useful for identifying prehistoric damage-inducing earthquakes ($M_w$ > 5.0) in South Korea because SSDSs have a lower formation threshold and higher preservational potential than geomorphic markers formed by surface ruptures. Thus, future combined studies of Quaternary surface faults and SSDSs are required to provide reliable paleoseismological information in Korea.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1996년도 제24회 추계학술대회
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• pp.163-167
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• 1996

The life of rolling elements depends on various factors such as operating conditions and material properties. In this work, the effect of microstructure on the rolling behavior is investigated. Specially, the deformations in the substrate regions before and after rolling are compared. It is found that rolling action causes severe flow of material in the direction opposite to the rolling direction in the case of dry rolling direction. With lubrication, the deformation is more severe at the subsurface region rather than at the surface.

• 한국재난정보학회 논문집
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• 제6권2호
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• pp.45-65
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• 2010

There has been tighten up the need of seismic retrofit about 31 public facilites since published "Korean Earthquake Damage Prevention Law". Therefore, seismic studies have been developed and enforced the studies. Measuring dynamic stiffness of subsurface materials influence on seismic performance evaluation to build up seismic retrofit. The soil dynamic properties for seismic performance evaluation are N-value from using SPT(standard penetration test), dynamic shear elastic modulus and dynamic deformation modulus using laboratory tests. The most unscientific element in ground dynamic properties involved uncertainties is obviously N-value using SPT. This study shows that effect of N-value included natural and artificial uncertainties to seismic performance evaluation of ground structures is not only approached probabilistic analysis using FOSM method and tornado diagram, but also review how to spread effect of seismic performance evaluation of ground structures.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2009년도 춘계학술대회 논문집
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• pp.606-611
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• 2009

MiStrut is a new method to establish structural stability in designing braced excavations by making a rigid connection between top-level steel beams and soldier beams. MiStrut has a function of working as a strut as well as supporting cover plates of top-level steel beams. The structural mechanism of MiStrut is supposed to reduce flexural deformation of soldier beams, which may lead to reduced lateral earth pressures behind excavation. In this research, for verification of the performance of MiStrut, shear-wave velocities of subsurface soil before and after excavation was compared. The rigid connection of main girder beams with soldir beams reduced shear-wave velocity by 67% and lateral earth pressures by 90%, which indicates that MiStrut is effective development in reducing lateral earth pressures on braced excavation.

• 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.

• Geomechanics and Engineering
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• 제19권2호
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• pp.167-178
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• 2019

Open-pit (OP) and underground (UG) mining are usually used to exploit shallow and deep ore deposits, respectively. When mine deposit starts from shallow subsurface and extends to a great depth, sequential use of OP and UG mining is an efficient and economical way to maintain mining productivity. However, a transition from OP to UG mining could induce significant rock movements that cause the slope instability of the open pit. Based on Yanqianshan Iron Mine, which was in the transition from OP to UG mining, a large-scale two-dimensional (2D) model test was built according to the similar theory. Thereafter, the UG mining was carried out to mimic the process of transition from OP to UG mining to disclose the triggered rock movement as well as to assess the associated slope instability. By jointly using three-dimensional (3D) laser scanning, distributed fiber optics, and digital photogrammetry measurement, the deformations, movements and strains of the rock slope during mining were monitored. The obtained data showed that the transition from OP to UG mining led to significant slope movements and deformations that can trigger catastrophic slope failure. The progressive movement of the slope could be divided into three stages: onset of micro-fracture, propagation of tensile cracks, and the overturning and/or sliding of slopes. The failure mode depended on the orientation of structural joints of the rock mass as well as the formation of tension cracks. This study also proved that these non-contact monitoring technologies were valid methods to acquire the interior strain and external deformation with high precision.

• Tribology and Lubricants
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• 제13권1호
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• pp.42-52
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• 1997

This paper deals with wear characteristics of ion-nitrided metal theoretically and experimentally in order to analysis of wear phenomena. Wear tests show that compound layer of ion-nitrided metal reduces wear rate when the applied wear load is mall. However, as th load becomes large, the existence of compound layer tends to increase wear rate. The residual stress at the surface of ion-nitrided metal is measured, and the internal stress distribution is calculated when the normal and tangential forces are applied to the surface of metal. Compressive residual stress is largeest at the compound layer, and decreases as the depth from the surface increases. Calculation shows that the maximum stress exists at a certain depth from the surface when normal and tangential force are applied, and that the larger the wear load is the deeper the location of maximum stress becomes. In the analysis, it is found that under small applied wear load the critical depth, where voids and cracks may be created and propagated, is located at the compound layer, as the adhesive wear, where hardness is an important factor, is created the existence of compound layer reduces the amount of wear. When the load becomes large the critical depth is located below the compound layer, and delamination, which may be explained by surface deformation, crack nucleation and propagation, is created, and the existence of compound layer increases wear rate.

• 소성∙가공
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• 제26권6호
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• pp.365-371
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• 2017

During sling wear of a ferrous metal, a surface layer is formed. Its microstructure, constituting phases, and mechanical property are different from those of the original wearing material. Since wear occurs at the layer, it is important to characterize the layer and understand how wear rate changes with different layers. Various layers are formed depending on external wear conditions such as load, sliding speed, counterpart material, and environmental conditions. In this research, sliding wear tests of pure iron were carried out against two different counterparts (AISI 52100 bearing steel and $Al_2O_3$) in the air and in an inert Ar gas atmosphere. Pure iron was employed to exclude other effects from secondary phases in steel on the wear. Wear tests were performed at room temperature. Worn surfaces, wear debris, and cross-sections were analyzed after the test. It was found that these two different counterparts and environments produced diverse layers, resulting in significant changes in wear rate. Against the bearing steel, pure iron showed higher wear rate in an Ar atmosphere due to severe adhesion than that in the air. On the contrary, the iron showed much higher wear rate in the air against $Al_2O_3$. Different layers and wear rates were analyzed and discussed by oxidation, severe plastic deformation, and adhesion at wearing surfaces.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2004년도 정기총회 및 제6최 특별 심포지움
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• pp.25-48
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• 2004

구조물의 시간경과에 따른 변형 및 성능저하 현상은 인위적 요인 및 시간경과에 따른 지반상태의 변화 혹은 지반 변위요인의 누적에 의해 발생한다. 본 연구에서는 경상남도 경주시에 위치한 첨성대를 연구대상으로 설정하였다. 첨성대는 약 1,300여 년 전 건립된 석축구조물로서 지반침하로 약간 기울어져 있으며, 일부 석재 사이의 틈이 벌어져 있는 상태이다. 본질적인 대책수립을 위하여 본 연구에서는 이러한 목적을 위하여 3차원 레이저스캐닝시스템에 의한 (형상)역공학적 연구, 물리탐사에 의한 지반공학적 특성 연구 및 고유진동수 측정에 의한 첨성대의 동적특성 등의 다음과 같은 연구들을 수행하였다. 첫째, 정밀측량에 의한 첨성대의 정밀한 변형량 측정 및 지속적인 변위측정을 위하여 3차원 레이저 스캐닝에 의한 첨성대의 3차원 공간위치정보를 취득하여 형상역공학에 의한 3차원 벡터이미지 형상구현 및 첨성대의 크기, 변위량, 변위방향 등 여러 가지 제원을 구하고자 하였다. 둘째, 다양한 비파괴적 물리탐사 방법들을 적용하여 첨성대 및 주변 지반의 물성분포 및 지반특성을 파악하고자 하였다. 한편, 다양한 물리탐사를 통하여 향후 유사한 조사에 있어서 적절한 물리탐사 방법을 제시하고자 하였다. 셋째, 경주 첨성대의 1/10 모형에 대한 동적특성실험 및 실물에 대한 고유진동수 측정을 통해 첨성대의 구조적 특성을 연구하여 첨성대의 구조특성 및 상태판단 및 동적특성 파악에 의한 내진성능을 판단하고자 하였다.