• Title/Summary/Keyword: Subsurface deformation

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STUDIES ON THE CHARACTERISTICS OF STONE STRUCTURES BY GEOTECHNICAL AND DYNAMIC STRUCTURAL ENGINEERINGS (석조구조물의 효율적 유지관리를 위한 지질공학적 및 구조동역학적 특성연구)

  • HoWoongShon;SungMinLee
    • Journal of the Korean Geophysical Society
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    • v.6 no.4
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    • pp.277-294
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    • 2003
  • Structures show the phenomena of deformation and lowering of function with time-lapse by artificial environments and changes of geotechnical conditions or accumulation of initial deformation elements. This study aims the structural assessment of cultural property, Chum-Sung-Dae, located in Kyeongjucity, Korea. It was built about 1,300 years ago, and has undergone deformation and ground-subsidence with time-lapse. Non-destructive evaluation techniques were applied to the Chum-Sung-Dae, to protect it from survey. Because of this reason, 3D precise laser scanning surveying system was applied to measure the exact size of Chum-Sung-Dae, displacement and declining angles. Geophysical exploration also was applied to study the subsurface distribution of geotechnical parameters or physical properties. Natural frequencies were measured from real and model of Chum-Sung-Dae to study the dynamic characteristics of vibration and/or earthquake load and stiffness of structures.

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Paleoseismological implications of liquefaction-induced structures caused by the 2017 Pohang Earthquake

  • Gihm, Yong Sik;Kim, Sung Won;Ko, Kyoungtae;Choi, Jin-Hyuck;Bae, Hankyung;Hong, Paul S.;Lee, Yuyoung;Lee, Hoil;Jin, Kwangmin;Choi, Sung-ja;Kim, Jin Cheul;Choi, Min Seok;Lee, Seung Ryeol
    • Geosciences Journal
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    • v.22 no.6
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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.

Relationship between Rolling Motion and Microstructural Change in Rolling Element (구름계의 미소조직 변화와 구름운동의 상호관계)

  • 차금환;김대은
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 1996.10a
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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.

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Effect of Uncertain N-values to Seismic Performance Evaluation of Underground Structures (불확실한 지반의 N값이 지중구조물의 내진성능평가에 미치는 영향)

  • Park, Ji-hwan;Lee, Tea-hyung
    • Journal of the Society of Disaster Information
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    • v.6 no.2
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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.

Effects of Main Girder Beams with Struts on Lateral Earth Pressure in Braced Excavation (버팀굴착에서 횡방향 토압에 대한 스트러트 주형보의 영향)

  • Kim, Gi-Beom;Ban, Jae-Ki;Joh, Sung-Ho;Chung, Young-Soo;Kim, Seok-Chul
    • Proceedings of the KSR Conference
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    • 2009.05a
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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.

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Performance Evaluation of OGS-FLAC Simulator for Coupled Thermal-Hydrological-Mechanical Analysis (열-수리-역학적 연계해석을 위한 OGS-FLAC 시뮬레이터의 성능 평가)

  • Park, Dohyun;Park, Chan-Hee
    • Tunnel and Underground Space
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    • v.32 no.2
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    • pp.144-159
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    • 2022
  • The present study developed a sequential approach-based numerical simulator for modeling coupled thermal-hydrological-mechanical (THM) processes in the ground and investigated the computational performance of the coupling analysis algorithm. The present sequential approach linked the two different solvers: an open-source numerical code, OpenGeoSys for solving the thermal and hydrological processes in porous media and a commercial code, FLAC3D for solving the geomechanical response of the ground. A benchmark test of the developed simulator was carried out using a THM problem where an analytical solution is given. The benchmark problem involves the coupled behavior (variations in temperature, pore pressure, stress, and deformation with time) of a fully saturated porous medium which is subject to a point heat source. The results of the analytical solution and numerical simulation were compared and the validity of the numerical simulator was investigated.

Model test on slope deformation and failure caused by transition from open-pit to underground mining

  • Zhang, Bin;Wang, Hanxun;Huang, Jie;Xu, Nengxiong
    • Geomechanics and Engineering
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    • v.19 no.2
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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.

Study on the Analysis of Wear Phenomena of Ion-Nitrided Steel (이온질화 처리강의 마모현상 분석에 관한 연구)

  • Cho, Kyu-Sik
    • Tribology and Lubricants
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    • v.13 no.1
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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.

Analysis of the Sliding Wear Mechanism of Pure Iron Tested Against Different Counterparts in Various Atmospheres (상대재와 분위기에 따른 순철의 미끄럼 마멸 기구 분석)

  • Koo, B.W.;Gwon, H.W.;Kim, Y.S.
    • Transactions of Materials Processing
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    • v.26 no.6
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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.

Studies on the characteristics of stone structures by shape reversal, geotechnical and dynamic structural engineerings (석조구조물의 효율적 유지관리를 위한 형상역공학적, 지반공학적 및 구조동역학적 특성연구 - 첨성대를 중심으로 -)

  • Shon, Bo-Woong;Kim, Seong-Beom
    • 한국지구물리탐사학회:학술대회논문집
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    • 2004.08a
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    • pp.25-48
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    • 2004
  • Structures show the phehomena of deformation and lowering of function with time-lapse by artificial environments and changes of geotechnical conditions or accumulation of initial deformation elements. This study aims the structural assessment of cultural property, Chum-Sung-Dae, located in Kyeongju city, Korea. It was built about 1,300 years ago, and has undergone deformation and ground-subsidence with time-lapse. Non-destructive evaluation techniques were applied to the Chum-Sung-Dae, to protect it from survey Because of this reason, 3D precise laser scanning surveying system was applied to measure the exact size of Chum-Sung-Dae, displacement and declining angles. Geophysical exploration also was applied to study the subsurface distribution of geotechnical parameters or physical properties. Natural frequencies were measured from real and model of Chum-Sung-Dae to study the dynamic characteristics of vibration and/or earthquake load and stiffness of structures.

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