• Structural Engineering and Mechanics
• /
• v.72 no.2
• /
• pp.275-291
• /
• 2019

In a super-large underground with "large span and high side wall", it is buried in mountains with uneven lithology, complicated geostress field and developed geological structure. These surrounding rocks are more susceptible to stability issues during the construction period. This paper takes the left bank of Baihetan hydropower station (span is 34m) as a case study example, wherein the deformation mechanism of surrounding rock appears prominent. Through analysis of geological, geophysical, construction and monitoring data, the deformation characteristics and factors are concluded. The failure mechanism, spatial distribution characteristics, and evolution mechanism are also discussed, where rock mechanics theory, $FLAC^{3D}$ numerical simulation, rock creep theory, and the theory of center point are combined. In general, huge underground cavern stability issues has arisen with respect to huge-scale and adverse geological conditions since settling these issues will have milestone significance based on the evolutionary pattern of the surrounding rock and the correlation analyses, the rational structure of the factors, and the method of nonlinear regression modeling with regard to the construction and development of hydropower engineering projects among the worldwide.

• International Journal of High-Rise Buildings
• /
• v.1 no.1
• /
• pp.37-51
• /
• 2012

New generation of tall and complex buildings systems are now introduced that are reflective of the latest development in materials, design, sustainability, construction, and IT technologies. While the complexity in design is being overcome by the availability and advances in structural analysis tools and readily advanced software, the design of these buildings are still reliant on minimum code requirements that yet to be validated in full scale. The involvement of the author in the design and construction planning of Burj Khalifa since its inception until its completion prompted the author to conceptually develop an extensive survey and real-time structural health monitoring program to validate all the fundamental assumptions mad for the design and construction planning of the tower. The Burj Khalifa Project is the tallest structure ever built by man; the tower is 828 meters tall and comprises of 162 floors above grade and 3 basement levels. Early integration of aerodynamic shaping and wind engineering played a major role in the architectural massing and design of this multi-use tower, where mitigating and taming the dynamic wind effects was one of the most important design criteria established at the onset of the project design. Understanding the structural and foundation system behaviors of the tower are the key fundamental drivers for the development and execution of a state-of-the-art survey and structural health monitoring (SHM) programs. Therefore, the focus of this paper is to discuss the execution of the survey and real-time structural health monitoring programs to confirm the structural behavioral response of the tower during construction stage and during its service life; the monitoring programs included 1) monitoring the tower's foundation system, 2) monitoring the foundation settlement, 3) measuring the strains of the tower vertical elements, 4) measuring the wall and column vertical shortening due to elastic, shrinkage and creep effects, 5) measuring the lateral displacement of the tower under its own gravity loads (including asymmetrical effects) resulting from immediate elastic and long term creep effects, 6) measuring the building lateral movements and dynamic characteristic in real time during construction, 7) measuring the building displacements, accelerations, dynamic characteristics, and structural behavior in real time under building permanent conditions, 8) and monitoring the Pinnacle dynamic behavior and fatigue characteristics. This extensive SHM program has resulted in extensive insight into the structural response of the tower, allowed control the construction process, allowed for the evaluation of the structural response in effective and immediate manner and it allowed for immediate correlation between the measured and the predicted behavior. The survey and SHM programs developed for Burj Khalifa will with no doubt pioneer the use of new survey techniques and the execution of new SHM program concepts as part of the fundamental design of building structures. Moreover, this survey and SHM programs will be benchmarked as a model for the development of future generation of SHM programs for all critical and essential facilities, however, but with much improved devices and technologies, which are now being considered by the author for another tall and complex building development, that is presently under construction.

• Journal of Korean Society of Forest Science
• /
• v.107 no.4
• /
• pp.393-401
• /
• 2018

The aim of this study was to analyze the characteristics of ground subsidence and land-creeping in four mining areas in Korea. Land creeping were occurred by large-scale sinkholes and tensile cracks in the mining areas. This ares showed the shape as large-scale landslides by the collapsed stone debris pushed in the direction of gravity. The rock type in the No. 4 survey area was sandstone and shale, whereas that of other three areas was limestone. The limestone was generally vulnerable to land creeping. The ground subsidence and land creeping in four mining areas were located near the ridge of the mountain. The land creeping by ground subsidence in the mining areas showed complex shapes due to the cavity of underground tunnel and the colluvial debris by gravity in the mountain area, whereas the land creeping in Korea are in the shape of landslide. The average slope of the mining area was ranged from $30.4^{\circ}$ to $33.7^{\circ}$. The values were higher ($1.5^{\circ}{\sim}4.8^{\circ}$) than the average slopes for landslide areas.

• Journal of Korean Society of Forest Science
• /
• v.108 no.2
• /
• pp.216-223
• /
• 2019

This study was conducted to measure the changes in the geological and soil properties following slow-moving landslide events in Yangbuk-myun and Gyungju-si, Gyeongsangbuk-do, South Korea. The geological characteristics of the study site comprised black shale in the Gyeongsang nodal group formed in the Cretaceous period and quartz feldspar carcinoma in the east side with conglomerate in the Yeonil group formed in the Quaternary period. The study site exhibited the geologic characteristics of a slow-moving landslide with severely weathered rocks. The maximum collapsing depth of the slow-moving landslide was 12.0 m with colluvial deposits. The strike and joint aspects in the slope areas of the slow-moving landslides were $N46^{\circ}E$ in lower slope and $N62^{\circ}E$ in upper slope, respectively. Soil hardness of ${\leq}20cm$ deep was not measured because of the completely disturbed soil resulting from soil creeping. Soil from 25 to 90 cm deep was 1.4-4.7 times softer in the slow-moving landslide areas than in the undisturbed or natural forests. Soil bulk density was $1.24-1.29g/cm^3$ in land creep areas. Soil bulk in both areas was 1.6 times denser than that in the natural forest. The soil pore space was 51.5-53.3% in the land creep areas. The values are 1.3-1.4 times lower than those within the natural forest. Black shale areas showed the lowest coefficient of permeability (8.75 E-06 cm/s) and mesopore ratio (pF 2.7: 9.8%) compared with those resulting from other study areas.

• Journal of the Korean Geosynthetics Society
• /
• v.10 no.4
• /
• pp.93-103
• /
• 2011

In order to design suitable geo-structures in cold region, it is generally required to consider the mechanical properties of permafrost soils. 'Frost heave' as one of the primary phenomenon is considered to be an important factor together with 'adfreeze bond-strength' and 'creep deformation' for structural design process in permafrost area. Therefore, the fundamental study for frost heave has to be preceded for design of geo-structures in cold region. While various experimental apparatuses have been developed, there still exist a certain level of limitation to evaluate the frost-heave characteristics as design parameters. In this paper, a new type of experimental apparatus is proposed to evaluate the engineering characteristics of frost heave in permafrost soils and a set of verification test results is presented. Based on the verification tests, the proposed apparatus is a suitable to obtain frost characteristics of soils.

• Geomechanics and Engineering
• /
• v.19 no.2
• /
• pp.115-126
• /
• 2019

The long-term settlement characteristics for the cast-in-place bored pile in the deep-thick soft soil are investigated by post-grouting field tests. Six cast-in-place bored engineering piles and three cast-in-place bored test piles are installed to study the long-term settlement characteristics. Three post-grouting methods (i.e., post-tip-grouting, post-side-grouting, and tip and side post-grouting) are designed and carried out by field tests. Results of the local test show that decreased settlements for the post-side-grouted pile, the post-tip-grouted pile and the tip and side post-grouted pile are 22.2%~25.8%, 30.10%~35.98% and 32.40%~35.50%, respectively, compared with non-grouted piles. The side friction resistance for non-grouted piles, post-side-grouted pile, post-tip-grouted pile and the tip and side post-grouted pile undertakes 89.6~91.3%, 94.6%, 92.4%~93.0%, 95.7% of the total loading, respectively. At last, the parameters back analysis method and numerical calculation are adopted to predict the long-term settlement characteristics of the cast-in-place bored pile in the deep-thick soft soil. Determined Bulk modulus (K) and a creep parameter (Ks) are used for the back analysis of the long-term settlement of the post-grouted pile. The settlement difference between the back analysis and the measurement data is about 1.11%-7.41%. Long-term settlement of the post-grouted piles are predicted by the back analysis method, and the predicted results show that the settlement of the post-grouted pile are less than 6 mm and will be stable in 30 days.

• Journal of Welding and Joining
• /
• v.30 no.6
• /
• pp.10-14
• /
• 2012

Recently the low alloy steel plate made with manganese-molybdenum is used widely in steam drum and separator of the new coal-fired power plant boiler. This material is suitable for the vapor storage of high pressure and high temperature. The high temperature creep strength of Mn-Mo alloy is higher than the carbon plate(SA516) that used in the subcritical pressure boiler. It reduces the thickness of the pressure vessel and makes the lightweight possible. Recently in the power plant boiler operation and production process, the damage has happened frequently in the heat affected zone and base material according to the hydrogen crack and delayed crack. This paper describes the research result about the damage case experienced in the boiler steam drum production process and present the optimum manufacture method for the similar damage prevention of recurrence.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.12 no.1
• /
• pp.71-84
• /
• 1992

Polymer-Impregnated Concrete(PIC) is a composite material of concrete and polymer. PIC has superior properties compared to conventional cement concrete, such as strength, stiffness, toughness, durability, water-proofing, chemical resistance. However, the usage of PIC has been limited to repairing materials and non-structural applications due to the lack of the design criteria and the analytical model to determine structural behavior. The objective of this study is experimentally to develop the optimum mixing proportions of polymer impregnants and the stress-strain responses, the strength characteristics, the fatigue and creep behaviors, and the durabilities of MMA(methyl methacrylate)-based PIC.

• Journal of Korean Association for Spatial Structures
• /
• v.16 no.1
• /
• pp.35-42
• /
• 2016

Until recently, almost all ETFE film structures that have been erected is the cushion type because there are problems at lower allowable strength under elastic range and viscosity behaviour such as creep and relaxation of ETFE films under long-term stresses. But the number of tension type structures is currently increasing. This paper proposes the stretch fabrication of ETFE film to verify the applicability of ETFE films to tensile membrane structures. First of all, to investigate the possibility of application on tensile membrane structures, the stretch fabrication test is carried out, and it is verified that it is possible to increase the yield strength of the film membrane structures. After simulating the experiment also carries out an analytical investigation, and the effectiveness of the elasto-plastic analysis considering the viscous behavior of the film is investigated. Finally, post-aging tension measurement is conducted at the experimental facilities, and the viscosity behavior resulting from relaxation is investigated with respect to tensile membrane structures.

• Magazine of the Korea Concrete Institute
• /
• v.10 no.1
• /
• pp.179-188
• /
• 1998

캔틸레버 공법으로 시공되는 프리스트레스트 콘크리트 박스거더 교량의 구조적 거동은 단계적 시공에 따른 구조물의 순차적 변화 및 콘크리트의 재료적 특성에 의해 시간 의존적 거동을 나타낸다. 콘크리트의 시간의존적 특성, 즉 콘크리트의 크리프 및 건조수축 특성은 현장타설 세그멘탈 캔딜레버공법으로 가설되는 콘크리트 교량의 설계 및 시공에서 매우 중요한 역할을 한다. 본 연구에서는 콘크리트의 크리프 및 건조수축 특성이 교량의 시간의존적 거동, 특히 처짐 및 텐던응력예측에 미치는 영향을 연구하였다. 교량해석은 본 연구진에 의해 개발된 프리스트레스트 콘크리트 교량해석기법 및 프로그램을 이용하여 크리프의 ACI 모델, CEB-FIB모델, 그리고 국내 도로교 시방서 모델을 고려하여 해석하였다. 해석결과 최종크리프 값의 크기에 따라 장기처짐의 발생량이 차이가 큰 것으로 나타나고 있으며, 최종건조수축량과 상대습도도 영향을 주는 것으로 나타났다. 또한 ACI 모델과 CEB-FIB모델간에도 차이가 큰 것으로 나타나 실제교량의 크리프 특성 및 건조수축 특성의 정확한 예측이 교량의 정밀시공 및 거동예측에 매우 중요한 것으로 나타나고 있다.