• Journal of the Korean GEO-environmental Society
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• v.3 no.4
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• pp.67-79
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• 2002

The purpose of this study is to present criteria of selection of optimum grout materials through analyzing the limitation of permeability of each materials(MSG-N, OPC), in various ground conditions by comparing presentation of strength and permeability of MSG method and LW method(or SGR method). To do that, physical and chemical characteristics of grout materials were analyzed and compressive tests of homogel, mixed coagulation materials and hardening materials in certain mixing ratio, and of milk paste. In addition, permeability tests for each ground soil, each injection pressure, and each materials in combined stratum were performed with massive chamber. The results of tests showed that ultra fine grout materials like grout of MSG is necessary to construct effective grouting in sand and silty sand ground. Also, it is expected to become chemical grouting guide data to layout construction engineers because presented proper injection pressure by kind of object ground in case using ultra-fine grout material.

• Journal of Korean Society of Steel Construction
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• v.28 no.5
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• pp.355-363
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• 2016

This study numerically investigates buckling behavior of press braked steel plates with a free edge that consists of the upper flange of U-shaped box girder. Since the press-braked plates include a rounded edge, the effective width to thickness ratio of the press-braked upper flange is obscure to determine the nominal compressive strength. This study performed 3D finite element analyses to evaluate an equivalent effective width of cold-formed plate with a free edge. Through the parametric numerical analyses, the elastic buckling stresses of the rounded corner plates were compared with those of general flat plates and then, the equivalent effective width has been estimated. A comparative study with Euler buckling formula speculated in the domestic design specifications has been conducted.

• Journal of the Korean Society of Industry Convergence
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• v.10 no.4
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• pp.213-219
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• 2007

Glass-to-metal contact should be prevented in the design of any structural glass component. Because glass is extremely brittle and will fracture readily if even a small point load is applied. If the assembly includes a glass component supported by metallic structure, designers should provide a pliable interface of some kind between the two parts. But there happens high demand of glass-to metal contact in semiconductor industries due to adoption of dry cleaning process as one of the good solution to reduce running cost - carry out equipments cleaning with high corrosive and etching gas such as CF4 with keeping process temperature as the same as high service temperature. Therefore the quartz glass have to be received compression by direct contact with metal as the form of weight itself and vacuum pressure and fatigue by vibrations caused by process during the process. In this paper investigation will be carried out on fracture behavior of quartz glass contacted with metal directly under local load and fatigue given by process vibration with apparatus which can give $lox{\backslash}cal$ load and vibration through PZT ceramics to give guideline to prevent unintended fracture of quartz glass.

• Steel and Composite Structures
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• v.29 no.1
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• pp.77-90
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• 2018

This paper presents a combined numerical, experimental, and theoretical study on the behavior of the concrete-filled double circular steel tubular (CFDT) stub columns under axial compressive loading. Four groups of stub column specimens were tested in this study to find out the effects of the concrete strength, steel ratio and diameter ratio on the mechanical behavior of CFDT stub columns. Nonlinear finite element (FE) models were also established to study the stresses of different components in the CFDT stub columns. The change of axial and transverse stresses in the internal and external steel tubes, as well as the change of axial stress in the concrete sandwich and concrete core, respectively, was thoroughly investigated for different CFDT stub columns with the same steel ratio. The influence of inner-to-outer diameter ratio and steel ratio on the ultimate bearing capacity of CFDT stub columns was identified, and a reasonable section configuration with proper inner-to-outer diameter ratio and steel ratio was proposed. Furthermore, a practical formula for predicting the ultimate bearing capacity was proposed based on the ultimate equilibrium principle. The predicted results showed satisfactory agreement with both experimental and numerical results, indicating that the proposed formula is applicable for design purposes.

• Geomechanics and Engineering
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• v.12 no.4
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• pp.611-626
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• 2017

The research reported herein is concerned with the model testing of piles socketed in soft rock which was simulated by cement, plaster, sand, water and concrete hardening accelerator. Model tests on a single pile socketed in simulated soft rock under axial cyclic loading were conducted and the bearing capacity and accumulated deformation characteristics under different static, and cyclic loads were studied by using a device which combined oneself-designed test apparatus with a dynamic triaxial system. The accumulated deformation of the pile head, and the axial force, were measured by LVDT and strain gauges, respectively. Test results show that the static load ratio (SLR), cyclic load ratio (CLR), and the number of cycles affect the accumulated deformation, cyclic secant modulus of pile head, and ultimate bearing capacity. The accumulated deformation increases with increasing numbers of cycles, however, its rate of growth decreases and is asymptotic to zero. The cyclic secant modulus of pile head increases and then decreases with the growth in the number of cycles, and finally remains stable after 50 cycles. The ultimate bearing capacity of the pile is increased by about 30% because of the cyclic loading thereon, and the axial force is changed due to the applied cyclic shear stress. According to the test results, the development of accumulated settlement is analysed. Finally, an empirical formula for accumulated settlement, considering the effects of the number of cycles, the static load ratio, the cyclic load ratio and the uniaxial compressive strength, is proposed which can be used for feasibility studies or preliminary design of pile foundations on soft rock subjected to cyclic loading.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.972-978
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• 2008

Quality Assurance of Deep Mixing to fulfill the requirements of geotechnical design cannot be achieved only by the process control During production conducted by the deep mixing contractor but it should involve relevant activities that are carried out prior to, during and after the construction by all the parties involved in a deep mixing project. The requirement is different for different application, and hence, QA/QC method/procedure and verification technique may be different for different application. In order to maintain the high quality of deep mixing work in the global market, it is necessary to conduct a research project, such as investigation of illustrations, the variety of existing QA/QC methods/procedures, the correlation between the outcomes of different QA/QC methods. In these reason, it has been held the international meeting to discuss them, in that kind of activities in 2009 it will be held Symposium. Also Collaborative study for QA/QC is on goin, and conduction by all participated members. The subject for collaborative study are, task 1 : investigation of laboratory tests procedures, task 2 : comparing of different laboratory tests procedures, task 3 : QA/QC method/procedures, task 4 : integrated Task1 ~task 3. The discussion of the results in all task will be held in the Symposium separately. In this paper, it was presented four tasks. Also the results in task 1 and 2 conducting domestically until now, such as investigation of laboratory test procedures, effect on the unconfined compressive strength by aging temperature and by delayed time.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.58-58
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• 2010

The purpose of this study is to evaluate the structural safety at the topside weldment of hull structure, which was welded after launching. For it, the variations of residual stress and distortion at the topside weldment with loading conditions such as hull girder hogging bending moment after launching and free initial loading state was evaluated by using FEA. And the maximum stress range at the weldment under design loads specified by classification society was evaluated by FEA. In this case, the residual stress and welding distortion at the topside weldment was assumed to be initial imperfection. In accordance with FEA results, regardless of initial loading condition, tensile residual stress was found. However, the residual stress and welding distortion at the topside weldment produced under hogging condition was less than those of topside weldment under free loading state. That is, the amount of residual stress at the topside weldment decreased with an increase in the amount of tension load caused by hogging condition. It was because the compressive thermal strain at the topside weldment produced during welding was reduced by tensile load. However, the maximum stress range at the topside weldment under maximum hull girder bending moment was almost similar regardless of initial loading condition. So, if the problem related to the soundness of weldment is not introduced by initial load, the effect of initial loading condition during welding on fatigue strength of topside weldment could be negligible.

• Journal of the Korean Geotechnical Society
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• v.21 no.9
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• pp.35-44
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• 2005

Recently, underground cavities such as limestone cavity and abandoned mine give rise to a lot of damage in SOC facilities. But there are many difficult problems such as delay of the working terms and enormous economic losses in finding a new method and changing construction design. In this study, a new filling material for underground cavities was developed using the stone-dust classified as industry waste polluting environment. As a result of test, filling material properties was that a compressive strength was $34{\~}60\;kgf/cm^2$, a change ratio in length was $0.268{\~}0.776\%$ and water absorption was $34.3{\~}46.9\%$. Also as a result of suspended mass test and pH test, it was confirmed that the developed filling material has a characteristic of non-separating in water and it was an environmentally friendly material.

• Journal of Korean Tunnelling and Underground Space Association
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• v.13 no.3
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• pp.243-260
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• 2011

To predict TBM performance in design stage is indispensable for its successful application. The NTNU model, one of the representative TBM performance prediction models uses two distinct parameters such as DRI and CLI obtained from three different tests on bored rock cores. Based on DRI and CLI, it is possible to predict TBM advance rate and cutter life in the NTNU model. In this study, NTNU testing methods and their related testing equipments were introduced to measure DRl and CLI for the NTNU model. Then, in order to derive their relationships, the two key parameters measured for 39 domestic rocks were compared with physico-mechanical properties of rock such as uniaxial compressive strength and quartz content. Lastly, the experimental results were also compared with NTNU database to verify their reliability.

• Resources Recycling
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• v.27 no.3
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• pp.39-47
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• 2018

According to Vietnam government establishes additional coal-fired power plants to secure generation capacity, emission of ashes is accelerating and processing them is urgent issue. This study targeted utilize fly ashes that occurred in circulating fluidized bed combusion (CFBC) power plant to use ground solidification materials. CFBC fly ashes are used to make solidification with ground granulated blast furnace slag (GGBFS), gypsum and cement. Then produced specimens by mixing with soft ground soil to confirm mixing effect of fly ash in solidification. As a result it was possible to find mixture design that is satisfied 3 MPa compressive strength in age 28 days and reduce weight loss rate over 50% in acid immersion test than plain specimens that using only ordinary portland cement.