• Journal of Korean Tunnelling and Underground Space Association
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• v.8 no.4
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• pp.365-375
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• 2006

The structural analysis for the secondary lining of tunnels is generally performed by a frame analysis model. This model requires a ground loosening load estimated by some empirical methods, but the load is likely to be subjective and too large. The ground load acting on the secondary lining is due to the loss of the supporting function of the first support members such as shotcrete and rockbolts. Therefore, the equilibrium condition of the ground and the first support members should be considered to estimate the ground load acting on the secondary lining. Ground-lining interaction model, shortly GLI model, is developed on the basis of the concept that the secondary lining supports the ground deformation triggered by the loss of the support capacity of the first support members. Accordingly, the GLI model can take into account the ground load reflecting effectively not only the complex ground conditions but the installed conditions of the first support members. The load acting on the secondary lining besides the ground load includes the groundwater pressure and earthquake load. For the structural reinforcement of the secondary lining based on the ultimate strength design method, the factored load and various load combination should be considered. Since the GLI model has difficulty in dealing with the factored load, introduced in this study is the superposition principle in which the section moment and force of the secondary lining estimated for individual loads are multiplied by the load factors. Finally, the design method of the secondary lining using the GLI model is applied to the case of a shallow subway tunnel.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.2
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• pp.109-120
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• 2007

Auxiliary support systems such as the reinforced protective umbrella method have been applied before tunnel excavation to increase ground stiffness and to prevent the large deformation. However, determination procedure of geotechnical parameters along the construction sequence contains various errors. This study suggests a method to characterize the time-dependent behavior of pre-reinforced zones around the tunnel using elastic waves. Experimental results show that shear strength as well as elastic wave velocities increase with the curing time. Shear strength and strength parameters can be uniquely correlated to elastic wave velocities. Obtained results from the laboratory tests are applied to numerical simulation of tunnel considering its construction sequences. Based on numerical analysis, initial installation part of pre-reinforcement and portal of tunnel are critical for tunnel stability. Result of the time-dependent condition is similar to the results of for $1{\sim}2$ days of the constant time conditions. Finally, suggested simple analysis method combining experimental and numerical procedure which considering time-dependent behavior of pre-reinforced zone on tunnel would provide reliable and reasonable design and analysis for tunnel.

• Journal of the Korea Concrete Institute
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• v.22 no.5
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• pp.641-650
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• 2010

The concrete cracking from the restrained stress caused by the shrinkage may play significant cause of deterioration of concrete structures by allowing the permeation of sulphate and chloride ions which in turn triggers corrosion of steel reinforcement. In particular, the cracking becomes more critical as water binder ratio (W/B) is reduced and concrete strength increases. Therefore, it needs to evaluate correctly the comprehensive shrinkage behavior of concrete with high strength: high-strength concrete (HSC), ultra-highstrength concrete (UHSC). The unrestrained shrinkage tests, however, cannot estimate the net shrinkage effectively which affects cracking after full development of strength and stiffness because it does not consider the degree of restraint, strength development, stress relaxation, and so on. Therefore, in this study, both free and restrained shrinkage tests with variables of W/B (W/B of 30, 25 and 16%) and admixtures (fly ash (FA) and granulated blast-furnace slag (BFS)) for HSC, very-high-strength concrete (VHSC) and UHSC were performed. The test results indicated that the autogenous shrinkage and total shrinkage at drying condition were reduced as W/B increased and FA, BFS were added, and the cracking behavior was suppressed as W/B increased and FA was added.

• Tunnel and Underground Space
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• v.22 no.6
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• pp.403-411
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• 2012

In recent, the using of the hydraulic filling method has increased on the underground reinforcement of the abandoned mine in Korea, however it is the lack of research on the efficient filling method. In this study, tank model tests and field tests were conducted for development of tip device for filling efficiency improvements on the hydraulic filling method. In tank model experiments, the filling efficiency was evaluated according to the form and angle of the nozzle on tip device in the same condition. Then tip device model designed by tank model tests was applied to the field experiment. As a result, the amount of filling of nozzle $90^{\circ}$ tube is increased by approximately 18% compared to the common vertical injection pipe. The angle of repose was $30.82^{\circ}$. Filling hole spacing in the field is usually designed from 5m up to 10m assumed to be $40^{\circ}$ of the angle of repose. According to the results of this study, it is possible that the filling hole spacing expands at least 10m up to 15m applied to be $30^{\circ}{\sim}35^{\circ}$ of the angle of repose. Therefore, it is expected to be economical and efficient mine filling.

• Journal of Conservation Science
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• v.29 no.4
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• pp.395-406
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• 2013

The conservation of damaged object should be restored by the similar material with the original and they have to reversibility as possible as. The characteristics of Buddhist mural paintings composed of clay are with soft material. So far, there have been a number of researches done on filling material that reinforces cracks and exfoliation of mural painting. Based on the application of traditional materials, it was found that they are appropriate to various applications. However, only based on those research results, there are some constraints to the application in the field. In addition, there has been only a few researches done on physical characteristics of filling materials. A major issue is that there is not any standard established on various mixing ratio, which is required for treatment of mural painting. This study was carried out to understand the physical characteristics of filling materials on clay mural painting. The 1st test was conducted to analyze test specimen in twelve different conditions by varying soil mixing ratio and organic medium. The 2nd test was conducted to manufacture filling materials appropriate to the mural painting, based on the result of stable condition from the 1st test, and which was applied to treatment in field.

• The Journal of Engineering Geology
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• v.17 no.4
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• pp.525-534
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• 2007

The peculiarity of end-expanded soil nailing method(EESNM) is in fixing the wedge-type steel body spreaded by collars and grouting its surroundings by cement milk within soils, after extending hole bottom over drilling hole diameter with top drill bit. The present study was done to establish the effect of this method. Laboratory model test were carried out to investigate the behavior characteristics with the performance of the pull-out test and failure experiment, after preparing soil test box having 1,300mm length, width 1,000mm, and height 1,100mm, and the same experimental condition was set up to compare with the general soil nailing method(GSNM). The pull-out force of about 23 percentage was increased, and the horizontal displacements 1.2 from 9.1 percentage in soil-nailed wall decreased in EESNM compare with GSNM. The axial force acting on nail increased considerably at load level over 7 ton in EESNM and 5 ton in GSNM. The predicted failure line from the maxima analyzed by axial tensile strain located at long distance from soil-nailed wall in EESNM. The EESNM demonstrated the superiority of reinforcement effect in comparison with GSNM from the results above mentioned.

• Journal of the Korea Concrete Institute
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• v.23 no.3
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• pp.377-384
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• 2011

Although concrete is considered as fire proof materials, high strength concrete shows severe material and structural damages when exposed to fire. To understand such damages in high strength concrete structures, the effects of various design parameters and fire condition on the thermal behaviors of high strength concrete structures are investigated in this study. In order to achieve this goal, fire tests are performed on high strength concrete columns with different fire conditions and design parameters including cross sectional area, cover thickness, and reinforcement alignment. To investigate thermal behaviors, temperature distributions and amount of spalling are measured. In overall, the columns show rapidly increasing inner temperatures between 30~60 mins of the fire tests due to spalling. In detail, the higher temperature distributions are observed from the columns with the larger cross section and less cover thickness. Moreover, among the columns with same reinforcing ratio, larger number of reinforcements with the smaller diameter causes the higher temperature distribution. The findings from the experimental study allow not only understanding of thermal behaviors of high strength concrete columns under fire, but also guidance in revising fire safety design.

• Journal of the Korea Concrete Institute
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• v.24 no.2
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• pp.111-120
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• 2012

This paper is a report about lap splice performance of rebar embedded in the strain-hardening cement-based composites (SHCCs) under monotonic and repeated tension loading. Ten mix proportions of cement-based composites such as SHCCs and normal concrete were investigated. The study parameters are comprised of (1) types of reinforcing fibers (polyethylene and steel fiber), (2) replacement levels of expansive admixture (EXA, 0% and 10%), and (3) compressive strength (30 and 100 MPa) of cement-based composites. Lap splice lengths (ld) of rebars in SHCC materials and normal concrete were 60% and 100% of splice length calculated by code requirements for structural concrete, respectively. Test results indicated that SHCCs materials can lead to enhancements in the lap splice performance of embedded rebar. All of the fiber reinforcement conditions (PE-SHCC and PESF-SHCC) considered in this study produced considerable improvements in the tensile strength, cracking behavior, and bond strength of lap-spliced rebar. Furthermore, adding EXA to SHCC matrix improved the tensile lap splice performance of rebar in SHCC materials. However, for controlling crack behavior, the performance of PE-SHCC was better than that of PESF-SHCC due to its mechanical properties. This study demonstrated an effective approach for reducing required development length of lap spliced rebar by using SHCC materials.

• The Journal of Sustainable Design and Educational Environment Research
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• v.17 no.2
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• pp.11-21
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• 2018

This study suggests desirable disaster safety education curriculum through analyzing the operational status of the school disaster safety management training course and demand survey of school staff. First, the problem of the disaster safety training course of the school is not connected with the lack of law and system and the school disaster safety job. Second, improvement of law and system and variety of training should be made to acquire professional knowledge. Third, it is necessary to divide curriculum into the following four categories, according to educational needs of public officials ; Educational administration officers course focused on facility safety, maintenance and disaster countermeasure. Educational officials in technical post course addressing approval and permission of school facility projects, seismic reinforcement of school building, etc. Educational supervisors course covering roles and responsibilities of the school safety supervisors in the event of disaster. Teaching staffs course focused on safety instructions for students. Fourth, it is found that lectures and experiential learning methods are the most desirable methods of teaching and learning, and the major ranks are earthquake disaster, fire, gas, typhoon, school road, and electrical safety.

• Journal of Adhesion and Interface
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• v.13 no.1
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• pp.45-50
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• 2012

Recently developed polyketone fiber has various applications in the mechanical rubber goods as reinforcement because of its good mechanical properties. However, its surface is not suitable for good adhesion with the rubber matrix. Thus, a surface modification is essential to obtain the good interfacial adhesion. Plasma treatment, in this study, has been conducted to modify the surface of the polyketone fiber. The morphological changes of the fibers by oxygen plasma treatment were observed by using SEM and AFM. The chemical composition changes of PK fiber surface treated with oxygen plasma were investigated using an XPS (X-ray photoelectron spectroscopy). Finally, the effect of these changes on the interfacial adhesion between fiber and rubber was analyzed by using a microdroplet debonding test. By the plasma treatment, oxygen moieties on the fiber surface increased with processing time and power. The surface RMS roughness increases until the proper processing condition, but a long plasma processing time resulted in a rather reduced roughness because of surface degradation. When the treatment time and power were 60 s and 80 W, respectively, the highest interfacial shear strength (IFSS) was obtained between the PK fiber and natural rubber. However, as the treatment time and power were higher than 60 s and 80 W, respectively, the IFSS decreased because of degradation of the PK fiber surface by severe plasma treatment.