• 한국해양공학회지
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• 제15권1호
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• pp.73-78
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• 2001

Soundness evaluation of a structure being constructed under the sea is usually difficult. In this study, a cross-hole sonic logging(CSL) which have been used for non-destructive test of concrete piles is adopted for the integrity test and monitoring of DCM(deep cement mixing) treated soils. Chemical and physical characteristics of raw ground materials are analysed to delineate ground environmental effects on the strength of DCM treated soils. In order to convert cross-hole sonic logging data into compressive strength, correlations between compressive strengths and wave velocities of core samples have been obtained. It is found that there is little effect of ground environment on the strength of the DCM treated soils, and the density distribution of core samples and cross-hole logging data show that a defective zone may exist in the DCM treated soils. With the time lapse, however, the defective zone has been cured and consequently, compressive strength of the DCM treated soils increases and satisfies the design parameter. From this study it can be concluded that the cross-hole sonic logging can be used for the integrity test as well as monitoring the curing stage of the structures, successfully.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 세계 도시지반공학 심포지엄
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• pp.809-814
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• 2009

Deep mixing method has been used for ground improvement and foundation system for embankment, port and harbor foundations, retaining wall, and liquefaction mitigations. It has attractive benefits because it is not only improved strength of soft ground but superior for prevention of settlement. However, the quality controls of improved mass affect to the efficiency of the deep mixing method is not properly established. These effects vary depending upon the construction environments and conditions of agitation in consideration of an agitator. The strength and shape of the improved column are not unique and these are affected by mechanical properties of agitators. In this study, in order to investigate the efficiency of deep mixing method for ground improvement on a soft clay ground, experimental studies are performed considering mechanical properties of agitator; the location of exit-hole of admixtures, an angle of mixing wing and a speed of revolution. The experiments are conducted with the simulated apparatus for deep mixing plant that reduced the scale in 1:8 of the real plant. According to the results, the diameter and shape of improved column mass vary depending on the mechanical properties and operating conditions of agitator. Its quality is better when the exit-hole of admixtures is located in the mixing wing, when an angle of mixing wing is large, and when the speed of revolution is rapid.

• 한국정밀공학회지
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• 제15권9호
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• pp.43-49
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• 1998

The deep hole drilling has an increasing demands because of its wide range applications and its good productivity. The BTA drills are capable of machining for having a large length to diameter ratio in single pass to higher degree of accuracy and surface finish. It's really necessary that the investigation for the deep hole drilling by the BTA drill because its required quality should be satisfied with single pass. This thesis deal with the experimental results obtained during single tube BTA system machining on SM55C steel for different machining conditions. The results of the investigation on the optimum cutting condition selecting and tool life reveals as follows. (1) The optimum cutting condition was cutting speed, V = 42 m/min and feed speed. F = 90 mm/min and the tool life was about 10 meters. (2) Surface roughness was $12\mum$ and the roundness was less using $16mum$single edge BTA drill in testing cutting condition.

• Geomechanics and Engineering
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• 제20권5호
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• pp.461-474
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• 2020

Analysing the incompatible deformation and damage evolution around the tunnels in mixed strata is significant for evaluating the tunnel stability, as well as the interaction between the support system and the surrounding rock mass. To investigate this issue, confined compression tests were conducted on upper-soft and lower-hard strata specimens containing a circular hole using a rock testing system, the physical mechanical properties were then investigated. Then, the incompatible deformation and failure modes of the specimens were analysed based on the digital speckle correlation method (DSCM) and Acoustic Emission (AE) data. Finally, numerical simulations were conducted to explore the damage evolution of the mixed strata. The results indicate that at low inclination angles, the deformation and v-shaped notches inside the hole are controlled by the structure plane. Progressive spalling failure occurs at the sidewalls along the structure plane in soft rock. But the transmission of the loading force between the soft rock and hard rock are different in local. At high inclination angles, v-shaped notches are approximately perpendicular to the structure plane, and the soft and hard rock bear common loads. Incompatible deformation between the soft rock and hard rock controls the failure process. At inclination angles of 0°, 30° and 90°, incompatible deformations are closely related to rock damage. At 60°, incompatible deformations and rock damage are discordant due that the soft rock and hard rock alternately bears the major loads during the failure process. The failure trend and modes of the numerical results agree very well with those observed in the experimental results. As the inclination angles increase, the proportion of the shear or tensile damage exhibits a nonlinear increase or decrease, suggesting that the inclination angle of mixed strata may promote shear damage and restrain tensile damage.

• 화약ㆍ발파
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• 제41권4호
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• pp.17-28
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• 2023

최근 연구시설 및 자원개발 등의 목적으로 지하공간 활용이 증가하고 있으며, 저심도 암반을 넘어 고심도 암반에 대한 개발이 증가하고 있다. 고심도 지하공간 개발은 높은 응력과 높은 온도 조건에서의 암반의 안정성을 고려해야 한다. 고심도의 경우 암반 구조와 불연속면의 상태 등이 안정성에 영향을 미칠 뿐만 아니라 지진 및 굴착을 위한 암반발파에 의한 지반진동 전파가 지하공동의 응력변화를 발생시켜 암반의 안정성에 영향을 미치게 된다. 발파공학 측면에서 지반진동을 예측하는 방법은 실측 데이터를 바탕으로 통계학적 회귀분석을 통한 경험적 회귀모형과 수치해석적 방법이 사용되고 있다. 본 연구에서는 단일공 발파에 의한 폭발압력 전파특성과 지반진동 전파특성에 대한 경험적 회귀모형을 획득하기 위하여 실험적 방법을 통해 연구를 수행하였다.

• 한국생산제조학회지
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• 제8권1호
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• pp.15-20
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• 1999

• 한국전기전자재료학회논문지
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• 제30권2호
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• pp.91-95
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• 2017

We were designed the hole transport layer of the new composite skeleton structure having a high charge mobility and thermal stability. In this paper, a hole transport layer material based on thiophene molecular structure capable of hole mobility characteristics and high triplet energy was designed and synthesized. The structures and properties of the synthesized compounds were characterized by NMR, fluorescence spectroscopy and energy band gap. As a result of NMR measurement, it was confirmed that when analyzing the integrated type with the position where the measured peak is displayed, it agrees with the structure of hole transport materials. The emission characteristics of the hole transport layer material showed absorption characteristics at 412 nm and 426 nm, respectively, and exhibited emission characteristics in the range of 469 nm and 516 nm.

• 한국정밀공학회지
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• 제15권1호
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• pp.117-129
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• 1998

Micro-hole drilling (holes less than 0.5 mm in diameter with aspect ratio larger than 10) is recently having more attention in a wide spectrum of precision production industries. Alternative methods such as EDM. laser drilling, etc. can sometimes replace the mechanical micro-hole drilling but are not acceptable in PCB manufacture because of the inferior hole quality and accuracy. The major difficulties in micro-hole drilling are related to small signal to noise ratios, wandering motions of the inlet stage, high aspect ratios, high temperatures and so forth. Of all the difficulties. the most undesirable one is the increase of drilling force as the drill proceeds deeper into the hole. This is caused mainly from the chip effects. Peck-drilling is thus widely used for deep hole drilling despite that it suffers from low productivity. In the paper, a method of cutting force regulation is proposed to achieve continuous drilling. A PD and a sliding mode control algorithms were implemented through controlling the spindle rotating frequency. Experimental results show that the sliding mode control reduces the nominal cutting force and the variation of the cutting force better than the PD control. The advantages of the regulation, such as increase of drill life, fast stabilization of a wandering motion, and the precise positioning of the hole are verified in experiment.

• 터널과지하공간
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• 제14권6호
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• pp.429-439
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• 2004

국내 원전에서 발생되는 36,000톤의 사용후핵연료를 처분하기 위해서는 약 $4km^2$의 지하 처분장이 필요하다. 본 연구에서는 굴착량과 처분장 면적을 최소화하기 위한 지하 심부 처분장 배치의 최적화를 실시하였다. 열 해석 결과를 토대로 처분 터널과 처분공 간격이 처분장 배치에 미치는 영향을 고려한 결과, 처분장 면적과 굴착량은 처분 터널의 길이가 길어짐에 따라 감소하였다. 주어진 열적 기준을 만족하면서 처분장 면적을 줄이기 위해서는 처분 터널의 간격을 줄이고 처분공 간격을 늘리는 것이 유리하였으며, 반면에 굴착량을 최소화하는 경우 처분공 간격을 줄이고 처분 터널 간격을 늘려주는 것이 효과적인 것으로 나타났다.

• Steel and Composite Structures
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• 제44권2호
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• pp.199-210
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• 2022

This study build finite element analysis (FEA) models describing the bending events of coiled tubing (CT) at the wellhead and trips into the hole, accurately provide the state of stress and strain while the CT is in service. The bending moment and axial force history curves are used as loads and boundary conditions in the diametrical growth models to ensure consistency with the actual working conditions in field operations. The simulation diametrical growth results in this study are more accurate and reasonable. Analysis the factors influencing fatigue and diametrical growth shows that the internal pressure has a first-order influence on fatigue, followed by the radius of the guide arch, reel and the CT diameter. As the number of trip cycles increase, fatigue damage, residual stress and strain cumulatively increase, until CT failure occurs. Significant residual stresses remain in the CT cross-section, and the CT exhibits a residual curvature, the initial residual bending configuration of CT under wellbore constraints, after running into the hole, is sinusoidal. The residual stresses and residual bending configuration significantly decrease the buckling load, making the buckling and buckling release of CT in the downhole an elastic-plastic process, exacerbating the helical lockup. The conclusions drawn in this study will improve CT models and contribute to the operational and economic success of CT services.