• Geomechanics and Engineering
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• 제30권4호
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• pp.325-336
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• 2022

This paper analyzes the ground surface settlements induced by side-by-side twin shield tunnels bored in sedimentary soils, which primarily consist of sand with clay strata above the tunnel crown. The measurements were obtained during the construction of twin tunnels underneath the Incheon International Airport (IIA) located in Korea. The measured surface settlement troughs are approximated with Gaussian functions. The trough width parameters i and K of the settlement troughs produced by the first and second tunnel passings are determined, along with those for the total settlement trough. The surface settlement troughs produced by the first shield passing are reasonably represented by a symmetric Gaussian curve. The surface settlement troughs induced by the second shield tunnel display marginal asymmetric shapes at selected sections. The total settlement troughs are fitted both with a shifted symmetric Gaussian function and the superposition method utilizing an asymmetric function for the incremental trough produced by the second tunnel. It is revealed that the superposition method does not always produce better fits with the total settlement. Instead, the shifted symmetric Gaussian function is overall demonstrated to provide more favorable agreements with the recordings. Therefore, the shifted symmetric Gaussian function is recommended to be used in the design for the prediction of the settlement in clays caused by twin tunneling considering the simplicity of the procedure compared with the superposition method. The amount of increase in the width parameter K for the twin tunnel relative to that for the single tunnel is quantified, which can be used for a preliminary estimate of the surface settlement in clay induced by twin shield tunnels.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 춘계학술대회 논문집
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• pp.375-378
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• 2007

The selection of the support system is an important design parameter in design and construction of the tunnel using the new Australian tunnel method. It is a common practice to select the support based on the rock mass grade, in which the rock mass is classified into five rock groups. The method is applicable if the characteristics of the rock mass are uniform in the direction of tunnel excavation. However, such case is seldom encountered in practice and not applicable when the properties vary along the longitudinal direction. This study performs comprehensive three dimensional finite difference analyses to investigate the ground deformation pattern for cases in which the rock mass properties change in the direction of the tunnel axis. The numerically calculated displacements at the tunnel crown show that the displacement is highly dependent on the stiffness contrast of the rock masses. The results strongly indicate the need to select the support type $0.5\sim1.0D$ before the rock mass boundary. The paper proposes a new guideline for selecting the support type based the results of the analyses.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 추계학술대회 논문집
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• pp.476-479
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• 2007

The selection of the support system is an important design parameter in design and construction of the tunnel using the new Australian tunnel method. It is a common practice to select the support based on the rock mass grade, in which the rock mass is classified into five rock groups. The method is applicable if the characteristics of the rock mass are uniform in the vertical direction. However, such case is seldom encountered in practice and not applicable when the properties vary along the vertical direction. This study performs comprehensive three dimensional finite difference analyses to investigate the ground deformation pattern for cases in which the rock mass properties change in the vertical direction of the tunnel axis. The numerically calculated displacements at the tunnel crown show that the displacement is highly dependent on the stiffness contrast of the rock masses. The results strongly indicate the need to select the support type $0.5{\sim}1.0D$(vertical direction) on the rock mass boundary. The paper proposes a new guideline for selecting the support type based the results of the analyses.

• 터널과지하공간
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• 제8권2호
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• pp.146-156
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• 1998

Nemerical algorithms were developed to analyze the behavior of the double lining as well as ground mass separately or simultaneously. A lining interface element was especially developed, verified and applied to the study on the coupled interaction of shotcrete and the concrete lining. It could be known fro parameter studys on double lining support systems that as the contact surface between shotcrete and concrete lining was rougher, the more decreased bearing capacity against the cracking of the system. If the thickness of the shotcrete increased, the bearing capacity of the double lining also increased linearly with the thickness. If the thickness of the concrete lining increased, the bearing capacity of the double lining had the relationship of the characteristic S-shape of a sigmoid function with the thickness. When the thickness increased over a given value, it was not useful to increase more the thickness because bearing capacity had no remarkable change. It could be concluded that the behavior of the shotcrete and concrete lining was generally reversed before and after the ratio of horizontal to vertical earth preassure of 1.0 and 0.5 respectively. Therefore, we could guess that the movement which two shotcrete and concrete lining deflect toward each other around the crown caused a friction between two linings and thus this disadvantageous effect could contribute to reducing the bearing capacity against the cracking.

• Journal of Periodontal and Implant Science
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• 제38권2호
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• pp.199-206
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• 2008

Purpose: Variation in the morphology of gingival papilla may be determined by the shape and position of anatomic crown as well as contact area and embrasure form of individual teeth. However, periodontal biotype classification is regarded to be subjective because of the lack of definite criteria. In this study, we defined the objective parameters which constitute the periodontal biotype and measured their relationship. Materials and Methods: 109 of dental casts were prepared using three dimensional scanner and specialized reconstruction software, then acquiredvirtual models were sent to the 20 professional dentists to define the specific periodontal biotypes. Several parameters around periodontal structures were measured from the virtual models; facial surface area of the anterior tooth (AT), anterior papillary area (AP), proportion of the dento-papillary complex, clinical papillary length (PL), and clinical papillary angle (PA). Statistical analysis was performed to confirm the relationship among parameters. Results: Coincidence rate of periodontal biotype within observers was $63.77{\pm}16.05%$. Coincidence rate between observers was $76.15{\pm}16.43%$. Among the parameters measured, PL showed the most positive correlations and PA presented the most negative correlations. The parameter of the AP and PL of six maxillary anterior teeth showed significant correlation coefficient. Conclusion: Anterior papillary area and clinical papillary length would be objective parameters for determining the consistent periodontal biotypes.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2006년도 추계학술대회 논문집
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• pp.1354-1363
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• 2006

Until now, NATM(New Austrian Tunneling Method) has been increasingly developed based on concept of making use of ground as support. Also, NATM in its essence is a method of risk based on monitoring behaviour of tunnel. This Monitoring is irreplaceable for the quality construction of tunnel, and safety of tunnel itself. Pre-reinforcement ahead of a tunnel face using long steel pipes in NATM, known as the RPUM(Reinforced Protective Umbrella Method), is the auxiliary method to sustain the stability of a tunnel face and reduce the ground settlements. Since design of RPUM has been dependent on the empirical design, it is necessary to develop the improved design methods. In this study, to understand behaviour of steel pipes, it is monitored displacement of tunnel crown, axial force of rock bolt, displacement and axial stress of steel pipes. Also, in order to clarify the mechanical behaviour and RPUM effects, 3-Dimensional numerical analysis is performed that various cases of different parameter combinations including original length and repeated length of steel pipes, installation width and angle, repeated length of steel. In the results of comparison monitoring with analysis, it is suggested more economical and efficient design technique than empirical design methods.

• Restorative Dentistry and Endodontics
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• 제18권1호
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• pp.205-213
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• 1993

The purpose of the study was to evaluate the degree of the marginal leakage of esthetic restorative materials on root caries restoration. 120 cavities were prepared to $90^{\circ}$ butt joint on all margins on the crown and root portion, and divided into 4 groups. The four groups of cavity were filled with Amalgam(Dongmuyung Dental Alloy Co., Ltd, KOREA), Silux$^{(R)}$(3M Co., USA)-Scotch Bond 2$^{(R)}$(3M Co., USA), Silux$^{(R)}$-All Bond$^{(R)}$(BISCO USA), and GC Fuji II$^{(R)}$(G-C Co., JAPAN) respectively. The apical margin of the preparation was finished to leave a flash of restorative material. The coronal margin of the preparation was finished not to leave a flash of restorative material. All specimens were sectioned longitudinally with Isomet Low speed saw(Buether Ltd, USA). The degree of dye penetration was evaluated as the parameter of marginal leakage under the stereoscope. The results were as follows. 1. At the enamel and dentin/cementum margins, the margin were finished to leave a flash of material showed less marginal leakage than that were finished not to leave a flash of material (P<0.001). 2. The enamel margins showed less marginal leakage than the dentin/cementum margins(P<0.001). 3. There was no significant difference in the degree of the marginal leakage between Silux$^{(R)}$-Scotch Bond 2$^{(R)}$ group and Silux$^{(R)}$-All Bond$^{(R)}$ group.

• The Journal of Advanced Prosthodontics
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• 제13권5호
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• pp.269-280
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• 2021

PURPOSE. The objective of this study was to evaluate the effect of thickness reduction and fatigue on the failure load of monolithic zirconia crowns. MATERIALS AND METHODS. 140 CAD-CAM fabricated crowns (3Y-TZP, inCorisTZI, Dentsply-Sirona) with different ceramic thicknesses (2.0, 1.5, 1.0, 0.8, 0.5 mm, respectively, named G2, G1.5, G1, G0.8, and G0.5) were investigated. Dies of a mandibular first molar were made of composite resin. The zirconia crowns were luted with a resin composite cement (RelyX Unicem 2 Automix, 3M ESPE). Half of the specimens (n = 14 per group) were mouth-motion-fatigued (1.2 million cycles, 1.6 Hz, 200 N/ 5 - 55℃, groups named G2-F, G1.5-F, G1-F, G0.8-F, and G0.5-F). Single-load to failure was performed using a universal testing-machine. Fracture modes were analyzed. Data were statistically analyzed using a Weibull 2-parameter distribution (90% CI) to determine the characteristic strength and Weibull modulus differences among the groups. RESULTS. Three crowns (21%) of G0.8 and five crowns (36%) of G0.5 showed cracks after fatigue. Characteristic strength was the highest for G2, followed by G1.5. Intermediate values were observed for G1 and G1-F, followed by significantly lower values for G0.8, G0.8-F, and G0.5, and the lowest for G0.5-F. Weibull modulus was the lowest for G0.8, intermediate for G0.8-F and G0.5, and significantly higher for the remaining groups. Fatigue only affected G0.5-F. CONCLUSION. Reduced crown thickness lead to reduced characteristic strength, even under failure loads that exceed physiological chewing forces. Fatigue significantly reduced the failure load of 0.5 mm monolithic 3Y-TZP crowns.

• 한국터널지하공간학회 논문집
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• 제8권2호
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• pp.151-163
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• 2006

대단면 터널에서 시공되는 사전보강공법에 의한 보강영역의 보강효과를 수치해석적으로 모델링하기 위한 다양한 방법이 제시되고 있지만 실무자들은 공학적인 방법보다는 경험적인 방법과 문헌을 참고하여 설계를 수행하고 있다. 따라서 본 연구에서는 상용 프로그램에서 직접적으로 적용할 수 있는 사전보강 영역의 물성치 결정에 있어서 거시적 접근법의 개념을 기반으로 미시적 접근법을 적용한 등가 물성치를 결정하는 기법을 제시하고 3차원 수치해석을 통한 실제모델 해석결과와 다른 여러 미시적 접근법들과의 비교 분석을 수행하여 타당한 보강영역 물성치 결정기법을 제시하였다. 해석 결과 구근과 강관의 병렬연결 강성이 원지반과 직렬로 연결되는 사전보강영역의 직병렬 강성 시스템과, 구근과 강관의 직렬 강성 시스템이 실해와 가장 근사한 변위를 예측하였으나 후자의 경우 그 모델링 과정이 복잡하므로 본 연구에서는 간편법으로써 직병렬 강성 시스템을 제안한다. 직병렬 강성 시스템은 천단변위에 대해 풍화암 지반에서는 약간 안전측으로, 내공변위와 지표면 변위에 대해서는 정밀모델의 결과와 거의 동일하게 거동하는 것으로 분석되었으며 풍화토와 풍화암 지반에서 동일한 변위 경향성을 나타낸다. 본 연구에서 제시된 사전보강영역의 직병렬 강성 시스템은 실제모델로 대표되는 보강지반의 거동 메카니즘을 효과적으로 나타내는 것으로 분석된다.

• 한국철도학회논문집
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• 제12권1호
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• pp.31-38
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• 2009

국내에서 터널 설계시 암반의 물리적, 역학적 특성에 따라서 $5{\sim}6$개의 암반등급으로 분류한 후 터널의 용도 및 특성을 고려하여 지보시스템을 결정하게 된다. 그러나 이와 같은 방법은 암반의 특성이 균일하다는 가정을 하고 있으며 암반특성이 종 방향으로 변화될 경우 이에 대한 지보시스템의 친정이 달라져야 한다. 본 연구는 3차원 수치해석 프로그램(FLAC3D)을 이용하여 NATM 터널시공시 암반특성의 종방향 변화가 암반분류 및 지보시스템 결정에 미치는 영향을 파악하고자 총 14Case를 현장의 시공순서를 고려한 해석을 수행하였다. 암반특성의 종방향 변화시 전 후방 암반의 강성차이가 작은 경우에는 암반경계를 기준으로 0.5D내외, 강성차이가 큰 경우에는 1.0D 내외의 범위에서 유리한 암반등급의 거동과는 다르므로 암반특성에 따라서 암반경계층을 기준으로 $0.5D{\sim}1.0D$구간을 안전측(보수적)으로 평가하여 설계에 반영하거나, 지보패턴을 하향조정하는 것이 시공성, 작업효율성, 공사기간 등의 측면에서 효과적일 것으로 판단된다.