• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.1828-1832
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• 2008

우수 관거 시스템에서 흐름은 중력에 의해서 흐르고 개수로 흐름과 같이 처리된다. 그러나 유입유량이 관거의 만관 상태를 초과하거나 하류 흐름의 제한 때문에 발생하는 역류의 영향을 받는다면, 우수 관거 시스템은 과부하(surcharge) 상태의 압력흐름이 된다. 개수로 상태에서 맨홀에서의 수두 손실은 일반적으로 무시되지만, 과부하 맨홀에서의 수두손실은 중요하며, 우수 관거 시스템의 전체 손실에 중요한 부분을 차지하게 된다. 이러한 현상은 여러 개의 맨홀을 가지는 우수 관거 시스템에서 특히 중요한 사항이 된다. 현재 계획 또는 설계단계에서 수행되고 있는 관거 시설의 수리계산에서는 연결관의 마찰손실만을 감안하여 수행하고 있으며, 맨홀에서의 수두손실은 고려되지 않는 실정이다. 본 연구에서는 일반적으로 3차원 유체거동의 특성분석에 많이 사용되는 Fluent 모형을 이용하여 과부하 원형 맨홀에서의 흐름특성을 수치모의 하였으며, 맨홀내 손실수두의 변화를 계산하여 손실계수를 산정하였다. 계산된 손실계수는 수리모형 실험을 통하여 산정된 손실계수와 비교하였다. 수치 모형에 의해서 산정된 손실계수 값이 수리모형 실험에 의해서 산정된 손실계수 값보다 약간 크게 산정되었다. 앞으로 난류 모형의 매개 변수들의 조정을 통한 정확한 수치모의 연구가 필요하다고 판단된다.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.11
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• pp.1221-1227
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• 2012

As demands on micro-products increase significantly with raising functional integration and increasing complexity, microfoming attracts a lot of attention in the manufacture of micro-products. Since the conventional big forming systems are not adequate to achieve sufficient tolerances of micro-scale parts, it is necessary to reduce the scale of the forming equipment and devices. In addition, understandings on the size effects, which exist in the material behavior and process characterization of microforming processes, need to be expanded. In this study, a miniaturized forming system based on the ball screw and servo motor actuator was developed for the efficient micro-parts production. In addition, tensile tests and cylindrical upsetting experiments were performed to evaluate the performance of the microforming system and to investigate the flow stress and friction size effects in microforming processes.

• Tunnel and Underground Space
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• v.21 no.3
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• pp.174-180
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• 2011

An anisotropic version of Mohr-Coulomb failure criterion is proposed in order to provide a strength criterion for transversely isotropic rock. The concept of fabric tensor introduced by Pietruszczak & Mroz (2001) is employed to define the friction angle and cohesion as scalar functions of the fabric tensors. The anisotroy in these two strength parameters are calculated in association with the consideration of the relative rotation between the principal stress coordinate and the principal material triad. The critical plane on which the anisotropic function maximized is found by an optimization technique based on the Lagrange multiplier method. To demonstrate the performance of the anisotropic failure criterion, conventional triaxial tests on the samples having various inclinations of weakness plane are simulated and the resulting triaxial strength and dip angle of failure plane are discussed.

• Tunnel and Underground Space
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• v.12 no.2
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• pp.83-91
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• 2002

Stability analysis of rocky embankment slopes is done by both the limit equilibrium method and the finite difference method. The height or the rocky embankment is approximately 40 m and the side slope is 1 vertical to 1.5 horizontal. The cohesion and internal friction angle of rock debris are assumed zero and 43$^{\circ}$, respectively. For finite difference analysis, strength reduction method is used to calculate the saft factor of the slope. As a result, the safety factor of the slope is discovered to be 1.4 by using either methods. Considering that the design criteria of the safety factor is 1.3, it can be judged that the rock fragments embankment slope is in a stable state.

• The Journal of Engineering Geology
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• v.24 no.2
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• pp.247-260
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• 2014

Rock masses at the site for the $2^{nd}$ step construction of the KAERI Underground Research Tunnel (KURT) are divided into six units to establish a rock mechanics model that is dependent on the geological characteristics and degree of joint development. The site primarily consists of three granitic units (G1, G2, and G3), two dykes (D1 and D3), and a fault zone of poor rock mass quality (F3). The F3 unit crosses the tunnel at the beginning of the site of $2^{nd}$ step construction. The rock masses of each unit are classified by RMR (Rock Mass Rating), Q-system, and RMi (Rock Mass Index), all based on borehole logging data. The deformation modulus, rock mass strength, cohesion, and friction angle for each unit are calculated using established empirical relationships. The representative rock mass classification and geotechnical parameters for the rock mass units are established, and a rock mechanics model for the site is proposed, which will be useful in the design and stability analysis of the $2^{nd}$ step construction of KURT.

• Journal of the Korean Geotechnical Society
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• v.18 no.2
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• pp.147-160
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• 2002

According to the Korean Design Code for port and harbor facilities, bearing capacity of rubble mound under eccentric and inclined load is calculated by the simplified Bishop method, and strength parameters are recommended to be c=0.2kg/$cm^2$ and \phi=35^P\circ}$ fur standard rubble if the compressive strength of parent rock is greater than 300kg/$cm^2$, according to research results by Junichi Mizukami(1991). But this facts have never been verified in Korea because there was no large-scale triaxial test apparatus until 2000 in Korea. For the first time in Korea, the large-scale triaxial test(sample diameter 30cm ; height 60cm) on the rubble originated from porous basalt rock in North-Cheju was accomplished. Then strength parameters for basalt rubble produced in North-Cheju are recommended to be c:0.3kg/$cm^2\; and \phi=36^{\circ}$ if the compressive strength of parent rock is greater than 400kg/$cm^2$. And the shear behavior characteristics of rubble, represented as particle breakage and dilatancy, are investigated.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.3 no.2
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• pp.127-135
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• 1983

A new approach is developed to analyze the reliability of the earth retaining wall using the concept of probability of failure, instead of conventional factor of safety. Many uncertainties, which are included in the conventional stability analysis, can be excluded by using the stochastic approach. And the reliability, more consistent with the reality, can be obtained by the simulation. The strength parameters of soil properties are assumed to be random variables to follow a generalized beta distribution. The interval [A, B] of the random variables could be determined using the maximum likelihood estimation. The pseudo-random values corresponding to the proposed beta distribution are generated using the rejection method. The probability of failure defined as follows, is obtained by using the Monte Carlo Method. $$P_f=\frac{M}{N}$$ where, $P_f$ : Probability of failure N : Total number of trials M : Total number of failure out of N A computer program is developed for the computation procedure mentioned above. Finally, a numerical example is solved using the developed program.

• Tunnel and Underground Space
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• v.27 no.4
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• pp.243-252
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• 2017

Since the failure behavior of transversely isotropic rocks is significantly different from that of isotropic rocks, it is necessary to develop a transversely isotropic rock failure function in order to evaluate the stability of rock structures constructed in transversely isotropic rock masses. In this study, a spatial distribution function for strength parameters of transversely isotropic rocks is proposed, which is based on the Cassini oval curve proposed by 17th century astronomer Giovanni Domenico Cassini to model the orbit of the Sun around the Earth. The proposed distribution function consists of two model parameters which could be identified through triaxial compression tests on transversely isotropic rock samples. The original Mohr-Coulomb (M-C) failure function is extended to a three-dimensional transversely isotropic M-C failure function by employing the proposed strength parameter distribution function for the spatial distributions of the friction angle and cohesion. In order to verify the suitability of the transversely isotropic M-C failure function, both the conventional triaxial compression and true triaxial compression tests of transversely isotropic rock samples are simulated. The predicted results from the numerical experiments are consistent with the failure behavior of transversely isotropic rocks observed in the actual laboratory tests. In addition, the simulated result of true triaxial compression tests hints that the dependence of rock strength on intermediate principal stress may be closely related to the distribution of the microstructures included in the rock samples.

• Journal of the Korean GEO-environmental Society
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• v.12 no.7
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• pp.57-65
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• 2011

Numerical simulations by three-dimensional Particle Flow Code($PFC^{3D}$, Itasca) considering distinct element method (DEM) were carried out for prediction of triaxial compression test with sand material. The effect of scale conditions for numerical model and distinct material on final prediction results was analyzed by numerical models under various scale conditions, and following observations were made from the numerical experiments. It is very useful to model the initial material condition without any porosity conversion from 2-D to 3-D DEM. Numerical experiments have shown that in all cases considered, 3D distinct element modeling could provide good agreement on stress-strain behavior, volume change and strength properties with laboratory testing results. It was important thing to assess reasonable scale ratio of numerical model and distinct elements for saving calculation time and securing calculation efficiency under condition with accuracy and appropriateness as numerical laboratory. As results of DEM simulations under various scale conditions, most of results show that shear strength properties as cohesion and internal friction angle are similar in condition of $D_{mod}/D_{gmax}$ < 10. It shows that 3-D distinct element method could be used as efficient tool to assess strength properties by numerical laboratory technique.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.1
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• pp.195-205
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• 2013

This study, using the MCC Model to consider consolidation, estimated the range within which no influences occur from lateral movement and its amount of the foundation pile and abutment on the soft ground. This study performed finite element analyses, with variations on the adhesiveness and internal friction angle, depth of soft clay, embankment height, consolidation parameters, and separation distance between the abutment and embankment. The abutment's horizontal displacement exhibits linear change with a longer separation distance, and changes into an exponential form as the embankment gets closer to the abutment. As the soft clay layer becomes 10 m deeper, the horizontal displacement tends to increase 1.5~3.0 times. However, it decreases at a rate of 0.3~0.95 when adhesiveness is increased by 10 $kN/m^2$ and internal friction angle is increased by $5^{\circ}$. The increase change rate in a lateral movement amount becomes greater if it is closer to the abutment when the abutment separation distance is long. When the distance is short, the change rate of horizontal displacement increases in similar a way, but it tends to be decreasing overall.