• Ocean Systems Engineering
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• v.9 no.3
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• pp.219-240
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• 2019

This paper presents the comparison between SFT response with linear and nonlinear cables. The dynamic response analysis of submerged floating tunnel (SFT) is presented computationally with linear and nonlinear tension legs cables. The analysis is performed computationally for two wave directions one at 90 degrees (perpendicular) to tunnel and other at 45 degrees to the tunnel. The tension legs or cables are assumed as linear and non- linear and the analysis is also performed by assuming one tension leg or cable is failed. The Response Amplitude Operators (RAO's) are computed for first order waves, second order waves for both failure and non-failure case of cables. For first order waves- the SFT response is higher for sway and heave degree of freedom with nonlinear cables as compared with linear cables. For second order waves the SFT response in sway degree of freedom is bit higher response with linear cables as compared with nonlinear cables and the SFT in heave degree of freedom has higher response at low time periods with nonlinear cables as compared with linear cables. For irregular waves the power spectral densities (PSD's) has been computed for sway and heave degrees of freedom, at $45^0$ wave direction PSD's are higher with linear cables as compared with nonlinear cables and at $90^0$ wave direction the PSD's are higher with non-linear cables. The mooring force responses are also computed in y and z directions for linear and nonlinear cables.

• Geotechnical Engineering
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• v.12 no.4
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• pp.5-20
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• 1996

In this study it was analyzed by 2-D FEM and 3-D FEM to evaluate the ground reinforceing effect of steel pipe reinforced multi -step grouting (SPRG) technique and the behavior of ground in the vicinity using the nonlinear FEM program for the ground condition of alluvium located on the top of tunnel applied by SPRG technique. It was found that the nonlinear 3-D analysis performed better than 2-D analysis in evaluating the usefulness of the SPRG technique, and it was also found that the safety was relatively secured by the stiffness of steel pipe to distribute the concentrated stress in the tunnel faceing. It was reported that the change of settlement on the top of tunnel becomes about 40% of the total expected settlement before tunnel faceing reaches tunnel gauging point, and 60% of the total expected settlement while tunnel facing passes tunnel gauging point and takes a distance about tunnel diameter. With the aid of the SPRG technique the control range of displacement and stress of the ground in the vicinity could be reached up to tunnel top, namely depth ratio from 0.38 to 0.83 or 2D(D : tunnel diameter) before the tunnel facing, and about 20% of settlement control in this particular case was possible.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.5
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• pp.779-797
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• 2017

Recently, underground road construction is attracting attention because the ground transportation facilities in the urban area have reached the saturation level and traffic volume has increased and the air pollution has risen. Construction of underground roads is not only reduce trafficjam in downtown but also design the city eco-friendly, so existing roads as well as new roads go underground. It is essential to construct divergence tunnels that serve as IC (interchage) and JC (Junction) when constructing underpasses. Therefore, the analysis of the effect of the existing tunnel by the divergence tunnel should be considered. In this study, numerical analysis is performed to analyze the effect of existing tunnel on the excavation of the divergence tunnel. The divergence tunnels were set in 5 cases at $45^{\circ}$ intervals in the clockwise direction starting from the lower part of the existing tunnel. In each case, numerical analyses were carried out by using the DCM (Displacement Controlled Model) for applying the volume loss of 0.5%, 1.0% and 1.5%. As a result, when the volume loss increased, the effect on displacement, fracture range, and effect on stability increased as well. In addition, it was confirmed that the divergence tunnel located directly underneath is the weakest for the stability, and the case where the divergence tunnel is located diagonally rather than the vertical and horizontal direction is found to be vulnerable to displacement and lining destruction.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.1
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• pp.11-22
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• 2009

Tunnel excavation with several sections and appropriate auxiliary measures such as face bolt and pre-grouting are widely used in case of weak and less rigid ground for the stability of a tunnel face during excavation. This papers first described the evaluation methods proposed in technical literature to maintain the tunnel face stable, and then studied by FEM analysis whether face reinforcement is need in what degree of ground deformation and strength features for the stability of a tunnel face when excavating by full excavation with sub-bench. Lastly, a three dimensional FEM analysis was performed to study how the tunnel face itself and the ground around the tunnel behave depending on different bolt layouts, length of bolts, number of bolts. There were relative differences in comparison of results on the stability of a tunnel face by a theoretical evaluation methods and FEM analysis, but the same in reinforced effect of face. It was found that the stability of a tunnel face can be obtained with face bolt installed longer than 1.0D (tunnel width), bolt density of about 1 bolt per every $1.5\;m^2$ (layout of grid type), and reinforcement area of $120^{\circ}$ arch area of upper section.

• Journal of the Korean GEO-environmental Society
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• v.8 no.6
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• pp.29-36
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• 2007

The control and prediction of surface settlement, gradient and ground displacement are the main factors in urban tunnel construction. This paper carried out the estimation and prediction of ground behavior around tunnel due to excavation using computational method and case study in detail for the analysis of deformation behavior in urban NATM tunnel. Computational method was performed by FLAC-2D with strain softening model and elastic plastic model. Field measurements of surface subsidence and ground displacement were adopted to monitor the ground behavior resulting from the tunneling and these values were applied to modify tunnel design parameters on construction.

• Tunnel and Underground Space
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• v.7 no.4
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• pp.323-333
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• 1997

A rock mass is usually classified by the results of geological survey and laboratory tests on rock specimens in order to obtain the adequate properties for the numerical analysis. For these purposes a rock mass strength is estimated based on the empirical criterion proposed by Hoek and Brown and a modulus of deformation is taken with the empirical relations developed by Bieniawski, Serafim and Pereira. In addition, the $K_o$ value which is the ratio of the horizontal stress to the vertical stress is one of the most important input data in the numerical analysis. Its role on a tunnel stability analysis could be verified with the numerical results taken by a finite difference code or a distinct element code. However, a deduced value used to be applied for the $K_o$ value in most of tunnel designs, even though the patterns of stress tensor are variable with regions and depths. Thus in situ stresses were measured by a hydraulic fracturing technique on several tunnel sites and applied directly to the tunnel design for the enhancement of its precision. With those informations on in situ stresses, the safe design should be obtained economically on the road or subway tunnels.

• New & Renewable Energy
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• v.2 no.2 s.6
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• pp.28-36
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• 2006

Numerical analysis of wind turbine scale effect was performed by using commercial CFD code, Fluent. For the numerical analysis of wind turbine, the three dimensional Navier-Stokes solver with various turbulence models was tested. As a turbulence mode, the realizable k-e turbulence model was selected for the simulation of wind turbines. To validate the present method, performance of NREL (National Renewable Energy Laboratory) Phase VI wind turbine model was analyzed and compared with its wind tunnel test and blind test data. Using the present method, numerical simulations for various size of wind tunnel models were carried out and characteristics were analyzed in detail. For wind tunnel test model, the size of nacelle may not be scaled down precisely because of available motor. The effect of nacelle size was also computed and analyzed though CFD simulation. The present results showed the good correlations in pre-stall region but much to be improved in post-stall region. In 2006 and 2007, the performance and the scale effect of standard wind turbine model will be tested in KARI(Korea Aerospace Research Institute) LSWT(Low Speed Wind Tunnel) and the present results will be validated with the wind tunnel data.

• Geomechanics and Engineering
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• v.23 no.1
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• pp.1-13
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• 2020

To give a solution for seismic stability of tunnel faces subjected to earthquake ground shakings, the pseudo-dynamic approach is originally introduced to analyze tunnel face stability in this study. In the light of the upper-bound theorem of limit analysis, an advanced three-dimensional mechanism combined with pseudo-dynamic approach is proposed. Based on this mechanism, the required support pressure on tunnel face can be obtained by equaling external work rates to the internal energy dissipation and implementing an optimization searching procedure related to time. Both time and space feature of seismic waves are properly accounted for in the proposed mechanism. For this reason, the proposed mechanism can better represent the actual influence of seismic motion and has a remarkable advantage in evaluating the effects of vertical seismic acceleration, soil amplification factor, seismic wave period and initial phase difference on tunnel face stability. Furthermore, the pseudo-dynamic approach is compared with the pseudo-static approach. The difference between them is illustrated from a new but understandable perspective. The comparison demonstrates that the pseudo-static approach is a conservative method but still could provide precise enough results as the pseudo-dynamic approach if the value of seismic wavelengths is large or the height of soil structures is small.

• Journal of Industrial Technology
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• v.25 no.A
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• pp.191-201
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• 2005

A numerical analysis was done for a tunnel fire in a 1000m road tunnel. A cartesian coordinate was adopted to make a computational grid sytem which has 448,000 computational cells. A transient flow phenomena in the tunnel was simulated by the commercial code of PHEONICS from the ignition of fire to 600 seconds by the interval of 100 seconds. Total computational time of about 44 hours was required to get a convered solution in each time step. The purpose of this research is to analyze of the backlayering pheonomena and recirculation flow in a tunnel. The compuational results say that the backlayering does not happens near the fire of vehicle in this case because the vehicle fire is located at the outside of recirculation zone of flow ocuured near the jet fan. In this research, onset of backlayering pheonomena could be escaped if jet fan is set 95m in front of the the fire of vehicle.

• Geomechanics and Engineering
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• v.17 no.1
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• pp.97-107
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• 2019

Based on the results of Han et al. (2016), in the failure zone ahead of the tunnel face it can be obviously identified that a shear failure band occurs in the lower part and a pressure arch happens at the upper part, which was often neglected in analyzing the face stability of shield tunnel. In order to better describe the collapse failure feature of the tunnel face, a new improved failure mechanism is proposed to evaluate the face stability of shield tunnel excavated in layered soils in the framework of limit analysis by using spatial discretization technique and linear interpolation method in this study. The developed failure mechanism is composed of two parts: i) the rotational failure mechanism denoting the shear failure band and ii) a uniformly distributed force denoting the pressure arch effect. Followed by the comparison between the results of critical face pressures provided by the developed model and those by the existing works, which indicates that the new developed failure mechanism provides comparatively reasonable results.