• Journal of the Korean Geotechnical Society
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• v.38 no.6
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• pp.29-39
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• 2022

This study investigates the behavior of a circular vertical shaft wall in the absence and presence of a groundwater table. The effects of wall deflection, backfill settlement, and earth pressure distribution around the circular vertical shaft caused by sequential excavations were quantified. The vertical shaft was numerically simulated for different excavation depths of the bearing layer (weathered soil, weathered rock, soft rock) and transient and steady-state flows in the absence of a groundwater table. The backfill settlements and influential area were much larger under transient flow conditions than in steady-state flow. On the contrary, the horizontal wall deflection was much larger in steady state than in the transient state. Moreover, less settlement was induced as the excavation depth increased from weathered soil to weathered rock to the soft rock layer. Finally, the horizontal stresses under steady- and transient-state flow conditions were found to exceed Rankine's earth pressure. This effect was stronger in the deeper rock layers than in the shallow soil layers.

• Geotechnical Engineering
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• v.1 no.2
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• pp.41-54
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• 1985

Generally, ground settlements and lateral displacements are accompanied by underground excavation associated with open-cut or tunnling. These ground movements cause a harmful influence upon nearby super.structures and sub-structures. Occasionally, the ground movements may pose serious problems as the function of the nearby structures may be disrupted. Therefore, prior to the subway construction in an urban area, it is necessary to identify the causes of ground settlements and estimating the extent St the magnitude of ground movements since any potential damage to the nearby structures such as gas lines, water mains, high buildings and cultural assets must be assessed. The research was performed mainly on ground movements such as surface settlements, lateral displacements, subsurface settlements and crown settlements to predict the maximum settlement and settlement zone, and to identify the causes of ground settlements in NATM sections of Busan subway. As a result, it was found that lateral distribution of settlements could be approximated reasonably by a Gaussian normal probability curve and longitudinal distribution of settlements by a cumulative Gaussian probability curve, and that the early closure of temporary invert was very important to minimize ground settlements.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.3
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• pp.37-44
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• 2004

This paper deals with the performance analysis of LIPCA(Light-weight Piezo-Composite actuator) including the material nun-linearity of the embedded 3203HD PZT wafer. For this analysis, we used a piezo-shell element code based on a nine-node assumed strain shell element formulation. The material non-linearity was implemented in the formulation due to a large observed discrepancy between the measured displacement and the computed actuation displacement based on the linear analysis. An experimentally extracted piezo-strain function of the PZT wafer and incremental formulation were incorporated into the linear finite element code to improve the accuracy of the estimated actuation displacement of the LIPCA. The non-linear piezo-shell program was used to predict the non-linear performance of the LIPCA. The simulated actuation displacement from the non-linear code showed much better agreement with the measured data.

• Journal of Korean Tunnelling and Underground Space Association
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• v.2 no.3
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• pp.59-69
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• 2000

Three-dimensional total station system which integrated the instrument with Target Pin and TEMS 3D software developed by SKEC R&D center was applied to a tunnel excavation for monitoring of convergence and crown settlement. The efficiency of the system was proved as the result in the aspects of exact monitoring and prediction of rock conditions ahead of the face. To monitor the behavior of tunnel lining at the maintenance stage, DOCS system was applied to the subway tunnel section. Such many effects as the vibration of sensors, verification of the system efficiency, the effect of test trains operation, the variation of temperature and the effect of high voltage was checked. Thus the management scheme for tunnel maintenance was laid out as a proposal.

• Journal of the Korea Concrete Institute
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• v.19 no.4
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• pp.491-497
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• 2007

In the current research, the scheme of displacement-based seismic design for seismic retrofit of concrete structures using FRP composite materials has been proposed. An algorithm of the nonlinear flexural analysis of FRP composite concrete members has been presented under multiaxial constitutive laws of concrete and composite materials. An algorithm for performance-based seismic retrofit design of reinforced concrete columns with FRP jacket has been newly introduced to modify the displacement coefficient method used in reinforced concrete structures. From applications of retrofit design, the method are easy to apply in the practice of retrofit design and give practical prediction of nonlinear seismic performance evaluation of retrofitted structures.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.7
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• pp.777-787
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• 2012

The transient analysis for the output voltage of a piezoresistive microaccelerometer takes a relatively high computation time because at least two iterations are required to calculate the piezoresistive-structural coupled response at each time step. In this study, the high computational cost for calculating the transient output voltage is considerably reduced by an approach integrating the mode superposition method and the least square method. In the approach, data on static displacement and output voltage calculated by piezoresistive-structural coupled simulation for three acceleration inputs are used to develop a quadratic regression model, relating the output voltage to the displacement at a certain observation point. The transient output voltage is then approximated by a regression model using the displacement response cheaply calculated by the mode superposition method. A high-impact microaccelerometer subject to several types of acceleration inputs such as 100,000 G shock, sine, step, and square pulses are adopted as a numerical example to represent the efficiency and accuracy of the suggested approach.

• Tunnel and Underground Space
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• v.13 no.2
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• pp.77-86
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• 2003

The finite element method and statistics of the convergence measurement are useful method of the stability analysis of the tunnel adjacent to the pier. It is the purpose of the this case study to certificate of validity of the application of those methods. The safety of the pilot tunnel method and LW pre-grouting has been evaluated from the FEM analysis. The three-dimensional finite element method is carried out for the decision of the level of stress redistribution at the two-dimensional numerical analysis. An analysis of the convergence is carried out by the estimation of preceding convergence at tunnel excavation. F-examination is applied for this estimation. As results of that analysis, The F-value is from 10.81 to 158.74 and the coefficient of determination is from 0.82 to 0.99. An analysis of convergence is carried out by using regression analysis. Consequently, it is shown that the convergence can be modeled as following function C(t)=a[1-exp(-bt)].

• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.6
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• pp.41-52
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• 2007

Earthquake time-history analyses have been carried out for a buried gas pipeline of X65 which is of popular use in Korea. Parameters included are shape of a buried gas pipeline, soil characteristics, single and multiple earthquake input ground motions and burial depths. Predicted response of strain and relative displacement are then compared with allowable strain and displacement capacity calculated by Guidelines for the Seismic Design of Buried Gas Pipelines, KOGAS. Comparative studies show that strains are in general affected by the burial depths together with change of soil conditions. Regarding the relative displacement, while axial relative displacement is not influenced by the burial depths, transverse relative displacement is affected by both burial depths as well as soil conditions. In all, the current study is encouraged to give a useful information for healthy earthquake evaluation of a buried pipeline.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.4
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• pp.51-61
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• 2003

This research is a park of a research program to develope a new design method for reinforced concrete bridge columns under axial load and cyclic lateral load. The objectives of this paper are to investigate the relationship between curvature ductility and displacement ductility and to propose a correlation equation for designing of reinforced concrete bridge columns under axial load and cyclic lateral load. Computer program NARCC was used for parametric study, which was proved to provide good and conservative analytical result especially for deformation capacity and ductility factor compared with test result. A total of 7,200 spirally reinforced concrete columns were selected considering the main variables such as section diameter, aspect ratio, concrete strength, yielding strength of longitudinal and confinement steel, longitudinal steel ratio, axial load ratio, and confinement steel ratio. A new equation between curvature ductility factor displacement ductility factor with the aspect ratio was proposed by investigation of 21,600 data produced from the selected column models by applying 3 different definitions of yield displacement.

• Journal of the Korean Geophysical Society
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• v.7 no.4
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• pp.313-324
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• 2004

The finite element method and statistics of the convergence measurement are useful method of the stability analysis of the tunnel adjacent to the pier. It is the purpose of the this case study to certificate of validity of the application of those methods. The safety of the pilot tunnel method and LW pre-grouting has been evaluated from the FEM analysis. The three-dimensional finite element method is carried out for the decision of the level of stress redistribution at the two-dimensional numerical analysis. An analysis of the convergence is carried out by the estimation of preceding convergence at tunnel excavation. F-examination is applied for this estimation. As results of that analysis, The F-value is from 10.81 to 158.74 and the coefficient of determination is from 0.82 to 0.99. An analysis of convergence is carried out by using regression analysis. Consequently, it is shown that the convergence can be modeled as following function C(t) = a[1-exp(-bt)].