• Geotechnical Engineering
• /
• v.10 no.2
• /
• pp.41-56
• /
• 1994

Under the groundwater level, the tunnel face is affected by the seepage force and the groundwater flow may cause a trouble to the tunnel support systems. The appropriate methods of analysis and design in the tunnel face and the lining, considering groundwater flow according to tunnel drainage condition are presented in this thesis. First, the effect of seepage on the stability of tunnel face was studied. Seepage force was estimated by the 3-D finite element analysis and the stability of tunnel face was checked by analytical method. Furthermore, using the finite difference method the stress and displacement on the face were computed for either case, where the seepage force is or is not considered, and the effect of seepage on the tunnel face stability was evaluated. Second, the effect of seepage force on the tunnel lining when construction is finished and steady state seepage flow occurs was studied and a design methodology considering seepage effect was made. Consequently, in case where the groundwater level remains almost unchanged and the steady state groundwater flow occurs, the proper countermeasures for face staility are required according to the condition of groundwater flow. Moreover, the tunnel lining should be designed and constructed considering the seepage force occuring by the groundwater flow toward the tunnel linings.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.22 no.6
• /
• pp.617-625
• /
• 2009

This study is devoted to the problems of thermal and autogenous expansion stresses in order to avoid cracking using chemically prestressing method. The chemical prestress can be induced by autogenous expansion characteristics of MgO concrete made in specific burning temperature. The volume change induced cracking has great influence on the long-term durability and serviceability. To evaluate risk of cracking, the computer programs for analysis of thermal and autogenous expansion stresses were developed. In these 3-D finite element procedures, long-term autogenous expansive deformation is modeled and its resultant stress is calculated and then verified by comparison with manual calculation results. In this study, the stress development is related to thermal and autogenous expansive deformation. Using the developed program, residual stresses of MgO concrete were compared and analysed in the example From the numerical results it is found that long-term, and temperature dependent expansive concrete with light-burnt MgO is most effective in controlling the risk of cracking of mass concrete because it has high temperature for long period. The developed analysis program can be efficiently utilized as a useful tool to evaluate the thermal and autogenous expansion stresses in mass concrete structures with lightly burnt MgO.

• Journal of the Korean Geotechnical Society
• /
• v.19 no.6
• /
• pp.189-206
• /
• 2003

During tunnel excavation in urban area a systematic monitoring is important for the purpose of determination of support type and quantity, as well as for the control of stability of both surface structures and the tunnel itself due to the frequently, and in many cases, abruptly changing ground condition. In Austria absolute displacement monitoring methods have replaced relative displacement measurements by geodetic methods to a large extent. Prompt detection of weak ground ahead of the tunnel face as well as better adjustment of excavation and support to the geotechnical conditions is possible with the help of the improved methods of data evaluation on sites. Deformation response of the ground to excavation starts ahead of the tunnel face, therefore, the deformation and state of the tunnel advance core is the key factor of the whole deformation process after excavation. In other words, the rigidity and state of the advance core play a determining role in the stability of both surface structures and the tunnel itself. This paper presents the results from detailed three-dimensional numerical studies, exploring vertical displacements, vector orientations and extrusions on tunnel face during the progressive advancement for the shallow tunnel in various geotechnical conditions.

• Tunnel and Underground Space
• /
• v.22 no.5
• /
• pp.310-320
• /
• 2012

This paper describes the design and construction of a 2-arch tunnel with varying section. This new design has advantages of 2-arch tunnels, which is rather expensive, but is still economically competitive compared to parallel tunnels. Economic analysis was also conducted. To secure the stability of the varying section tunnel, excavated part was reinforced by tie-bolts and RRS, and 2-arch part was supported by EPS blocks and concrete walls. Stability of the pillar was theoretically analyzed and also examined by numerical simulations for various widths. Displacement monitoring was conducted and results were compared with numerical results. Economic analysis showed reductions in construction cost and period by 11% and 10 months respectively.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.26 no.1A
• /
• pp.55-65
• /
• 2006

This paper presents the closing analysis of a symmetric steel cable-stayed bridge erected by a free cantilever method. Two independent structural systems are formed before the closing procedure of a bridge is performed, and thus the compatibility conditions for vertical displacement and rotational angle are not satisfied at the closing section without the application of proper sectional forces. Since, however, it is usually impossible to apply sectional forces at the closing section, the compatibility conditions should be satisfied by proper external forces that can be actually applicable to a bridge. Unstrained lengths of selected cables and the pull-up force of a derrick crane are adjusted to satisfy nonlinear compatibility conditions, which are solved iteratively by the Newton-Raphson method. Cable members are modeled by the elastic catenary cable elements, and towers and main girders are discretized by linear 3-D frame elements. The sensitivities of displacement with respect to the unstrained lengths of selected cables and the pull-up force of the derrick crane are evaluated by the direct differentiation of the equilibrium equation. A Monte-Carlo simulation approach is proposed to estimate expected construction errors for a given confidence level. The proposed method is applied to the second Jindo Grand Bridge to demonstrate its validity and effectiveness.

• Journal of Korean Society of Steel Construction
• /
• v.16 no.4 s.71
• /
• pp.407-414
• /
• 2004

Bridges in common use are expected to have more varieties of load in their connected members and bolts than in construction. Faults in connection members or bolts occur so often according to the time flow. One of the purposes of this study is to find out the behavior and structural features of high-tension bolted joints with faults that are very difficult and cost much to find out through experimentation with finite element analysis. Another purpose of this study is to provide sufficient data, estimated experimental results, and the scheme of the test plate for an economical experimental study in the future. Surveys of bridges with a variety of faults and statistical classifications of their faults were performed, as was a finite element analysis of the internal stress and the sliding behavior of standard and defective bridge models. The finite element analysis of the internal stress was performed according to the interval of the bolt, the thickness of the plate, the distance of the edge, the diameter of the bolt, and the expansion of the construction. Furthermore, the analysis explained the sliding behavior of high-tension bolt joints and showed the geometric non-linear against the large deformation, and the boundary non-linear against the non-linear in the contact surface, including the material non-linear, to best explain the exceeding of the yield stress by sliding. A normally bolted high-tension bolt joint and deduction of bolt tension were also analyzed with the finite element analysis of bridge-sliding behavior.

• Journal of Korea Water Resources Association
• /
• v.36 no.1
• /
• pp.129-142
• /
• 2003

In this study, the conduct of underground water flow system with 3 dimensions is interpreted in order to examine closely the actual condition regarding the flow of the underground water which is forecast from the tunnel segment and the interpretation result which selects the design and the construction technique of the tunnel segment was applied. Also, an obstacle to construct that relates with the underground water flow in construction duration in advance will be able to apply with information that is necessary in order to establish the countermeasure. The objective tunnel is the BEOPGI tunnel segment that is 2 parallel tunnels that are a one-way 2 lane and the parameters of the MODFLOW model executing the boring investigation and the permeability examination were presumed. The underground water flow of the excavation tunnel inside was interpreted by the MODFLOW model using the parameters which is presumed and two values which compared with calculated value and observed value are the same almost. Also, when the underground water discharge quantify that followed in tunnel excavation tries to compare, the underground water total discharge quantity from tunnel point of start until destination was presumed as 0.0269㎥/day/$m^2$.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.10
• /
• pp.640-647
• /
• 2018

Many harbor structures have been constructed, and some structures are now under construction in Korea, which is a peninsular state and a logistics hub in Northeast Asia. Expansions and extensions of existing harbors are also being planned to meet increasing natural disaster threats. Wave-dissipation concrete blocks are recycled or discarded based on the personal experience of engineers only, and there are no safety checks or criteria. To check the safety of used blocks, material evaluations were done by visual inspection of blocks on the ground and under water and from 20 non-destructive measurements of the rebound hardness test and 3 concrete core samples. Wave-dissipation blocks are sometimes fully or partially damaged in the process of transferring and mounting them or during construction. Therefore, a safety check is essential for recycling blocks with an evaluation of materials while considering the construction phases. To do this, a block was modeled with a 3D finite element method using ADINA, and impact analyses were done according to the transfer, mounting, and construction phases. From the results of the impact analyses and material evaluation, the safety checks and reasonable evaluation of used blocks were examined, and detailed construction methods are proposed. The methods are expected to maximize the reuse of used wave-dissipation blocks from an economical point of view.

• Journal of the Korean Geotechnical Society
• /
• v.19 no.2
• /
• pp.39-48
• /
• 2003

Previous analytical models for key blocks have been based on the assumption of infinite persistent discontinuities. In this paper, a key block analysis method considering the finite persistence of discontinuities is proposed as a stability evaluation method in tunnel constructions, and then applied to an actual example site. Three-dimensional rock block identification with consideration of the persistence of discontinuities is performed by using discontinuity disk model. The removability and stability analyses of rock blocks formed by the identification method are performed. The identification method can handle convex and concave shape blocks. In order to demonstrate the applicability of this developed numerical method to the stability evaluation in tunnel constructions, the analytical results are examined and compared one another.

• Journal of the Korean Geotechnical Society
• /
• v.19 no.5
• /
• pp.109-122
• /
• 2003

In order to release the pressure fluctuations and micro-pressure wave induced by the entering of train into the small cross sectional tunnel, it has been reported that the construction of air shaft has more advantages with respect to economy and constructability than the enlargement of cross section of existing tunnel. The field monitorings and analytical studies were conducted simultaneously in this study to analyze the mechanical behavior of existing railway tunnel, new cross tunnel and new shaft by the construction of new shaft nearby. The results showed that the minimum distance from existing tunnel to new shaft which secures the stability of existing tunnel was found to be half diameter of existing tunnel. On the three dimensional mechanical behavior of existing tunnel by the construction of new shaft, the results from the analytical study and field monitoring had a similar trend. The analytical study and field monitoring results, however, produced somewhat different results on the mechanical behavior of new shaft itself. These conclusions induce that the analytical method which has been applied on the analyses of horizontal tunnel could not be applied in the same way on the analysis of vertical shaft.