• Structural Engineering and Mechanics
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• v.50 no.3
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• pp.257-273
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• 2014

This paper introduces a novel optimization technique based on gravitational search algorithm (GSA) for numerical optimization and multi-objective optimization of foundation. In the proposed method, a chaotic time varying system is applied into the position updating equation to increase the global exploration ability and accurate local exploitation of the original algorithm. The new algorithm called global-local GSA (GLGSA) is applied for optimization of some well-known mathematical benchmark functions as well as two design examples of spread foundation. In the foundation optimization, two objective functions include total cost and $CO_2$ emissions of the foundation subjected to geotechnical and structural requirements are considered. From environmental point of view, minimization of embedded $CO_2$ emissions that quantifies the total amount of carbon dioxide emissions resulting from the use of materials seems necessary to include in the design criteria. The experimental results demonstrate that, the proposed GLGSA remarkably improves the accuracy, stability and efficiency of the original algorithm.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.10c
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• pp.103-122
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• 2001

For prediction of ground movement per the excavation step, observational results of ground movement during the construction was very different with prediction during the analysis of design. step because of the uncertainty of the numerical analysis modelling, the soil parameter, and the condition of a construction field, etc. however accuratly numerical analysis method was applied. Therefore, the management system through the construction field measurement should be achieved for grasping the situation during the excavation. Until present, the measurement system restricted by ‘Absolute Value Management system’only analyzing the stability of present step was executed. So, it was difficult situation to expect the prediction of ground movement for the next excavation step. In this situation, it was developed that ‘The Management system TOMAS-EXCAV’ consisted of ‘Absolute value management system’ analyzing the stability of present step and ‘Prediction management system’ expecting the ground movement of next excavation step and analyzing the stability of next excavation step by‘Back Analysis’. TOMAS-EXCAV could be applied to all uncertainty of earth retaining structures analysis by connecting ‘Forward analysis program’ and ‘Back analysis program’ and optimizing the main design variables using SQP-MMFD optimization method through measurement results. The application of TOMAS-EXCAV was confirmed that verifed the three earth retaing construction field by back analysis.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.494-503
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• 2010

This paper reviews research trend in suction bucket foundation. Wind energy farm has been considered as an efficient alternative to fuel energy as world markets attempt to discover renewable resources. Recently, Korean government initiated the research projects investigating installation method of offshore wind energy foundation and design guideline as well as verifying feasibility of offshore wind farm. In fact, the installation of monopile and gravity type foundation has been sucessfully carried out in European and other advanced countries, and design guideline of those foundations are well established; however, various types of foundation would be necessary in the near future as offshore wind farm demands abundant wind resources in deep sea. In this paper, bucket foundation is spot lighted as a powerful and economic alternative applicable to deep sea condition.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.569-579
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• 2010

Tolerable vertical displacement of a bridge is dependent on the superstructure-type, slope, span, and etc.. In the design stage, however, resultant force of cross section is examined supposed that the settlement is 1 cm at the bearing point. And the 1cm is sometimes considered as if the criteria of allowable foundation settlement. It is needed to establish the criteria of the tolerable displacement for the small and middle bridges which are widely used in domestic area. The design data of domestic bridges including expressway bridges were collected and analyzed according to the types of superstructures and foundations. And numerical simulations were conducted for RC rigid frame bridges, PSC girder bridges, IPC girder bridges, PSC box girder bridges, and steel box girder bridges to examine the tolerable displacements.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.3-25
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• 2010

The paper deals with two bearing capacity problems of shallow footing under combined loading. The first is a FEM study of shallow strip footing on two-layer clay deposits subjected to a vertical, horizontal and moment combined loading, while the second is a centrifuge study of shallow rectangular footing on dry sand under double eccentricity. The FEM results revealed that the existence of top soft layer sensitively affects more on horizontal and moment capacity than vertical capacity for cases of footing on soft clay overlying stiff clay. Practical design charts are presented to evaluate bearing capacities of footing for various combinations of the ratio of the depth of the upper layer to the footing width and the ratio of undrained strength of the upper layer to that of the lower. The centrifuge tests indicated that current design practice of calculating failure load of rectangular surface footing under double eccentricity underestimates the centrifuge loading test data. This trend is more marked when the eccentricity becomes larger. The decreasing trend in failure load with an increase of double eccentricity is rather uniquely expressed by a single curve, using a newly defined resultant eccentricity and the diagonal length of the footing base.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.1314-1321
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• 2010

The west express way which links south west area of the central city of Seoul has been notorious for extremely heavy traffics since its first opening in 1991(i.e. the average vehicle speed is less than 25km/h, a daily traffic is 112,000 and among them, more than 94% of the vehicles are the light vehicles). The city government recently initiated a new BTO(Build-Transfer-Operate) project as an alternative in releasing heavy traffic and a high construction cost. The proposed underground express road is the first double-level tunnel (i.e. a total length of road is 10,91km and the tunnel is 9.308km long) ever built in South Korea, while such tunnel system is not new worldwide as such A86 East tunnel in France, SMART tunnel in Malaysia, and Fuxing tunnel in China. This paper discusses major design issues regarding the internal structures such as deck slab, and secondary liner.

• Tunnel and Underground Space
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• v.7 no.3
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• pp.191-201
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• 1997

Geological and geotechnical surveys, in general, should precede the excavation to ensure the safety of the tunnel and should be followed up according to the various geological condition during the excavation. However actually the standard support patterns which were decided during the design step used be insisted for the whole excavation steps in spite of the various geological conditions. OO tunnel was excavated with NATM and a support pattern type-V in weak rocks. When the tunnel was excavated up to 25m long, the severe displacement was generated in the portal area and the shotcrete was damaged to make the cracks and the tunnel face was totally collapsed. It might happen owing to the one-day heavy rain, but the exact reason for that accident should be found out and the new optimal support patternt needed. Consequently three dimensional numerical analysis was applied for the evaluation of the cause of the tunnel collapse instead of two dimensional analysis, because three dimensional analysis can show better the real field phenomenon than two dimensional analysis in which the load distribution methods are adopted for the tunnel excavation. We could simulate the actual situations with three dimensional finite difference code and propose the new optimal support patterns.

• Earthquakes and Structures
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• v.19 no.2
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• pp.145-156
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• 2020

The 24 January 2020 (Mw=6.8) earthquake with epicentre in Elazığ (Sivrice) on the East Anatolian Fault Zone caused loss of life and property. The information was given about the seismotectonic setting and regional seismicity along this fault zone and aftershock activity and ground motion data of this earthquake. Earthquake parameters were obtained for five different earthquake stations which were closer to the epicentre. Horizontal and vertical design spectra were obtained for the geographic locations for each earthquake station. The obtained spectra for the earthquake epicentre were compared with selected appropriate attenuation relationships. The damages after earthquake were evaluated via geotechnical and structural aspects. This study also aims to investigate the cause-effect relationships between structural damage in reinforced-concrete and masonry structures, respectively. The lack of engineering services was effective on the amount of damage in masonry structures. Insufficient reinforcement and concrete strength, dimensions and inadequate detailing increased the amount of damage in reinforced-concrete structures. Importance should be given to negative parameters that may weaken the defence mechanisms of structures for earthquake-resistant structural design.

• Structural Engineering and Mechanics
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• v.58 no.2
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• pp.259-276
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• 2016

Lead-rubber bearings (LRBs) have been used worldwide in seismic design of buildings and bridges owing to their stable mechanical properties and good isolation effect. We have investigated the effectiveness of LRBs in framed underground structures on controlling structural seismic responses. Nonlinear dynamic time history analyses were carried out on the well-documented Daikai Station, which collapsed during the 1995 Hyogoken-Nanbu earthquake. Influences of strength ratio (ratio of yield strength of LRBs to yield strength of central column) and shear modulus of rubber on structural seismic responses were studied. As a displacement-based passive energy dissipation device, LRBs reduce dynamic internal forces of framed underground structures and improve their seismic performance. An optimal range of strength ratios was proposed for the case presented. Within this range, LRBs can dissipate maximum input earthquake energy. The maximum shear and moment of the central column can achieve more than 50% reduction, whereas the maximum shear displacement of LRBs is acceptable.

• Journal of Industrial Technology
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• v.28 no.B
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• pp.111-116
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• 2008

Since the hydraulic fracturing field testing method was introduced first to Korean geotechnical engineers in 1994, there have been lots of progresses in a hardware system as well as an interpretation tool. The hydrofracturing system of first generation was the pipe-line type, and it has been developed to a wire-line system at their second generation. The current up-to-date system is more compact and is able to be operated by all-in-one system. With a progress in a hardware system, the software for analyzing in-situ stress regime has also been progressed. The shut-in pressure, which is the most ambiguous parameter to be obtained from hydrofracturing pressure curves, can now be acquired automatically from the various methods. While the hardware and software for hydrofracturing tests are being developed during the last decade, the author could accumulate the field test results which can cover the almost whole area of South Korea. Currently these field data are used widely in a feasibility study or a preliminary design step for tunnel construction in Korea. Regarding the difficulties in a site selection and a test performance for the in-situ stress measurement at an off-shore area, the in-situ stress regime obtained from the field experiences in the land area can be used indirectly for the design of a sub-sea tunnel. From the hydrofracturing stress measurements, the trend of magnitude and direction of in-situ stress field was shown identically with the geological information in Korea.