• Journal of the Korean Geotechnical Society
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• v.15 no.4
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• pp.43-56
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• 1999

The use of berms can be an effective method to restrain excessive movements of wall and ground caused by deep excavations in urban area. But generally in construction sites, no berm remains for the sake of construction convenience or the geometry and magnitude of remaining berm is determined by individual experiences due to scarce research results. In this research, laboratory model tests and numerical analyses are used mainly for sandy soils. And efficient berms for restraining excessive movements by deep excavations are analyzed. Model tests were performed for the cases of cantilever and braced wall excavations, and the behaviors of retaining wall were analyzed according to the geometry and magnitude of berms. And also, numerical methods were used for analyzing efficient berms which are available in the soil and construction conditions in urban areas of Korea.

• Tunnel and Underground Space
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• v.34 no.4
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• pp.413-420
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• 2024

When planning gripper TBM, which is highly applicable to urban areas, the excavation characteristics are not considered. In addition the excavation stability and constructability are degraded by installing reinforcements in the adjacent construction site considering the relaxation load theory of the pre-existing NATM. In this study, a rationalization plan for the support was proposed considering the excavation characteristics of gripper TBM when planning reinforcements for adjacent pre-existing construction. The effect of excavation on the surrounding ground was analyzed by conducting three-dimensional stability analyses considering the construction stage for each excavation phase. In NATM, relaxation phenomenon is concentrated in tunnel face due to non-supporting time occurring simultaneously with excavation, but gripper TBM supports the ground around the tunnel face through the cutter head and skin plate, simultaneously causing ground relaxation behind the skin plate. Considering these excavation characteristics, problems in reinforcement planning for adjacent construction at the study site were pointed out. A performance improvement plan for a reasonable supporting system was proposed.

• Journal of the Korean Geosynthetics Society
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• v.12 no.3
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• pp.43-53
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• 2013

In this study, an analysis about the causes of different types of excavation on accidents is required in order to prevent the frequently occurring accidents related to the earth retaining structure and excavation. Also, analysis of influence was performed by using numerical typical soil conditions and construction trend using numerical analysis method. According to the analysis results of 25 accident cases, the main influence factors were found as following: insufficient of soil survey, instability of temporary facility and lack of groundwater treatment, etc. Furthermore, in the numerical analysis result of 22 cases, drainage method was occurred larger settlement than waterproof method in the Inland. In case of applying the earth anchor method, it needs more detailed in the regions, which are discovered soft ground or rock discontinuities. Also, The consolidated clay absolutely needs further consideration of excess hydrostatic pressure.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.2
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• pp.129-144
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• 2010

The earth pressure acting on the vertical shaft is less than that acting on the retaining wall due to three dimensional arching effect. Thus, it might be essential to estimate the earth pressure actually acting on the shaft when designing the vertical shaft. In this paper, large-sized model tests were conducted as Part II of companion papers to verify the newly suggested earth pressure equation proposed by Kim et al. (2009: Part I of companion papers) that can be used when designing the vertical shaft in cohesionless soils as well as in c-$\phi$ soils and multi-layered soils. The newly developed model test apparatus was designed to be able to simulate staged shaft excavation. Model tests were performed by varying the radius of vertical shaft in dry soil. Moreover, tests on c-$\phi$ soils and on multi-layered soils were also performed; in order to induce apparent cohesion to the cohesionless soil, we add some water to the dry soil to make the soil partially-saturated before depositing by raining method. Experimental results showed a load transfer from excavated ground to non-excavated zone below dredging level due to arching effect when simulating staged excavation. It was also found that measured earth pressure was far smaller than estimated if excavation is done at once; the final earth pressure measured after performing staged excavation was larger and matched with that estimated from the newly proposed equation. Measured results in c-$\phi$ soils and in multi-layered soils showed reduction in earth pressures due to apparent cohesion effect and showed good matches with analytical results.

• Journal of the Korean Geotechnical Society
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• v.26 no.7
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• pp.171-186
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• 2010

It is generally known that the mechanism of behavior in the flexible earth retaining system is relatively more complicated than in the rigid earth retaining system. Moreover in the case of long span strut supporting system the analysis of strut axial force change becomes more difficult when the differences of ground condition and excavation work progress on both sides of excavation section are added. When deeper excavation than the specification or installation delay of supporting system or change of ground condition happen during construction process, lots of axial force can be induced in some struts, which threaten the safety of construction. This paper introduces two examples of long span deep excavation where struts and rock bolts were used as a supporting system with flexible wall structure. The characteristics of ground deformation and strut axial force change, which were measured in the sections of two examples that are 50 meters apart in one construction site and have almost similar design and construction conditions were analysed, the similarity and difference between measurement results of two examples were compared and investigated. This article aims to improve and develop the technique of design and construction in future projects having similar ground condition and supporting method.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.1
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• pp.183-195
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• 2018

Recently, the need for research on vertical shaft excavation is increasing with the increase of the demands for the underground and utility tunnels. As a part of the R&D project of the Ministry of Land, Infrastructure and Transport, CUT (center for utility tunnel) has developed "Ring cut method". "Ring cut method" is a method to improve the stability of the ground against the basal heave by excavator wall pre-penetration during vertical shaft excavation. In this study, the basal heave was simulated by centrifugal model test. The basal heave, ground subsidence, and ground deformation of surrounding ground were analyzed by soil plug effect from wall pre-penetration. It was found that the soil plug could control the basal heaving and ground subsidence, and verified that the 'Ring cut method' could be a good countermeasure for the ground stability against the basal heave.

• Journal of the Korean GEO-environmental Society
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• v.16 no.2
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• pp.27-31
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• 2015

In urban area, many design projects related to geotechnical projects are controlled by serviceability rather than stability requirements. Accordingly, control of ground deformation has become more crucial and many researchers have studied soil stiffness. Recent experimental studies on the stress-strain response of Chicago glacial clays showed that the nonlinearity and anisotropy are the two key factors in evaluating the soil stiffness. In this study, experimental results are applied to analyze the deep excavation site locating in downtown Chicago. The stress paths observed from the observation points located behind and front of the supporting wall yield typical stress paths. Changes in soil stiffness nonlinearity and anisotropy were discussed by comparing experimental and computed stress paths. The stiffness anisotropy were significant even at the first few excavations. The stiffness degradation characteristics are significantly different according to relative location to the support wall even at the same elevation.

• Journal of Korean Tunnelling and Underground Space Association
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• v.26 no.1
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• pp.1-17
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• 2024

Analyzing the tunnel excavation behavior and its effect on the surrounding ground involves large deformation behavior. Therefore, in order to properly simulate the tunnel excavation process and rigorously investigate the actual effect of excavation on surrounding ground and tunnel structure large deformation analysis method is required. In this study, two major numerical approaches capable of considering large deformations behavior were applied to investigate the effect of tunnel boring machine excavation on the surrounding ground: coupled Eulerian-Lagrangian (CEL) and the automatic remeshing (AR) method. Relative performance of both approaches was evaluated through the ground response due to TBM excavation. The ground response will be quantified by estimating the range of the excavation damaged zone (EDZ). By comparing the results, the range of the EDZ will be suggested on the vertical and horizontal direction along the TBM excavation surface. Based on the computed results, it was found that the size of EDZ around the excavation surface and the tendencies was in good agreement among the two approaches. Numerical results clearly show that the size of the EDZ around the tunnel tends to be larger for rock with higher RMR rating. The size of the EDZ is found to be direct proportional to the tunnel diameter, whereas the depth of the tunnel is inversely proportional due to higher confinement stress around the excavation surface.

• Journal of the Korean Geotechnical Society
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• v.15 no.5
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• pp.111-124
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• 1999

When deep excavation adjacent to an existing structure is performed, it is very important to minimize damage on the structure through the prediction of ground movement. In this paper, finite element analysis was performed to predict the ground movement, based on the data from site investigation and laboratory tests, when deep excavation close to a buried water tank was carried out in soft clay ground. The movement and stabilities of the soil-cement wall(SCW) and the adjacent structure were checked using the results of the analysis and the field measurement. The comparison between the measured and the predicted ground movements showed the significance of the excavation procedure and lowering of water level in the analytical model. In the future, it is needed to improve the prediction method for better estimation of the ground movement.

• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.6
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• pp.559-575
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• 2021

Due to the increase in ground excavation work, the possibility of ground subsidence accidents is increasing. And it is very difficult to prevent these risk fundamentally through institutional reinforcement such as the special law for underground safety management. As for the various cases of urban ground excavation practice, the ground subsidence behavior characteristics which is predicted using various information before excavation showed a considerable difference that could not be ignored compared to the results real construction data. Changes in site conditions such as seasonal differences in design and construction period, changes in construction methods depending on the site conditions and long-term construction suspension due to various reasons could be considered as the main causes. As the countermeasures, the safety management system through various construction information is introduced, but there is still no suitable system which can predict the effect of excavation and risk assessment. In this study, a web-based system was developed in order to predict the degree of impact on the ground subsidence and surrounding structures in advance before ground excavation and evaluate the risk in the design and construction of urban ground excavation projects. A system was built using time series analysis technique that can predict the current and future behavior characteristics such as ground water level and settlement based on past field construction records with field monitoring data. It was presented as a geotechnical data visualization (GDV) technology for risk reduction and disaster management based on web-based system, Using this newly developed web-based assessment system, it is possible to predict ground excavation impact prediction and risk assessment.