• Journal of Korean Society of Disaster and Security
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• v.10 no.1
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• pp.11-17
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• 2017

The case study on ground subsidence was conducted and the cause of ground subsidence was evaluated, main cause were insufficient site exploration, inaccurate strength parameters, defective temporary wall, insufficient reaction for boiling and heaving, excessive excavation and so on. Risk factors during excavation were identified from the cause of ground subsidence and risk factors were site exploration, selecting excavation method, structure analysis, measurement plan, excavation method construction, underground water level change, natural disaster and construction management. The survey of the experts on risk factors identified was conducted to evaluate the importance of risk factors, and confidence analysis was performed to evaluate the significance level between survey result and survey respondent using Chi-square Test.

• Geomechanics and Engineering
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• v.15 no.3
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• pp.851-859
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• 2018

There are two primary causes of the ground movement due to tunnelling in urban areas; firstly the lost ground and secondly the groundwater depression during construction. The groundwater depression was usually not considered as a cause of settlement in previous research works. The main purpose of this study is to analyze the combined effect of these two phenomena on the transverse settlement trough. Centrifuge model tests and numerical analysis were primarily selected as the methodology. The characteristics of settlement trough were analyzed by performing centrifuge model tests where acceleration reached up to 80g condition. Two different types of tunnel models of 180 mm diameter were prepared in order to match the prototype of a large tunnel of 14.4 m diameter. A volume loss model was made to simulate the excavation procedure at different volume loss and a drainage tunnel model was made to simulate the reduction in pore pressure distribution. Numerical analysis was performed using FLAC 2D program in order to analyze the effects of various groundwater depression values on the settlement trough. Unconfined fluid flow condition was selected to develop the phreatic surface and groundwater level on the surface. The settlement troughs obtained in the results were investigated according to the combined effect of excavation and groundwater depression. Subsequently, a new curve is suggested to consider elastic settlement in the modified Gaussian curve. The results show that the effects of groundwater depression are considerable as the settlement trough gets deeper and wider compared to the trough obtained only due to excavation. The relationships of maximum settlement and infection point with the reduced pore pressure at tunnel centerline are also suggested.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.5C
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• pp.239-250
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• 2009

Tunnelling-induced settlements and lateral ground movements have been investigated by numerical parametric studies considering ground condition, excavation characteristics, and ground layers. Before the numerical study the existing methods of ground movement estimation have been collected and analysed to have some information of ground movements and to improve them providing a fundamental material for the numerical study. Numerical model simulation has been performed of a physical model test of tunnel excavation in which the ground movements were measured reliably and the results have been used to determine the numerical approach and the appropriate soil constitutive mode. With this procedure done, the results of numerical parametric studies have been put together to analyze and understand tunnelling-induced settlements and lateral ground movements.

• Geomechanics and Engineering
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• v.16 no.3
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• pp.309-320
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• 2018

In this paper, a numerical study using finite element method with considering soil-structure interaction was conducted to investigate the stress and deformation behavior of a sheet pile wall structure. In numerical model, one of the nonlinear elastic material constitutive models, Duncan-Chang E-v model, is used for describing soil behavior. The hard contact constitutive model is used for simulating the behavior of interface between the sheet pile wall and soil. The construction process of excavation and backfill is simulated by the way of step loading. We also compare the present numerical method with the in-situ test results for verifying the numerical methods. The numerical analysis showed that the soil excavation in the lock chamber has a huge effect on the wall deflection and stress, pile deflection, and anchor force. With the increase of distance between anchored bars, the maximum wall deflection and anchor force increase, while the maximum wall stress decreases. At a low elevation of anchored bar, the maximum wall bending moment decreases, but the maximum wall deflection, pile deflection, and anchor force both increase. The construction procedure with first excavation and then backfill is quite favorable for decreasing pile deflection, wall deflection and stress, and anchor forces.

• Geomechanics and Engineering
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• v.16 no.6
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• pp.577-588
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• 2018

A major concern in deep excavation project in soft clay deposits is the potential for adjacent buildings to be damaged as a result of the associated excessive ground movements. In order to accurately determine the wall deflections using a numerical procedure such as the finite element method, it is critical to use the correct soil parameters such as the stiffness/strength properties. This can be carried out by performing an inverse analysis using the measured wall deflections. This paper firstly presents the results of extensive plane strain finite element analyses of braced diaphragm walls to examine the influence of various parameters such as the excavation geometry, soil properties and wall stiffness on the wall deflections. Based on these results, a multivariate adaptive regression splines (MARS) model was developed for inverse parameter identification of the soil relative stiffness ratio. A second MARS model was also developed for inverse parameter estimation of the wall system stiffness, to enable designers to determine the appropriate wall size during the preliminary design phase. Soil relative stiffness ratios and system stiffness values derived via these two different MARS models were found to compare favourably with a number of field and published records.

• Proceedings of the Korean Geotechical Society Conference
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• 1991.10a
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• pp.152-165
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• 1991

Elasto-plastic and Visco-elastic sytress analyses were conducted for standard cross-section of subway tunnel in Seoul . Considering the procedure of excavation and reinforcement, excavated region was divided to multiple elements. And the progress of tunnel is simulated to be the removal of a series of layerd elements by means of diminishing the stiffness of the portion progressively. Another method is to be free of stress due to excavation instead of stiffness. In the analysis multiple element method was conducted with ADINA program, the stiffness removal method was adopted . For the same model, stress release method was carried out with Visco-Elastic Analysis program developed in Rock mechanics laboratory, Seoul National University(SNU-VBA) . When upper tunnel excavated, displacements in roof were same for two results, but when bottom tunnel removed completely , displacement changes of rock in the stress release method exhibited very small amount compared with stiffness removal method.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.568-569
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• 2011

As an answer for need for minimizing the road excavation of a box type tunnel, a method of vertical snake was developed, which is very economical and easy to construct. The reason why it is good is, the road excavation width, steel accessories, the road occupation space decreases with the technology. The pros and cons of 345kV XLPE $2,500mm^2$ horizontal and vertical snake are listed below. In this study, topics such as 345kV XLPE $2,500mm^2$ vertical snake construction standard and the development process of steel accessories, vertical snake construction procedure will be covered.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.902-911
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• 2009

There appeared many difficulties due to various construction factors during the recent construction adjacent to the housing for the aging. In particular, the study is going to summarize and overview the selection procedure and construction details of the excavation engineering of this site, which could ensure workability and economic efficiency through the construction of a shorter anchor than the length of the existing anchor with a minimal marginal space without invading the nearby private land.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.783-790
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• 2004

In this study, a newly modified soil nailing technology named as the PSN(pretensioned soil nailing) system, is developed to reduce both facing displacements and ground surface settlements in top-down excavation process as well as to increase the global stability. Up to now, the PSN system has been investigated mainly focusing on an establishment of the design procedure. In the present study, the analytical procedure and design technique are proposed to evaluate maximum pretension force and stability of the PSN system. Also proposed arc techniques to determine the required thickness of a shotcrete facing and to estimate probability of a failure against the punching shear. Based on the proposed procedure and technique, effects of the radius of a influence circle and dilatancy angle on the thickness of a shotcrete facing, bonded length and safety factors arc analyzed. In addition, effects of the reduction of deformations expected by pretensioning of the soil nails are examined in detail throughout an illustrative example and $FLAC^{2D}$ program analysis. And a numerical approach is further made to determine a postulated failure surface as well as a minimum safety factor of the proposed PSN system using the shear strength reduction technique with the $FLAC^{2D}$ program. Global minimum safety factors and local safety factors at various excavation stages computed in case of the PSN system arc analyzed throughout comparisons with the results expected in case of the general soil nailing system. The efficiency of the PSN system is also dealt with by analyzing the wall-facing deformations and the adjacent ground surface settlements.

• Korean Journal of Heritage: History & Science
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• v.53 no.3
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• pp.4-23
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• 2020

In this article, the excavation and research of cultural assets were set as a process and the improvement measures were considered. To this end, we examined the process of excavating cultural assets to diagnose problems, suggested changes in the format of reports and the establishment of a database, and drew up improvement models for Silla's ancient tombs and research. The problems of the current process of excavating cultural assets are as follows. First, investigation and research fail to integrate and merely comprise 'examination as an administrative procedure' or 'investigation for the sake of investigation', which ultimately hamper research and achievement. Second, there are differences in the composition or description of the report by surveyors or excavation agencies, which make it difficult to integrate data at a higher level. Third, the current form of reporting remains in analog format such as books and PDFs, which not only reduces continuity and efficiency to the research phase, but also lags behind the rapidly changing times. We believe that the improvement of these problems should be achieved by computerizing reports, converting them into digital formats, and establishing them in a database. First, regarding the transition to report format, it was pointed out that the form of excavation data, the final stage of the excavation process, remains analog and the improvement model was presented from the perspective of linking it to excavation and research, and the justification was emphasized through comparison with other cases. Second, the database reviewed the build model for Silla tombs. To this end, the purpose and expected effects, targets, progress, attributes, categories, and interfaces were examined.