• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.192-197
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• 2003

It can be said that rock mass properties are characterized not by a mean value but by values with variation due to its characteristic uncertainty. This characteristic is one of the most important parts for the design of underground structures, but yet to be fully examined. Stochastic finite element method (SFEM) has been developed in order to take the randomness of structural systems into account. Using SFEM, the response variability of structural system can be obtained and it leads probabilistic stability of structure to be analyzed. In this study, displacements response variability of circular opening with hydrostatic stress field are analyzed in terms of rock mass properties having a certain mean and a standard deviation using the SFEM. The analyzed response variability shows that the necessity of probabilistic stability analysis of underground structures using reliable mean value and standard deviation of deformation modulus.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.904-909
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• 2008

Most of current slope safety analysis consider only the effect of the rise of underground water level. However, because the infiltration of surface water into the ground is believed to have signification effect on slope stability, the present study performed slope safety analysis in case of the rise of underground water level, infiltration of surface water, and both resulting from rainfall, and examined their effect.

• Tunnel and Underground Space
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• v.7 no.1
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• pp.58-64
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• 1997

A pilot plant of underground cold storage for food has been excavated as a R&D program. For the stability assessment of underground cold storage opeinengs in shallow jointed rocks, three kinds of stability problems were analyzed by numerical methods. For the analysis of unstability by rock block movements, DEM was used considering the statistical distribution of rock joints. Concerning thermally induced cracking, FDM was used with thermomechanical stress analysis. Finally, in order to evaluate the joint failure during the thawing process, BE algorithm was applied. Numerical examples applied for the pilot plant show that the possibility of unstable failure of opeings exists but can be avoided with proper rock reinforcements provided.

• Earthquakes and Structures
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• v.22 no.3
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• pp.277-287
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• 2022

The ancient underground cities are a collection of self-supporting spaces that have been manually excavated in the soil or rock in the past. Because these structures have a very high cultural value due to their age, the study of their stability under the influence of natural hazards, such as earthquakes, is very important. In this research, while introducing the underground city of Ouyi Nushabad located in the center of Iran as one of the largest man-made underground cities of the old world, the analysis of dynamic stability is performed. For this purpose, the dynamic stress-displacement analysis has been performed through numerical modeling using the finite element software PLAXIS. At this stage, by simulating the Khorgo earthquake as one of the large-scale earthquakes that occurred in Iran, with a magnitude of 6.9 on the Richter scale, dynamic analysis by time history method has been performed on three selected sections of underground spaces. This study shows that the maximum amount of horizontal and vertical dynamic displacement is 12.9 cm and 17.7 cm, respectively, which was obtained in section 2. The comparison of the results shows that by increasing the cross-sectional area of the excavation, especially the distance between the roof and the floor, in addition to increasing the amount of horizontal and vertical dynamic displacement, the obtained maximum acceleration is intensified compared to the mapping acceleration applied to the model floor. Therefore, preventive actions should be taken to stabilize the excavations in order to prevent damage caused by a possible earthquake.

• Geomechanics and Engineering
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• v.33 no.5
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• pp.439-451
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• 2023

The construction of shield tunnelling in urban sites is facing serious risks from complex and changeable underground conditions. Construction problems in the sand-clay mixed ground have been more reported in recent decades for its poor control of soil loss in tunnel face, ground settlement and supporting pressure. Since the limitations of observation methods, the conventional physical modelling experiments normally simplify the tunnelling to a plane strain situation whose results are not reliable in mixed ground cases which exhibit more complicated responses. We propose a new method for the study of the mixed ground tunnel through which mixed lays are simulated with transparent soil surrogates exhibiting different mechanical properties. An experimental framework for the transparent soil modelling of the mixed ground tunnel was established incorporated with the self-developed digital image correlation system (PhotoInfor). To understand better the response of face stability, ground deformation, settlement and supporting phenomenon to tunnelling excavation in the sand-clay mixed ground, a series of case studies were carried out comparing the results from cases subjected to different buried depths and mixed phenomenon. The results indicate that the deformation mode, settlement and supporting phenomenon vary with the mixed phenomenon and buried depth. Moreover, a stratigraphic effect exists that the ground movement around mixed face reveals a notable difference.

• Journal of Korean Tunnelling and Underground Space Association
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• v.15 no.6
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• pp.585-597
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• 2013

In this study, in order to evaluate stability of the room-and-pillar underground structure, a series of preliminary numerical analyses were performed. Design concept and procedure of an underground structure for obtaining a space are proposed, which should be different from structural design for the room-and-pillar in mine. With assumed material properties, a series of numerical analyses were performed by varying size ratios of room and pillar and then the failure modes and location at yielding initiation were investigated. From the results, relationship between the ratio of pillar width to the roof span (w/s) and overburden pressure at failure initiation shows a relatively linear relation, and the effect of w/s on structural stability is much more critical than the ratio of pillar width and height (w/H) which is a crucial parameter in design of the room-and-pillar mining. It means that roof tensile failure and shear failure at shoulder and pillar are necessary to be considered together for confirming overall structural stability of the room-and-pillar structure, rather than considering the pillar stability only in mining. Failure modes and location at failure initiation were varied with respect to the ratio of room and pillar widths. Therefore, it is necessary to simultaneously consider stability of both roof span and pillar for design of underground structure by the room-and-pillar method.

• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.1
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• pp.91-104
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• 2014

An Excavation Damaged Zone (EDZ), in which rock properties are permanently changed due to blasting impact or stress redistribution, can influence the behavior and stability of structures. In this study, the mechanical stability of an underground opening was simulated by using FLAC, which is a two-dimensional modeling code, with a consideration of EDZ. A sensitivity analysis was also carried out with fractional factorial design. From the modeling, it was found that the behavior and the stability of an underground tunnel are strongly dependent on the existence of the EDZ. The sensitivity analysis showed that the key parameters affecting the factor of safety around the tunnel are in-situ stress ratio, depth, cohesion, reduction ratio, internal friction angle, and height and width of the tunnel. It is necessary to consider the EDZ, which can significantly affect mechanical stability in tunnel design.

• Tunnel and Underground Space
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• v.28 no.5
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• pp.457-475
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• 2018

For increase of reality in numerical analysis, a blasting vibration waveform obtained from field blast operations has been directly used for input parameters of dynamic analysis in the form of vibration velocity. A numerical model was built considering the geological characteristics of underground limestone opening as well as the mining stages in this opening, and the effect of blast operations on stability of underground limestone opening was investigated by dynamic numerical analysis. The adequacy of applying the real vibration waveform to dynamic analysis has been approved from the preliminary analysis, and the dynamic numerical analysis results show that the continuous mining operation can cause the collapse of roof in openings and the active yield zone around openings. Therefore, the additional reinforcements should be applied for ensuring the stability of underground limestone openings.

• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.5
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• pp.497-506
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• 2014

In this study, analysis results described in the companion paper was used to determine shapes of room-and-pillar underground structure. To select optimized shapes, structural stability, space applicability and vehicle applicability were considered. In the structural stability step, ratio between strength and stress of the pillar and the critical strain at the roof span were adopted. The space applicability was used to retain the sufficient space of underground structure as its purpose is for human activity. The vehicle applicability was used to consider a radius for rotation of construction equipments in the room-and-pillar underground structure. From the given procedure in this study, proper shapes of rock pillar and room can be selected to design supports at the pillar and roof.

• Journal of the Korean GEO-environmental Society
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• v.15 no.10
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• pp.43-51
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• 2014

Recently, National Emergency Management Agency constructs integrated information system for preventing national earthquake based on underground information. In the past, there are numerous difficulties in construction and management of underground information, because underground information is constructed by each management agency. But a link and application of underground information are available because of government 3.0. This study shows the integrated information system for preventing national earthquake based on real-time link of underground information. The integrated information system for preventing national earthquake developed in this study consists of boring information input modules, underground information search/analysis modules based on V-world tile map, user authority management modules, user management modules and real-time liaison interface modules. Also, this study proposes enhancement plan to construct integrated information system for preventing national earthquake stably and strongly. Stability test conduct on stability of data storage, system stability and consistency of processing speed test results show stability of the integrated information system for preventing national earthquake is high.