• Tunnel and Underground Space
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• v.18 no.4
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• pp.243-251
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• 2008

Recently, the mining methods are changing from surface mining to underground mining because of the increment of the environmental issues and legal regulations. Therefore, the stability of underground openings is a major concern for the safety and productivity of mining operations. In this paper, a survey of structural geology and discontinuities were carried out at a limestone mine. The relevant mechanical properties of rocks were determined by the laboratory tests and rock mass classifications (RMR and Q-system) for the mine design and input data for the stability analysis. The dimensions of unsupported span for underground openings and pillar were decided based on the RMR values of rock mass classifications. The stability analysis for the suggested mine design was examined through the empirical methods (stability graph method and critical span curve) and 3-D numerical analysis (Visual-FEA).

• Tunnel and Underground Space
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• v.19 no.6
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• pp.498-506
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• 2009

The stability assessment of a concrete liner of a compressed air storage tunnel should be performed by an approach which is different from that commonly used for the liners of road tunnels, since the liner is exposed to high air pressure. In this study, the stability analysis method for the liner of compressed air storage tunnel is proposed based on the elastic and elasto-plastic solutions of the thick-walled cylinder problem. In case of elastic analysis, the yield initiation condition at the inner boundary is considered as the failure condition of the liner, while the condition which results in the extension of yielding zone to a certain depth is taken as a failure indicator of the liner in the elasto-plastic analysis taking Mohr-Coulomb criterion. The application of the proposed method revealed that the influence of the relative magnitude of boundary loads on the stability of liner is considerable. In particular, noting that the estimation of the outer boundary load may be relatively difficult, it is thought that the precise prediction of outer boundary load is very important in the analysis. Accordingly, the emphasis is put on the selection of the liner installation time, which may govern the magnitude of outer boundary load.

• Journal of Korean Tunnelling and Underground Space Association
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• v.15 no.5
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• pp.483-496
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• 2013

This paper presents the shield TBM technology in soft ground tunnelling. In order to perform this study, a scale model test was carried out using the developed small scaled shield TBM machine. The various instrumentations were conducted during the simulation of tunnelling. In addition, the ground behavior due to the shield TBM operation parameters was measured during the simulation. Based on the simulation results, the stability of the ground was evaluated and the fundamental shield TBM tunnelling technique in the soft ground was suggested. In conclusion, design's reliability through laboratory small scale model test about Shield-TBM section was obtained, and both the improvement plan for safety during construction and the construction plan for securing airport runway's safety during tunnel passing by Shield-TBM propulsion were suggested.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.24 no.3
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• pp.251-259
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• 2006

For the electrification of the existing railways, the security of the restriction boundary of building with mechanistic stability research on the antiquated tunnel must be accomplished essentially. If the tunnel don't secure its restriction boundary of building, the reconstruction based on improvement of tunnel alignment are generated and its surveying data are required. The precise surveying was conducted with the same coordinate system for three tunnels of Youngdong tramline, and the restriction boundary of building of the straight and curve section were analyzed effectively by acquiring the data of profile and cross section, profile rail-height, rail-grade, cross tunnel height, and restriction boundary of building. This study is presented for valuation data of the stability of the electrification design to construct and analyze restriction boundary of building, which compared with the drawing and its existing design using profile and cross section. After this, it is interoperable to increase the development of real-time monitoring system on the tunnel structures.

• Journal of Korean Tunnelling and Underground Space Association
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• v.10 no.1
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• pp.91-104
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• 2008

In tunnels, safety factor concept has been suggested to estimate their stability quantitatively. It is merely limited in the framework of mechanical analysis. However safety factor concept has not been applied in hydro-mechanical coupled analyses due to their modelling complexity. Recently studies on this topic are being actively made. In this study, induced drainage modelling methods for hydro-mechanical coupled analyses are compared and analyzed to estimate safety factor of a subsea tunnel exactly. To this end, methods both controlling hydraulic characteristic of shotcrete and using a drainage well are considered. Sensitivity analysis were carried out on rock class, thickness of shotcrete, and hydraulic properties of rock mass. As the results of this study, it turned out that the induced drainage modelling using a drainage well would give more reliable results than that of controlling hydraulic characteristic of shotcrete in estimating tunnel stability in hydro-mechanical coupled analyses.

• Tunnel and Underground Space
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• v.22 no.5
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• pp.297-309
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• 2012

The stability assessment of abandoned gangway for the purpose of services was performed. Among the many factors that affect the stability of openings, the span of the opening in a given rock mass condition provides an important element of design. In this paper, the stability of gangway was assessed by the critical span curves proposed by Lang, the modified Mathews'stability graph method and using support measures of the Q system. In the evaluation of stability as a whole the gangway is considered as stable. But the rockfalls of wedge-shaped blocks were expected in the area in which the horizontal joints of low angle appear. The support measures such as local rock bolts are required to use for commercial purposes of the abandoned gangway. And entrance section may require the particular attention as unstable section. Since there are so many spalling due to bad blasting in the roof and sidewall of gangway, the scaling operations should be followed primarily.

• Tunnel and Underground Space
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• v.17 no.6
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• pp.503-510
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• 2007

Rock classification schemes such as RMR, Q-system were applied to investigate the stability of large-scale gangways mined in a limestone mine. 22 areas for engineering geological surveys were selected and rock classifications at each survey point had been carried out. Considering the fact that the observed gangways have not experienced some severe failure and have been stably maintained till now, it is found that Q-system is more reasonable than RMR in evaluating the stability of unsupported span. Also, extended Mathews stability graph method which is a kind of revised Q-system was used to assess the stability of gangways and the results represent that all gangways except for one area are under stable condition. Based on above the mentioned results, the empirical equations to design the maximum unsupported span and critical height of a large-scale gangway are suggested.

• Journal of Korean Tunnelling and Underground Space Association
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• v.5 no.2
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• pp.135-146
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• 2003

This paper presents the effect of ground vibration induced by vibrohammer and RCD on adjancent subway tunnel performance using FDM program. Firstly, the stability criteria for structures near vibration source were proposed according to existing data, then peak particle velocity around tunnel was estimated based on detailed information of vibrohammer and existing formula for dynamic loads through numerical analysis. The peak particle velocity induced by RCD bit rotation was also estimated using surveyed data and formula. Consequently, displacement and stress responses were obtained at crown, shoulder and spring line and compared with the criteria to check stability of tunnel.

• Journal of the Korean GEO-environmental Society
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• v.11 no.8
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• pp.49-55
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• 2010

Safety estimation of the pillar between parallel tunnels are very important considering stress concentration in case the piller width is not enough to secure the stability. Pillar width needs to be determined properly because of the progressive failure-risk of pillar due to stress-concentration. In this research, the effect of element size in numerical analysis was evaluated based on that yield pillar's stability and proposed systematic analysis about pilar's stability examination. In consequence of it, element size does not give any effect on intensity stress ratio. On the other hand, the analysis using the smaller element size results in lower safety factor in strength reduction technique. In case of the weathered re.k on the main ground layer, the analysis of result was not reliable. In conclusion, the smaller element size is, the more stable factor is.

• Journal of Korean Tunnelling and Underground Space Association
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• v.25 no.1
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• pp.1-11
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• 2023

In this study, the stability of the room-and-pillar underground method was investigated using numerical analysis method. In-situ geotechnical investigation was conducted, and a supporting pattern was selected based on the geotechnical investigation data. For the supporting pattern, Type-1, 2, 3 were selected for each ground condition. A 3D numerical analysis model was developed for effective simulation as the room-and-pillar underground method consist of a pillar and room. As a review of numerical analysis, it was confirmed that the crown settlement, convergence, shotcrete and rock bolt were all stable in all supporting patterns. As a result of the analysis by the construction stage, it was confirmed that excessive stress was generated in the room when the construction stage of forming pillar. So, precise construction is required during the actual construction stage of the pillar formation.