• Tunnel and Underground Space
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• v.17 no.2 s.67
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• pp.90-101
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• 2007

With increasing development of underground space, underground pumped storage power plants, which generate power by felling water in upper reservoir to lower reservoir, have been continuously constructed. For efficient and safe design, construction and maintenance or such power plants, it is very important to understand in-situ stress and the mechanical properties of the surrounding rock mass at the design stage. The power plant presented in this paper is under construction at a depth of $320{\sim}375m$. For stability evaluation of the structure, in-situ stress was measured by over-coring method. Also pressurementer test and a series or laboratory tests were performed to obtain the mechanical properties. Numerical analyses were conducted to check the efficiency of designed support patterns. The results showed that unstable areas occurred partly in the numerical model, and therefore supports were additionally applied. Finally complete stability was obtained and the following excavation has been operated successfully until now.

• Journal of the Korean Geosynthetics Society
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• v.18 no.1
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• pp.55-65
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• 2019

This paper describes results of experimental and numerical analyses, in order to analyze a reinforcement effect of concrete mat on open cut restoration of underground cavity. The plate loading tests were conducted to evaluate a reinforcement effect of concrete mat, at reinforcement depths from the ground surface of 10 cm, 20 cm, and 30 cm. The result showed that the reduction ratio of stress (earth pressure) was about 60% at all reinforcement depth. The reinforcement effect considering ground surface settlement and reduction ratio of stress based on laboratory tests and numerical analysis was significant, at reinforcement depths from the ground surface of 10 cm~20 cm. LFWD test results showed that subgrade modulus was the largest when concrete mat was installed 20 cm below ground surface. Therefore, it is effective to reinforce concrete mat within 20 cm from the surface, when the underground cavity due to damage of underground utilities was formed in the height direction to the bottom of the pavement layer.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.1
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• pp.155-166
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• 2019

It is necessary to construct underground in the metropolis. Road traffic has reached saturation point. The city has several underground road construction projects. In abroad, double deck tunnels are planned and constructed. It is attained a high level of underground development technology. In case the double deck tunnel (2 lane) is planed instead of the bidirectional tunnel (2 lane), excavation area is similar. But tunnel width is decreased. The reduced width can cut cost for the tunnel reinforcement. This study evaluates the stability of excavation on double deck tunnel. By the assessment of the strength-stress ratio and strength reduction method, quantitative analysis is conducted between double deck tunnel and the bidirectional tunnel.

• 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.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1845-1850
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• 2003

The underground utility tunnels are important facility as a mainstay of country because of communication developments. The communication and electrical duct banks as well as various utility lines for urban life are installed in the underground utility tunnel systems. If a fire breaks out in this life-line tunnel, the function of the city will be discontinued and the huge damages are occurred. In order to improve the safety of life-line tunnel systems and the fire detection, the behaviors of the fire-induced smoke flow and temperature distribution are investigated. In this study we assumed that the fire is occurred at the contact or connection points of cable. Numerical calculations are carried out using different velocity of ventilation in utility tunnel. The fire source is modeled as a volumetric heat source. Three-dimensional flow and thermal characteristics in the underground tunnel are solved by means of FVM (Finite Volume Method) using SIMPLE algorithm and standard ${\kappa}-{\varepsilon}$ model for Reynolds stress terms. The numerical results of the fire-induced flow characteristics in an underground utility tunnel with different velocity of ventilation are graphically prepared and discussed.

• 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.

• Journal of Korean Tunnelling and Underground Space Association
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• v.3 no.1
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• pp.51-62
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• 2001

In-situ stress measurement using AE (Acoustic Emission) and DRA (Deformation Rate Analysis) is usually carried out under uniaxial loading in the laboratory and it consumes delay time from drilling to testing. Therefore, it should be considered how the lateral stress and delay time influence on the test results for the in-situ stress determination. As the delay time increased, the accuracy of estimating the pre-stress decreased. The pre-stress of the specimen loaded only axially was determined within an error of less than 9% (using AE) and 4% (using DRA). And the specimen on which axial pre-stress and the confining pressure were loaded had an error of less than 17% (using AE) and 14% (using DRA). The results of AE and DRA for field specimens were very similar with each other but smaller than those of hydraulic fracturing method.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.1
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• pp.25-32
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• 2015

This study analyzed a monitoring data, based on the initial limit values of monitoring in subway, of concrete lining stress and reinforcement stress. The data is obtained from 7 sections of the Seoul metropolitan subway line No 6, 7, and 9 in about 5 years. Also, a research is performed to set up the limit values of management monitoring, which will be applied to management monitoring in tunnel, through comparing the limit values of overseas management monitoring data and that of domestic management monitoring data. And the result obtained from comparison shows that the safety phase is 60% of allowable stress, the attention phase is 80% of allowable stress and the precision analysis phase is 100% of allowable stress. Also, we presented a method of management monitoring by the absolute value which can be easily applied in practical affairs.

• Tunnel and Underground Space
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• v.6 no.2
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• pp.101-121
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• 1996

The thermomechanical characteristics of rocks such as temperature dependency of strength and deformation were experimentally investigated using Iksan granite, Cheonan tonalite and Chung-ju dolomite for proper design and stability analysis of underground structures subjected to temperature changes. For the temperature below critical threshold temperature $T_c$, the variation of uniaxial compressive strength, Young's modulus, Brazilian tensile strength and cohesion with temperature were slightly different for each rock type, but these mechanical properties decreased at the temperatures above $T_c$ by the effect of thermal cracking. Tensile strength was most affected by $T_c$, and uniaxial compressive strength was least affected by $T_c$. To the temperature of 20$0^{\circ}C$ with the confining prressure to 150 kg/$\textrm{cm}^2$, failure limit on principal stress plane and failure envelope on $\sigma$-$\tau$ plane of Iksan granite were continuously lowered with increasing temperature but those of Cheonan tonalite and Chung-ju dolomite showed different characteristics depending on minor principal stress on principal stress plane and normal stress on $\sigma$-$\tau$ plane. The reason for this appeared to be the effect of rock characteristics and confining pressure. Young's modulus was also temperature and pressure dependent, but the variation of Young's modulus was about 10%, which was small compared to the variation of compressive strength. In general, Young's modulus increased with increasing confining pressure and increased or decreased with increasing temperature to 20$0^{\circ}C$ depending on the rock type.

• Journal of Korean Tunnelling and Underground Space Association
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• v.7 no.2
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• pp.133-141
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• 2005

The behavior of the ground in crossed zone due to the excavation of new lower tunnel rectangularly crossed to that was studied by model tests and numerical analysis in shallow cover. Results of the model tests show that earth pressure of the ground in crossed zone were redistributed due to the longitudinal arching effect by the excavation of lower tunnel. By the numerical analysis, minimum principal stress in crown of single tunnel has more decrease than parallel tunnel or crossed tunnel. Vertical stress at rectangularly crossed tunnel decrease more than single tunnel by stress shadow.