• Tunnel and Underground Space
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• v.27 no.4
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• pp.195-204
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• 2017

This case study introduces the construction of large cross section tunnel for underground ventilation system in Sillim-Bongcheon Tunnel Project. In order to grant the safety and efficiency in connecting the ventilation shaft (7.8 m of width, and 6.6 m of height) to a tunnel for axial fan facility (20.8 m of width, and 12.3 m of height), gradual enlargement of tunnel cross section was employed between those and temporary support method was determined based on Q system. In addition, some original designs were revised during construction stage to improve the efficiency of excavation in large cross section tunnel. The advance length was optimized and top heading of the tunnel was excavated without partition in accordance with ground condition and numerical stability analysis results. It is believed that some experiences and considerations in this case study will be useful for the future design and construction in similar large cross section tunnel such as large underground ventilation system or road tunnel with four lanes.

• Journal of the Korean Geotechnical Society
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• v.15 no.4
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• pp.99-112
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• 1999

When there exists a fault zone ahead of the tunnel face and a tunnel is excavated without perceiving its existence, it will cause stress concentration in the region between the tunnel face and the fault zone because of the influence of the fault zone on the arching phenomena. Because the underground structure has many unreliable factors in the design stage, the prediction of a fault zone ahead of the tunnel face by monitoring plans during tunnel construction and the rapid establishment of appropriate support system are required for more economical and safer tunnel construction. Recent study shows that longitudinal displacement changes during excavation due to the change of rock property, and if longitudinal displacement and settlement, which are measured in the field, are considered together in displacement analysis, the prediction of change in rock mass property is possible. This study provided the method for the prediction of fault zones by analyzing the changes of L/C and (Ll-Lr)/C ratio (L= longitudinal displacement at crown, C = settlement at crown, Ll = longitudinal displacement at left sidewall, Lr = longitudinal displacement at right sidewall) and the stereographic projection of displacement vectors which were obtained from the 3-D numerical analysis of hybrid method in various initial stress conditions.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.5
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• pp.733-747
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• 2017

In the shallow tunnel, the surrounding ground could be loosened and deformed, which could be the cause of stress change in the ground. Terzaghi has clarified the development of a ground arching induced by the deformation of a tunnel crown in the trap door tests. However, he considered only the case in which that the tunnel crown deformed uniformly. He did not consider the effect of deformation shapes. Therefore, the relation between the shape of the ground relaxation above the tunnel crown and the deformation shape of the tunnel crown is not clear yet. In this study, model tests were performed for the three types of the tunnel crown, such as uniform, concave and convex shapes. As results, it was found that the vertical load would be transferred in various types depending on the deformation shapes of the tunnel crown.

• The Journal of Engineering Geology
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• v.19 no.4
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• pp.483-492
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• 2009

During construction of a tunnel and underground structure, it is very important to acquire accurate information of the rock mass will be excavated. In this study, the drill monitoring method was applied for rapid prediction of geological condition ahead of the tunnel face. Mechanical data(speed, torque and feed pressure) from drilling process using a hydraulic drilling machine were analyzed to assess rock mass characteristics. Rock mass information acquired during excavation from drilling monitoring were compared with results from horizontal boring and tunnel seismic profiling(TSP). As the result, the drilling monitoring method is useful to assess rock mass condition such as geological structures and physical properties ahead of the tunnel face.

• Tunnel and Underground Space
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• v.21 no.3
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• pp.192-204
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• 2011

In this study, 3-D analyses were conducted while taking every construction stage into account. Then 2-D analyses were conducted which yield the same results with the 3-D results. The crown settlement normalized by the ultimate value was compared during the process to overcome the discrepancy caused by different dimensions. When a bench or a core is left uncut to give extra support to the face and eventually the whole excavation boundary, this extra supporting effect also has to be included in the analysis. In this study, this effect is also implemented in terms of the load distribution factor. When the length of the bench is very short compared to the diameter of the tunnel in such cases as in short bench cut or in mini-bench cut, the supporting effect of the face does not disappear even after the bench is completely excavated and supported since the face is still too close to the point of interest. The 4th load distribution factor was defined to stand for the advance of the face after the completion of the excavation cycle. The 4th load distribution factor turned out to be very useful in determining the load distribution factors when a tunnel is excavated by bench cut with various bench lengths under different initial conditions.

• Explosives and Blasting
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• v.25 no.1
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• pp.31-43
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• 2007

In most tunnel constructions in South Korea, blasting has been widely used as an excavation method. In tunnel blasting, the center-cut to induce first free surface is very important for enhancing excavation efficiency and reducing vibration caused by exploding. This paper introduces new center-cut method named SAV-cut (Stage Advance V-cut) developed on the concept of V-cut. Significant features of SAV-cut are the center hole and stepwise ignition. Many field tests and numerical analysis were carried out to analyze the mechanical behavior and blasting vibration. From the results, the newly developed SAV-cut was proved as an effective center-cut method for both increasing blasting efficiency and decreasing blasting vibration.

• Journal of Korean Tunnelling and Underground Space Association
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• v.25 no.6
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• pp.403-421
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• 2023

As the number of underground structures has increased in recent decades, it has become crucial to predict geological hazards ahead of a tunnel face during tunnel construction. Consequently, this study developed a finite element (FE) numerical model to simulate electrical resistivity surveys in tunnel boring machine (TBM) operations for predicting mixed ground conditions in front of tunnel faces. The accuracy of the developed model was verified by comparing the numerical results not only with an analytical solution but also with experimental results. Using the developed model, a series of parametric studies were carried out to estimate the effect of geological conditions and sensor geometric configurations on electrical resistivity measurements. The results of these studies showed that both the interface slope and the difference in electrical resistivity between two different ground formations affect the patterns and variations in electrical resistivity observed during TBM excavation. Furthermore, it was revealed that selecting appropriate sensor spacing and optimizing the location of the electrode array were essential for enhancing the efficiency and accuracy of predictions related to mixed ground conditions. In conclusion, the developed model can serve as a powerful and reliable tool for predicting mixed ground conditions during TBM tunneling.

• Explosives and Blasting
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• v.26 no.2
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• pp.64-76
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• 2008

Bulk Emulsion blasts using mechanized charging system, which is generally used in foreign countries, have recently introduced and gradually increased in Korea. The Bulk Emulsion are safe and able to increase the charging density for improvement of fragmentation and advancement especially in tunneling, and minimizing environmental problem. Because of less toxic gas generation, the explosives are called, namely ech-friendly products. There are two kinds of Bulk Emulsion; one is for open cut and the other is for tunneling. According to features of blast sites and its purpose, the compositions are different, but the principle is the same. In this study, trial blasts using Bulk Emulsion for tunneling had executed at 10 sites in Korea. The major result of the major job-sites is the following. First of all, compared with cartridge explosive, Bulk Emulsion was able to increase its charging density up to $35{\sim}60%$, to decrease the blast holes to approximately $10{\sim}30%$ down, and the advancement was improved up to $8{\sim}20%$ and also 30% up in its fragmentation. Toxic gas production after cartridge blasting showed 34.44ppm of its CO. Bulk Emulsion, however, showed 20.13ppm, which was 58.45% production of the cartridge explosive, and NOx was below 2ppm. The mechanized charging system of Bulk Emulsion should be applied to large sized tunnel blasting, long advanced tunnel which can secure the advancement of over $4{\sim}5m$, and the sites required finishing rapidly.

• The Journal of Engineering Geology
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• v.25 no.3
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• pp.395-401
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• 2015

An investigation of the tunnel face, as well as related measurement data collected during tunneling, is necessary for rock classification and to determine tunnel stability and the cost efficiency of tunneling. However, systematic management and efficient use of such data have yet to be successfully implemented domestically, and the number of experts in this field in Korea is limited. Thus, measures to develop and implement systematic management and effective use of data and expertise are urgently needed. This study aimed to develop measures to efficiently provide online tunnel design and construction data using a building information model (BIM)-based data visualization approach, based on an integrated 3D tunnel model generation module and a web viewer module. The development technology was verified through ○○ tunnel design and construction. Directions for future study and system improvement are proposed.

• Explosives and Blasting
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• v.24 no.2
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• pp.1-8
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• 2006

In this study, a charging density has been differently applied to all holes to improve an excavated length per round on excavating a tunnel in quartzite mine and to prevent a dead pressure phenomena and sintering phenomena. A composition initiating system using simultaneously a direct initiating system and a indirect initiating system with 2 detonators in one hole has been introduced to cut holes. As a bottom part which is difficult to make a free face are charged with a higher charging density and a column part are charged with a lower charging density, the composition charging and initiating system which the power of explosives works effectively in the rock mass is developed. As the results, a dead pressure phenomena and a sintering phenomena being often produced in a hard rock or in a long hole could be prevented. Besides, the workability was improved by about 15% and the specific charge was reduced to about 20%, as an excavated length vs. a drilled length per round could be increased over 95%.