• Journal of Korean Tunnelling and Underground Space Association
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• v.10 no.2
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• pp.167-175
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• 2008

The construction cost for the single shell tunnel is cheaper than that of the double shell tunnel according to the case studies performed in several domestic and foreign tunnels. However, the economic advantage of single shell tunnel drops drastically as the condition of the rock mass deteriorates. Therefore, the single shell tunnelling method should be applied to the good rock mass conditions. The application of the single shell tunnelling method to tunnels in Korea should be determined considering the ratio between the good rock and poor rock masses along the tunnel section. The use of the single shell tunnel is expected to offend depending on the cheap supply of high quality shotcrets and rock bolts developed for single shell tunnels.

• Journal of Korean Tunnelling and Underground Space Association
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• v.26 no.3
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• pp.223-242
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• 2024

Single-shell tunnels, introduced to South Korea in the early 2000s, have not been adopted for the main tunnels of roads or railways over the past two decades despite several attempts starting with the Gwangju City Bypass. This reluctance likely arises from concerns about the long-term performance of supporting materials and the absence of relevant criteria and specifications. However, recent progress, including the incorporation of high-strength shotcrete standards and corrosion-resistant rock bolt specifications, alongside equipment and technique enhancements, necessitates a reassessment of single-shell tunnels. While the single-shell tunnel method offers advantages in environmental impact, construction cost and period compared to the conventional NATM, it is crucial to address the challenges, such as limited design and construction experience, incomplete detailed standards, and insufficient construction specifications, through further research and pilot projects. This paper reviewed the basic principles of single-shell tunnel, current application and research status, technical development trends, criteria and specifications, and remaining challenges. It aims to reignite discussions on the feasibility of applying single-shell tunnels in South Korea.

• Journal of Korean Tunnelling and Underground Space Association
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• v.8 no.3
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• pp.273-287
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• 2006

This study investigates the failure mechanism and load-carrying capacity of a single-shell lining which has no disturbance in transfer of shear force, with respect to a conventional double-shell lining which has separation between layers of shotcrete lining and secondary concrete lining by water-proof membrane. In order to evaluate the capacity, a 2-D numerical investigation is preliminarily carried out and then real-scale loading tests with tunnel lining section specimens are performed on the condition given by the numerical investigation. In the test, a concentrated load is applied for considering a released ground load or rock wedge load. Through this study, it appears that the single-shell lining takes the load-bearing capacity 20% higher than in case of the double-shell lining. In addition, a possibility of a composite single-shell shotcrete layer composed by multiple bonded layers partly involving different contents of high-capacity additives is shown thereby leading to use of less amount of the high-capacity additives on the condition of taking a similar load-bearing capacity.

• The Journal of Engineering Geology
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• v.16 no.3 s.49
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• pp.283-291
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• 2006

Shotcrete is used as a permanent lining in single shell tunnels even though shotcrete has been used as a temporary lining in NATM tunnels. Therefore, the accurate evaluation of strength parameters is very crucial because the reliable estimation of loads acting on the shotcretes is necessary to maintain the stability of tunnels. The evaluation of strength parameters of the ground far the single shell tunnels should be investigated to adapt the method in Korea because the geological condition of Korea is different from that of other country. Rock classification and strength parameters obtained from 25 tunnel sites were investigated for this study. Support types fur the different rock classes are suggested for the single shell tunnels in Korea based on the NMT because Q-system has been widely used in Korea. The support types in terms of both Q and RMR values are given based on the correlation of Q and RMR values obtained from the case studies.

• Journal of the Korean GEO-environmental Society
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• v.17 no.1
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• pp.39-48
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• 2016

In this study, it can be shortened tunnel construction work period by introducing a single-shell tunnel does not placing the secondary concrete lining, a global research trend, reduction of the cost of the lining placement and number of benefits that can ensure the safety of long-term tunnel with a single shell it was to study the tunnel method. First, we analyze the design and construction practices relating to delete lining of the domestic design and construction practices and a comprehensive analysis of the stability study found a rock in good condition interval (1~3 grades), we propose that the lining uninstalled. In the case of domestic changes on the ground floor is very heavy underfoot conditions many so tunneling method by single shell as ground conditions are good and one preferred the water points that apply in less soil, the soil health and poor sections (4~5 grades) reflecting with respect to the concrete lining that is expected reasonable.

• Tunnel and Underground Space
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• v.14 no.1
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• pp.1-15
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• 2004

The development of high-performance shotcrete lining is essential in improving the long-term durability of tunnels and in introducing single-shell tunnelling methods, where shotcrete as well as rockbolts are used as permanent support members. In this paper, new and advanced admixtures to improve shotcrete performance are introduced. In addition, requirements for mechanical properties as well as test items for quality control of shotcrete are summarized. A case study on the application of the pneumatic pin penetration test which can estimate compressive strength of shotcrete more easily and quickly is also illustrated. Previous studies to analyze the behaviors of shotcrete lining by considering its transient hardening and to carry out the sensitivity analysis of the design parameters of shotcrete lining are discussed to give fundamental concepts on rock-support interactions. Representative single-shell tunnelling methods where high-performance shotcrete lining is applied as a permanent support are also introduced.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2006.03a
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• pp.73-78
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• 2006

• Journal of Korean Tunnelling and Underground Space Association
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• v.8 no.3
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• pp.237-247
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• 2006

The use of high-performance shotcrete lining is indispensable to improve long-term durability of a tunnel and to apply the single-shell tunnelling method. Among a lot of shotcrete admixtures, pozzolan materials such as silica fume have positive effects on increasing the strength and the durability of shotcrete. It is also well known that a cement-based accelerator is much faster in setting time and more eco-friendly than conventional accelerators. This study aimed to improve the properties of wet-mix shotcrete by incorporating with Metakaolin and the calcium aluminate based accelerator. To compare Metakaolin with silica fume, mixing ratios of each material were varied as 4% and 8% of cement weight. Moreover, Metakaolin was blended with silica fume, and their binder was also set to 4% and 8% of cement weight. At each mixing condition, setting time, compressive strength, flexural strength, permeability and freezing-thawing resistance were measured. From the experiments, it was revealed Metakaolin could be a substituting material for silica fume.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.6
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• pp.675-683
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• 2015

The room-and-pillar construction method for underground space is adopted from the room-and-pillar mining method which is one of the most popular underground mining method in the world. Drainage system in the room-and-pillar underground construction method can be similar with the concept of single shell in tunnel because additional reinforcement except the TSL (thin spray-on liner) is not applied in the room-and-pillar construction method. That is, to decrease groundwater level and maintain safety in tunnel, the drainage pin hole inside lining (shotcrete) can be used. However, if total amount of outflow in the underground structure is relatively small or groundwater is not detected, such drainage system will not be useful and cause additional construction cost. In this study, outflow of conventional tunnels in South Korea was investigated and the criteria to determine whether the drainage pin hole is effective was suggested. And the guided drainage system was suggested when drainage pin hole was not applied in the room-and-pillar construction method.