• Journal of the Korean GEO-environmental Society
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• v.13 no.11
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• pp.69-79
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• 2012

This pre-supported nail method is able to decrease ground displacements more than NATM because this method reinforces ground with grouted steels before tunnel excavation. Therefore this method has advantage of being able to increase the stability and workability. This study presents applicability of pre-supported nail method with case of site measurement for shallow tunnel composed with high groundwater level and unconsolidated soil, performs this research the mechanism of new supporting system is compared with the conventional existing supporting system in terms of soil reinforcement. NATM has characteristics that construction stage displacement of the apparent height difference is observed in the step of divided excavation processing. Otherwise it is analyzed that pre-supported nail method is not sensitive in the displacement problem of excavation processing in comparison to NATM. It is found that this method is very applicable in shallow depth tunnel such as portal area, tunnel in soil and weak zone without arching effect.

• Journal of the Korean Geotechnical Society
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• v.35 no.5
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• pp.21-30
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• 2019

While the study of the shallow tunnel has been mainly on the longitudinal load transfer and horizontal surface conditions, the study of the ground behavior of shallow tunnel under the slope is not sufficient. Therefore, in this study on the ground behavior around a tunnel due to the sidewall deformation of shallow tunnel under the slope that is excavated in longitudinal direction, a scale-down model test has been performed. The model tunnel has the dimension of 320 mm wide, 210 mm high and 55 mm long with enough material strength in aluminum and the model ground has the uniform ground conditions by 3 types of carbon rods. The model test has been performed with the variables of slopes and the cover depths by controlling the tunnel sidewall deformation, and the change of sidewall-load, load transfer, ground subsidence was monitored and analyzed. According to the increase of the slope, the maximum ground subsidence increased by 20~39% compared to the horizontal surface. The load ratio increased by maximum 20% in the tunnel crown and decreased in sidewall according to the surface slope. The load transfer shows maximum 128% of increase at the cover depth of 1.0D, while at the 1.5D cover depth it shows non-critical difference from horizontal surface. The slope has major effects on load transfer at the cover depth of 1.0D.

• 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.

• Tunnel and Underground Space
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• v.23 no.2
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• pp.87-98
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• 2013

Around 70% of Korea is mountainous, an increase in tunnel construction. It's due to the growing interest of the public for the environment and land required for the road construction is very scarce. During construction of 'Daedong 1 tunnel' in the expressway expansion project between Naengjeong and Busan, there are shallow shaft due to this tunnel located in the valley and the shafts are separated, and penetrating location change was inevitable for construction was delayed because of complaint. So, we change the position of the penetrating by applying multi-channel TSP, and conducted a stability analysis. The analysis results showed that there is no problem on the stability of the tunnel. To secure the construction of additional stability, We installed instrument, performed mechanical excavation, added reinforcement at shallow shaft and conducted bench cut.

• Tunnel and Underground Space
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• v.15 no.2 s.55
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• pp.102-110
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• 2005

○ ○ tunnel that is located at Iksan - Jangsu freeway ○ ○, has collapsed during construction at the valley with shallow depth. Although, the site investigations, such as TSP, drilling exploration and so of indicated the presence of discontinuities in this section. The RMR was upgraded and the construction were carried out because that not only actual rock qualities were relatively good during construction but also the tunnel foe was stabilized. However, the tunnel was collapsed at the same time blasting of full face, and surface and underground water was infiltrated due to the settlement of the upper part of the tunnel face. To restore the collapsed section, 3-d tunnel stability analysis was performed and suitable reinforcement methods were chosen. The cavity of the upper tunnel face was stabilized by means of UAM and ALC injection. And the settlement was restored using L.W grouting method.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.5
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• pp.499-509
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• 2016

In recent years, the use of underground spaces becomes more frequent and the demands for urban tunnels are rapidly increasing. The urban tunnels constructed in the ground with a shallow and soft cover might be deformed in various forms on the face, which would lead, the tunnels to behavior 3-dimensionally, which may have a great impact on the longitudinal load transfer. The tunnel face might deform in various forms depending on the construction method, overburden and the heterogeneity of the ground. And accordingly, the type and size of the distribution of the load transferred to the ground adjacent to the tunnel face as well as the form of the loosened ground may appear in various ways depending on the deformation form of the tunnel face. Therefore, in this study was conducted model tests by idealizing the deformation behavior of the tunnel face, that were constant deformation, the maximum deformation on the top and the maximum deformation on the bottom. And the test results were analyzed focusing on the deformation of the face and the longitudinal load transfer at the ground above the tunnel. As results, it turned out that the size and the distribution type of the load, which was transferred to the tunnel as well as the earth pressure on the face were affected by the deformation type of the face. The largest load was transferred to the tunnel when the deformation was in a constant form. Less load was transferred when the maximum deformation on the bottom, and the least load was transferred when the maximum deformation on the top. In addition, it turned out that, if the cover became more shallow, a longitudinal load transfer in the tunnel would limited to the region close to the face; however, if the cover became higher than a certain value, the area of the load transfer would become wider.

• Geotechnical Engineering
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• v.13 no.3
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• pp.101-122
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• 1997

A spiting reinforcement system is composed of a series of radially installed reinforcing spites along the perimeter of the tunnel opening ahead of excavation. The reinforcing spill network is extended into the in-situ soil mass both radially and longitudinally The sailing reinforcement system has been successfully used for the construction of underground openings to reinforce weak rock formations on several occasions. The application of this spiting reinforcement system is currently extended to soft ground tunneling in limited occasions because of lack of reliable analysis and design methods. A method of threetimensional limit equilibrium stability analysis of the smile-reinforced shallow tunnel in soft ground is presented. The shape of the potential failure wedge for the case of smile-reinforced shallow tunnel is assumed on the basis of the results of three dimensional finite element analyses. A criterion to differentiate the spill-reinforced shallow tunnel from the smile-reinforced deep tunnel is also formulated, where the tunnel depth, soil type, geometry of the tunnel and reinforcing spites, together with soil arching effects, are considered. To examine the suitability of the proposed method of threedimensional stability analysis in practice, overall stability of the spill-reinforced shallow tunnel at facing is evaluated, and the predicted safety factors are compared with results from twotimensional analyses. Using the proposed method of threetimensional limit equilibrium stability analysis of the smile-reinforced shallow tunnel in soft ground, a parametric study is also made to investigate the effects of various design parameters such as tunnel depth, smile length and wadial spill spacing. With slight modifications the analytical method of threeiimensional stability analysis proposed may also be extended for the analysis and design of steel pipe reinforced multi -step grouting technique frequently used as a supplementary reinforcing method in soft ground tunnel construction.

• Geomechanics and Engineering
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• v.15 no.5
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• pp.1039-1046
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• 2018

This paper presents a limit analysis of the series of construction stages of shallow tunneling method by investigating their respective safety factors and failure mechanisms. A case study for one particular cross-section of Beijing Subway Line 7 is undertaken, with a focus on the effects of multiple soil layers and construction sequencing of dual tunnels. Results show that using the step-excavation technique can render a higher safety factor for the excavation of a tunnel compared to the entire cross-section being excavated all at once. The failure mechanisms for each different construction stage are discussed and corresponding key locations are suggested to monitor the safety during tunneling. Simultaneous excavation of dual tunnels in the same cross-section should be expressly avoided considering their potential negative interactions. The normal and shear forces as well as bending moment of the primary lining and locking anchor pipe are found to reach their maximum value at Stage 6, before closure of the primary lining. Designing these struts should consider the effects of different construction stages of shallow tunneling method.

• Computers and Concrete
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• v.17 no.4
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• pp.435-453
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• 2016

The main purpose of this study is to perform optimum cost design of cut and cover RC shallow tunnels using Artificial bee colony and genetic algorithms. For this purpose, mathematical expressions of objective function, design variables and constraints for the design of cut and cover RC shallow tunnels were determined. By using these expressions, optimum cost design of the Trabzon Kalekapisi junction underpass tunnel was carried out by using the cited algorithms. The results obtained from the algorithms were compared with the results obtained from traditional design and remarkable saving from the cost of the tunnel was achieved.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.742-753
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• 2008

Currently an increasing number of urban tunnels with small overburden are excavated according to the principle of the New Austrian Tunneling Method (NATM). Therefore, a possibility of a tunnel collapse during excavation is getting higher in a proportionate manner. This paper will analyze causes the failure mechanism of a shallow NATM tunnel for different geological conditions, ground-water and invert solutions by investigation typical collapse site during tunnel construction. In this paper, this analysis performed two phase, firstly, the field investigation considering displacement measurement, ground-water level, geological characteristic, secondly, the numerical simulation considering the exist of invert construction and the effect of ground-water. It has been found that environmental factors such as state of underground water or construction sequences could influence failure mechanism of a shallow tunnel.