• Proceedings of the KSR Conference
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• 2007.05a
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• pp.1774-1781
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• 2007

In this study, Matsuda's formula, which has been used to evaluate the acting load on the concrete pillar in 2-Arch tunnels, is investigated and a load reduction factor $({\alpha})$, which has been estimated from numerical parametric studies, is proposed for a better design of 2-Arch tunnels in the future. Numerical parametric studies show that the concrete pillar is subjected to a stress concentration on the excavation side during the first tunnel driving and when tunnel excavation is completed, the induced stress on the pillar in a poor quality of ground condition is 1.5 to 1.8 times the stress developed during the first tunnel driving. In addition, the numerical studies indicate that the acting load on the pillar is in the range of $14{\sim}83%$ of the load estimated by Matsuda's formula. From these results, a load reduction factor $({\alpha})$ is determined and it would make 2-Arch tunnel design more economically.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.10a
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• pp.601-612
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• 2005

In mountainous area, Two parallel tunnels have been usually recognized as a road tunnel which has benefits in aspects of cost and stability. However, Design and construction of 2-Arch road tunnel are growing recently due to environmental destruction, compensation of land and difficulty of route separation. As studies are mainly undergoing on only guaranteeing stability and developing a waterproofing-drainage system to avoid water leakage through comprehension for characteristics of 2-arch tunnel behaviors, there is a tendency to evaluate quantity of support by empirical method with a tunnel which has a complicated cross-section and lack of construction ability. In this study, therefore, we made a plan of tunnel cross-section which had shown good construction ability and developed the waterproofing-drainage system which is able to solve the water leakage problem fundamentally by analyzing precedented 2-arch tunnels and investigating their sites in and out of nation. We also determined fixed quantity of support by a large-scale model test and numerical analysis. We want to contribute to 2-arch tunnel design hereafter introducing design procedure and method applied here.

• Journal of Korean Tunnelling and Underground Space Association
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• v.15 no.2
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• pp.113-122
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• 2013

Recently there has been increased interest for the portal and shallow tunnel for an eco-friendly tunneling method. Semi cut & cover tunnel excavation techniques applied to concrete slab and construction and a growing number of cases, but there is no load combinations and arch concrete cross section for the applicable standards. Therefore, in this study, ground conditions and tunnel overburden thickness, thickness of backfill, overburden surface slope angle changes to a variety of conditions in order to propose standards for the semi cut & cover method was performed numerical analysis. Regression analysis method to the analysis of the results of numerical analysis, and linear regression equations derived to classify and organize a rational, economical, and safe semi cut & cover tunneling method based proposed.

• Journal of the Korean Geotechnical Society
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• v.25 no.5
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• pp.65-73
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• 2009

Large scale model tests and numerical analyses are performed to investigate the stress distribution of pillar due to surface loading nearby two-arch tunnel which is constructed in the regularly jointed rocks. It is observed that the influence of discontinuities on the stress distribution in the discontinuous rock mass and the underground stresses induced by surface loading are greater than those of linear elastic theory. Especially, lines of equal stresses are developed to the direction of inclination according to the inclined grade. In cases of discontinuities imbedded in parallel with or vertical to the ground, the pressure bulbs are formed symmetrically, however, the inclined ones result in stress distribution in parallel with and vertical to the planes of discontinuities. Results indicated that stress distribution is seriously affected by the angle of discontinuity. When stresses propagating to the pillar need to be estimated, relative location of surface loading, grade of discontinuous plane, and location of two-arch tunnel should be carefully considered.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.1
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• pp.41-56
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• 2017

Recently, the necessity of deep and double-deck tunnels has been grown day by day due to the increase of traffic volume at metropolitans and thus the study on the divergence of those tunnels becomes required. Therefore sensitivity analyses were conducted with FLAC 2D program by selecting ground condition, coefficient of lateral pressure, support pattern, and depth of rock cover as parameters. Ultimately, this study is to find the optimal shape and support method of a diverged section. As the results of this study, it turned out that the box type gave higher stability of the section than arch type unlike the general thought. It can be explained that the arch type has about 30% bigger excavation area than the box type. When the ground conditions are poor, steel pipe grouting reinforcement gives higher stability than rockbolt reinforcement, but its thickness and range do not give a great influence on the stability of the enlarged section.

• Journal of the Korean Geosynthetics Society
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• v.16 no.4
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• pp.177-190
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• 2017

This paper presents the results of an experimental study on the effect of large underground station construction method under an existing pile supported bridge using reduced-scale model tests. A series of tests were conducted on design alternatives using 1g models for different design options for which tunnel structures were created considering the similitude law. Deformation fields obtained using the PIV analysis and LVDTs together with strains in tunnel structures were used to investigate the effect of the construction methods on the pile supported bridge. The results of the tests demonstrated that the pipe roof structure is more efficient in limiting the ground deformation as well as the settlement of bridge foundation than a 2-Arch tunnel. It is also shown that the PIV analysis can be effectively used in analyzing ground tunneling induced ground movement for cases in which a construction sequence governs ground movement.

• Geotechnical Engineering
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• v.23 no.2
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• pp.44-51
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• 2007

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.6
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• pp.407-416
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• 2010

A new tunnel auxiliary method is proposed in this paper which utilizes the concept of cavity expansion for tuunel reinforcement by forming an umbrella arch on the roof of tunnel. When an inflatable pipe is inserted and expanded by pressure in the bore hole of umbrella arch, the ground around the bore hole can be compacted so that the stress condition above the tunnel perimeter is favorably changed. In order to verify the reinforcement effect of new concept, pilot-scale chamber test, trapdoor test and numerical analysis were performed and compared. In pilot-scale chamber test, three types of inflatable pipes are tested to verify the capability of expansion, and the results arc compared with analytical results obtained by applying cavity expansion theory and with results obtained from finite clement analysis, and the experimental results showed agreeable matches with analytical and numerical ones. Numerical analysis of a tunnel and trapdoor test applied with the inflatable pipes are also performed to figure out the reinforcement effect of the proposed techniques, and the results implied that the new method with 3 directional inflatable pipe (no pressure to downward direction) can contribute to reduce tunnel convergence and face settlement.

• Journal of Korean Tunnelling and Underground Space Association
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• v.6 no.2
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• pp.113-128
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• 2004

To investigate major influencing factors on earth pressure acting on an arch-shaped cut and cover tunnel, Monte Carlo simulation based quantitative sensitivity analysis was carried out for mechanical properties of ground as well as excavation configuration-related design factors. From the sensitivity analysis, it was intended that effects of earth pressures from different influencing factors on a cut and cover tunnel should be numerically identified. Output factors used in the sensitivity analysis such as vertical and horizontal earth pressures at different tunnel positions were obtained from the finite element analysis. In this study, it was revealed that depending upon positions where horizontal as well as vertical earth pressures were acting, they were differently influenced by the same input factors. In addition, earth pressures acting an cut and cover tunnel depended mainly on the embankment at crown and the inclination of cut slope.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.1
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• pp.83-97
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• 2018

Tunnels are widely used for special purposes including roads, railways and culvert for power transmission, etc. Its cross-section shape is determined by uses, ground condition, environmental or economic factor. Many papers with respect to behaviours of adjacent ground and existing structure tunnelling-induced have been published by many researchers, but tunnel cross-section have rarely been considered. A collapse of tunnel causes vaster human and property damage than structures on the ground. Thus, it is very important to understand and analyse the relationship between behavoiurs of ground and cross-section type of tunnel. In this study, the behaviour of ground due to tunnel excavation for underground station below the grouped pile supported existing structure was analysed through laboratory model test using a trap-door device. Not only two cross-section types, 2-arch and box, as station for tunnel, but also, offset between tunnel and grouped pile centre (0.1B, 0.25B, 0.4B) are considered as variable of this study. In order to measure underground deformation tunnelling-induced, Close Range Photogrammetry technique was applied with laboratory model test, and results are compared to numerical analysis.