• Geomechanics and Engineering
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• v.10 no.4
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• pp.471-526
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• 2016

In order to investigate water flow characteristics after inrushing in process of karst tunnel excavation, numerical simulations for five case studies of water inrush from the tunnel floor are carried out by using the FLUENT software on the background of Qiyueshan high risk karst tunnel. Firstly, the velocity-distance curves and pressure-distance curves are drawn by selecting a series of probing lines in a plane. Then, the variation characteristics of velocity and pressure are analyzed and the respective optimized escape routes are made. Finally, water flow characteristics after inrushing from the tunnel floor are discussed and summarized by comparing case studies under the conditions of different water-inrush positions and excavation situations. The results show that: (1) Tunnel constructors should first move to the tunnel side wall and then escape quickly when water inrush happens. (2) Tunnel constructors must not stay at the intersection area of the cross passage and tunnels when escaping. (3) When water inrush from floor happens in the left tunnel, if tunnel constructors meet the cross passage during escaping, they should pass through it rapidly, turn to the right tunnel and run to the entrance. (4) When water inrush from floor happens in the left tunnel, if there is not enough time to escape, tunnel constructors can run to the trolley and other equipment in the vicinity of the right tunnel working face. In addition, some rescuing equipment can be set up at the high location of the cross passage. (5) When water inrush from floor happens in the cross passage, tunnel constructors should move to the tunnel side wall quickly, turn to the tunnel without water inrush and run to the entrance. (6) When water inrush from floor happens in the cross passage, if there is not enough time to escape, tunnel constructors can run to the trolley and other equipment near by the left or the right tunnel working face. The results are of important practical significance and engineering value to ensure the safety of tunnel construction.

• Journal of the Korean Society of Hazard Mitigation
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• v.5 no.4 s.19
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• pp.49-57
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• 2005

The purpose of this study is to closely examine the influence of the surcharge load applied to the retaining wall through some model tests, in which wall stiffness in each stage of excavation, horizontal displacement of the retaining wall and surface displacement of the backfill according to wall stiffness and ground conditions, and change and distribution of the earth pressure applied to it were measured and their values were produced, then these values were mutually compared with their theoretical values and their values after analysis of the data obtained at the field, and they were analytically studied, in order to closely examine the influence of the surcharge load applied to the retaining wall. Findings from this study are as follows: The shape of ground surface settlement curve on the model ground under surcharge load, different from the distribution curve of regular probabilities which is of a shape of ground surface settlement under no surcharge load, appears in that settlement in an arching shape shows where the center part of surcharge load shows the maximum settlement. In examining the maximum horizontal displacement with the surcharge load applied to each stage of excavation, it occured at the point of 0.8H(excavation depth) when finally excavated. Regarding the range in which the displacement of the retaining wall increases according to application of surcharge load, the increment of displacement showed till the point of depth which is of two times of the distance of load from the upper part of the wall. Also since each displacement of the foundation plate caused by the ground surface settlement according to each stage of excavation occured most significantly at the final stage. Also since regarding wall stiffness, the wall of its thickness of 4mm(flexible coefficient $p:480m^3/t$), produced maximum 3 times of wall stiffness than its thickness of 9mm(flexible coefficient $p: 40m^3/t$), it was found out that influence of wall stiffness is so significant.

• The Journal of Engineering Geology
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• v.27 no.2
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• pp.153-164
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• 2017

The geological factors for causing ground subsidence are very diverse. It can be affected by any geological or extrinsic influences, and even within the same geological factor, the soil depression impact factor can be determined by different physical properties. As a result of reviewing a large number of papers and case histories, it can be seen that there are seven categories of ground subsidence factors. The depth and thickness of the overburden can affect the subsidence depending on the existence of the cavity, whereas the depth and orientation of the boundary between soil and rock are dominant factors in the ground composed of soil and rock. In case of soil layers, more various influencing factors exist such as type of soil, shear strength, relative density and degree of compaction, dry unit weight, water content, and liquid limit. The type of rock, distance from the main fracture and RQD can be influential factors in the bedrock. When approaching from the hydrogeological point of view, the rainfall intensity, the distance and the depth from the main channel, the coefficient of permeability and fluctuation of ground water level can influence to ground subsidence. It is also possible that the ground subsidence can be affected by external factors such as the depth of excavation and distance from the earth retaining wall, groundwater treatment methods at excavation work, and existence of artificial facilities such as sewer pipes. It is estimated that to evaluate the ground subsidence factor during the construction of underground structures in urban areas will be essential. It is expected that ground subsidence factors examined in this study will contribute for the reliable evaluation of the ground subsidence risk.

• Korean Journal of Heritage: History & Science
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• v.45 no.3
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• pp.100-113
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• 2012

In the midst of recent active excavation, lots of Silla(新羅) roof-end tiles are unearthed in Yeongnam area(嶺南地域). These are confirmed the same tile frame as the Silla tiles excavated in Gyeongju(慶州). It is represented by the Silla tiles excavated in Ingaksa Temple(麟角寺) excavation research. Roof-end tile with arabesque design(唐草文平瓦當) etc. including roof-end tile with lotus design(蓮花文圓瓦當) are judged to be the tile frame produced by the same frame of roof-end tile that was excavated in Gyeongju, Wolseong(月城) and Hwangyongsa Temple(皇龍寺址). There are three kinds of cases concerning the transportation of tile manufacture ; the roof-end tile manufactured in Gyeongju directly moved to each region, only tile frame moved to site to be manufactured there, and tile manufacturer moved to site to manufacture there. This article considers the case of the roof-end tile manufactured in Gyeongju that was directly moved to each region. In case of the Silla tiles excavated in region especially Ingaksa Temple, the aspects of tiles in accordance with different era show the repeated coexistence, expansion and maintenance. This situation is significant as a clue to understand the supply from Gyeongju not as temporary, but as continuous. On the other hand, if the Gyeongju tiles flowed directly into each region, and if the road was built of gravels and the means of transportation was cart, the damage from movement must never be prevented. On the contrary, transportation through waterway might be advantageous due to the reduction of labor and damage rate and the easiness of loading. Accordingly, it tells us why the ruins where roof-end tiles were excavated located near big and small rivers or streams. Of course there are some ruins located in a fixed distance, but the distance may be enough to endure the impact put on tiles from the overland movement. Therefore, in case of direct inflow form long distance, transportation must be finished by overland movement after waterway movement.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.4
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• pp.323-330
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• 2007

Recently, due to the effective land utilization and environmental protection, the construction of 2-arch tunnel has been gradually increased. In spite of this tendency, the mechanical information for the 2-arch tunnel, especially such as its behavior characteristics and mechanism are not enough. Therefore in this study, the theoretical and numerical studies on the behavior characteristics of 2-arch tunnel are carried out and longitudinal optimum separated distance of tunnel face is proposed by considering the analysis results from the behavior of advanced excavation of tunnel and stress of central pillar. As a result, longitudinal optimum separated distance of tunnel face is in 0.5D for the better safety of 2-arch tunnel by rapidly decreasing the stress concentration of central pillar.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.3
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• pp.255-264
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• 2009

This paper concerns the behavior of 2-Arch tunnel constructed under various conditions. A 2-Arch tunnel section adopted in a subway tunnel construction site is considered in this study. A calibrated 3D finite element model was adopted to conduct parametric studies on a variety of construction scenarios including lagged distance between left and right tunnels, overburden, and geological condition. The results of analyses were examined in terms of crown settlement, shotcrete lining stress, and load on center column in relation to the lagged distance, cover depth, and the ground condition. The results indicate that the shotcrete lining stress and the center pillar load are more influenced by the second tunnel excavation than the tunnel deformation. Also shown is that a greater lagged distance is required to minimize the interaction between two tunnels when the ground condition becomes weaker. Fundamental mechanisms of 2-arch tunnel were also discussed based on the results.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.1
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• pp.85-95
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• 2009

In urban areas, blast excavation adjacent to tunnels is carried out frequently. It is generally required to secure static and dynamic stability of nearby tunnel structures for any such activities. Although there is some national guidelines for static safety, there is little guides to risk zoning controling the dynamic behavior of the underground structures. In this study, impacts on the blast-induced vibration are investigated using numerical study. An attempt to define the restricted area of blast adjacent to subway tunnels was also made. Particular concerns were given to tunnel depth and ground types. By carrying out the parametric study on depth and ground patterns, the envelope of blast distance of which dynamic response on the lining is controlled under 1 cm/sec, is established. It is shown that the increase in depth has increased the required safety distance slightly until the distance of 3.5 times of the tunnel diameter. Despite small changes in safety distance, it can be generally said that the effects of depth and stiffness of the ground is not significant in controlling the particle velocity of the tunnel linings.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.23 no.5
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• pp.42-49
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• 2009

The effects of various forces acting on concrete pole are analyzed using finite element method how the forces affect on ground displacement. The soil types, wind load location of anchor block embedded depth of pole, and distance between poles are varied to find out effects on lateral displacement. Anchor block is effective when it is located at 1/4 of embedded depth The displacement is decreases as elastic modulus increases. Concrete reinforcement for loosened ground is necessary for double poles because double poles cause large excavation. When embedded depth ratio decrease, lateral displacement increase as closer to ground surface. Large embedded depth is effective to reduce lateral displacement, and the distance between poles is not much large factor.

• Journal of Korean Tunnelling and Underground Space Association
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• v.14 no.5
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• pp.517-528
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• 2012

Inserting a nozzle assembly into a removed cutting space during a continuous cutting operation is necessary in rock excavation using an abrasive waterjet. In this study, a combined two nozzle assembly is used to secure enough removal width. The shape of the cut space is affected by the geometric parameters (standoff distance, nozzle angle, and vertical distance between the nozzle tips) of the combined nozzle assembly. Abrasive waterjet cutting tests are performed with various geometric parameters for granite rock specimens. Optimized geometric parameters for the nozzle inserting process are determined and verified through the experimental tests.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.159-169
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• 2008

In general, it is considered that a pillar between closely-spaced tunnel is sensitive for stress concentration. Stability of a pillar is key factor for excavation of closely-spaced tunnel. In this paper, the study is focused on tracing the behaviors, displacement and plotting damages around tunnels that is modelled with Particle Flow Code, $PFC^{2D}$. Parametric study was performed with changing distance between center of tunnels and coefficient of earth pressure(K). Scaled-model tests were also carried out to validate a numerical analysis model. It was found that $PFC^{2D}$ could show dynamic visualized result in quite good agreement with the experimental test.