• Title/Summary/Keyword: Longitudinal arching

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Longitudinal arching effect of an under-passing tunnel on the existing tunnel undergoing a load of upper structures (상부 구조물 하중의 영향을 받는 기존터널에 직각 교차하는 하부 터널의 종방향 아칭효과)

  • Lee, Yong-Jun;Lee, Sang-Duk
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.12 no.6
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    • pp.417-427
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    • 2010
  • In the ease that a new cross tunnel is constructed under the existing tunnel, development of a longitudinal arching would be influenced by the existing tunnel. But it is not enough to investigate. Especially, the influence of the structure loads on the ground surface on the new tunnel, which the under-passes existing tunnel has been rarely studied. This study, therefore, aimed to clarify the effect of the existing tunnel and the structure on the ground surface on the development of a longitudinal ground arching during the excavation of a cross tunnel under the existing tunnel. Two-dimensional model tests were carried out in the test box, whose dimension was 30 cm (wide) ${\times}$ 113 cm (deep) ${\times}$ 87 cm (high). The existing tunnel was made of S21 steel tube in 16 cm diameter and 1 mm thickness. The ground surface load was 4.9 kPa and was loaded on the model structure in the size with 30 cm width ${\times}$ 16 cm height. New tunnel was excavated in 250 mm height by a bench cut method. As results, the longitudinal arching would be developed but it was severely influenced by not only the existing upper tunnel but also the ground surface load. The influence of the ground surface load on the development of longitudinal ground arching around a new tunnel showed the highest value when the tunnel face located direct under the surface load.

Behavior of the ground in rectangularly crossed area due to tunnel excavation under the existing tunnel (I) (기존터널에 근접한 직각교차 하부터널의 굴착에 따른 교차부지반의 거동 (I))

  • Kim, Dong-Gab;Kim, Seung-Hyun;Hong, Suk-Bong;Lee, Sang-Duk
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.7 no.1
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    • pp.3-12
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    • 2005
  • The behaviors of the ground in crossed zone and the existing upper tunnel in shallow cover due to the excavation of new lower tunnel Rectangularly crossed to that was studied. Model tests were performed in the large scale test pit, the size was '$4.0m(width){\times}3.8m(height){\times}4.1m(length)$'. Test ground was constructed uniformly by sand in middle density. Results of the model tests show that earth pressure and settlement of the ground in crossed zone were redistributed due to the longitudinal arching effect by the excavation of lower tunnel. Upper tunnel blocks stress flow due to the longitudinal arching effect by excavation of lower tunnel.

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Longitudinal Arching Characteristics Around the Face of a Soil-Tunnel with Crown and Face-Reinforcement (굴진면 천단 및 수평보강에 따른 굴진면 전후의 종방향 아칭 특성)

  • Kwon Oh-Yeob;Choi Yong-Ki;Lee Sang-Duk;Kim Young-Gun
    • Journal of the Korean Geotechnical Society
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    • v.20 no.9
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    • pp.133-144
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    • 2004
  • Pre-reinforcement ahead of a tunnel face using long steel or FRP (Fiberglass Reinforced Plastic) pipes in NATM(New Austrian Tunnelling Method), known as the RPUM(Reinforced Protective Umbrella Method) or UAM (Umbrella Arch Method), is the promising method to sustain the stability of a shallow tunnel face and reduce the ground settlements. In addition, horizontal reinforcing of the face is recently emphasized to improve the stability of the face. However, the characteristics on longitudinal arching around the face have not yet been established quantitatively with the RPUM (crown-reinforcing) and/or the face horizontal reinforcing. In this study, therefore, the behavior of cohesionless soil around the face reinforced by the reinforcing member representing the RPUM and horizontal reinforcing is investigated through two-dimensional laboratory model tests. A series of tests were carried out on various conditions by changing lengths and angles of the reinforcing members. Based on the vertical pressure around the face, the characteristics of longitudinal arching have been found for the case of the non-reinforced and the reinforced.

Behavior of the Ground in Obliquely Crossed area Due to Tunnel Excavation Under the Existing Tunnel (기존터널에 근접하여 경사로 교차되는 하부터널굴착에 따른 교차부지반의 거동)

  • Kim, Dong-Gab;Lee, Sang-Duk
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.7 no.4
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    • pp.285-294
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    • 2005
  • The behaviors of the ground in crossed zone and the existing upper tunnel in shallow cover due to the excavation of new lower tunnel crossed to that was studied. Model test was performed in the large scale test pit, the size was '$4.0m(width){\times}3.8m(height){\times}4.1m(length)$'. Test ground was constructed uniformly by sand in middle density and test with the crossed angle of $56^{\circ}$ (obliquely) were performed. The numerical analysis was performed on equal condition with model test. Results of the study by model test and numerical analysis show that earth pressure and settlement of the ground in crossed zone were redistributed due to the longitudinal arching effect by the excavation of lower tunnel. Model test shows that upper tunnel blocks stress flow due to the longitudinal arching effect by excavation of lower tunnel.

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A study on critical strain based damage-controlled test for the evaluation of rock tunnel stability (암반터널 안정성 평가를 위한 손상제어실험 기반의 한계변형률에 관한 연구)

  • Lee, Kang-Hyun;Kim, Do-Hoon;Park, Jeong-Jun;Lee, In-Mo
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.13 no.6
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    • pp.501-517
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    • 2011
  • In general, the tunnel stability during excavation is assessed by comparing measured displacements at roof and sidewall to control criteria. The control criteria were established based on the past experience that considered ground conditions, size of the tunnel cross section, construction method, supports, etc. Therefore, a number of researches on the control criteria using the critical strain have been conducted. However, the critical strain obtained from uniaxial compression tests have drawbacks of not taking damage in rock mass due to increase of stress level and longitudinal arching into account. In this paper, damage-controlled tests simulating stress level and longitudinal arching during tunnel excavation were carried out in addition to uniaxial compression tests to investigate the critical strain characteristics of granite and gneiss that are most abundant rock types in Korean peninsula. Then, the critical strains obtained from damage-controlled tests were compared to those from uniaxial compression tests; the former showed less values than the latter. These results show that the critical strain obtained from uniaxial compression tests has to be reduced a little bit to take stress history during tunnel excavation into account. Moreover, the damage critical strain was proposed to be used for assessment of the brittle failure that usually occurs in deep tunnels.

3-Dimensional Tunnel Analyses for the Prediction of Fault Zones (파쇄대 예측을 위한 터널의 3차원 수치해석)

  • 이인모;김돈희;이석원;박영진;안형준
    • 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.

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Failure Modes in Piled Embankments (말뚝으로 지지된 성토지반의 파괴형태)

  • 홍원표;윤중만;서문성
    • Journal of the Korean Geotechnical Society
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    • v.15 no.4
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    • pp.207-220
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    • 1999
  • Model tests were performed to investigate the failure modes in embankments on soft ground supported by piles with cap beams. In the model tests, Jumunjin standard sand was placed on simulated cap beams and soft ground. The cap beams are placed perpendicular to the longitudinal axis of the embankment. The colored sand and the Jmniin standard sand were placed one after the other above cap beams and soft ground to make lateral stripes with 3mm thickness in the embarkment. The colored sand was prepared by coating the Jumunjin sand with black lead powder. The photographs illustrate the two characteristic modes of failure in embarkments. One is the soil arching failure and the other is the punching shear failure. The failure mode depends on the height of embankment and the space between cap beams. That is, if the embankment is high enough compared with the space between cap beams, it will fail in arching failure. On the other hand if the embarkment is relatively low or the space between piles is too wide, it will fail in punching shear failure. The soil arching develops in embarkment as a semicylindrical arch with a thickness equal to the width of the cap beam. And the soil wedge developed above the cap beams remains intact during both arching and punching failures. The boundary of punching shear failure of the displaced soil mass can be defined on the basis of observation of the photographs.

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Theoretical Analysis of Embankment Loads Acting on Piles (성토지지말뚝에 작용하는 연직하중의 이론해석)

  • 홍원표;이재호;전성권
    • Journal of the Korean Geotechnical Society
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    • v.16 no.1
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    • pp.131-143
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    • 2000
  • Several theoretical analyses are performed to predict the vertical load on embankment piles with cap beams. The piles are installed in a row in soft ground below the embankment and the cap beams are placed perpendicular to the longitudinal axis of the embankment. Two failure mechanisms such as the soil arching failure and the punching shear failure are investigated according to the failure pattern in embankment on soft ground supported by piles with cap beams. The soil arching can be developed when the space between cap beams is narrow and/or the embankment is high enough. In the investigation of the soil arching failure, the stability in the crown of the arch is compared with that above the cap beams. The factors affecting the load transfer in the embankment fill by soil arching are the space between cap beams, the width of cap beams and the soil parameters of the embankment fill. The portion of the embankment load carried by cap beams decreases with increment of the space between cap beams, while it increases with the embankment height, the width of cap beams, the internal friction angle and cohesion of the embankment fill. Thus, the factors affecting load transfer in embankment should be appropriately decided in order to maximize the effect of embankment load transfer by piles.

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Derivation of a 3D Arching Formula for Tunnel Excavation in Anisotropic Ground Conditions and Examination of Its Effects (비등방 지반에서 터널굴착을 위한 3차원 아칭식의 유도 및 그 영향 조사)

  • Son, Moorak
    • Journal of the Korean Geotechnical Society
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    • v.34 no.12
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    • pp.19-27
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    • 2018
  • Terzaghi proposed a 2D formula for arching based on the assumption of a vertical sliding surface induced in the upper part due to the downward movement of a trapdoor. The formula was later expanded to consider 3D tunnel excavation conditions under inclined sliding surfaces. This study further extends the expanded formula to consider the effects of different ground properties and inclined sliding conditions in the transverse and longitudinal directions considering anisotropic ground conditions, as well as 3D tunnel excavation conditions. The 3D formula proposed in this study was examined of the induced vertical stress under various conditions (ground property, inclined sliding surface, excavation condition, surcharge pressure, earth pressure coefficient) and compared with the 2D Terzaghi formula. The examination indicated that the induced vertical stress increased as the excavation width and length increased, the inclination angle increased, the cohesion and friction angle decreased, the earth pressure coefficient decreased, and the surcharge pressure increased. Under the conditions examined, the stress was more affected at low excavation lengths and by the ground properties in the transverse direction. In addition, The comparison with the 2D Terzaghi formula showed that the induced vertical stress was lower and the difference was highly affected by the ground properties, inclined sliding conditions, and 3D tunnel excavation conditions. The proposed 3D arching formula could help to provide better understanding of complex arching phenomena in tunnel construction.

A Study on the Characteristics of Stress Transfer around Cavern due to Cavern size and Rock Joint Orientation by Laboratory Model Test (모형실험을 통한 공동규모와 절리 방향성에 따른 공동배면의 응력전이 특성에 대한 연구)

  • Kim, Sang-Hwan;Shin, Beom-Seok
    • Proceedings of the Korean Geotechical Society Conference
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    • 2009.03a
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    • pp.595-606
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    • 2009
  • This paper presents the characteristics of stress transfer around carven due to cavern size and rock joint properties by laboratory model test. In order to perform this study, eight different scaled model tests were carried out according to excavation stage. The limited numerical analysis were also performed to verify the model test results. The amount of stress transfer around the cavern is increased and then decreased by longitudinal arching effect according to tunnel excavation. It is founded that the stress developed around the cavern during excavation is increased when the cavern size and joint orientation are increased. It is also investigated that shear behaviour (such as stress, deformation) developed around cavern is considerably depended on the characteristic of fill material, dip and direction of joints. It is suggested that the behaviour will be verified throughout the 3D numerical prediction.

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