• Title/Summary/Keyword: 연속굴착

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Modeling the Effect of Water, Excavation Sequence and Reinforcement on the Response of Tunnels

  • Kim, Yong-Il
    • Journal of the Korean Geotechnical Society
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    • v.15 no.3
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    • pp.161-176
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    • 1999
  • A powerful numerical method that can be used for modeling rock-structure interaction is the Discontinuous Deformation Analysis (D D A) method developed by Shi in 1988. In this method, rock masses are treated as systems of finite and deformable blocks. Large rock mass deformations and block movements are allowed. Although various extensions of the D D A method have been proposed in the literature, the method is not capable of modeling water-block interaction, sequential loading or unloading and rock reinforcement; three features that are needed when modeling surface or underground excavation in fractured rock. This paper presents three new extensions to the D D A method. The extensions consist of hydro-mechanical coupling between rock blocks and steady water flow in fractures, sequential loading or unloading, and rock reinforcement by rockbolts, shotcrete or concrete lining. Examples of application of the D D A method with the new extensions are presented. Simulations of the underground excavation of the \ulcornerUnju Tunnel\ulcorner in Korea were carried out to evaluate the influence of fracture flow, excavation sequence and reinforcement on the tunnel stability. The results of the present study indicate that fracture flow and improper selection of excavation sequence could have a destabilizing effect on the tunnel stability. On the other hand, reinforcement by rockbolts and shotcrete can stabilize the tunnel. It is found that, in general, the D D A program with the three new extensions can now be used as a practical tool in the design of underground structures. In particular, phases of construction (excavation, reinforcement) can now be simulated more realistically.

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The study on the effect of fracture zone and its orientation on the behavior of shield TBM cable tunnel (단층파쇄대 규모 및 조우 조건에 따른 전력구 쉴드 TBM 터널의 거동 특성 분석)

  • Cho, Won-Sub;Song, Ki-Il;Kim, Kyoung-Yul
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.16 no.4
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    • pp.403-415
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    • 2014
  • Recently, the temperature rise in the summer due to climate change, power usage is increasing rapidly. As a result, power generation facilities have been newly completed and the need for ultra-high-voltage transmission line for power transmission of electricity to the urban area has increased. The mechanized tunnelling method using a shield TBM have an advantage that it can minimize vibrations transmitted to the ground and ground subsidence as compared with the conventional tunnelling method. Despite the popularity of shield TBM for cable tunnel construction, study on the mechanical behavior of cable tunnel driven by shield TBM is insufficient. Thus, in this study, the effect of fractured zone ahead of tunnel face on the mechanical behavior of the shield TBM cable tunnel is investigated. In addition, it is intended to compare the behavior characteristics of the fractured zone with continuous model and applying the interface elements. Tunnelling with shield TBM is simulated using 3D FEM. According to the change of the direction and magnitude of the fractured zone, Sectional forces such as axial force, shear force and bending moment are monitored and vertical displacement at the ground surface is measured. Based on the stability analysis with the results obtained from the numerical analysis, it is possible to predict fractured zone ahead of the shield TBM and ensure the stability of the tunnel structure.

Numerical Study on the Effects of Air Decking in Half Charge Blasting Using AUTODYN (AUTODYN을 이용한 하프장전 발파공법의 에어데크 효과에 대한 수치해석적 연구)

  • Baluch, Khaqan;Kim, Jung-Kyu;Kim, Seung-Jun;Jin, Guochen;Jung, Seung-Won;Yang, Hyung-Sik;Kim, Nam-Soo;Kim, Jong-Gwan
    • Explosives and Blasting
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    • v.36 no.4
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    • pp.1-8
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    • 2018
  • This numerical study was intended to evaluate the applicability of the half charge blasting to mining and tunnelling. The half charge blasting is a method that two separate rounds are sequentially blasted for the rock burdens in which long blast holes have already been drilled at one operation. The aim of the method is to decrease the construction cost and period in mining and tunnelling projects as well as to increase the blasting efficiency. Several numerical analyses were conducted by using the Euler-Lagrange solver on ANSYS AUTODYN to identify the effects of the suggested method on the blasting results in underground excavations. The overall performance of the suggested method was also compared to an ordinary blasting method. The analysis model was comprised of the Eulerian parts (explosive, air, and stemming materials) and the Lagrangian parts (rock material). As a result, it was found that, owing to the air decks formed in the bottom parts of the long blast holes, the first round of the suggested method presented a higher shock pressure and particle velocities in the vicinity of the blast holes compared to the ordinary blasting method.

A preliminary study for numerical and analytical evaluation of surface settlement due to EPB shield TBM excavation (토압식 쉴드 TBM 굴착에 따른 지반침하 거동 평가에 관한 해석적 기초연구)

  • An, Jun-Beom;Kang, Seok-Jun;Kim, Jung Joo;Kim, Kyoung Yul;Cho, Gye-Chun
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.23 no.3
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    • pp.183-198
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    • 2021
  • The EPB (Earth Pressure Balanced) shield TBM method restrains the ground deformation through continuous excavation and support. Still, the significant surface settlement occurs due to the ground conditions, tunnel dimensions, and construction conditions. Therefore, it is necessary to clarify the settlement behavior with its influence factors and evaluate the possible settlement during construction. In this study, the analytical model of surface settlement based on the influence factors and their mechanisms were proposed. Then, the parametric study for controllable factors during excavation was conducted by numerical method. Through the numerical analysis, the settlement behavior according to the construction conditions was quantitatively derived. Then, the qualitative trend according to the ground conditions was visualized by coupling the numerical results with the analytical model of settlement. Based on the results of this study, it is expected to contribute to the derivation of the settlement prediction algorithm for EPB shield TBM excavation.

A feasibility study on the estimation of a potential relaxed zone in the discontinuum coupled analysis of a subsea tunnel (해저터널의 불연속체 연계해석 시 잠재적 이완영역 평가 방법의 타당성 연구)

  • You, Kwang-Ho
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.11 no.2
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    • pp.141-150
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    • 2009
  • When constructing a subsea tunnel in discontinuous rock mass, fluid flow in joints has a great influence on the behavior of the tunnel so that hydro-mechanical coupled analysis should be performed for the stability estimation. In practice, relaxed rock load is generally used for the design of tunnel concrete lining. In a continuum analysis, a method based on the distribution of local safety factor around a tunnel was proposed for the estimation of a potential relaxed zone. However, in the case of discontinuous rock mass in which joints are developed, the whole stability of tunnels depends on the behavior of the joints. In this study, therefore, a method is proposed for the estimation of a potential relaxed zone occurred by the excavation of a tunnel in discontinuous rock mass. The suggested method is validated by sensitivity analysis and the comparison with the results of continuum analysis.

Compression Test of a TBM Thrust Jack for Validating Buckling Stability (TBM 추진잭의 좌굴 안정성 검토를 위한 압축시험)

  • Mun-Gyu Kim;Min-Gi Cho;Jung-Woo Cho;Han-Young Jeong
    • Tunnel and Underground Space
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    • v.33 no.5
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    • pp.339-347
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    • 2023
  • As the jacks provide a thrust force on the inclined surface, bending deformations by a side force occur in the pedestal and rod parts. This can induce disorder or degradation of the thrust module, buckling stability on the inclined compression condition should be clarified to secure the reliability of shield TBM. For analyzing the stability, a buckling testing method for hydraulic cylinder was investigated and compression testing system was installed. Before the test, a numerical analysis was conducted to check the stress concentration parts. The maximum allowable force was loaded on the cylinder specimen at 0 degree surface condition as a preliminary test. After the test, plastic deformations or hydraulic leakage was not observed. The static stability of it was verified at 0 degree condition.

The Fluid Loss and Sealing Mechanisms in Slurry Trench Condition (I) : A Large Scale Test and Design Procedure (Slurry wall 공법에서 안정액의 역할 (I) : 대형모형실험과 설계절차)

  • Kim, Hak-Moon
    • Journal of the Korean Geotechnical Society
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    • v.18 no.4
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    • pp.239-248
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    • 2002
  • Bentonite slurries in a slurry wall construction must fulfill a stabilizing function by forming impermeable membrane (surface cake and penetrated cake) on the excavated soil faces. Thus problems are occurring in practice for the construction of diaphram walls and cut-off walls with a low permeability for wastes disposal areas in some deep excavations or different grounds. In this paper, the fundamental mechanics of fluid loss and filter cake formation in various soil beds are investigated using large scale laboratory apparatus. The sealing efficiency of filter cake from the large scale tests and the significance of fluid loss in a slurry trench are utilized for practical situation as a recommended design procedure.

Effects of geometric parameters of a combined nozzle for rock cutting using an abrasive waterjet (연마재 워터젯 암석절삭을 위한 결합 노즐의 기하학적 변수 영향)

  • Oh, Tae-Min;Cho, Gye-Chun
    • 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.

Static and Dynamic Analysis for Railway Tunnel according to Filling Materials for overbroken tunnel bottom (철도터널 하부 여굴처리 방법에 대한 정적 및 동적 안정성 검토)

  • Seo, Jae-Won;Cho, Kook-Hwan
    • Journal of the Korean Society for Railway
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    • v.20 no.5
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    • pp.668-682
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    • 2017
  • Alignments of railways recently constructed in Korea have been straightened due to the advent of high-speed rail, which means increasing the numbers of tunnels and bridges. Overbreak during tunnel construction may be unavoidable, and is very influential on overall stability. Over-excavation in tunneling is also one of the most important factors in construction costs. Overbreak problems around crown areas have decreased with improvements of excavation methods, but overbreak problems around bottom areas have not decreased because those areas are not very influential on tunnel stability compared with crown areas. The filling costs of 10 cm thickness of overbreak at the bottom of a tunnel are covered under construction costs by Korea Railway Authority regulations, but filling costs for more than the covered thickness are considered losses of construction cost. The filling material for overbreak bottoms of tunnels should be concrete, but concrete and mixed granular materials with fractured rock are also used for some sites. Tunnels in which granular materials with fractured rock are used may have a discontinuous section under the concrete slab track. The discontinuous section influences the propagation of waves generated from train operation. When the bottom of a tunnel is filled with only concrete material, the bottom of the tunnel can be considered as a continuous section, in which the waves generated from a train may propagate without reflection waves. However, a discontinuous section filled with mixed granular materials may reflect waves, which can cause resonance of vibration. The filled materials and vibration propagation characteristics are studied in this research. Tunnel bottom filling materials that have ratios of granular material to concrete of 5.0 %, 11.5 %, and 18.0 % are investigated. Samples were made and tested to determine their material properties. Static numerical analyses were performed using the FEM program under train operation load; test results were found to satisfy the stability requirements. However, dynamic analysis results show that some mixed ratios may generate resonance vibration from train operation at certain speeds.

Analysis of a Groundwater Flow System in Fractured Rock Mass Using the Concept of Hydraulic Compartment (수리영역 개념을 적용한 단열암반의 지하수유동체계 해석)

  • Cho Sung-Il;Kim Chun-Soo;Bae Dae-Seok;Kim Kyung-Su;Song Moo-Young
    • The Journal of Engineering Geology
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    • v.16 no.1 s.47
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    • pp.69-83
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    • 2006
  • This study aims to evaluate a complex groundwater flow system around the underground oil storage caverns using the concept of hydraulic compartment. For the hydrogeological analysis, the hydraulic testing data, the evolution of groundwater levels in 28 surface monitoring boreholes and pressure variation of 95 horizontal and 63 vertical water curtain holes in the caverns were utilized. At the cavern level, the Hydraulic Conductor Domains(fracture zones) are characterized one local major fracture zone(NE-1)and two local fracture zones between the FZ-1 and FZ-2 fracture zones. The Hydraulic Rock Domain(rock mass) is divided into four compartments by the above local fracture zones. Two Hydraulic Rock Domains(A, B) around the FZ-2 zone have a relatively high initial groundwater pressures up to $15kg/cm^2$ and the differences between the upper and lower groundwater levels, measured from the monitoring holes equipped with double completion, are in the range of 10 and 40 m throughout the construction stage, indicating relatively good hydraulic connection between the near surface and bedrock groundwater systems. On the other hand, two Hydraulic Rock Domains(C, D) adjacent to the FZ-1, the groundwater levels in the upper and lower zones are shown a great difference in the maximum of 120 m and the high water levels in the upper groundwater system were not varied during the construction stage. This might be resulted from the very low hydraulic conductivity$(7.2X10^{-10}m/sec)$ in the zone, six times lower than that of Domain C, D. Groundwater recharge rates obtained from the numerical modeling are 2% of the annual mean precipitation(1,356mm/year) for 20 years.