• Title, Summary, Keyword: Rockbolts

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Load-Settlement Characteristics of Drilled Shafts Reinforced by Rockbolts (락볼트로 보강된 심형기초의 하중-침하 분석)

  • 윤경식;이대수;정상섬
    • Proceedings of the Korean Geotechical Society Conference
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    • pp.366-373
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    • 2002
  • This paper describes the load distribution and settlement of rockbolted-drilled shafts subjected to axial and lateral loads with the view to shortening the embedded depth of the pile shaft. The emphasis was on quantifying the reinforcing effects of rockbolts placed from the shafts to surrounding weathered rocks based on small-scale model tests peformed on instrumented piles. The major influencing parameters on reinforcing drilled shaft behavior are the number, the positions on the shaft, the grade, and the inclination angle at which the rockbolts are placed. The model tests was 1/40 scaled simulations of the behavior of the drilled shafts with varying combinations of the major influencing parameters. The incremental effects of reinforcement based on the various parameters have been weighed against load transfer characteristics before and after rockbolt installations.

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DEVELOPMENT OF NUMERICAL MODEL FOR THE VISCO-PLASTIC BEHAVIOUR OF THE JOINTED ROCK MASS REINFORCED BY ROCKBOLTS (록볼트로 보강한 절리암반의 점소성거동에 관한 수치해석 모델 개발)

  • Lee, Yeon-Gyu;Lee, Jeong-In;Jo, Tae-Jin
    • Proceedings of the Korean Geotechical Society Conference
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    • pp.149-157
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    • 1994
  • In this study two dimensional visco-plastic finite element model capable of handling the multi-step excavation was developed for investigating the effect of excavation support sequences on the behavior of underground openings in the jointed rock mass. First, the finite element model which is capable of handling the multi-step excavation is developed and verified. And then the model is combined with visco-plastic joint model. Ubiquitous joint pattern was considered in the model and joint properties in cach set were assumed to be indentical. Passive, full-grouted rockbolts were cosidered in the numerical model. The visco-plastic deformations of joints and rockbolts were assumed to be governed by Mohr-Conlomb and von Mises yield criteria, respectively. With the ability of removing elements, the model can simulate the multi-step excavation-suppport sequences. The reliability and applicability of the model to the stability analysis for the underground excavation in pratice was checked by simulating the behavior of underground crude oil storage caverns under construction.

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A Study on the visco-plastic behavior of the jointed rock mass reinforced by rockbolts during excavation (굴착과정에서 록볼트로 보강된 절리암반의 점소성 거동 분석)

  • 이연구;이정인;조태진
    • Tunnel and Underground Space
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    • v.5 no.2
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    • pp.123-133
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    • 1995
  • A two dimensional visco-plastic finite element model capable of handling the multistep excavaton was developed for investigating the effect of excavation-support sequences on the behaviour of underground openings in the jointed rock mass. Ubiquitous joint pattern was considered in the model and joint properties in each set were assumed to be identical. Passive, fully-grouted rockbolts were considered in the model. Visco-plastic deformations of joints and rockbolts were assumed to be governed by Mohr-Coulomb and von Mises yield criteria, respectively. With the ability of removing elements, the model can von Mises yield criteria, respectively. With the ability of removing elements, the model can simulate the multi-step excavation-support sequences. The reliability of the model to the stability analysis for the underground excavation in practice was checked by simulating the behavior of underground crude oil storage caverns under construction.

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Modeling the Effect of Excavation Sequence and Reinforcement on the Response of Tunnels with Discontinuous Deformation Analysis Method (불연속 변형 해석법에 의한 굴착순서 및 지반보강이 터널의 거동에 미치는 영향 모델링)

  • 김용일;김영근
    • Tunnel and Underground Space
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    • v.10 no.1
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    • pp.25-32
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    • 2000
  • This paper presents two new extensions to the DDA method. The extensions consist of sequential loading or unloading and rock reinforcement by rockbolts, shotcrete or concrete lining. Examples of application of the DDA method with the new extensions are presented. Simulations of the underground excavation of the Unju Tunnel of Kyungbu High Speed Railway Project in Korea were carried out to evaluate the influence of excavation sequence and reinforcement on the tunnel stability. The results of the present study indicate that 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 DDA program with the three new extensions can now be used as d 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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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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Numerical Analysis on the Crack Control of Concrete Lining Reinforced by Composite Fibers (복합섬유보강 콘크리트 라이닝 부재의 균열제어를 위한 수치해석적 연구)

  • Yang, Woo-Shik
    • Journal of the Korean Geosynthetics Society
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    • v.9 no.2
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    • pp.41-50
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    • 2010
  • The concrete lining of a tunnel constructed by NATM used to be regarded as facing material which does not support any load from the surrounding ground. But the recent appraisal of the decrepit tunnels revealed that rockbolts and shotcrete deteriorate with time resulting in loss of supporting capability. Consequently, concrete lining has to support part of the load which used to be supported by rockbolts and shotcrete, and thus should be regarded as the final supporting structure in a tunnel. One of the common, and perhaps the most serious problem in concrete lining is the longitudinal cracks taking place at the tunnel crown. The longitudinal cracks, mostly related to the construction procedures, can be developed by many reasons such as the lack of thickness, wrong materials, bad curing environment, and excessive external forces. Many efforts has been made to control and suppress these cracks but efficient and economic way is yet to be found. For efficient crack control in concrete lining, reinforcement by composite fibers, which is the mixture of steel fiber and nylon fiber, is suggested in this study.

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Numerical Analysis on the Performance Evaluation of Cablebolts as Tunnel Supports (터널 지보재로서 케이블볼트의 성능평가에 관한 수치해석적 연구)

  • Park, Yeon-Jun;Park, Joon-Hyoung
    • Tunnel and Underground Space
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    • v.22 no.2
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    • pp.130-143
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    • 2012
  • Cablebolts used to be employed as auxiliary supports where long or high capacity bolts are needed, but become competitive by the improvements in supportability and easiness in handling. Based on the test results obtained from various researches, the performance of the cablebolts was analyzed numerically while varying lengths and fixing conditions. The supporting effecte is assessed by monitoring displacements and stress taken place in shotcrete. When cablebolts are grouted without being tensioned, supporting effect was not as good as that of rockbolts. But, their supportability was good enough to substitute rockbolts if tensioned properly. Post grouting right after tensioning of the cablebolts shows reduction in supportability, but long term stability could be achieved without losing supportability if grouted when the bolt is far enough from the face. Further study is necessary including laboratory and in-situ tests under various conditions to use cablebolts as main support in tunnels.

Analysis of Rock Masses and Rock Supports by Rigid Block Method (강성블록법에 의한 지반 및 지보재 해석)

  • 김문겸;황학주;엄인수;허택녕
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • pp.84-90
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    • 1991
  • Underground structures usually consist of rock masses or concretes which can be cracked or have cracks. This study aims to develop an analysis program which can deal with the effect of discontinuous behavior due to those cracks using the block theory. It is assumed that rock masses form blocks along the discontinuity lines, and deformation within the block is relatively small. The behavior of discontinuity plane of the structures is divided into sliding along the discontinuity plane. separation of discontinuity by tensile force, and degradation of asperity angle of discontinuity plane by external force with sliding of rock Basses. These behaviors are implemented using constitutive relation and relevent load-displacement relation defined through normal and shear stiffnesses. Time varying displacements and block velocities are calculated by explicit time stepping algorithm. The effect of rock supports including rockbolts is also considered, and the tending effects which occurs in relatively thin lining is also considered.

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Design of the secondary tunnel lining using a ground-primary support-secondary lining interaction model

  • Chang, Seok-Bue;Seo, Seong-Ho;Lee, Sang-Duk
    • 한국지구물리탐사학회:학술대회논문집
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    • pp.109-114
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    • 2003
  • It is the common practice to reinforce excessively the secondary tunnel lining due to the lack of rational insights into the ground loosening loads. The main load of the secondary lining for drained-type tunnels is the ground loosening. The main cause of the load for secondary tunnel lining is the deterioration of the primary support members such as shotcrete, steel ribs, and rockbolts. Accordingly, the development of the analysis model to consider the ground-primary supports-secondary lining interaction is very important for the rational design of the secondary tunnel lining. In this paper, the interaction is conceptually described by the simple mass-spring model and the load transfer from the primary supports to the ground and the secondary lining is showed by the characteristic curves including the secondary lining reaction curve for the theoretical solution of a circular tunnel. And also, the application of this model to numerical analysis is verified in order to review the potential tool for practical tunnel problems with the complex conditions like non-circular shaped tunnels, multi-layered ground, sequential excavation and so on.

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Field Evaluation of the Swelled Steel Tube Rockbolts (튜브형 강관 록볼트의 현장 적용성 평가)

  • Son, Sung-Gon;You, Jin-O;You, Joung-Hoon;Chung, Jae-Min
    • Proceedings of the KSR Conference
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    • pp.1149-1156
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    • 2011
  • A rockbolt is one of the most important reinforcement of on-site soil, as with the shotcrete and steel rib. The rockbolt by setting within the tunnel can prevent the deformation of the ground profile; furthermore it improves the structural behavior of soil and rock. In general, the rockbolt is mainly used with reinforced steel. However, steel pipe or the materials with the same strength can be used depending on the soil conditions, ground water outflow condition, and the surrounding of applying location. In Korea, most tunnel construction sites have used cement mortar or resin for steel reinforcement on the rock. Due to the ground water outflow in the construction site, the usability of steel reinforcement is poor and it requires curing time especially after installation. To improve exist above problems, this study introduces the development of a swelled steel pipe rockbolt, as well as presents the field testing and performance results.

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