• Title, Summary, Keyword: rock bolt

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Anchorage mechanism and pullout resistance of rock bolt in water-bearing rocks

  • Kim, Ho-Jong;Kim, Kang-Hyun;Kim, Hong-Moon;Shin, Jong-Ho
    • Geomechanics and Engineering
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    • v.15 no.3
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    • pp.841-849
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    • 2018
  • The purpose of a rock bolt is to improve the mechanical performance of a jointed-rock mass. The performance of a rock bolt is generally evaluated by conducting a field pullout test, as the analytical or numerical evaluation of the rock bolt behavior still remains difficult. In this study, wide range of field test was performed to investigate the pullout resistance of rock bolts considering influencing factors such as the rock type, water bearing conditions, rock bolt type and length. The test results showed that the fully grouted rock bolt (FGR) in water-bearing rocks can be inadequate to provide the required pullout resistance, meanwhile the inflated steel tube rock bolt (ISR) satisfied required pullout resistance, even immediately after installation in water-bearing conditions. The ISR was particularly effective when the water inflow into a drill hole is greater than 1.0 l/min. The effect of the rock bolt failure on the tunnel stability was investigated through numerical analysis. The results show that the contribution of the rock bolt to the overall stability of the tunnel was not significant. However, it is found that the rock bolt can effectively reinforce the jointed-rock mass and reduce the possibility of local collapses of rocks, thus the importance of the rock bolt should not be overlooked, regardless of the overall stability.

Support Characteristics of Rock Bolt and Spiral Bolt (록 볼트 및 스파이럴 볼트의 지보특성)

  • Cho, Young-Dong;Song, Myung-Kyu;Lee, Chung-Shin;Kang, Choo-Won;Ko, Jin-Seok;Kang, Seong-Seung
    • Tunnel and Underground Space
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    • v.19 no.3
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    • pp.181-189
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    • 2009
  • This study is to evaluate an effect of supports with respect to these supports after comparing the characteristic of support between rock bolt of a widely used type and spiral bolt of a new type. For these purposes, we performed pull-out test in laboratory about rock and spiral bolts in the case of cement-mortar grout curing periods, 7 and 28 days, then calculated pull-out load, displacement, external pressure, inner pressure and shear stress using data obtained from the results of pull-out test, respectively. In relation between pull-out load and displacement, displacement of spiral bolt is larger than one of rock bolt. It is considered that mechanical property of rock bolt is due to larger than one of spiral bolt. In addition, displacement of supports shows nearly same or decreasing with curing periods. We found that because adhesive force between supports and cement-mortar grout is increasing with compressive strength of grout according to curing periods. The inner pressure of spiral bolt is represented larger than one of rock bolt at a step of same pull-out load. It is suggested that spiral bolt is more stable than rock bolt, maintaining stability of ground or rock mass, when supports are installed in a ground or rock mass under the same condition. Putting together with above results, we can consider that spiral bolt as a new support on an aspect of pull-out load and inner pressure is larger than rock bolt in a ground or rock mass under the same condition. Moreover, spiral bolt is more effective support than rock bolt, considering an economical and constructive aspects of supports, as well as ground or rock stability before or after installing supports.

Theoretical solutions for displacement and stress of a circular opening reinforced by grouted rock bolt

  • Zou, Jin-Feng;Xia, Zhang-Qi;Dan, Han-Cheng
    • Geomechanics and Engineering
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    • v.11 no.3
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    • pp.439-455
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    • 2016
  • This paper presented solutions of displacement and stress for a circular opening which is reinforced with grouted rock bolt. It satisfies the Mohr-Coulomb (M-C) or generalized Hoek-Brown (H-B) failure criterion, and exhibits elastic-brittle-plastic or strain-softening behavior. The numerical stepwise produce for strain-softening rock mass reinforced with grouted rock bolt was developed with non-associative flow rules and two segments piecewise linear functions related to a principle strain-dependent plastic parameter, to model the transition from peak to residual strength. Three models of the interaction mechanism between grouted rock bolt and surrounding rock proposed by Fahimifar and Soroush (2005) were adopted. Based on the axial symmetrical plane strain assumption, the theoretical solution of the displacement and stress were proposed for a circular tunnel excavated in elastic-brittle-plastic and strain-softening rock mass compatible with M-C or generalized H-B failure criterion, which is reinforced with grouted rock bolt. It showed that Fahimifar and Soroush's (2005) solution is a special case of the proposed solution for n = 0.5. Further, the proposed method is validated through example comparison calculated by MATLAB programming. Meanwhile, some particular examples for M-C or generalized H-B failure criterion have been conducted, and parametric studies were carried out to highlight the influence of different parameters (e.g., the very good, average and very poor rock mass). The results showed that, stress field in plastic region of surrounding rock with considering the supporting effectiveness of the grouted rock bolt is more than that without considering the effectiveness of the grouted rock bolt, and the convergence and plastic radius are reduced.

An experimental investigation on mechanical property and anchorage effect of bolted jointed rock mass

  • Li, Yong;Li, Chao;Zhang, Lei;Zhu, Weishen;Li, Shucai;Liu, Jian
    • Geosciences Journal
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    • v.21 no.2
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    • pp.253-265
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    • 2017
  • Apparent discontinuities can be easily found in natural rock medium owing to the constant motion and change of the Earth's crust, which contains large amount of discontinuous surfaces such as faults, joints, cracks and so forth. Rock bolt is one of the most effective and economical reinforcing tools in practical geotechnical engineering for a long time. This paper investigates the mechanical properties, anchorage effect, cracking, and coalescence process of intact rock-like specimens, rock-like specimens containing flaws, and bolted rock-like specimens containing flaws. A series of uniaxial compression tests, splitting tests, and biaxial compression tests are performed on these specimens. Some findings can be observed from this study. (1) The number of rock bolt(s) and the anchoring angle have a great influence on the anchorage effect of rock bolt(s). With the increasing number of rock bolt(s), the uniaxial compressive strength (UCS), the splitting peak strength (which can be converted to the tensile strength), and biaxial compressive strength (BCS) can all be improved, whose variation tendencies do not follow a linear relationship. (2) The contributions to the tensile strength for rock bolt is greater than that to the UCS for the same-type specimen. (3) In the biaxial compression tests, with the increasing of the lateral pressures, the anchorage effect of rock bolt gradually declines and the lateral pressure plays a dominant role in improving the strength of the specimen. The failure characteristics of three types of laboratory tests have also been systematically analyzed in this paper.

A Study on the Problem and Improvement Plan of Rock Bolt Pull Test for Railroad Tunnel Construction (철도 터널 공사용 록볼트 인발 시험의 문제점과 개선방안에 관한 연구)

  • Jang Seog-Jae;Gwak Su-Jeong;Kim Doo-Jun
    • Journal of the Korean Society for Railway
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    • v.9 no.1
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    • pp.89-94
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    • 2006
  • We, presently, don't have clear diagram methods and analysis criteria in rock bolt pull test usable for tunnel reinforcement. So this paper has suggested that; first, 'scheme of apposite diagram method at hard rock and the different application method of rock bolt pull test at weathered and hard rock', and second, 'the pullout capacity specification criteria for design and construction of rock bolt', based on foreign criteria and field test.

Supporting Characteristics of a Spiral Bolt through Pull-out Test (인발시험을 통한 스파이럴 볼트의 지보특성)

  • Kim, Jang-Won;Kang, Choo-Won;Song, Ha-Lim
    • Explosives and Blasting
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    • v.29 no.1
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    • pp.10-16
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    • 2011
  • To make large slopes or rock structures stable, supporting systems, such as anchor bolt, rock bolt and spiral bolt which are developed recently, are commonly used. In this study, in-situ pull-out tests were carried out to compare the characteristics of rock bolt that is most widely used with ones of spiral bolt that is newly developed. Re-pull-out test for the spiral bolt in which loading and unloading cycles are repeated three times showed that the maximum pull-out load is almost constant irrespective of the number of loading cycles, which may be due to no failure between spiral bolt and filler. On the other hand, the maximum pull-out load for the conventional rock bolt decreases with the number of loading cycles due to the partial failure between rock bolt and filler.

Analysis for Mechanical Behavior of GFRP Rock Bolt for Permanent Support of Tunnel (영구 터널지보재로서의 활용을 위한 GFRP 록볼트의 역학적 거동 분석)

  • Sim, Jong-Sung;Kang, Tae-Sung;Lee, Yong-Taek;Kim, Hyun-Joong
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.14 no.6
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    • pp.124-131
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    • 2010
  • Rock Bolt generally utilizes deformed reinforcing bar welded from structural steel of which strength is higher than required for making advantageous use of the support function of ground. In the condition with highly corrosive underground water, however, problem frequently occurs on tunnel and slope stabilization in terms of repair, rehabilitation and maintenance issues due to the destruction of Rock Bolt by corrosion of steel. A structural performance evaluation for GFRP Rock Bolt was conducted for the purpose of resolving the foregoing problem and at the same time developing a permanently-usable support material. This study intended to evaluate the safety factor of GFRP Rock Bolt by implementing the slope stability interpretation via structural analysis on the basis of its structural characteristics derived from both tensile force function test and shear force function test. It is judged based on the results that GFRP Rock Bolt would secure sufficient ground stability as an alternative material for existing Steel Rock Bolt.

A Study on the Supporting Effect of a Spiral Bolt as a Support System (Spiral bolt의 지보효과에 관한 연구)

  • Cho, Young-Dong;Kang, Choo-Won;Kim, Jae-Woong
    • Tunnel and Underground Space
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    • v.20 no.5
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    • pp.332-343
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    • 2010
  • This study aims to evaluate the supporting effect of a spiral bolt that is superior to a rock bolt in terms of constructability, stability, environmental and economic aspects as a support system. This study thus analyzed the mechanical properties of a rock bolt which is widely used as a support and a spiral bolt. In addition, laboratory pull-out tests were conducted for the evaluation of properties of the supports such as displacement, pull-out load, confining pressure etc. Moreover, the differences between a rock bolt and a spiral bolt were drawn by comparing the two results of laboratory pull-out tests and in-situ pull-out tests. Then, the differences of the supporting effect of the two supports were analysed by comparing the results of the two pull-out tests with a numerical analysis using FLAC3D.

New reinforcement algorithms in discontinuous deformation analysis for rock failure

  • Chen, Yunjuan;Zhu, Weishen;Li, Shucai;Zhang, Xin
    • Geomechanics and Engineering
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    • v.11 no.6
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    • pp.787-803
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    • 2016
  • DDARF (Discontinuous Deformation Analysis for Rock Failure) is a numerical algorithm for simulating jointed rock masses' discontinuous deformation. While its reinforcement simulation is only limited to end-anchorage bolt, which is assumed to be a linear spring simply. Here, several new reinforcement modes in DDARF are proposed, including lining reinforcement, full-length anchorage bolt and equivalent reinforcement. In the numerical simulation, lining part is assigned higher mechanical strength than surrounding rock masses, it may include multiple virtual joints or not, depending on projects. There must be no embedding or stretching between lining blocks and surrounding blocks. To realize simulation of the full-length anchorage bolt, at every discontinuity passed through the bolt, a set of normal and tangential spring needs to be added along the bolt's axial and tangential direction. Thus, bolt's axial force, shearing force and full-length anchorage effect are all realized synchronously. And, failure criterions of anchorage effect are established for different failure modes. In the meantime, from the perspective of improving surrounding rock masses' overall strength, a new equivalent and tentative simulation method is proposed, it can save calculation storage and improve efficiency. Along the text, simulation algorithms and applications of these new reinforcement modes in DDARF are given.

Numerical Study on the Behavior of Fully Grouted Rock Bolts with Different Boundary Conditions (경계조건의 변화에 따른 전면접착형 록볼트 거동의 수치해석적 연구)

  • Lee, Youn-Kyou;Song, Won-Kyong;Park, Chul-Whan;Choi, Byung-Hee
    • Tunnel and Underground Space
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    • v.20 no.4
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    • pp.267-276
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    • 2010
  • In modern rock engineering practice, fully grouted rock bolting is actively employed as a major supporting system, so that understanding the behavior of fully grouted rock bolts is essential for the precise design of rock bolting. Despite its importance, the supporting mechanism of rock bolts has not been fully understood yet. Since most of existing analytical models for rock bolts were developed by drastically simplifying their boundary conditions, they are not suitable for the bolts of in-situ condition. In this study, 3-D elastic FE analysis of fully grouted rock bolts has been conducted to provide insight into the supporting mechanism of the bolt. The distribution of shear and axial stresses along the bolt are investigated with the consideration of different boundary conditions including three different displacement boundary conditions at the bolt head, the presence of intersecting rock joints, and the variation of elastic modulus of adjacent rock. The numerical result reveals that installation of the faceplate at the bolt head plays an important role in mobilizing the supporting action and enhancing the supporting capabilities of the fully grouted rock bolts.