• Title, Summary, Keyword: 록볼트

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A study on the development and field application of SP-Rockbolt with high-strength steel pipe (고강도 강관을 적용한 SP-록볼트 개발 및 현장 적용을 위한 연구)

  • Shin, Hyunkang;Jung, Hyuksang;Ahn, DongWook
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.19 no.4
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    • pp.651-668
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    • 2017
  • For initial stability of the tunnel, the primary support, Shotcrete and rockbolt shall be placed in the most appropriate time. This is because the role of such support plays a vital role in long-term and short-term tunnel stability. In this study, the rock bolt is an important supporting system that receives the external pressure generated by the stress relaxation during tunnel excavation as axial force and transmits it to the shotcrete on the tunnel excavation surface. Until now, most of the materials of rock bolts have been used in the field, but there have been many problems such as uncertain quality of Chinese materials entering the market, poor packing due to falling down of rock bolts when filled with mortar, and corrosion due to water. Therefore, in this study, we have developed a high strength steel pipe rock bolt using Autobeam material to solve and improve various problems of existing rock bolts. In order to evaluate the performance of the developed bolt, field tests were carried out and the existing mortar filler in order to improve the performance of the rock bolt, the design and construction criteria were studied and the results were included in this paper.

Reinforcing Effect of Pre-Tensioned Rock Bolts in the Jointed Rocks Condition (록볼트 긴장에 의한 수평절리암반의 보강효과)

  • An, Joung-Hwan;Lee, Sang-Duk
    • Tunnel and Underground Space
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    • v.19 no.5
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    • pp.388-396
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    • 2009
  • Rock bolt is one of the most important supports for tunnelling to prevent excessive ground relaxation at the primary tunnel excavation stage. It forms a ground arch band by confining the ground around a tunnel. Rock bolt has various effects, such as support or hanging effect, internal pressure effect, arching effect, ground improvement effect etc. Most studies on rock bolt focused on the concept of support, but only a few researches on the ground reinforcing effect by pre-tensioning a rock bolts. In this study, large scale model tests are performed to investigate the ground reinforcing effect of rock bolts for regularly jointed rocks. Simple beam model was built to find out the reinforcing effect of jointed rocks, which was reinforced by pre-tensioned rock bolts. Settlement of model beam was analyzed through measuring its sagging for various installation intervals.

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.

Integrity evaluation of rock bolts in the field by using hammer-impact reflection method (해머 타격 반사법을 이용한 현장 록볼트 건전도 평가)

  • Yu, Jung-Doung;Bae, Myeong-Ho;Lee, Yong-Jun;Min, Bok-Ki;Lee, In-Mo;Lee, Jong-Sub
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.11 no.1
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    • pp.47-56
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    • 2009
  • Rock bolts and shotcrete play a crucial role as a main support system in the underground space. Thus, the safety of the underground space may be affected by the defect of rock bolts. In order to evaluate the rock bolt integrity by using non-destructive technique, the transmission method of the guided ultrasonic waves, which are generated by using the piezo disk elements has been successfully performed. The energy generated by the piezo disk elements, however, is not enough for the rock bolts in the field. In addition, the piezo disk elements should be installed at the end of the steel bar during construction of the rock bolts. The purpose of this study is the devolvement of the reflection method, which may generate enough energy, and the application in the field rock bolts. Both laboratory and field tests are carried out. The guided ultrasonic waves with high energy are generated by the hammer impact with the center punch, and the AE sensor is used to measure the reflected guided waves. The received guided waves are analyzed by the wavelet transform. The peak value of the wavelet transform produces the energy velocity, which is used for the evaluation of the rock bolt integrity. The energy velocity increases with an increase in the defect ratio in both laboratory and field rock bolts. This study demonstrates that the hammer-impact reflection method may be a suitable method for the evaluation of the rock bolt in the field.

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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.

Evaluation on Reinforcing Effect of Inclined System Bolting by Model Tests and Numerical Analysis (모형시험 및 수치해석을 통한 경사 시스템 록볼트의 보강효과 분석)

  • Lee, Jea-Dug;Kim, Byoung-Il;Yoo, Wan-Kyu;Han, Jin-Tae
    • Journal of The Korean Society of Civil Engineers
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    • v.33 no.4
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    • pp.1529-1539
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    • 2013
  • Recent case studies in Japan have shown that rockbolts are commonly installed at an oblique angle to the excavation direction of the tunnel, instead of at a right angle, due to restriction of the working space. In particular, in the case of expansion in an existing tunnel, the working space can be very small, due to the large protective structures necessary to operate within an existing tunnel. In this case, where both the current use of the existing tunnel, and the reinforcement of the ground around the tunnel are required, the effects of installation angles and patterns of rockbolts are important factors in the design process. Therefore, in this study, a total number of 24 model tests are performed, to investigate the reinforcing effects of system bolting installed obliquely from the excavation direction of the tunnel, by changing the installation angle of bolts, longitudinal distance, and bonded length of bolts. The model test results indicate that the relaxed load ratio decreases, with the increase of both the bonded lengths and the number of the installed bolts, resulting in the decrease of the supported area by one bolt. Two-dimensional numerical analysis, which considered the reinforcement effect of inclined system bolting as the change of engineering properties near the tunnel, demonstrated that the deflection patterns at the tunnel crown in the numerical simulations, show a similar tendency to those measured in the model tests.

A Study on the Reinforcement Effects of Fully-Grouted Rock Bolts (전면접착형 록볼트의 보강효과에 관한 연구)

  • 정해성;문현구
    • Tunnel and Underground Space
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    • v.9 no.3
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    • pp.194-203
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    • 1999
  • The axial stress in rock bolt, the shear stress at the bolt-grout interface and the neutral point are analyzed to understand the mechanical behavior of rook bolt. To analyze the support effects of rock bolt in various geological conditions, numerical analyses are performed with regard to bolt spacing and bolt length in several geological conditions and tunnel sizes. Through the numerical analyses, the distributions of maximum tensile stress and shear stress are determined. And the excavation width of underground opening affects the position of the neutral point. In the circular opening supported by pattern bolting, the increase of confining pressure, the reduction of plastic zone, and that of ground displacement are determined by using the radial stress increase ratio, the plastic zone reduction ratio and the displacement reduction ratio respectively. The results of this study can be applied to a practical tunnel design through understanding of the trends of these support effects.

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Integrity evaluation of rock bolt grouting using ultrasonic transmission technique (초음파 투과법을 이용한 록볼트 그라우팅의 건전도 평가)

  • Han, Shin-In;Lee, Jong-Sub;Lee, Yong-Jun;Nam, Seok-Woo;Lee, In-Mo
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.9 no.1
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    • pp.75-82
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    • 2007
  • As one of the main support systems, rock bolts play a crucial role in the reinforcement of tunnels. Numerical and experimental studies using a transmission method of ultrasonic guided waves are performed to evaluate the integrity of rock bolts encapsulated by grouting paste. Numerical simulations using "DISPERSE" are carried out for the selection of the optimal experimental setup, i.e. non-destructive testing (NDT) system of the rock bolt. Based on results of the numerical simulation, the calculated frequency range for NDT testing is between 20kHz and 70kHz with the first longitudinal L(1) mode. Laboratory transmission tests are performed by attaching the piezo electric sensor at the tip of the rock bolt before embedding. Both of analytical and experimental results show that the amplitude of signals as well as the wave velocity increases with increase in the defect ratio of grouting paste. The defect in grouting paste means that the space around the rock bolt is not fully filled with the grouting paste. Experimental results also show that the increase of the wave velocity is more sensitive to the defect ratio increase than that of the amplitude. This study demonstrates that the transmission technique of ultrasonic guided waves may be a valuable tool in the evaluation of the rock bolt integrity.

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A Study on the Problem and Improvement Plan of Pull Test Method and Test Result Judgment of Rock Bolts Usage for Tunnel Construction (터널 공사용 록볼트의 인발 시험 방법 및 시험 결과 판정시의 문제점과 개선방안에 관한 연구)

  • Jang, Suk-Jae
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.9 no.4
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    • pp.135-140
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    • 2005
  • In case of rock bolt useable by tunnel reinforcement methods at field is applied problem of typical rock bolt pull test diagram method propositional in documents and is not thesis of clearness analysis basis about result of rock bolt pull test. So this paper suggested in consideration of foreign basis and field condition that the first, "suggestion of apposite diagram method at tight ground and difference application of rock bolt pull test method at loose and tight ground" and the second, "thesis of estimation basis non-thesis of design and specification, test etc".

A Study on the Support Characteristics of the High Strength Lightweight Steel Pipe Rockbolt (경량 고강도 강관 록볼트의 지보특성에 관한 연구)

  • Kim, Jong Woo;Kim, Myeong Kyun;Kim, Dong Man;Kim, Kyung Hun;Baek, Jae Wook
    • Tunnel and Underground Space
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    • v.24 no.5
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    • pp.395-403
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    • 2014
  • In this study, a steel pipe type rockbolt manufactured from special material was developed which has high strength and lightweight characteristics. Achievement of grout filling between rockbolt and hole wall was investigated through grout injection tests. Yield force of the developed rockbolt was also examined through tensile tests, which was compared with that of the deformed bar type rockbolt. In addition, the strength and elongation properties of the developed rockbolt were investigated through pull-out tests at three domestic sites showing different RMR classes. It is finally supposed that the developed rockbolt can be suitable for the permanent tunnel support because it has high strength and high durability rather than deformed bar type rockbolt.