• Title, Summary, Keyword: Rockbolts

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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.

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.

Analysis of Deformation Behavior of Underground Caverns in a Discontinuous Rock Mass Using the Distinct Element Method (개별요소법을 이용한 불연속 암반내 지하공동의 변형 거동 해석)

  • Jung, Wan-Kyo;Lim, Han-Uk
    • Journal of Industrial Technology
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    • v.23 no.A
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    • pp.69-81
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    • 2003
  • Numerical analysis is important for the design, construction and maintenance of large caverns. The rock mass contains generally discontinuities such as faults, joints and fissures. The mechanical behavior and geometric characteristics of these discontinuities would have a significant impact on the stability of the caverns. In this research the Distinct Element Method(DEM) was used to analyze the structural stability of the large cavern. The Barton-Bandis Joint Model (B-B J.M) was used as a constitutive model for the joint. In addition, two different cases 1) analysis with a support system and 2) analysis with no support system, were analyzed to optimize a support system and to investigate reinforcing effects of a support system. The most significant parameters of in-situ stress, JRC of in-situ natural joints, and spatial distribution characteristics of discontinuities were acquired through field investigation. Displacement (horizontal, joint shear), maximum joint opening, maximum and minimum principal stresses, range of relaxed zone, rockbolt axial forces and shotcrete stresses were calculated at each excavation stage. As a result of analysis the calculated values proved to be under the allowable value Rockbolts also proved to be an efficient support measure to control joint shear displacement which had significant effects on extending the relaxed zone. As a consequence, the structural stability of the cavern was assured with an appropriate support system.

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A Study on the Support System of Large Caverns Under High Initial Stress (과지압 하에 있는 대규모 지하공동의 지보 시스템에 관한 연구)

  • 박연준;유광호;최영태;김재용
    • Tunnel and Underground Space
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    • v.14 no.2
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    • pp.154-166
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    • 2004
  • A numerical stability analysis was conducted on the large oil storage caverns excavated in a rock mass under high initial horizonal stress. The behaviors of the surrounding rock mass, rockbolts, and shotcrete were analyzedr and stability of the support members were assessed. For a proper support system design, the effect of the modelling technique, cavern shape and rockbolt length on the stability of the cavern was investigated. Results show that installation timing of supports and the change in cavern shape due to stepwise excavation affect the stress induced in support members. Also found was desperate need for a numerical technique which can properly reflect the behavior of the steel fiber reinforced shotcrete.

Study on performance verification of dual-purpose rockbolt for reinforcement and drainage (지반 보강과 배수를 위한 이중기능 록볼트 성능 검증에 관한 연구)

  • Jung, Young-Hoon;Kim, Doo-Rae;Kim, Kyeong-Cheol;Shin, Jong-Ho
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.20 no.5
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    • pp.869-886
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    • 2018
  • Rockbolt is one of the most common supports used to reinforce discontinuous rock during underground excavation. Extra drain pipes are installed to improve excavation workability and the anchorage of rockbolts in water bearing ground. The drain pipe is effective in improving the workability by providing drainage path, but it is difficult to expect the reinforcement effect, increasing disturbance of the discontinuous rock mass and the construction cost. To solve this problem, dual purpose rockbolt (DPR) has been developed for the reinforcement of rock and the drainage of ground water. DPR was able to improve the mechanical and hydraulic stability of the rocks quickly and economically. Two kinds of DPRs using FRP (Fiber Reinforced Plastic) and steel were investigated for the mechanical and hydraulic performance. Also, the workability and stability of DPR were analyzed.

Study on rock reinforcement process and the effect of produced strength right after rockbolt installation (록볼트의 타설 직후의 강도발현 과정 및 효과에 관한 연구)

  • Itoh, Jhun;Park, Hae-Geun;Kim, Dong-Wan;Kim, Jea-Kwon
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.5 no.2
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    • pp.189-198
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    • 2003
  • For the huge section of tunnel, it is highly required to observe the role of each rock support and their effect of rock reinforcement in order to investigate more reasonable rock support structure. Especially for unstable tunnel situation with no shotcrete strength right after an excavation, sufficient investigation is needed for rock support structure. In this paper, we clarify the relations of compressive strength and material age, cohesion strength and material age, and cohesion stiffness and material age of grout with time-dependence through tests and numerical analysis simulation with trial rock mass considering hardening of bolt grouting material. By means of this process, effect of rock reinforcement for rockbolt is investigated right after an excavation and modelling and physical constants of young aged rockbolts are obtained. Additionally, the effect of rock reinforcement with hydraulic tensile friction bolt is examined right after an excavation, which grout effect is no need to be waited.

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An Analysis Model of the Secondary Tunnel Lining Considering Ground-Primary Support-Secondary Lining Interaction (지반-1차지보재-2차라이닝의 상호작용을 고려한 터널 2차라이닝 해석모델)

  • 서성호;장석부;이상덕
    • Tunnel and Underground Space
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    • v.12 no.2
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    • pp.107-114
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    • 2002
  • It is the common practice to over design the reinforcement for the secondary tunnel lining due to the lack of rational insight into the ground loosening loads. and due to the conservative application of the empirical design methods. The main loads of the secondary lining are the ground Loosening loads and the ground water pressure, and the ground load is critical in the reinforcement design of the secondary lining in the case of drained tunnel. If the external load is absent around a tunnel, the reasons of the load far secondary tunnel lining are the deterioration of the primary supports such as shotcrete, steel rib, and rockbolts. Accordingly, the analysis method considering the ground-primary supports-secondary lining interaction should be required tar the rational design of the secondary tunnel lining. In this paper, the interaction was conceptually described by the simple mass-spring model and the load transfer from the ground and primary supports to the secondary lining is showed by the ground-primary supports-secondary lining reaction curves fur the theoretical solution of a circular tunnel. And also, the application of this proposed model to numerical analysis is verified in order to check the potential far the tunnel with the complex analysis conditions.

A Case study on the construction of a long tunnel in the youngdong railroad (Mt. Dongbaek-Dokye) (영동선 동백산-도계간 장대터널 시공사례 연구)

  • Kim, Yong-Il;Yoon, Young-Hoon;Cho, Sang-Kook;Yang, Jong-Hwa;Lee, Nai-Yong
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.4 no.2
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    • pp.155-165
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    • 2002
  • This paper presents a case study on the construction of a long tunnel named as "Solan tunnel", which connects between Mt. Dongbaek station and Dokye station in the Youngdong Railroad. The tunnel will be the longest tunnel with length of 16.4 km in Korea when completed. The tunnel site is located in a complex geological region with faults, cavities and coal measures. In construction of adit No. 2, geophysical investigation methods such as electrical resistivity method and GPR(Ground Penetration Radar) were used to detect faults, cavities and coal measures in advance with some success. The geophysical investigation results and in-situ boring data were used as feedback to improve tunnel reinforcement design. Also, the tube umbrellas of grouted steel pipes were found to have a good reinforcement and grouting effects in zones of faults, cavities. In zones of coal measures, swellex rockbolts with mortar grouting were verified as successful.

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Recent Issues in the Design and Construction of High-Performance Shotcrete Lining (고성능 숏크리트 라이닝의 설계 및 시공기술 분석)

  • 배규진;이석원;박해균;이명섭;김재권;장수호
    • Tunnel and Underground Space
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    • v.14 no.1
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    • pp.1-15
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    • 2004
  • The development of high-performance shotcrete lining is essential in improving the long-term durability of tunnels and in introducing single-shell tunnelling methods, where shotcrete as well as rockbolts are used as permanent support members. In this paper, new and advanced admixtures to improve shotcrete performance are introduced. In addition, requirements for mechanical properties as well as test items for quality control of shotcrete are summarized. A case study on the application of the pneumatic pin penetration test which can estimate compressive strength of shotcrete more easily and quickly is also illustrated. Previous studies to analyze the behaviors of shotcrete lining by considering its transient hardening and to carry out the sensitivity analysis of the design parameters of shotcrete lining are discussed to give fundamental concepts on rock-support interactions. Representative single-shell tunnelling methods where high-performance shotcrete lining is applied as a permanent support are also introduced.

Stability Analysis on the Intersection Area of Subway Tunnels by Observational Method (계측에 의한 지하철터널 교차부의 안정성 검토)

  • Kim Chee-Hwan
    • Tunnel and Underground Space
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    • v.15 no.1
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    • pp.71-79
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    • 2005
  • The stability of the intersection area of two tunnels is analyzed by observational method. The depth from ground surface to the intersected area is shallow and the geology around the area consists of soil and/or weathered rock. The tunnel is supported by reinforced protective umbrella method with 12 m long 3-layer steel-pipes and the intersected area is additionally reinforced with 6 m long rockbolts. The measured displacements are converged and mechanical stability of the intersected area of two tunnels is confirmed; tunnel arch settles to 6-7 mm at the crown and the sidewalls converges to about 5 mm. So based on the displacement measurements, the supporting system for the tunnel intersection proves to be effective to not only reduce the deformation of tunnels but also maintain the stability of tunnels.