The influence of rock bolt location on the reinforcement of horizontally bedded roofs by full column grouted bolts

Anchor support currently represents a significant reinforcing technique in underground constructions. The principles of rock bolt reinforcement action are derived from various concepts of the underground excavation stability. In recent times, rock bolt design techniques have been complemented by numerical calculations procedures. The paper describes FEM modelling of a rock bolt system for mechanical and grouted bolts.

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Validation of friction-anchored rock bolt characteristics

MINING INFORMATIONAL AND ANALYTICAL BULLETIN ◽

10.25018/0236-1493-2019-10-0-35-43 ◽

2019 ◽

Vol 10 ◽

pp. 35-43

Author(s):

A.A. Zubkov ◽

◽

V.N. Kalmykov ◽

I.M. Kutlubaev ◽

M.S. Naydenova ◽

...

Keyword(s):

Rock Bolt

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Pull-out and Critical Embedment Length of Grouted Rebar Rock Bolts-Mechanisms When Approaching and Reaching the Ultimate Load

Rock Mechanics and Rock Engineering ◽

10.1007/s00603-020-02318-6 ◽

2021 ◽

Author(s):

Are Håvard Høien ◽

Charlie C. Li ◽

Ning Zhang

Keyword(s):

Ultimate Load ◽

Failure Mechanisms ◽

Concrete Block ◽

Rock Bolts ◽

Rock Stratum ◽

Pull Out ◽

Deformation Length ◽

Embedment Length ◽

Pull Tests ◽

Grouted Bolts

AbstractRock bolts are one of the main measures used to reinforce unstable blocks in a rock mass. The embedment length of fully grouted bolts in the stable and competent rock stratum behind the unstable rock blocks is an important parameter in determining overall bolt length. It is required that the bolt section in the stable stratum must be longer than the critical embedment length to ensure the bolt will not slip when loaded. Several series of pull tests were carried out on fully grouted rebar bolts to evaluate the pull-out mechanics of the bolts. Bolt specimens with different embedment lengths and water/cement ratios were installed in either a concrete block of one cubic meter or in steel cylinders. Load displacement was recorded during testing. For some of the bolts loaded beyond the yield load, permanent plastic steel deformation was also recorded. Based on the test results, three types of failure mechanisms were identified, corresponding to three loading conditions: (1) pull-out below the yield strength of the bolt steel; (2) pull-out between the yield and ultimate loads, that is, during strain hardening of the steel; and (3) steel failure at the ultimate load. For failure mechanisms 2 and 3, it was found that the critical embedment length of the bolt included three components: an elastic deformation length, a plastic deformation length and a completely debonded length due to the formation of a failure cone at the borehole collar.

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Studying the performance of fully encapsulated rock bolts with modified structural elements

International Journal of Coal Science & Technology ◽

10.1007/s40789-020-00388-z ◽

2021 ◽

Author(s):

Jianhang Chen ◽

Hongbao Zhao ◽

Fulian He ◽

Junwen Zhang ◽

Kangming Tao

Keyword(s):

Shear Stress ◽

Load Transfer ◽

Maximum Shear Stress ◽

Coupling Model ◽

Numerical Approach ◽

Rock Bolt ◽

Structural Elements ◽

Rock Bolts ◽

Two Stage ◽

Bolt Diameter

AbstractNumerical simulation is a useful tool in investigating the loading performance of rock bolts. The cable structural elements (cableSELs) in FLAC3D are commonly adopted to simulate rock bolts to solve geotechnical issues. In this study, the bonding performance of the interface between the rock bolt and the grout material was simulated with a two-stage shearing coupling model. Furthermore, the FISH language was used to incorporate this two-stage shear coupling model into FLAC3D to modify the current cableSELs. Comparison was performed between numerical and experimental results to confirm that the numerical approach can properly simulate the loading performance of rock bolts. Based on the modified cableSELs, the influence of the bolt diameter on the performance of rock bolts and the shear stress propagation along the interface between the bolt and the grout were studied. The simulation results indicated that the load transfer capacity of rock bolts rose with the rock bolt diameter apparently. With the bolt diameter increasing, the performance of the rock bolting system was likely to change from the ductile behaviour to the brittle behaviour. Moreover, after the rock bolt was loaded, the position where the maximum shear stress occurred was variable. Specifically, with the continuous loading, it shifted from the rock bolt loaded end to the other end.

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Weightage Effect during Back-Calculation of Rock-Mass Quality from the Installed Tunnel Support in Rock-Mass Rating and Tunneling Quality Index System

Applied Sciences ◽

10.3390/app9102065 ◽

2019 ◽

Vol 9 (10) ◽

pp. 2065 ◽

Cited By ~ 3

Author(s):

Jonguk Kim ◽

Hafeezur Rehman ◽

Wahid Ali ◽

Abdul Muntaqim Naji ◽

Hankyu Yoo

Keyword(s):

Rock Mass ◽

Quality Index ◽

Rock Bolt ◽

Rock Mass Rating ◽

Rock Mass Quality ◽

Back Calculation ◽

The Difference ◽

Bolt Spacing ◽

Q System ◽

Selection Of

In extensively used empirical rock-mass classification systems, the rock-mass rating (RMR) and tunneling quality index (Q) system, rock-mass quality, and tunnel span are used for the selection of rock bolt length and spacing and shotcrete thickness. In both systems, the rock bolt spacing and shotcrete thickness selection are based on the same principle, which is used for the back-calculation of the rock-mass quality. For back-calculation, there is no criterion for the selection of rock-bolt-spacing-based rock-mass quality weightage and shotcrete thickness along with tunnel-span-based rock-mass quality weightage. To determine this weightage effect during the back-calculation, five weightage cases are selected, explained through example, and applied using published data. In the RMR system, the weightage effect is expressed in terms of the difference between the calculated and back-calculated rock-mass quality in the two versions of RMR. In the Q system, the weightage effect is presented in plots of stress reduction factor versus relative block size. The results show that the weightage effect during back-calculation not only depends on the difference in rock-bolt-spacing-based rock-mass quality and shotcrete along with tunnel-span-based rock-mass quality, but also on their corresponding values.

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