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Chen Cao - One of the best experts on this subject based on the ideXlab platform.
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analytical approach in optimising selection of rebar bolts in preventing Rock Bolting failure
International Journal of Rock Mechanics and Mining Sciences, 2014Co-Authors: Chen Cao, Ting Ren, Christopher David Cook, Yijia CaoAbstract:Abstract The interaction of the rebar bolt profile with the surrounding medium is investigated analytically. The grout/bolt interface failure is categorised into dilational slip and parallel shear failure based on experimental observations. For each failure mode, an analytical expression for the failure is derived after introducing Mohr–Coulomb׳s failure criterion. The theoretical predictions are compared to, and showed good agreement with, experimental data. After introducing the concept of the most vulnerable slip angle in dilational slip failure, the role of the rebar profile is identified quantitatively with respect to bond failure. It is found that the optimal profile geometry is related to the mechanical properties of the grout and the confining pressure when failure occurs. Therefore, bolt profile studies must take into account the mechanical properties of the grout and confine pressure. In addition, conclusions drawn from laboratory pull out tests should be evaluated properly considering both the testing and in-situ conditions before any application. A case study has been included to demonstrate the application of the developed theory. In a coal mine roadway primary reinforcement design, Rock bolts have to be selected out of the four most popular types currently used in the Australian mining industry. The advantages and disadvantages of each bolt are discussed analytically for each case, providing a way for engineers to select the optimal bolt in their application.
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introducing aggregate into grouting material and its influence on load transfer of the Rock Bolting system
International journal of mining science and technology, 2014Co-Authors: Chen Cao, Ting Ren, Cook ChrisAbstract:A fully grouted bolt provides greater shear load capacity for transmitting the load from the Rock to the bolt, and vice versa. When grout fills irregularities between the bolt and the Rock, a keying effect is created to transfer the load to the bolt via shear resistance at the interface and within the grout. Previous research has revealed that the mechanical properties of the grout had a great impact on the load transfer capacity of the Rock Bolting system. This paper presents a method to enhance the Rock Bolting strength by introducing metal granules into the grouting material. Experimental results suggest that both the average peak load of pullout tests and the total energy absorption of the system will increase if some metal granules are mixed into the resin.
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A study of Rock Bolting failure modes
International Journal of Mining Science and Technology, 2013Co-Authors: Chen Cao, Nemcik Jan, Ting Ren, Aziz NajAbstract:Abstract Rock Bolting has advanced rapidly during the past 4 decades due to a better understanding of load transfer mechanisms and advances made in the bolt system technology. Bolts are used as permanent and temporary support systems in tunnelling and mining operations. A review of has indicated that three systems of reinforcement devices have evolved as part of Rock bolt and ground anchor while the Rock is not generally thought of as being a component of the reinforcement system. A classification of Rock Bolting reinforcement systems is presented, followed by the fundamental theory of the load transfer mechanism. The failure mode of two phases of Rock Bolting system is formularised. The failure modes of cable Bolting are discussed using a bond strength model as well as an iterative method. Finally, the interfacial shear stress model for ribbed bar is introduced and a closed form solution is obtained using a tri-line stress strain relationship.
Aziz Naj - One of the best experts on this subject based on the ideXlab platform.
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Innovative approach to strata reinforcement in coal mines with reference to evaluation cable bolts shear strength
'Sociological Research Online', 2018Co-Authors: Aziz Naj, Mirza Ali, Yang Guanyu, Khaleghparast Saman, Resekh HAbstract:There is an increasing need to determine accurately the strength properties of tendons for an effective ground control on mines and underground structures as well as on modelling simulations. The strength properties of cables, used as cable bolts, have been evaluated mainly by their ultimate tensile strength, as this kind of test can be carried out in the field as well as in the laboratory. Only recently, there has been a growing interest in cable bolt failures in shear because of the documented field failure evidence. Accordingly, this paper reports various methods of shear testing of Rock bolts and cables using different shear testing rigs, some have been developed by the Rock Bolting research team at the University of Wollongong. A programme of shear testing of a variety of cable bolts marketed in Australia was undertaken, the results of which were reported and conclusions were drawn. It was concluded that plain cable bolts were de-bonded during shearing when compared to spiral cables under the same testing conditions. In addition, both the single shear and double shear testing methodologies will result in the same outcome if there is no de-bonding, and a proper confinement is applied
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Factors influencing the quality of encapsulation in Rock Bolting
Research Online, 2016Co-Authors: Aziz Naj, Craig Peter, Mirza Ali, Nemcik JanAbstract:Bolt installation quality is influenced by various factors, some are well known and others are less recognised. A programme of field and laboratory studies was undertaken to examine various factors of relevance to the load transfer mechanism between the bolt, resin and Rock to ensure test methods truly represent field performance. Short encapsulation tests were undertaken as part of the Australian Coal Association Research Program (ACARP) funded project (C21011) with the ultimate aim of developing standard test methods for assessing bolt encapsulation with chemical resin anchor installations. The field study consisted of a series of Short Encapsulation Pull Tests (SEPT) carried out in three mines with different geological conditions to determine the most representative and practical method of SEPT. Additional field work included installation of bolts into threaded steel tubes for subsequent removal and laboratory evaluation. A series of pull tests was carried out by installing bolts in overhead rig mounted sandstone block, cast in concrete with controlled encapsulation length. Factors of importance considered included; borehole diameter, resin annulus thickness, installation time (including bolt spin to the back and spin at back ), the effect of gloving and hole over drill. It was found that the borehole diameter had a detrimental effect on the encapsulation bonding strength. Bolt installation time of approximately 10 s constituted an acceptable time for effective bolt installation and within the resin manufacturers recommended time of 14 s. Maintaining constant length of encapsulation was paramount for obtaining consistency and repeatability of the test results. Finally, a numerical simulation study was carried out to assess the capabilities of FLAC 2D software in simulating the pull testing of Rock bolts
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A study of Rock Bolting failure modes
International Journal of Mining Science and Technology, 2013Co-Authors: Chen Cao, Nemcik Jan, Ting Ren, Aziz NajAbstract:Abstract Rock Bolting has advanced rapidly during the past 4 decades due to a better understanding of load transfer mechanisms and advances made in the bolt system technology. Bolts are used as permanent and temporary support systems in tunnelling and mining operations. A review of has indicated that three systems of reinforcement devices have evolved as part of Rock bolt and ground anchor while the Rock is not generally thought of as being a component of the reinforcement system. A classification of Rock Bolting reinforcement systems is presented, followed by the fundamental theory of the load transfer mechanism. The failure mode of two phases of Rock Bolting system is formularised. The failure modes of cable Bolting are discussed using a bond strength model as well as an iterative method. Finally, the interfacial shear stress model for ribbed bar is introduced and a closed form solution is obtained using a tri-line stress strain relationship.
Ting Ren - One of the best experts on this subject based on the ideXlab platform.
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analytical approach in optimising selection of rebar bolts in preventing Rock Bolting failure
International Journal of Rock Mechanics and Mining Sciences, 2014Co-Authors: Chen Cao, Ting Ren, Christopher David Cook, Yijia CaoAbstract:Abstract The interaction of the rebar bolt profile with the surrounding medium is investigated analytically. The grout/bolt interface failure is categorised into dilational slip and parallel shear failure based on experimental observations. For each failure mode, an analytical expression for the failure is derived after introducing Mohr–Coulomb׳s failure criterion. The theoretical predictions are compared to, and showed good agreement with, experimental data. After introducing the concept of the most vulnerable slip angle in dilational slip failure, the role of the rebar profile is identified quantitatively with respect to bond failure. It is found that the optimal profile geometry is related to the mechanical properties of the grout and the confining pressure when failure occurs. Therefore, bolt profile studies must take into account the mechanical properties of the grout and confine pressure. In addition, conclusions drawn from laboratory pull out tests should be evaluated properly considering both the testing and in-situ conditions before any application. A case study has been included to demonstrate the application of the developed theory. In a coal mine roadway primary reinforcement design, Rock bolts have to be selected out of the four most popular types currently used in the Australian mining industry. The advantages and disadvantages of each bolt are discussed analytically for each case, providing a way for engineers to select the optimal bolt in their application.
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introducing aggregate into grouting material and its influence on load transfer of the Rock Bolting system
International journal of mining science and technology, 2014Co-Authors: Chen Cao, Ting Ren, Cook ChrisAbstract:A fully grouted bolt provides greater shear load capacity for transmitting the load from the Rock to the bolt, and vice versa. When grout fills irregularities between the bolt and the Rock, a keying effect is created to transfer the load to the bolt via shear resistance at the interface and within the grout. Previous research has revealed that the mechanical properties of the grout had a great impact on the load transfer capacity of the Rock Bolting system. This paper presents a method to enhance the Rock Bolting strength by introducing metal granules into the grouting material. Experimental results suggest that both the average peak load of pullout tests and the total energy absorption of the system will increase if some metal granules are mixed into the resin.
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A study of Rock Bolting failure modes
International Journal of Mining Science and Technology, 2013Co-Authors: Chen Cao, Nemcik Jan, Ting Ren, Aziz NajAbstract:Abstract Rock Bolting has advanced rapidly during the past 4 decades due to a better understanding of load transfer mechanisms and advances made in the bolt system technology. Bolts are used as permanent and temporary support systems in tunnelling and mining operations. A review of has indicated that three systems of reinforcement devices have evolved as part of Rock bolt and ground anchor while the Rock is not generally thought of as being a component of the reinforcement system. A classification of Rock Bolting reinforcement systems is presented, followed by the fundamental theory of the load transfer mechanism. The failure mode of two phases of Rock Bolting system is formularised. The failure modes of cable Bolting are discussed using a bond strength model as well as an iterative method. Finally, the interfacial shear stress model for ribbed bar is introduced and a closed form solution is obtained using a tri-line stress strain relationship.
Abbas Taheri - One of the best experts on this subject based on the ideXlab platform.
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Effect of Contributing Parameters on the Behaviour of a Bolted Rock Joint Subjected to Combined Pull-and-Shear Loading: A DEM Approach
Rock Mechanics and Rock Engineering, 2019Co-Authors: Mahdi Saadat, Abbas TaheriAbstract:The mechanical performance of fully grouted Rock bolts is essential in the stability of underground excavations in jointed Rock masses. This research implements a new cohesive contact model in distinct element codes (PFC2D) to investigate the fracturing response of Rock-like and grout material, as well as the bolt–grout interface. The results are compared in detail with experimental observations. The proposed modelling approach, used in conjunction with the distinct element method (DEM), successfully predicted the behaviour of grout failure and the bolt–grout interface’s shear response. We then developed a novel numerical, stepwise pull-and-shear test (SPST) scheme to further analyse the mechanical behaviour of bolted Rock joints subjected to simultaneous pull–shear loading. The cohesive DEM framework proposed in this paper was used to carry out the SPST scheme numerically. The mechanism involved in enhancing the shear strength of bolted Rock joint was determined by monitoring the $$ \sigma_{\text{n}}^{\text{i}} $$ σ n i and its corresponding contact chain force network during the pull-out test. The influence of pretension stress, the rig angle of the bolt profile, and the constant normal stiffness (CNS) condition are assessed systematically. In particular, the pretension stress magnitude at which the synthetic Rock Bolting system exhibits the highest shear resistance is identified. The findings from this research highlight the sensitivity of bolted Rock joints to the simultaneous pull-and-shear loading, boundary conditions, and bolt–grout interface configurations.
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A Modified Coal Mine Roof Rating Classification System to Design Support Requirements in Coal Mines
Journal of The Institution of Engineers (India): Series D, 2017Co-Authors: Abbas Taheri, Mario Andres Guardado MedinaAbstract:The coal mine roof rating (CMRR) classification system has been applied in a number of coal mines worldwide including Australia. However, the current system cannot be used directly to design support measures in underground mines. Two case studies, the Eliza Hill project in Australia and Tabas coal mine in Iran were analyzed to assess the impact of various Rock properties and gallery geometry on stability and to modify the CMRR classification system. Having considered the CMRR system as a working classification system, applicable information and related coal mine data were selected from the two case records. The CMRR value was evaluated and analysed by undertaking correlation between CMRR and factor of safety, followed by a parametric study based on various Rock properties and gallery geometries. To improve the applicability of the current system, the CMRR system was then modified by adding additional parameters, namely, the width of roof span and the density of overburden Rock. Consequently, based on the modified CMRR system (mCMRR) roof support requirements were recommended to select the suitable Rock Bolting system including length and spacing of Rock bolt. Numerical modelling were then undertaken to verify the support requirements recommended. The support requirements recommended by the mCMRR were found to be relatively identical with numerical analysis results. Support systems proposed by mCMRR can assist mining engineers to assess the stability of underground coal mines or verify the results of other design tools.
Che Yulong - One of the best experts on this subject based on the ideXlab platform.
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the design and application of Rock Bolting in coal mine
Energy Procedia, 2012Co-Authors: Qian Kun, Xin Xiaodong, Che YulongAbstract:Abstract In order to provide scientific and rational support plan, this paper through combining theoretical calculation and field application, designed the support means of suiting this coal in different geological conditions, the scheme must change with the actual changes to achieve the purpose of safety supporting. This scheme has important reference meaning to the support work of the follow-up new roadways. The innovation point of this paper is comparing the theoretical design with the practical support plan, to proof that the theoretical calculation is scientific and practical.
