Abstract
Mining engineering plays a significant role in the current society. It provides the energy resources including coal and hard rocks to guarantee the normal operation of the society. Therefore, not only developed countries but also developing countries still pay much attention to their mining industry.
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1.1 Background
Mining engineering plays a significant role in the current society. It provides the energy resources including coal and hard rocks to guarantee the normal operation of the society. Therefore, not only developed countries but also developing countries still pay much attention to their mining industry.
This is more obvious in China. For example, the statistical data shows that more than a half of the electricity still comes from the thermal power generation. Therefore, continuous production of coal resources is important in guaranteeing the normal power generation and convenient running of the society.
To make sure that coal mines can operate stability, the ground control techniques are significant. It is well known that after the rock masses around the mineral resources are excavated, the rock masses around the excavation tend to move towards the excavation direction. Therefore, to maintain the stability of the underground excavations, ground control techniques and instruments should be used.
Among kinds of ground control techniques and instruments, rock bolts are widely accepted and used by mines. The rock bolt is a bar or a cable that is installed in the rock mass. Although rock bolts can be divided into frictional bolts or mechanical bolts, the laboratory and in situ tests show that the mechanical bolts have better performance.
For mechanical rock bolts, either resin-based or cement-based grout can be used as the anchorage agent. These different grouts can be poured into the drilled borehole to bond the rock bolt with the surrounding rock mass. As for the in situ practice, the point-anchored method or the fully grouted method can be used. However, previous research shows that when the fully grouted method is used, there is a better load transfer between the rock bolt and the surrounding rock masses [1].
Nevertheless, when the fully grouted rock bolts are used, failure of the rock bolting system still occurs. A summary of the rock bolting failure modes shows that the rock bolting system can fail by different types, including the bond failure at the bolt/grout interface, the bond failure at the grout/rock interface, shear failure of the grout column, shear failure of the rock mass and tensile rupture of the rock bolt [2].
However, it is more common to encounter the bond failure at the bolt/grout interface [3]. The reason is that the shear strength of the bolt/grout interface is much smaller than the tensile strength of the rock bolt. Moreover, in the rock bolting system, the bolt/grout interface has the relatively smaller contact area. This leads to the shear stress concentration at the bolt/grout interface. Consequently, bond failure of the bolt/grout interface is more likely to occur.
To better understand the load transfer mechanism of fully grouted rock bolts and prevent bond failure of the bolt/grout interface, this book summarised the previous research work conducted by the authors regarding the anchorage performance of rock bolts. This book is divided into seven chapters. Within those seven chapters, the shear behaviour of the bolt/grout interface, the shear failure of the cement-based grout, the load transfer performance of rock bolts and the parameter analysis on the performance of rock bolts are studied. This book is beneficial for researchers and engineers to better understanding the load transfer performance of rock bolts. Moreover, it can help researchers and engineers to propose and develop new approaches to prevent failure of the rock bolting system.
1.2 Book Outline
This chapter aims at providing the general introduction for this book. The general background of rock bolting is illustrated. Then, the basic structure of this book is presented.
Chapter 2 gives a literature review on the shear stress propagation mechanism in the rock reinforcement system. More attention is paid to the bolt/grout interface. The investigation approaches used in previous research are summarised. Moreover, the shear stress propagation process at the bolt/grout interface is elaborated. And a detailed discussion is added to analyse the shear stress propagation mechanism of the bolt/grout interface.
Chapter 3 studies the shear behaviour of the cement-based grout. Two different water-cement (w/c) ratios are used: 0.4 and 0.5. The numerical compressive strength tests are conducted to calibrate the input parameters. Then, the direct shear test is simulated to study the shear behaviour of the cement-based grout. Experimental direct shear tests are used to confirm the accuracy of the numerical direct shear test. Moreover, the shear stress distribution in the cement-based grout is analysed.
Chapter 4 presents an analytical modelling to investigate the shear behaviour of the bolt/grout interface. The bond-slip behaviour of the bolt/grout interface is simulated with a tri-linear model. An analytical model is developed based on the shear stress propagation mechanism at the bolt/grout interface. The pull-out performance of the rock bolts is divided into the elastic, elastic-softening, elastic-softening-debonding, softening-debonding and debonding stages. Credibility of the analytical model is validated with experimental pull-out tests.
Chapter 5 studies the influence of the confining medium on the load transfer performance of rock bolts. In this chapter, the tri-linear model is still used to depict the shear behaviour of the bolt/grout interface. Then, this tri-linear model is incorporated into the rock bolting system. After that, based on this analytical model, the influence of the confining medium on the load transfer capacity of rock bolts is studied. Moreover, the critical influence diameter of the confining medium for the rock bolts is analysed.
Chapter 6 conducts a comprehensive parameter study on the load transfer performance of rock bolts. The influence of the bolt diameter, elastic modulus of bolts, grouted length of bolts and bond slipping when bond strength reaches is studied. The maximum load transfer capacity of rock bolts is analysed and compared. Moreover, when the rock bolt reaches the maximum load transfer capacity, the shear stress distribution state of the bolt/grout interface is analysed.
Chapter 7 proposes an analytical model for fully grouted rock bolts based on a nonlinear bond-slip model. In this chapter, an exponential nonlinear model is used to depict the shear behaviour of the bolt/grout interface. Then, the load transfer performance of rock bolt is successfully simulated. Experimental pull-out tests are used to confirm that this nonlinear model can be used to simulate the pull-out performance of rock bolts. Moreover, the load distribution along the axial direction of rock bolts is studied.
References
A. Kilik, E. Yasar, A.G. Celik, Effect of grout properties on the pull-out load capacity of fully grouted rock bolt. Tunn. Undergr. Space Technol. 17, 355–362 (2002). https://doi.org/10.1016/S0886-7798(02)00038-X
J. Chen, B. Zeng, L. Liu, K. Tao, H. Zhao, C. Zhang, J. Zhang, D. Li, Investigating the anchorage performance of full-grouted anchor bolts with a modified numerical simulation method. Eng. Fail. Anal. 141, 1–14 (2022). https://doi.org/10.1016/j.engfailanal.2022.106640
S. Ma, X. Zhu, W. Qin, S. Hu, Determination of the bond-slip relationship of fully grouted rockbolts. Environ. Earth Sci. 77(9), 325–326 (2018). https://doi.org/10.1007/s12665-018-7495-2
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Chen, J., Li, Y., Zhang, J. (2023). Introduction. In: Bond Failure Mechanism of Fully Grouted Rock Bolts. SpringerBriefs in Applied Sciences and Technology. Springer, Singapore. https://doi.org/10.1007/978-981-99-0498-3_1
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DOI: https://doi.org/10.1007/978-981-99-0498-3_1
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