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| Research on the large deformation control mechanism of high pre-tension energy-absorbing bolts in tunnels |
| Tao Zhigang1,2, Zhan Jiawang1,2*，Yin Qian1,2,3, Ren Shulin1,2, Ma Zhigang1,2, Wei Hong1,2
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| (1.State Key Laboratory for Tunnel Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China; 2.School of Mechanics and Civil Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China; 3.State Key Laboratory for Intelligent Construction and Healthy Operation of Deep Underground Engineering, China University of Mining and Technology，Xuzhou 221116, Jiangsu，China) |
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Abstract Bolt support technology has been progressively developed toward the “three highs” of high pre tension, high strength, and high elongation. To explore the control mechanism of this type of bolt against large deformation disasters in tunnels, the NPR?DDA numerical simulation method and an NPR bolt with a pre?tension force of 100 kN, a tensile strength of 950 MPa, an elongation of 30%, and a diameter of 18 mm were employed. A systematic investigation was conducted on the evolution and control effects of large tunnel deformations under different support densities and with or without pre?tension. A numerical tunnel model with a diameter of 10 m and a thickness of 1 m under a uniform in?situ stress of 20 MPa was established. Bolts of 5 m length were installed with circumferential spacings of 0.98 m, 0.65 m, and 0.49 m, and pre?tension forces of 0 kN and 100 kN. The results showed that the tunnel failed under unsupported conditions and under a circumferential spacing of 0.98 m (both with and without pre?tension) and 0.65 m without pre?tension. In contrast, the tunnel deformation converged under a circumferential spacing of 0.65 m with pre?tension and under a spacing of 0.49 m (both with and without pre?tension). In the early stage of excavation, large deformation of the surrounding rock occurred in the form of shear cracks, and the shear resistance of the bolts could not be ignored. When tensile cracks appeared in large numbers, the surrounding rock rapidly failed. Compared with the case without pre?tension, applying pre?tension to the bolts enabled them to quickly rise from 100 kN to a constant resistance state exceeding 200 kN, which significantly enhanced the control effect on the surrounding rock. However, in the high in?situ stress soft rock numerical model used in this research, the rock mass was weak and prone to deformation. When the support density was insufficient (circumferential spacing of 0.98 m), the use of pre?tensioned supports caused the tunnel to fail more rapidly. The pre?tension was found to cause the local soft rock to enter a plastic flow state sooner than in the non pre tensioned case. Sudden increases in bolt axial force and in the number of tensile cracks could be taken as precursors to surrounding rock failure. A reference for understanding the mechanisms of large tunnel deformations and for developing support technologies was provided by this research.
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Received: 02 June 2026
Published: 20 August 2026
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