Failure Mechanism and Minimum Safe Thickness of Grouting Reinforcement Ring in Tunnels Excavated by Borehole Blasting

Failure Mechanism and Minimum Safe Thickness of Grouting Reinforcement Ring in Tunnels Excavated by Borehole Blasting

Chunquan DaiYunlong Lv

College of Civil Engineering and Architecture, Shandong University of Science and Technology, Qingdao 266590, China

Corresponding Author Email:
21 January 2019
18 March 2019
31 March 2019
| Citation



During tunneling by borehole blasting, the grouting reinforcement (GR) ring may lose stability, leading to water and mud inrush. To prevent these disasters, this paper establishes a GR model for tunnels excavated by borehole blasting, after summing up the relevant theories. Meanwhile, the failure mechanisms of the GR layer were deliberated under different geological conditions, from the perspective of mechanics, revealing that the instability hinges on the quality of the GR layer and the external water pressure. On this basis, the instability modes were classified into two categories: hydraulic fracturing and overall instability. After that, the minimum safe thickness (MST) formulas were derived for the GR layer of different failure modes, according to the elastic beam elastic model and the theories on blasting excavation disturbance belt and hydraulic fracturing belt. Finally, the proposed formulas were proved rational and universal through a FLAC3D numerical simulation on Xiamen Xiang’an Subsea Tunnel, Fujian, China.


borehole blasting, grouting reinforcement (GR), reinforcement ring instability, minimum safe thickness (MST)

1. Introduction
2. Instability Modes
3. Mechanical Models
4. Example Verification
5. Conclusions

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