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)
 Li L, Lei T, Li S. (2015). Risk assessment of water inrush in karst tunnels and software development. Arabian Journal of Geosciences 8(4): 1843-1854. https://doi.org/10.1007/s12517-014-1365-3
 Li L, Zhou ZQ, Li SC. (2015). An attribute synthetic evaluation system for risk assessment of floor water inrush in coal mines. Mine Water and the Environment 34(3): 288-294. https://doi.org/10.1007/s10230-014-0318-0
 Luo XW, He FL. (2014). A study of geological structures inclined to disaster and models of water burst in deep-buried long tunnels. Modern Tunnelling Technology 51(1): 21-25, 53. https://doi.org/10.13807/j.cnki.mtt.2014.01.006
 Li SC, Wang K, Li LP. (2017). Mechanical mechanism and development trend of water-inrush disasters in karst tunnels. Chinese Journal of Theoretical and Applied Mechanics 49(1): 22-30. https://doi.org/10.6052/0459-1879-16-345
 Guo JQ. (2011). Study on against-inrush thickness and water burst mechanism of karst tunnel. Beijing Jiaotong University.
 Kuzentsov SV, Troflmov VA. (2002). Hydrodynamic effect of coal seam compression. Journal of Mining Science 39(3): 205-212. https://doi.org/10.1023/A:1021981716467
 Li SC, Yuan YC, Li LP. (2015). Water inrush mechanism and minimum safe thickness of rock wall of karst tunnel face under blast excavation. Chinese Journal of Geotechnical Engineering 37(2): 313-320. https://doi.org/10.11779/CJGE201502015
 Zhang JW, Meng ZH, Zeng Y. (2017). Mechanism of water burst in the tunnel near faults in karst area. The Chinese Journal of Geological Hazard and Control 28(3): 73-79. https://doi.org/10.16031/j.cnki.issn.1003-8035.2017.03.11
 Li LP, Li SC, Zhang QS. (2010). Study of mechanism of water inrush induced by hydraulic fracturing in karst tunnels. Rock and Soil Mechanics 31(2): 523-528. https://doi.org/10.16285/j.rsm.2010.02.016
 Chi MJ, Zhao CG, Yang XL. (2004). Study on controlling vibration hazard of tunnel cave blasting in karst area. China Safety Science Journal 14(9): 72-75, 2. https://doi.org/10.16265/j.cnki.issn1003-3033.2004.09.016
 Liu Y. (2010). Grouting Technology of Rock Mass in Fractured Zone of Shallow Tunnel. Central South University.
 Li SC, Zhang WJ, Zhang QS. (2014). Research on advantage-fracture grouting mechanism and controlled grouting method in water-rich fault zone. Rock and Soil Mechanics 35(3): 744-752. https://doi.org/10.16285/j.rsm.2014.03.030
 Li LP, Lu W, Li SC. (2010). Research status and developing trend analysis of the water inrush mechanism for underground engineering construction. Journal of Shandong University (Engineering Science) 40(3): 104-112, 118.
 Chen J, Wei YS, Jiang H. (2017). Causes analysis and countermeasures for water inrush and sand gushing in fault and fracture zone during mined metro tunnel excavation. Tunnel Construction 37(7): 857-863. https://doi.org/10.3973/j.issn.1672-741X.2017.07.012
 Liu YS, Peng L, Wang MS. (2015). Blast-induced fractured zone of fractured rock-mass tunnel. China Journal of Highway and Transport 28(10): 83-89. https://doi.org/10.19721/j.cnki.1001-7372.2015.10.011
 Lu WB, Hustrulid W. (2003). Design approach for excavation blasting near contour of rock slope. Chinese Journal of Rock Mechanics and Engineering 22(12): 2052-2056. https://doi.org/10.1142/S0252959903000104
 Li YZ, Li ZG, Wang QS. (2013). On the grouting reinforcement and waterproofing techniques for mined subsea tunnels in soft fractured strata. Tunnel Construction 50(2): 26-33. https://doi.org/10.13807/j.cnki.mtt.2013.02.010
 Zhang X，Li SC. (2007). Stability analysis of rock cover of Qingdao Kiaochow bay sub-sea tunnel under explosive loads. Chinese Journal of Rock Mechanics and Engineering 26(11): 2348-2355.
 Li XY, Zhang DL, Fang Q. (2015). On water burst patterns in underwater tunnels. Modern Tunnelling Technology 52(04): 24-31, 40. https://doi.org/10.13807/j.cnki.mtt.2015.04.004
 Huang RQ, Wang XN, Chen LS. (2000). Hydro-splitting off analysis on underground water in deep-lying tunnels and its effect on water gushing out. Chinese Journal of Rock Mechanics and Engineering 19(5): 573-576.
 Berta G. (1994). Blasting-induced vibration in tunnelling. Tunneling and Underground Space Technology 9(2): 175-187. https://doi.org/10.1016/0886-7798(94)90029-9
 Sakural S, Kitamura Y. (1977). Vibration of tunnel due to adjacent blasting operation. Proceedings of International Symposium on Field Measurements in Rock Mechanics 61-74.
 Dai CQ, Zhao ZH. (2018). Survey on rheological behaviour of weakly cemented soft rock considering water deterioration. Journal of Advanced Oxidation Technologies 21(2): 334-342. https://doi.org/10.26802/jaots.2018.01824
 Dai CQ, Zhao ZH. (2015). Fuzzy comprehensive evaluation model for construction risk analysis in urban subway. International Journal of Modeling, Simulation, and Scientific Computing 6(3): 11-17. https://doi.org/10.1142/S1793962315500245
 Dai CQ, Lv YL. (2018). A novel image enhancement technique for tunnel leakage image detection. Tunnel Leakage Image Detection Technique 35: 209-222. https://doi.org/10.3166/TS.35.209-222