# A Finite Element Analysis of Tunnel Lining Demolition by Blasting for Subway Tunnel Expansion
###### Abstract  
In this paper, a practical project of subway tunnel lining demolition via blasting for the construction of a subway station under the action of the blasting load and the weight of collapsed rock mass was proposed. The tunnel overbreak and underbreak quality, the failure mechanism of the tunnel lining structure, the particle peak velocity (PPV), and the stress evolution law of the surrounding rock caused by tunnel blasting were researched using LS-DYNA. Firstly, the results show that the blasting parameters presented in this paper can maintain the cross-section of a smooth outline of tunnel excavation and the overbreak or underbreak quality in control. Secondly, the tensile stress in the existing tunnel lining caused by blasting exceeded the concrete tensile strength, and the radius of the burst fracture was 0.86 m, which is greater than the thickness of the tunnel lining (0.7 m). Thirdly, the blasting stress in the surrounding rock peaked within 0.1 \(\times\) 10\({}^{-3}\) s after the blasting, and failure of the surrounding rock occurred. Moreover, the relationship between the PPV and the distance from the blasting center shows that the blasting parameters used in this paper can effectively control the PPV. Therefore, this study reveals that the expansion of existing tunnels into subway stations using this method can improve the efficiency of construction.  
subway tunnel; expansion excavation; tunnel lining demolition; blasting load; failure mechanism; particle peak velocity (PPV) +
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a subway station by drilling and blasting. Considering newly built tunnel excavation and conventional tunnel in situ expansion engineering cases, some research achievements have been published regarding the influence of blasting shock waves on the surrounding rock and the tunnel lining structures of adjacent non-expanded tunnels. The mechanical responses of the surrounding rock and the tunnel structure have been studied during tunnel blasting excavation [7; 8; 9; 10; 11; 12; 13; 14; 15; 16]. For conventional tunnel in situ expansion engineering, [PERSON] et al. [17] determined the blasting vibration velocity law with multiple free surfaces by conducting a numerical analysis. [PERSON] et al. [18] analyzed the vibration velocity of the key parts of a tunnel structure by comparing the results from a numerical simulation and a field measurement of tunnel expansion using blasting. [PERSON] et al. [19; 20; 21; 22] proposed a basis for blasting safety evaluation based on the particle vibration acceleration index according to the impact of tunnel expansion using blasting on the existing tunnel lining. The aforementioned research achievements of the mechanical response of the surrounding rock and lining structure in the drilling and blasting construction process can be used as references in the study of blasting mechanical characteristics analysis if the subway station was expanded from an existing subway tunnel using in situ blasting.  
In this paper, based on the project background of the in situ blasting expansion of a subway tunnel to a subway station, a method of rapid removal of the tunnel lining is put forward, which aims to crush the existing pre-cut tunnel lining under the action of blasting shock waves and the weight of collapsed rock mass during the tunnel in situ expansion excavation process. The overbreak and underbreak of the tunnel excavation outline, the blasting response during the tunnel expansion construction, the stress evolution of the surrounding rock caused by the blasting shock waves, and the vibration velocity of the surrounding rock were analyzed according to a numerical simulation of a subway tunnel expanded in situ to a subway station by drilling and blasting. The findings can provide theoretical support to determine the blasting parameters of in situ expansion excavation during the subway station construction process.