Response of existing lining subjected to closed blasting in zero-spacing twin tunnels and its damping measures

•Through on-site vibration monitoring, the dynamic response patterns of the existing tunnel during the construction of zero-spacing tunnels.•The study has exposed the vibration and stress characteristics of the existing tunnel induced by the blasting in different steps of the new tunnel.•The influence mechanism of blasting stress waves on the existing tunnel has been analyzed.•Considering the influence of excavation sequence, excavation footage and thickness of damping layer, the corresponding measures are put forward to protect the existing tunnel lining. The blasting excavation of a new tunnel significantly impacts the lining of existing tunnels during the construction of zero-spacing twin tunnels. In this study, a field test was first carried out to study the vibration velocity of an existing lining in zero-spacing twin tunnels. LS-DYNA software was then employed to investigate the dynamic response characteristics under various blasting factors. Finally, the use of damping layer was considered to analyze its effects on the dynamic response of the existing tunnel lining. The maximum vibration velocity was found at the hance adjacent to the new tunnel, with a value of 17.51 cm/s in the tests. The maximum principal tensile stress(PTS) from the simulation was also shown at the same hance of the existing lining to have an intensity of 3.27 MPa. Additionally, the blasting of the rock mass close to the existing tunnel in the first step would result in a higher PTS intensity of 3.54 MPa within the lining, compared to the blasting of the rock mass away from the existing tunnel in the first step. However, the cumulative stress disturbance caused by the former to the lining was smaller than that of the latter. The maximum PTS at the hance was also found to linearly decrease with the reduction of the excavation footage and the maximum PTS was 2.3 MPa at an excavation footage of 0.9 m. The damping layer of the existing tunnel would contribute to a significant reduction of PTS. Therefore, a damping layer thickness of 2.5 cm was suggested in the study considering the effects of the damping and mechanics of the lining.