Effect of Constructing a New Tunnel on the Adjacent Existed Tunnel in Weak Rock Mass: A Case Study

This study takes a new Shidao tunnel where the left line constructing in weak rock mass as a case study, and the effect of the new constructing tunnel on the existed tunnel are studied by the numerical analysis. High-precision field investigations are conducted to provide accurate parameters for the numerical model. The modified generalized Zhang-Zhu (GZZ) constitutive model is applied, and the numerical analysis results containing horizontal convergence displacement of side walls of the new constructing tunnel and a longitudinal crack in existed tunnel are validated by real-time monitoring. The vertical displacement of the vault, the horizontal displacement of the adjacent side wall, the plastic zone of the new constructing tunnel are studied. The effect of the new constructing tunnel on the existed tunnel is studied by analyzing the vertical displacement of the vault and the horizontal displacement of the adjacent side wall of the existed tunnel. During the constructing process of new tunnel, the maximum width variation of longitudinal crack is less than 0.3 mm. The maximum vertical displacement of the vault is less than 1 mm, and the maximum horizontal displacement of the adjacent side wall is less than 0.5 mm for the existed tunnel. Finally, the effects of tunnel spacing between new constructing and existed tunnels and geological condition represented by geological strength index (GSI) are investigated. The result shows that the maximum vertical displacements of the vault and the maximum horizontal displacement of adjacent side wall can reach −10.4 mm and −4.9 mm respectively when tunnel spacing is 0.5 d (d is actual spacing). When GSI is increased from 15 to 30, the maximum vertical displacement of the vault is reduced obviously.