A case study on rock damage prediction and control method for underground tunnels subjected to adjacent excavation blasting

Abstract

The effects of tunnel blast excavation on the surrounding rock mass and the lining systems of adjacent existing tunnels are comprehensively studied for the Damaoshan highway tunnel project as a case study. The damage of the surrounding rock and the lining system under different blast loads are analyzed by field tests and numerical simulations. It is observed that the rock damage extent around the tunnels linearly increases with the peak particle velocity (PPV) of the existing tunnel. A feasible PPV-based damage control method is then proposed for different portions of the tunnels. For the Damaoshan tunnel project, a PPV threshold of 0.22m/s in the adjacent existing tunnel is prescribed to limit the damage extent to approximately 1.6m at the tunnel exit and entrance portions. Furthermore, the PPV criteria for the other portions are also determined accordingly. It is also shown that no failure occurs in the linings or at the rock–lining interfaces if the PPV is less than 0.30m/s. The control method and the threshold PPV proposed in this study have been successfully applied to restrict blast-induced damage during the new tunnel excavation of the Damaoshan tunnel project.