Abstract:

DalongshanHuahuiyuan running tunnel on Line 6 of Chongqing Metro has a 500 mlong closelyspaced stacked tunnel section, which is located in mediumthick layered rocks. The blasting excavation of the stacked tunnel may have adverse impact on the tunnel structure, as well as on the rocks between the twin tunnel tubes. It is proposed that the upper tunnel tube should be excavated before the lower tunnel tube and that countermeasures should be taken according to the thickness of the rocks between the twin tunnel tubes. Theoretical calculations made shows that, for the twin tunnel tube section with thin rocks between the tunnel tubes, vibrationreducing blasting technology and nonblasting excavation technology should be adopted so as to ensure the safety of the tunnel structure. For the 25 mlong twin tunnel tube section with less than 3.5 mthick rock between the tunnel tubes, the top heading of the upper tunnel tube should be excavated, while the bench of the upper tunnel tube should be reserved; Then the lower tunnel tube is excavated by blasting means before the bench of the upper tunnel tube is excavated by nonblasting means, so as to minimize the adverse effect on the rocks between the twin tunnel tubes and, in the end, to ensure the safety of the tunnel structure and the tunneling activity.

Key words: stacked tunnel, layered rock, small clearance, vibrationreducing blasting, nonblasting excavation, rock between twin tunnel tubes