Abstract:

In order to decrease the blasting damage to tunnel surrounding rocks, a new charging structure and its mechanism are proposed based on the traditional smooth blasting charging structure. The PVC-U material is placed beside the burn-cut cavities to protect the surrounding rocks of the tunnel. The Φ100 mm Hopkinson test equipment is used for the purpose of researching the weakening level of the PVC-U pipe. The analysis is made on macroscopic damage of the test sample, attenuation of stress wave and dissipation of energy respectively. The test results show that: the stress state of rock is changed by the protective layer and the damage of the rock without protective layer is worse than that with the protective layer; and as increasing of the thickness of protective layer from 0 to 6.24 mm, the degree of rock damage decreases; the stress peak shows decreasing trend; and the reduction rate of peak stress value increases instantly. The ratio of dissipation of energy and the incident is reduced from 61.08% to 39.97%. Thus the conclusion can be drawn that the impact damage of rock is protected by the protective layer. Good results have been obtained in a roadway excavation project.

Key words: tunnel surrounding rock, blasting, damage protection, split Hopkinson pressure bar, protective layer