Abstract: It is very important for protective design of tunnel entrance that assessing anti-detonating performance of surrounding rock using pipe roof reinforcement. Based on principle of similarity simulation, nature or grouting rockmass and steel pipe were replaced using cement soil of different cement-mixing ratios and plastic pipe respectively. Using the model tests, anti-detonating performance of tunnel entrance reinforced with pipe roof under explosive load was simulated. Length, width and height of three models are 2 m, 2.2 m and 2 m respectively. The dynamic response and failure characteristic on tunnel entrance reinforced with none, one layer and three layers pipe roof were simulated using the three models respectively under direct explosion in the model top. Experiments show that the pipe roof supporting can reinforce surrounding rock effectively, enhance integrity and make the distributions of stress more reasonable; the entrance failure decreases significantly with the increase of pipe roof layer, such as failure range from 1.55 m to 0.45 m, the maximum main crack width from 25 mm to 3 mm, the maximum netty crack width from 24 mm to 0.3 mm, the crack number from 14 to 3 in the arch crown of tunnel, and the blasting pit volume from 0.12 m3 to 0.05 m3 in the model top. The pipe roof advance support can control effectively explosion damage outside the pipe roof reinforced layer.

Key words: tunnel entrance, pipe roof reinforcement, model experiments, anti-detonating performance