Abstract:

Several construction schemes are studied for a doublearch tunnel with concealed central wall by means of numerical simulation, so as to select reasonable construction scheme. Conclusions drawn are as follows: The tunnel structure with concealed central wall can maintain the construction safety; The symmetrical temporary central wall method and the parallel temporary central wall method are more favorable in structural safety and deformation control; In the case of parallel temporary central wall method, the scheme of driving the main tunnel and secondary tunnel simultaneously with some distance delay is the most costeffective, the quickest and the most environmentfriendly scheme, which can greatly improve the construction efficiency of doublearch tunnels; The comprehensive tunneling index of the mentioned scheme is increased by 107% compared to the conventional central pilot method，and by 79% compared to threepilot method. Analysis also shows that the excavation and support removing of the top heading is the key process in deformation control, and the joint between the arch of the secondary tunnel and the central wall and the joint between the invert of the secondary tunnel and the central wall are critical points in structural safety control.

Key words: doublearch tunnel, concealed central wall, selection of construction method, parallel temporary central wall