Abstract:

The unsymmetrical load conditions and countermeasures for the construction of the exit portal section of Gaoyangzhai tunnel, the exit portal section of No. 1 Dayaoshan tunnel, the entrance portal section of Jiufenghe diversion tunnel, the exit portal section of Sayram lake tunnel and the exit portal section of No.2 Zhongzui tunnel are presented. It is concluded that the unsymmetrical loads of the tunnel portal sections should be treated prior to the commencement of the tunnel excavation, unloading method should not be used for the unsymmetrical loads, insidetunnel construction should be first made on the deepburied side in tunnel sections under unsymmetrical loads, the bench excavation should be made in the direction from the inside tunnel toward the portal, and insidetunnel treatment measures and outsidetunnel treatment measures, which should be taken in an order that depends on the actual conditions in the site, must be taken in case that displacement occurs to the mountain after the tunnel excavation has been started.

Key words:  unsymmetrical loaded mountain tunnel, portal section construction technology