Model test and in-situ monitoring of double-arch tunnel with integrated middle wall

In order to study the complex characteristics of double-arch tunnel during excavation, model and in-situ monitoring based on a double-arch tunnel with integrated middle wall are conducted to study the displacement and the stress of middle wall during excavation by bench cut method with middle drift. The effect of each excavation stages is analyzed in detail. The test results show that the displacement and stress are effected more significantly by the excavation of calotte than by the excavation of bench. The displacement-time curve is in a shape of S and the maximum displacement locates at the top of later excavated tunnel. Because the excavation of tunnel makes the stress in the other side of middle wall increase greatly and the stress in the excavation's side increase slightly or decrease, the bending moment in middle wall is induced with the direction from the earlier constructed tunnel to the other by the excavation of earlier excavated tunnel and decreases with the excavation of later excavated tunnel.