Mechanical characteristics for linings of shallow excavation metro tunnel in loess region

In order to precisely understand the mechanical characteristics for secondary linings of shallow excavation metro tunnels in loess region, large scale field tests are conducted at Xi'an metro line No. 2 site. The contacting pressure on the surrounding rock and the initial support system, contacting pressure on the initial supports and secondary linings and the stress of the secondary linings are monitored. The test results indicate that the surrounding rock pressures of each part in the initial support in earlier excavation chamber are larger than those in later excavation chamber of three-arched metro tunnel, and the pressures at the top and bottom parts of left and right center pillars are the largest due to large load at the upper part. The loading ratio is 52.81% and 47.19% respectively for the initial supports and secondary linings. The stress of the secondary linings is pressure stress, which is the largest at the left and right center pillars. The surrounding rock pressures in the wall foot at the left and right on standard section metro tunnel are the largest due to large load at the upper part. The loading ratio is 40% and 60% respectively for the initial supports and secondary linings. The stress of the secondary lining is pressure stress, which is the largest on the upper arch loin and is smaller on the inverted arch.