Model Test on Longitudinal Mechanical Properties of Single and Double Layered Linings for Railway Shield Tunnel

Taking Shiziyang underwater shield tunnel of Guangzhou-Shenzhen-Hongkong passenger dedicated line as engineering background,model tests on the longitudinal mechanical properties of single and double layered linings were conducted using equivalent axial stiffness model.Combined with numerical calculations,the variations of longitudinal settlement and bending moment of shield tunnels with single and double layered linings under the junction of hard and soft strata in the conditions that the surface upon the tunnel is partially loaded were studied.Results show that the longitudinal settlement of single-layered lining is significantly influenced by the change of strata when the tunnel is located at the junction of hard and soft strata.Both larger settlement and differential settlement occur on the side of soft strata.Double-layered lining can resist uneven settlement caused by the change of strata to some extent.Both the maximum settlement and differential settlement at the longitudinal center of tunnel are smaller.After concrete lining is continuously applied to the inner side of segment lining,the longitudinal bending moment of tunnel is doubled,and the maximum positive bending moment occurs slightly at the soft strata side of the tunnel center.Most bending moment is borne by concrete lining.When the load is located within three times of tunnel diameter from tunnel axis,the longitudinal deformation and internal force of tunnel will be affected.