Study on the Mechanical Behavior and the Model Test of Segmental Linings for the Shield Tunnel Undercrossing the Yellow River

The Yellow River tunnel of Lanzhou Metro Line No. 1 is the first underwater tunnel to be going through the Yellow River that is used for urban rail transit. The shield tunnel of the Lanzhou metro undercrossing the Yellow River is built in a high-permeability sandy gravel stratum and bears high water pressure. To research the mechanical behavior of segmental linings for the shield tunnel undercrossing the Yellow River. Sand and gravel used for the model test was compounded using the similar grading method. A device for an external loading test was developed which introduced controllable air pressure between the linings and grouting layer; by regulating the pressure difference, equivalent water pressure in the test can be simulated. Using this device together with a tunnel-ground simulation facility, a model test with a geometric similarity ratio of 1:10 was conducted. The device could reach the point that the water pressure and the earth pressure were controlled separately. The mechanical characteristics of the segmental lining with respect to different external water pressures and soil pressure were analyzed. At the same time, finite element simulation software ANSYS was applied to the verification of the model test result. As external water pressure increases, a significant increasing trend of thrust force and a gentle decrease trend of bending moment was observed, eccentricity decreases obviously as water pressure rises, changes in water pressure have little effect on the distribution of thrust force and bending moment. As the soil pressure increases, a gentle increase of thrust force and bending moment and eccentricity was observed, and changes in soil pressure have little effect on the distribution of internal forces.