Mechanical behaviors and field tests of steel sleeves during shield receiving

Water inrush and gushing can be easily induced during shield receiving in water rich sandy ground. Based on shield receiving practice at Longhua Station of Shanghai Metro Line 11, the rules of stress and deformation of steel sleeves are analyzed by using the FEM numerical method, and the field tests on deformation of steel sleeves and settlement of flood wall are carried out to verify the feasibility. The results show that the maximum tension stress location gradually changes from the back plate to the bottom of connection area between sleeve and diaphragm wall during shield arriving. The circumferential stress is 2 to 7 times the longitudinal stress. The mechanical states at the following locations change obviously: circumferential axial force below the spring, longitudinal axial force at the bottom and longitudinal moment at the spring, and the accumulated deformation at the spring reaches 10 mm. As the shield advances, the bottom will deform outward while the spring inward, therefore, the radial deformation of the sleeve changes from a lying duck egg to a standing duck egg, and finally similar to the shape of 8, with the ovality reaching nearly 3‰. However, the stress and strain have no significant changes at the back plate because of bracing constraint. The joints between the steel sleeve and the diaphragm wall and those at the spring and the bottom of blocks are the weak positions of steel sleeve for stress and deformation control during shield receiving, and the most disadvantage state occurs when the shield is completely into the steel sleeve. The in-situ measurements show that the steel sleeve receiving technology is safe and feasible when adopting the current design parameters. However, the large fluctuations and instability of field data at the spring, bottom and back plate should be paid great attention to, and standard operating