Numerical Analysis for Mechanical Properties of Bundled Integrate Structure Joints

[Objective] The U-BIT (underground bundled integrate tunnel) method can solve the problems of steel pipe sections inability in collaborative work and poor support efficiency of the traditional pipe curtain method. The mechanical properties of U-BIT joints determine those of the overall U-BIT, so it is necessary to study the mechanical properties and failure mechanism of the U-BIT joints. [Method] A beam-rigid plate-spring finite element numerical model is proposed and compared with the experimental data for verification; the full-process stress mechanism of the U-BIT joints is analyzed, as well as the influence of factors such as the bonding strength between the joint concrete and the steel pipe section, the size of the prestressed tension force, and the position of the pre-stressed tendons on the mechanical properties of U-BIT joints. [Result & Conclusion] The joint separation, prestressed tendon yielding, lock contact and lock failure are important performance points in joint failure; increasing the bonding strength of the joint can increase its separation bending moment, reduce the joint separation safety factor, lowering its safety reserve to some extent. Increasing the pretension of the prestressed tendon can effectively improve the joint separation bending moment, but cannot increase the yield bending moment and ultimate bending moment of the joint, and the ductility coefficient of the structure in limit state is relatively low. Adjusting the position of the prestressed tendon to make it closer to the joint tensile side can effectively increase joint separation bending moment.