Construction of cross passages by mechanical methods between segmental concrete tunnels provides a new concept for the rapid connection of underground structures. However, it is limited by geological and geometrical conditions, especially for small diameter tunnels in soft soils. Based on a shell-contact model, the behaviour of the main tunnel when a cross passage is opened is studied. It is found that the structural response changes from one segmental ring to another. Some of the rings are totally cut by the cross-passage shield while some others are just partially cut. It is found that the governing ring is the central ring which is totally cut. The force reaction counterbalancing the thrust gradually moves from the central ring, which is the ones first bored, to the adjacent ones. Shear forces transmitted through the longitudinal joints between rings are carefully studied in the different steps of the construction to avoid slipping between joints. The stress distribution through the joints changes under different load cases. A real scale test is used to calibrate the model. The different phases of the construction process are simulated. By comparing simulation results and experimental results, the applicability of the model is validated. The simulation model can be used to study real construction design with other geometries and soil conditions.