Reasonable determination for limit supporting pressure calculation and stability assessment of shield tunnel surface

it is basic and difficult to determine the unstable soil shape of shield tunnel surface. A numerical model is established to simulate the process of losing stability. According to the Mohr-Coulomb failure criterion

the Handy soil arching theory is used to get the calculation method determine the position and shape of unstable soil. The results show that the horizontal pressure arch is generated due to supporting effect of tunnel left and right sides in the horizontal direction

which causes that the unstable soil has a limit boundary. Catenary minimum principal stress arch is generated due to vertical soil movement in the limit boundary

the shape of unstable soil is similar to the shell-shaped. Taking the tunneling project of Nanjing Metro Puzhulu-Binjianglu section for example

theoretical calculation and numerical simulation results of the project are in good agreement.