In this chapter, the stability of a circular tunnel and dual circular tunnels in cohesive-frictional soils subjected to surcharge loading is investigated by using the node-based smoothed finite element method (NS-FEM). In the NS-FEM, the smoothing strain is calculated over smoothing domains associated with the elements’ nodes. The soil is assumed as a uniform Mohr-Coulomb material, and it obeys an associated flow rule. By using the second-order cone programming (SOCP) for solving the optimization problems, the ultimate load and failure mechanisms of the circular tunnel are considered. This chapter discusses the influence of the soil weight γD/c, the tunnel diameter ratio to its depth H/D, the vertical and horizontal spacing ratio (L/D, S/D) of two tunnels and soil internal friction angle ϕ on the stability numbers σs/c are calculated. The stability numbers obtained from the present approach are compared with the available literature for tunnels.
Part of the book: Theory and Practice of Tunnel Engineering