Stability analysis of a deep buried elliptical tunnel in cohesive–frictional (c–ϕ) soils with a nonassociated flow rule

Abstract

The stabilities and associated collapse mechanisms of deep buried unlined elliptical tunnels in cohesive–frictional (c–[Formula: see text]) soils with the action of soil weight are investigated by the “upper-bound finite element method with rigid translatory moving elements” (UBFEM–RTME). The soil masses are assumed to obey the Mohr–Coulomb yield criterion and a nonassociated flow rule. Upper-bound stability coefficients (γcrD/c, where γcr is critical unit weight; D is tunnel height; c is cohesion) are deduced for different values of friction angles ([Formula: see text]), dilatancy coefficients (ψ/[Formula: see text], where ψ is dilation angle), and dimensionless spans (B/D, where B is span). The obtained collapse mechanisms do not extend to the ground surface and are primarily composed of a series of mutually movable rigid blocks. The γcrD/c values increase while the collapse zones decrease with an increasing [Formula: see text] and ψ/[Formula: see text] and a decreasing B/D.