Stability of unlined square tunnels in Hoek-Brown rock masses based on lower bound analysis

In this paper, the lower bound (LB) finite element limit analysis in conjunction with semidefinite programming (SDP) is developed and employed to investigate the stability of unlined square tunnels in Hoek-Brown (HB) material. Extensive parametric studies on the load factor of unlined square tunnels are conducted on practical ranges of the cover-depth ratio of tunnels, normalized uniaxial compressive strength of intact rock, geological strength index (GSI) and FIB material constant (m(i)). The presented results are useful for a reliable and accurate assessment of the stability of unlined square tunnels in rock masses in practice.