Stability of Unlined Rectangular Tunnels in Rock Masses Subjected to Surcharge Loading

Abstract

This paper investigates the stability of unlined rectangular tunnels in rock masses subjected to surcharge loading using adaptive finite element limit analysis based on the generalized Hoek-Brown failure criterion. Both upper and lower bound solutions are employed to calculate the stability number of the problem, and the relative errors are found to be within ±7%. A sensitivity study relevant to the Hoek-Brown parameters (σci, GSI, and mi), the normalized cover depth of the tunnel (C/H), and the width to height ratio of tunnels (W/H) are conducted. At a given value of C/H, the stability number is found to be increasing continuously with decreasing W/H and with increasing GSI and mi. The computational results are summarized in the form of design tables and charts for practitioners to use, and potential collapse mechanisms are provided and discussed in detail.