Tunnel Stability Analysis by Finite Element Method
Jun Xie, Ph.D., P.Eng.
Exp. Services Inc., 1595 Clark Boulevard, Brampton, ON L6T 4V1, Canada
Abstract:
This paper presents the stability analysis for the circular tunnels in undrained clay by Finite
Element Method. The soil which the tunnels are located in is assumed as a Tresca material (the
friction angle of soil = 0). Natural stability ratio, field stability ratio, critical stability ratio,
stability analysis plot and stability analysis line are introduced. The analysis procedure is carried
out via the Cambridge finite element program package CRISP and the stability analysis plot. The
critical stability ratios of single circular tunnels and two parallel circular tunnels, which are
obtained from this method, are compared with the stability ratios from the bound theorems of
plasticity limit analysis in examples. In the end, the relationship between the factor of safety
(FOS) and stability ratio (N) of the tunnels is discussed.
Key words: circular tunnels, tunnel stability, finite element analysis, stability ratio