Influence of the scale of fluctuation of the friction angle on the face stability of a pressurized tunnel in sands

Abstract

The present paper makes use of a 2D limit analysis mechanism developped in Mollon et al. 2011 to study the influence of the scale of fluctuation of the friction angle in a soil mass on the critical collapse pressure of a pressurized tunnel face. The variability of the soil is simulated by random fields in the framework of the Karhunen-Loeve Expansion method, with various scales of fluctuation. A Monte-Carlo sampling scheme is used to examine the probabilistic impact of this variability as well as possible emergent behaviours that may be qualitatively different from well known behaviours associated with homogeneous sand. Probabilistic results show that L/D ratio (i.e. autocorrelation length of the friction angle random field, over tunnel diameter D) has an important influence on the dispersion of the critical collapse pressure. For a small to moderate value of this scale of fluctuation with respect to the tunnel diameter, it appears that there are several critical positions of the failure mechanism, whereas such phenomenon is unlikely for large values of L/D. © 2011 ASCE.