Assessment of Tunnel Stability under Varying Conditions Using Numerical Modelling

Abstract

The stability of underground openings is governed by a combination of geological, geometrical, and loading conditions, which may vary considerably along a tunnel alignment. Numerical modelling provides an effective means of examining these factors and assessing tunnel response before construction. The present study investigates the stability behaviour of underground tunnels under varying overburden depths and rock-mass conditions using numerical modelling. Particular attention is given to changes in tunnel deformation, stress redistribution, and yielded zones around the excavation. A series of two-dimensional numerical models was developed using PLAXIS 2D under plane-strain conditions. The Hoek–Brown failure criterion was adopted to represent the non-linear strength behaviour of the rock mass. The initial stress state was first established, after which the tunnel material was directly removed in the subsequent calculation phase to simulate full tunnel excavation. Overburden depths of 10–50 m and GSI values of 25–55 were considered. Circular, horseshoe, and D-shaped tunnel configurations were also analysed under selected ground conditions. Tunnel response was evaluated using maximum displacement, stress distribution, and the extent of plastic or yielded zones around the excavation. The numerical results show that increasing overburden generally leads to increased tunnel deformation and changes in stress distribution around the opening. Rock-mass quality also influences the magnitude of deformation and the development of yielded zones. Different tunnel configurations show different deformation and stress responses under comparable ground conditions. The study provides a simple numerical framework for evaluating tunnel stability under varying overburden, rock-mass quality, and tunnel configuration, and provides useful insights for preliminary assessment of underground excavation behaviour.