Depth-Dependent Tunnel Behavior and Support Performance: Insights from Numerical Modelling and Analytical Solutions
Abstract
The influence of overburden depth on tunnel behavior and support performance is a critical yet insufficiently addressed parameter in empirical support design. Empirical support design methods, which are extremely prevalent in engineering practice, do not explicitly incorporate the effect of increasing depth on support demand, although they account for rock mass quality and stress conditions. In this study, a highway tunnel was examined that was planned to progress along the same rock mass but was excavated to varying depths to evaluate depth-dependent behavior in the tunnel. The tunnel was analysed using three-dimensional numerical models based on the Mohr-Coulomb failure criterion with depth-dependent dilation angles, combined with the analytical convergence-confinement method, at 50 m intervals up to a depth of 370 m along the route. The tunnel alignment was modeled under supported and unsupported conditions at specified intervals and the results were verified by comparing in situ deformation monitoring data taken from a representative depth. The results reveal that excavation depths result in a progressive increase in displacements and stresses on the tunnel walls as well as a concentration of stresses within the supporting mechanism, with significant thresholds occurring at a depth greater than 200 meters. This study emphasizes that empirical support design alone is insufficient for depth-varying conditions, and recommends integrating depth-dependent numerical and analytical assessments into tunnel design practice for more reliable and robust ground-support interaction assessments.