TOPOGRAPHY INDUCED STRESS AND ITS INFLUENCE ON TUNNEL EXCAVATION IN HARD ROCKS – A NUMERICAL APPROACH

Abstract

In-situ stress characterisation is essential for anticipating the viability of underground structures. In areas with rugged topography, the in-situ stress varies within short distances and cannot be characterized by limited in-situ stress measurements. The in-situ stress at a point below the ground surface results from the combined effect of topography, tectonic forces, material properties and many others. The impact of topography on subsurface in-situ stress can be significant in areas with rugged topography. In this study, 3D finite element modelling utilising the Digital Elevation Model of a tunnelling project site is used to characterise the in-situ stress. Gravity loading was assumed to simulate the impact of topography on the subsurface in-situ state of stress. The reliability of the results was validated by analysing the stress-induced brittle failures in a section of the tunnel. The simulated in-situ principal stresses and the corresponding stress-induced failure zones were in good agreement with the actual observations in the tunnel. The results suggest that the present-day topography dominates the in-situ stress in the study area.