Geological models modifying the application of the term discontinuity and its importance in reducing costs in tunnel support

Abstract

While rock mechanics traditionally groups bedding, foliation, and joints as "discontinuities," this study focuses on their differentiated impact on tunnel support costs through stress-aware modeling. Building on established principles (e.g., joint development depends on stress redistribution), we demonstrate how explicitly accounting for this relationship in numerical models (FEM) enables cost-efficient design. Refraction microseismic tests map the decompressed zone (near-excavation) by tracking joint prevalence via seismic velocity gradients, revealing stress-dependent zonation. Our models incorporate strength recovery with distance from the excavation, proving that support costs can be reduced by 80% (3 m tunnels) and 30% (12 m tunnels) compared to conventional methods. Critical thresholds emerge: beyond 0.5D (3 m tunnels) to 1.0D (9 m tunnels), minimal support is needed as stress confinement restores Critical decompressed zone thresholds were identified: for zones extending beyond 0.5D (3 m tunnels) to 1.0D (9 m tunnels), additional increases in decompressed zone size no longer necessitate thicker supports, as confirmed by stabilization of lining thickness requirements in numerical analyses. This approach replaces lithology-based assumptions with stress-adaptive zonation, where support intensity aligns with mechanically verified zones—eliminating overdesign without compromising safety.

The article is available for download at:

https://doi.org/10.53243/ICSMGE2026-1384