Characterization of Excavation Damage Zones in a Himalayan Transportation Tunnel via Numerical Analysis

Tunneling induced stress redistribution results in stress concentration and formation of the excavation damage zone (EDZ), which degrades the engineering properties of host rocks. Retrofitting the EDZ is crucial for long- and short-term tunnel stability. This study uses continuum-based finite element modeling (FEM) software RS2 to analyze the EDZ formation around an under-construction transportation tunnel in Jammu & Kashmir. Strains (maximum shear strain and total volumetric strain) and stresses were evaluated to characterize the highly damaged zone (HDZ), EDZ, and excavation influence zone (EIZ). The study also explored the variations in damage zone radius (R-d) with varying geotechnical parameters such as geological strength index (GSI), overburden depth, tunnel radius, in situ stress ratio (K), pattern of the sequential excavation scheme, and numerical parameters (type and size of finite elements). Results showed that GSI, tunnel radius, and in situ stress ratio significantly affect the shape and extent of the EDZ, with variations in engineering parameters causing up to similar to 14.8 -17.5% changes in the EDZ's spatial extent.