Effects of spatially variable weathered rock properties on tunnel behavior

Design parameters commonly used in numerical modeling for tunnel stability analyses tend to be representative (or average) values of global-scale properties. However, the spatial variability of design parameters, such as geotechnical and geological properties, greatly affects the behavior of tunnels during and after construction as well as their long-term responses. Thus, this study presents a simple but robust procedure for stochastic numerical analyses using the finite difference method (FDM) and explores the effects of spatially variable weathered rock properties on various tunnel behaviors, such as deformation, elastic–plastic interface, ground reaction curve, and failure mechanism. It was found that the inherent spatial variability of stiffness and strength parameters affects the deformation behavior of tunnels and even changes its failure mechanism: Elastic modulus for the Mohr–Coulomb model and geological strength index (GSI) for the Hoek–Brown model play a key role in deformation characteristics. Considering the wide range of spatial variability in in-situ deposits, the accurate estimation of elastic modulus and GSI is very important. The spatial variability of the ground can affect the ground reaction behavior and can bring on an unfavorable ground reaction curve (GRC). It can cause an increase in the tunnel support pressure, and can induce a larger displacement than the homogeneous case. The shear failure mechanism of the tunnel can be significantly affected by a large relative correlation length. It is suggested that we should estimate and consider the variability of rock properties accurately as part of a routine tunnel design framework.