Have We Underestimated the Influence of Geological Uncertainty on Tunnel Deformational Performance in the Uncertain Stratum?

The geological uncertainty and the inherent spatial variability of soil properties are two main uncertainties in geotechnical engineering that will significantly affect the embedded geo-structures. The influence of spatial variability of soil properties on tunnel deformation has been widely studied, while geological uncertainty is usually not considered. Is this simplification reasonable? Have we underestimated the influence of geological uncertainty on tunnel deformational performance? This study aims to present a method for tunnel probabilistic analysis by considering both the geological uncertainty and spatial variability of soil properties. The comparisons of tunnel deformational performance between only considering soil spatial variability and coupling considering these two types of uncertainty are presented to reveal the role of geological uncertainty in tunnel probabilistic analysis. An improved coupled Markov chain (CMC) model is used to simulate geological uncertainty based on spare limited boreholes. Moreover, the spatial variability of soil properties within each soil layer is modelled using random fields. The results indicate that the proposed method can effectively evaluate the tunnel structural response considering these two types of uncertainty. With the borehole number increases, the influence of geological uncertainty gradually decreases. The uncertainty of calculations only considering the soil spatial variability may be overestimated if the geological uncertainty is ignored.

Keywords: Tunnel, geological uncertainty, spatial variability, probabilistic analysis.