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Groundwater inflow assessment is essential for\ud the design of tunnel drainage systems, as well as for\ud assessment of the environmental impact of the associated\ud drainage. Analytical and empirical methods used in\ud current engineering practice do not adequately account\ud for the effect of the jointed-rock-mass anisotropy and\ud heterogeneity. The impact of geo-structural anisotropy of\ud fractured rocks on tunnel inflows is addressed and the\ud limitations of analytical solutions assuming isotropic\ud hydraulic conductivity are discussed. In particular, the\ud study develops an empirical correction to the analytical\ud formula frequently used to predict groundwater tunnel\ud inflow. In order to obtain this, a discrete network flow\ud modelling study was carried out. Numerical simulation\ud results provided a dataset useful for the calibration of\ud some empirical coefficient to correct the well-known\ud Goodman’s equation. This correction accounts for geostructural\ud parameters of the rock masses such as joint\ud orientation, aperture, spacing and persistence. The\ud obtained empirical equation was then applied to a\ud medium-depth open tunnel in Bergamo District, northern\ud Italy. The results, compared with the monitoring data,\ud showed that the traditional analytical equations give the\ud highest overestimation where the hydraulic conductivity\ud shows great anisotropy. On the other hand, the empirical\ud relation allows a better estimation of the tunnel inflow

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