Effect of the Distribution of Joints in the Tunnel Excavation Phase Simulation: A Case Study

Résumé

This work aims to show the effect of joint distribution taking into account during the excavation phase simulation of the tunnel, in our case, Tunnel 4 of Kherrata (Algeria). At this effect, a comparison is made between the simulation of a sequential excavation phase using the Finite Element Method (FEM) with an equivalent model and a simulation that incorporates the presence of the sets of joints in the Model. The first simulation represents an equivalent model representing the whole rock mass with the Hoek and Brown Generalized criterion. Conversely, a Discrete Fracture Network (DFN) combined with the finite element method represents the distribution of the sets of joints used in the second Model. In our case study, the geomechanical classification of the rock mass, carried out using the Rock Mass Rating (RMR) and the Rock Mass Quality (Q) system methods, with values of 33 and 1.06, respectively, indicates that the south portal zone of Tunnel 4 exhibits poor quality. To assess the stability of the tunnel during the excavation phase, we conducted a numerical simulation using two models: an equivalent model and a second model that took into account the distribution of discontinuities. Finally, the results indicate that the presence of joints has a significant impact on the simulation outcomes.

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