During the drilling of galleries in the deep underground laboratory of ANDRA in Meuse Haute Marne, it has been observed that the excavation process created in the surrounding ground fractures with very specific shapes.A research programme was undertaken to model the mechanical behaviour of the fractured zone and the influence of radial bolts on the ground deformation around the galleries. For simplicity, the tunnel section is assumed to be circular and the problem is analyzed in axisymmetric mode.An original approach was used, that combines two homogenization procedures, to account for the role of the fractures and of the bolts. This approach was implemented in the finite element code CESAR-LCPC. Computations give larger wall displacements if fractures are taken into account, and show that the most efficient way to reduce wall convergence is to place bolts perpendicular to the axis of tunnel, regardless of the inclination of fractures.

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