Tunnel face reinforced by longitudinal bolts: Analytical model and in situ data

In this paper, we are interested in the displacement behaviour of the tunnel face during excavation taking in account the face reinforcement in the farm of longitudinal fibreglass. This technique is now commonly used and is at times a viable alternative to tunnelling machines in difficult ground. For design and analysis, an analytical model, based on the main hypotheses of spherical symmetry and using homogenisation approach, was developed at ENTPE by Wong et al (1996, 1997). Recently, in situ data have become available from a tunnel project in France, which showed, among others, the existence of a perturbed zone of roughly one diameter ahead of the tunnel face. The predictions of the analytical model concorded remarkably well with in situ data. Such good results give Confidence on the validity of the model, and encourage its use in practical designs and its further development to incorporate more sophisticated soil behaviour.