Face stabilization of deep tunnels using longitudinal fibreglass dowels

When the stability of an excavation face in a deep tunnel is not ensured by the strength characteristics of the rock mass, it is current practice to proceed with reinforcement of the face using longitudinal fibreglass dowels. An analysis of the effect of these reinforcements and a correct dimensioning can be obtained through three-dimensional numerical modelling, which is very burdensome from a computational point of view. The simplified methods that are at present available do not allow the maximum force in the dowels to be obtained and cannot therefore be used for their dimensioning.A finite difference procedure for deep tunnels is presented in this paper. This procedure is able to analyse the presence of dowels in the rock mass in a distinct manner, and it adopts the conceptual schematisation of a spherical geometry void for the approximation of the tunnel face zone. A calculation comparison of the simplified procedure and the three-dimensional numerical modelling has offered satisfactory results. The procedure has also been applied to a real case and the results agree with in situ measurements.

► When the stability of the tunnel face is not guaranteed fibreglass reinforcements are usually installed.
► No adequate calculation instruments have been developed to analyse fibreglass dowels.
► A new calculation procedure is presented for the analysis of a reinforced face in deep tunnels.
► The procedure was used to perform a parametric analysis and it was compared with 3D numerical modelling.
► A real case was analysed: the results adhered to the in situ measurements.