Effect of Joint Roughness on the Support Requirements for the Stabilization of Single and Twin Highway Tunnels Constructed in Jointed Rock

In this paper, the influence of joint roughness on the support requirements for the stabilization of highway tunnels constructed in jointed rock is investigated. For the numerical analysis, UDEC program which is based on distinct element method (DEM) is used. Several models are included in UDEC including elastic model, Mohr Coulomb model and null model for the blocks and point contact, area contact and Bandis-Barton model for the joints. Mohr Coulomb model is used for the blocks and area contact model is used for the joints in this research. Two joint sets dipping 70 and 130? with spacing of 1m are considered and it is assumed that all base characteristics of the joints remain the same in various analyses except the roughness of joints. The analyses are carried out both for single and twin tunnels. The distance between the twin tunnels have been selected in such a way that they do not affect each other. For the support system, a combination of shotcrete and rockbolt is used.
The results of the analyses indicate that the increase in joint roughness leads to the decrease in support requirements to a certain degree which are discussed in detail both for single and twin tunnels. It is also concluded that in general, twin tunnels each comprising two lanes for one direction require less support compared with the equivalent single tunnel.